Conj and cornea and refractive error Flashcards

Question

You are measuring the curvature of your keratoconic patient's cornea using a manual keratometer. You are experiencing difficulty measuring the steep keratometry value as the drum reading does not go high enough. You extend the range by adding a +1.25 trial lens and are able to obtain a reading of 50.50D. Which of the following MOST closely represents the true keratometry value in his steep meridian? 61. 75D 51. 75D 66. 50D 50. 50D 59. 00D 56. 50D

Answer 1

59.00D if pt is too steep --> drum can not read it --> use +1.25 trial if pt is too flat --> drum can not read it --> use -1.00 D trial trial 1- +1.25 --> add 8-9D to drum reading 2. +2.25 --> add 16 D TO 3- IF TOO FLAT (-1.00 )--> SUBSTARCAT 6 D FROM THE READING When measuring the keratometry values utilizing a manual keratometer there are certain circumstances in which the reading may be out of the range of the drum values. In these cases, one will need to add a trial lens to the keratometer in order to extend the ranges (lenses are added to the patient's side of the keratometer). Cases in which the curvature is steeper than the drum reading, plus trial lenses are required, and when the reading is flatter than the drum reading, minus trial lenses are necessary. In patients with steeper curvatures, typically a +1.25 trial lens is tried first. If a measurement can be found with this lens one will need to add about 8-9D to the drum reading in order to obtain the true value. A +1.25 lens will extend the range from about 52D to 60 or 61D. In the case of the above patient, adding about 8.5D will result in a true value of 59.00D. If keratometry values are even steeper (in the 60-68D range), a +2.25 trial lens can be utilized to extend the drum range even more. In these cases, about 16D is added to the drum reading to reach the true keratometry value. If the curvature is flatter than can be measured with the manual keratometer, a minus lens can be added to extend the range in the opposite direction. Typically a -1.00 trial lens will encompass a keratometry reading from about 32-38D. If a -1.00 lens is added, one will need to subtract 6D from the drum reading.

Answer 2

Contact lenses of all types can have an effect on a patient's tear film, corneal topography, and refractive error. Therefore, it is important to have a patient discontinue wear of their contact lenses for a certain timeframe prior to surgery. The FDA requires patients to be out of soft contact lenses for a minimum of 2 weeks prior to any customized procedure. Because rigid gas-permeable lenses can have a more dramatic effect on corneal topography and thus on refractive error, they require a longer time for the cornea to normalize. The FDA requirement is a minimum of 1 month with the recommendation of 1 month for every decade of wear or until the corneal topography is stable.

Answer 3

Hyaline deposition between the epithelium and Bowman's membrane Salzmann's nodular degeneration appears as blue/white hyaline plaque deposits between the epithelium and Bowman's membrane, generally around the pupillary area of the cornea. This condition stems from other pathologies, primarily old phlyctenula. Treatment is generally not required unless vision is affected.

Answer 4

Corneal erosion Recurrent corneal erosions occur secondary to an abnormally weak attachment between the basal cells of the corneal endothelium and their basement membrane. Symptoms most commonly occur upon wakening, in which minor injuring resulting from opening the eyes after sleep causes shearing forces that are sufficient enough to tear the corneal epithelium. Patients typically present with severe ocular pain, watering, and photophobia that occurs during the night or shortly after wakening. There is usually a history of prior trauma or surgery (that could have occurred several years prior), or in association with an epithelial membrane dystrophy or anterior stromal dystrophy. Slit-lamp examination of these patients will usually reveal a frank epithelial defect, particularly in the interpalpebral zone or lower half of the cornea. There may also be a larger area surrounding the epithelial defect that represents the extent of the loose epithelium and may be highlighted with pooling of sodium fluorescein.

Answer 5

Collagen The corneal stroma is comprised mostly of collagen and water. The stroma itself makes up roughly 90% of the thickness of the cornea. This layer is made up of around 250 lamellae organized in a precise orthagonal arrangement to ensure corneal transparency. The space between the collagen bundles that make up the lamellae is maintained by proteoglycans which are composed of protein and carbohydrate. The proteoglycans have a negative charge and thus repel each other. The collagen is upheld and maintained by keratocytes.

Answer 6

-40 mmHg The imbibition pressure of the corneal stroma is due to the anionic (negatively charged) repulsive forces of the glycosaminoglycans (GAGs), which causes the tissue to expand and suck fluid into the cornea. In vitro, the imbibition pressure (IP) and the stromal swelling pressure (SP) are equivalent. However, in vivo, the IP is lower than the SP because the hydrostatic pressure induced by the intraocular pressure must be accounted for. Therefore, the average imbibition pressure of the corneal stroma is approximately -40 mmHg.

Answer 7

Controlled type II diabetes LASIK is a procedure that results in thinning of the cornea; therefore, a person who has thin corneas to begin with or any corneal conditions resulting in irregular astigmatism or ectasia is not a good candidate. The presence of an active ocular disease such as conjunctivitis, microbial keratitis, or corneal erosions would also contraindicate a patient, as these diseases can lead to very serious post-LASIK infections and unpredictable surgical outcomes. A keloid former is a patient who is prone to producing a lot of scar tissue in the event of trauma or tissue manipulation. If a lot of scar tissue is present after surgery, this can increase the perception of light scatter and haloes, thereby decreasing acuity levels. Also, extreme scarring may also alter the shape of the cornea and offset the desired final outcome causing over- or under-correction or undesired astigmatism.

Answer 8

Trachoma Trachoma is more common in lesser-developed countries and can cause blindness if not treated appropriately. Trachoma presents in several stages, initially starting with mucopurulent discharge, lymphadenopathy, red eye, small superior tarsal follicles, and mild superior pannus. This infection eventually progresses to horrible scarring of the eyelid and cornea, causing extremely poor visual acuity. Arlt's lines denote the characteristic linear scarring that occurs on the palpebral conjunctival surface. This scarring of the eyelids can cause entropion and trichiasis which abrade the cornea leading to scarring and/or ulceration. Herbert's pits are conjunctival depressions or excavations caused by scarring of limbal follicles that occurs along the limbocorneal junction. Treatment includes oral doxycycline, tetracycline, azithromycin, or erythromycin along with topical tetracycline or erythromycin ointment. A recurrent corneal erosion generally occurs in response to a corneal abrasion incurred by something organic (like a finger-nail or a tree branch). The initial abrasion heals but a short time afterwards the patient will experience another episode without any new incidence of trauma. The second occurrence tends to transpire first thing in the morning; the eyelids stick to the unstable flap of tissue and rip it off like a band-aid when the eyes open. The best way to treat a recurrent corneal erosion is through the use of a topical antibiotic (unpreserved is best) to ensure sterility (as the cornea is exposed) as well as a bandage contact lens to speed up the healing process. Some argue that a bandage contact lens can pose more problems than it solves as the lens must be worn continually for a minimum of 10-12 weeks (the lens should be changed intermittently). Hyperosmotic drops or artificial tears should be prescribed for roughly 10-12 weeks to ensure healing and to allow for proper formation of hemidesmosomes to alleviate future episodes. Other treatments include stromal micropuncture or debridement. VKC is a condition of the young and presents with an increased frequency in males. This type of allergy typically develops before age 14 and lasts for 4-10 years before the child outgrows it; it occurs predominantly in the spring and summer. The condition progressively improves, with the first episode being the most severe. Usually VKC is seen in patients who are prone to atopy and therefore they suffer from eczema, asthma or hay fever. Patients typically suffer from itchy eyes and photophobia. The condition basically presents as a very severe type of allergic conjunctivitis. Signs include cobblestone papillae of the upper lid, lid swelling, and ropy discharge that is worse in the morning. Corneal defects (usually superiorly) known as keratitis of Togby may also be present. Occasionally, patients will develop a shield ulcer and Tranta's dots, which are calcified eosinophils seen circumlimbally (they appear as chalky concretions) and may lead to the feeling of an associated foreign body sensation. Treatment includes mast cell stabilizers that should be started several weeks prior to re-occurring episodes, pulse steroid therapy, cool compresses, and sunglasses to help alleviate ensuing photophobia. Epidemic keratoconjunctivitis (EKC) is a very common and contagious infection of viral etiology. EKC is caused by the adenovirus; there are many different strains, but the two most common to cause ocular infections are serotypes 8 and 19. EKC is said to follow the "rule of 8s" because type 8 is the type most frequently isolated; on the 8th day, the patient will present will diffuse superficial punctate keratitis (SPK), followed 8 days later (16 days from inoculation) by the formation of sub-epithelial infiltrates (SEIs). Once SEIs are present, the patient is no longer considered contagious. Signs of EKC include follicular conjunctivitis, positive lymph adenopathy, and mild lid edema. Small sub-conjunctival hemorrhages, pseudo-membranes, and iritis may also be present. Treatment for this condition is generally palliative and consists of ocular lubrication, topical vasoconstrictors, cool or warm compresses, topical NSAIDs, and sunglasses. Some clinicians use a Betadine® (5%) ophthalmic solution off-label treatment in office, which seems to be rather effective. The use of steroids is still controversial because EKC and the Herpes simplex virus (HSV) can initially present similarly, and steroid use on HSV can lead to horrendous corneal damage. Topical steroids are very effective if the patient suffers from SEIs that are visually debilitating, but be sure to taper the steroid use.

Answer 9

Recurrent corneal erosions occur in an area where the epithelium is not secured to the anterior stroma, usually from either an abrasion or epithelial basement membrane dystrophy. The mechanical action of creating a corneal flap either with a microkeratome or a femtosecond laser can cause the epithelium to erode in the "weakly adherent" area. Therefore, it is not advisable to use either of those methods to treat the eye. Phototherapeutic keratectomy (PTK) has been shown to be an effective treatment of recurrent erosions, therefore simultaneously adding refractive correction (Photorefractive keratectomy) is also an effective treatment with the added benefit of correcting the patient's refractive error.

Answer 10

The palisades of Vogt The epithelial stem cells are located within the palisades of Vogt. These white, linear structures traverse radially around the cornea and are more prominent inferiorly than superiorly. They are clearly evident right on the edge of the limbus and extend to blend invisibly with the cornea. The palisades serve as housing for blood vessels, nerves, connective tissue and lymphatics. Most importantly, the palisades have been proven to contain stem cells that can be stimulated for renewal of aging/damaged epithelial cells. Axenfeld loops are generally seen in the sclera as sometimes raised areas of pigment. These loops are formed by nerves that initially course one way and then turn back on themselves. Goblet cells secrete the mucous layer of the tear film and are found primarily in the conjunctiva

Answer 11

Cat-scratch diseaseOculoglandular syndrome can be caused by a myriad of organisms and presents as a unilateral follicular conjunctivitis along with lymphadenopathy on the same side as the affected eye. Other signs and symptomology vary depending on the causative organism. Causes include but are not limited to: cat-scratch disease, tularemia, syphilis, tuberculosis, sprotrichosis, mononucleosis, coccidioidomycosis, sarcoidosis, Hansen's disease, mumps, actinomycosis, Listeria and Herpes simplex. Based solely upon the age of the child, one would first assume cat-scratch disease, which is the most common cause of oculoglandular syndrome. This assumption would be verified by asking if the child had recently been scratched by a cat and by performing the Hanger-Rose skin test for confirmation. Coccidioidomycosis can cause oculoglandular syndrome, but it is contracted via exposure to a fungus that is found in soil and vegetables through an opening in the skin and is frequently encountered in gardeners, farm workers, or botanists. Children do not generally contract oculoglandular syndrome in this fashion. Diabetes, measles, and toxoplasmosis do not display a correlation with the development of oculoglandular syndrome.

Answer 12

14 days Epidemic keratoconjunctivitis typically runs a common clinical course that begins with characteristic signs and symptoms following an 8-10 day incubation period. Initially, patients will usually complain of eyelid edema, pain, photophobia, and lacrimation. Early conjunctival clinical signs include a mixed papillary and follicular response, hyperemia, chemosis, and subconjunctival hemorrhages that typically last for 7-21 days. In more severe cases, the development of a conjunctival membrane or pseudomembrane is possible. Corneal involvement in patients with EKC is variable, but most patients develop diffuse, fine, superficial keratitis within the first week of the onset of the disease. After about 6-13 days, focal punctate epithelial lesions that appear elevated and stain with sodium fluorescein often occur, and by day 14, subepithelial opacities develop under these focal lesions in about 20% of patients. These subepithelial infiltrates may affect vision and can persist for months to years but typically will eventually resolve without scarring or neovascularization.

Answer 13

Watch the patient, as the red blood cells will usually reabsorb on their own Red blood cells are occasionally seen after a LASIK procedure when neovascular vessels are severed during the creation of the corneal flap. Red blood cells are seen more often when a microkeratome is used versus a femtosecond laser. They have not been shown to cause an increase in inflammation or progress, nor have any effect on the patient's visual outcome.

Answer 14

Extended wear contact lenses should be removed for a minimum of 2 weeks prior to the procedure Soft contact lenses should be removed 2 weeks prior to the procedure Contact lenses of all types can have an effect on a patient's tear film, corneal topography, and refractive error. Therefore, it is important to have a patient discontinue wear of their contact lenses for a certain timeframe prior to surgery. The FDA requires patients to be out of soft contact lenses for a minimum of 2 weeks prior to any customized procedure. Because rigid gas-permeable lenses can have a more dramatic effect on corneal topography and thus on refractive error, they require a longer time for the cornea to normalize. The FDA requirement is a minimum of 1 month with the recommendation of 1 month for every decade of wear or until the corneal topography is stable.

Answer 15

Stroma Corneal arcus appears as a white/yellow circular band of cholesterol that deposits in the stromal periphery, leaving a clear zone adjacent to the limbus. It is important to refer patients with corneal arcus who are unaware of their cholesterol levels for evaluation of their serum cholesterol.

Answer 16

Basal cells The corneal epithelium can be further subdivided into three zones. The most posterior zone is comprised of a single layer of basal cells which adhere to the epithelial basement membrane. These cells give rise to all of the other zones. Moving exteriorly, the basal cells move more anteriorly and flatten out to become wing cells. This zone is two to three layers thick. The most anterior zone is one to two layers thick and is made up of superficial cells. These cells are flat, plate-like cells . Superficial cells are constantly sloughed off.

Answer 17

The posterior surface The anterior surface of the corneal endothelial cells is in contact with Descemet's membrane. The posterior surface (the apical aspect) of the cells is bathed in aqueous humor.

Answer 18

Type I Hypersensitivity According to the Gell and Coombs classification of hypersensitivity reactions, Type I reactions are IgE-mediated reactions that result in an immediate response occurring within minutes of exposure. This type of reaction is seen in allergic disease. Type II reactions are antibody-dependent cytotoxic reactions that are mediated by IgM/IgG and complement. Type III reactions are due to immune complex formation. Immune complex diseases include systemic lupus erythematosus, arthus reactions and serum sickness. Type IV hypersensitivity is delayed-type hypersensitivity and is the result of T-lymphocyte response. Typically, symptoms will occur 2 days after exposure. Prime examples include the PPD test for TB, contact dermatitis, and chronic organ transplant rejection.

Answer 19

Hypoesthesia Corneal sensation has been shown to variably decrease with the presence of certain ocular diseases such as herpes simplex, keratoconus, diabetes, and other corneal dystrophies. Additionally, following surgical procedures (mostly involving the anterior segment of the eye) such as photorefractive keratectomy or laser-assisted in-situ keratomileusis, desensitization of the cornea is common due to the disruption of corneal nerves during the procedure. This decrease in corneal sensitivity (regardless of the etiology) is known as hypoesthesia. Following surgical injury, it is thought that it may take 3-12 months or longer for corneal innervation and sensitization to maximally recover, as nerve regeneration typically occurs at a rate of about 1mm per month. Hyperalgesia is an increase in sensitivity to pain. Hypoxia is a condition of tissues of the body in which the region is deprived of an adequate supply of oxygen. Lastly, hypercapnia is the condition of abnormally high levels of carbon dioxide levels in the blood.

Answer 20

Ascorbic acid Ultraviolet radiation, violet light, and blue light exposure can potentially cause damage to certain structures of the eye through the generation of reactive oxygen species. These products can cause cellular and extracellular damage through reactions with DNA, proteins, and lipids. In healthy eyes, the cornea and anterior segment have naturally occurring methods to protect themselves from the potential deleterious effects of the reactive oxygen species. Most notably, the anterior segment produces and maintains sufficient levels of both low-molecular weight and high-molecular weight antioxidants. Ascorbic acid is considered to be the primary antioxidant present in the cornea and anterior segment, as it is produced in significantly high concentrations in the aqueous humor. In fact, the high amounts of ascorbic acid in the corneal epithelium are responsible for the complete absorption of UV-C and the significant attenuation of UV-A and UV-B light as it passes through the eye.

Answer 21

Descemet's membrane Descemet's membrane is a homogenous layer of the cornea that resides between the stroma and corneal endothelium. It acts as a basement membrane for the corneal endothelium and is continuously secreted by the corneal endothelial cells throughout a person's lifetime. The anterior portion of Descemet's membrane is formed in utero and is about 3um in thickness. The posterior 2/3 portion of the membrane is formed after birth and allows for the membrane to thicken to 20-30um with age.

Answer 22

Endothelium From superficial to deep, the layers of the cornea are: epithelium, Bowman's layer, substantia propria (stroma), Descemet's membrane, endothelium. The epithelial layer consists of squamous cells that occupy the superficial position transitioning to wing cells and then basal cells. Bowman's layer is a sheet of dense collagen that serves as a transition to the substantia propria (stroma) which is composed of collagen, keratocytes (fibroblastic cells), and ground substance. Descemet's membrane is considered the basement membrane for the endothelium. The corneal endothelium is adjacent to the anterior chamber and is a single flattened layer of cells that form tight junctional complexes and serves as a mechanism to control corneal thickness. Endothelial cells do not replicate.

Answer 23

Riboflavin Corneal collagen cross-linking is a surgical procedure in which UVA light and riboflavin are utilized to stiffen the collagen matrix of the corneal stroma. The procedure varies between surgeons, but typically involves either full or partial debridement of the corneal epithelium to allow for maximal absorption of isotonic riboflavin into the stromal tissue. Drops of riboflavin are instilled until the yellow-color of the riboflavin is apparent in the anterior chamber (by use of a lit-lamp and blue light). The thickness of the cornea is then measured, as it must be greater than 400 microns to continue with the UV light exposure. Once this is confirmed, UVA radiation is then applied to the cornea (with riboflavin drops still being instilled) until the desired treatment time has elapsed. The cornea is then irrigated thoroughly, and a bandage contact lens is placed on the eye.

Answer 24

Desmosomes, hemidesmosomes, and adherens junctions are anchoring type junctions that allow cells within organs or tissues to attach and become anchored to one another and to components of the extracellular matrix. Hemidesmosomes attach corneal epithelial cells to their basal membrane. Desmosomes attach basal epithelial cells to one another. Zonula occludens are tight junctions that act to create a barrier to the movement of water and solutes between epithelial layers in tissues of the body. This is the type of junction that is present between the superficial squamous cells of the corneal epithelium. Gap junctions are communicating junctions that allow for direct communication between adjacent cellular cytoplasm by means of diffusion and without contact of the extracellular components.

Answer 25

Every 7 days The cornea is truly an amazing structure. The corneal epithelial cells transition from basal to columnar to wing cells and are ultimately sloughed off over a 7 day period. A small, superficial corneal abrasion (that is, one that does not penetrate Bowman's layer) can heal completely within 24-48 hours without leaving a scar!

Answer 26

11.7mm, 10.6mm The human cornea has an elliptical configuration in which the mean horizontal diameter is 11.7mm and the mean vertical diameter is 10.6mm, when viewed anteriorly. Contrastingly, when viewed posteriorly, the cornea is actually circular, with mean horizontal and vertical diameters of 11.7mm. This discrepancy is due to the anterior extension of the opaque sclera superiorly and inferiorly.

Answer 27

Total Cholesterol The white or grey ring is a deposition of lipid material and has been referred to in the past as arcus senilis. It is common in African-Americans, and its prevalence increases with age. In a young male with higher gender-based risk, the association with elevated cholesterol makes the test mandatory so that statin treatment can be instituted as early as possible. Arcus cornealis and arcus juvenilia (that is, discoloration around the cornea in younger people) are independently associated with an increased risk of cardiovascular disease, probably reflective of the deposition of lipid material in the blood vessels as it has been demonstrated in the cornea.

Answer 28

Bitot spots Vitamin A deficiency can lead to the loss of goblet cells, resulting in dryness of the conjunctiva and eventual keratinization in severe cases. Bitot spots are triangular patches that represent keratinized conjunctival epithelium. They have a foamy appearance and typically occur in the interpalpebral zone. Tranta's dots are discrete white spots that are found at the apices of limbal papillae associated with vernal keratoconjunctivitis. Roth's spots are retinal hemorrhages that have whitish centers. They are commonly observed in association with certain systemic conditions such as bacterial endocarditis, leukemia, diabetes, and pernicious anemia. Herbert's pits are depressed, round, thin areas that are the result of resolved limbal follicles in trachoma disease. Concretions are common observations that appear as small, chalky, whitish-yellow deposits typically found in the inferior tarsal and fornical conjunctiva. They frequently occur in association with meibomian gland disease.

Answer 29

The cornea flattens and overall diameter increases Corneal curvature from birth to age 6 months of age averages approximately 47.6D. As a child ages, the corneal curvature flattens to about 45.4D at 2 years of age, and continues to flatten to about 42.7 at 5 years old. Studies have shown that the corneal curvature from age 5 on is relatively stable, unless a person experiences a corneal injury, undergoes corneal surgery, or wears contact lenses. Most literature states that the average corneal curvature in adults is about 43D or 7.85mm.

Answer 30

Ophthalmia neonatorum is a conjunctivitis that typically develops within the first 3 weeks after birth as a result of transmission of infection from mother to child during delivery. This condition is particularly serious due to the lack of immunity in infants as well as the immaturity of the ocular surface (poor tear film and undeveloped lymphoid tissue). Ophthalmia neonatorum secondary to N. gonorrhoeae typically develops within 2-5 days postpartum as hyperacute conjunctivitis. Most cases present bilaterally with periorbital edema, conjunctival chemosis, and excessive amounts of purulent discharge. It is extremely important to quickly and aggressively treat this infection due to the ability of N. gonorrhoeae to penetrate an intact corneal epithelium. When C. trachomatis is the organism responsible for ophthalmia neonatorum, mild to moderate symptoms of unilateral or bilateral conjunctivitis commonly occur between 5 to 14 days after birth. C. trachomatis is the most common cause of ophthalmia neonatorum. These patients present with lid edema, conjunctival chemosis, punctate corneal opacities, and occasionally micropannus formation.

Answer 31

Epithelium The corneal epithelium is the first to swell due to the fact that this layer is bathed by the tear film which supplies the epithelium with oxygen. During periods of hypoxia, mitochondrial function slows and the cornea switches to glycolysis for ATP production which is termed the Pasteur Effect. Anaerobic metabolism will cause a build-up of lactic acid and hydrogen ions which changes the pH of the cornea causing osmotic swelling.

Answer 32

Lissamine green Rose bengal Rose Bengal is an iodine derivative of fluorescein that preferentially stains the nuclei of devitalized cells, dead cells, and mucin. It is typically applied via a moistened filter paper strip or in drop form to the conjunctiva and is very helpful in evaluating keratoconjunctivitis sicca, herpes simplex lesions, corneal abrasions, ulcerations, foreign bodies, and conjunctival tissue changes. Rose Bengal has also been shown to have some antiviral properties. Lissamine green stains degenerated cells, dead cells, and mucous in a very similar manner to that of Rose Bengal; however, lissamine green is preferentially used due to marked ocular irritation and discomfort that tends to occur more frequently with the use of Rose Bengal. Methylene blue has properties similar to Rose Bengal but also has the ability to stain corneal nerves. Sodium fluorescein is the most widely utilized dye for use in eye care due to its low toxicity and excellent fluorescent properties. It is most commonly used in the assessment of corneal and conjunctival lesions, foreign bodies, in the fitting and management of contact lenses, and in the measurement of intraocular pressure.

Answer 33

Keratoconus Patients with vernal keratoconjunctivitis are more likely than the general population to develop keratoconus. This is due to the association of atopic disease in both conditions. Additionally, patients with VKC and keratoconus tend to have a more severe form of keratoconus that is commonly complicated by corneal hydrops and a greater tendency for corneal neovascularization.

Answer 34

Eating or drinking the day of the surgery There are no restrictions placed upon the ingestion of food or drink the day of the surgery; however, the consumption of alcohol the day of surgery is not recommended. The patient should absolutely not wear their contact lenses since a clear, clean and defect-free cornea is essential the day of the surgery. Contact lenses can alter the shape of the cornea (and the prescription) which will alter the final visual outcome. Legally, the patient will not be allowed to drive home after the surgery. In case of an accident, the surgeon may be held liable. Patients are not allowed to swim or go into a hot tub for at least one week post-LASIK (two weeks is preferable). Patients are also advised not to get water or shampoo in their eyes while showering for a week post-surgery.

Answer 35

Lattice dystrophy Lattice dystrophy is an autosomal dominant dystrophy (except for type III, which is autosomal recessive) with four sub-types categorized according to age of onset, systemic involvement, causative mutation, and appearance. Essentially, this condition is due to a deposition of amyloid that causes a decrease in visual acuity. The opacifications in this dystrophy appear as thick or thin lines and dots (depending on the sub-type). Granular dystrophy results from a deposition of eosinophilic hyaline in the anterior stroma. Again, this condition is autosomal dominant and onsets in the first decade of life. As time passes, the deposits tend to coalesce and cause a decrease in visual acuity. Granular dystrophy presents with a clear limbal zone. The stroma between the opacities remains clear in the early stages of the condition. Macular dystrophy occurs secondary to a deposition of glycosaminoglycans (mucopolysaccharides) in the stroma during the first decade of life. This condition is autosomal recessive and causes poor vision by the time the patient reaches roughly 20-30 years of age due to corneal thinning and enlargement of opacities that involves all of the corneal layers. This dystrophy extends to the limbus. The preferred surgical intervention is a corneal transplant. Macular dystrophy is the most visually devastating of the three stromal dystrophies mentioned here. A good mnemonic for committing this to memory is: Marilyn Monroe Got Hers in Los Angeles (Macular-Mucopolysaccharide, Granular-Hyaline, Lattice-Amyloid). Fleck dystrophy is an autosomal dominant condition that has an onset in the first decade of life and occurs due to fleck or comma-like deposition of glycosaminoglycan in the stroma. This dystrophy rarely requires any intervention.

Answer 36

Interstitial keratitis Interstitial keratitis (IK) is an inflammation of the corneal stroma in the absence of primary involvement of the corneal epithelium or endothelium. It is most often associated with congenital syphilis but may occur with other conditions such as tuberculosis, leprosy, Lyme disease, and other viral infections.

Answer 37

Lamellar keratoplasty A lamellar keratoplasty involves a partial thickness excision and transplantation of the corneal epithelium and stroma only, leaving the deep stroma and corneal endothelium intact. This type of procedure is typically indicated in patients with localized corneal thinning, marginal corneal thinning or infiltration, or opacification of the superficial 1/3 of the corneal stroma. A deep anterior lamellar keratoplasty is a transplantation procedure in which all of the opaque corneal tissue is removed almost all the way to the level of Descemet's membrane. It is indicated in patients who have a corneal disease involving 95% of the corneal thickness but who maintain a healthy corneal endothelium with an absence of breaks in Descemet's membrane. A penetrating keratoplasty is a surgical procedure in which the full thickness of the cornea is replaced by donor tissue. This procedure is used in cases where the endothelium is compromised, there is dense and deep corneal scarring, severely infected corneal tissue, or degenerative diseases that could potentially recur.

Answer 38

Horizontal bowtie The orientation of the bowtie on corneal topography is aligned with the location of the steep keratometric meridian (90 degrees away from the axis). Therefore, in against-the-rule astigmatism (axis near 90 degrees), the bowtie will be oriented horizontally. With-the-rule astigmatism (axis near 180 degrees) will reveal a vertically aligned bowtie pattern on topography. Additionally, patients with oblique astigmatism will have the bowtie slanted either left or right. For example, if a patient reveals astigmatism with an axis of 45 degrees, topography will show a bowtie pattern that is slanted to the right by 45 degrees (aligned with the 135 degree meridian).

Answer 39

Epithelial layer The epithelial cells store glycogen, which is used as an energy source when oxygen is not available. The stores can last for about 2 hours before being depleted. Once glycogen is no longer accessible, the cornea will not produce enough ATP and the epithelial cells will begin to die.

Answer 40

Hyperthyroidis Superior limbic keratoconjunctivitis (SLK) is predominantly found in middle-aged women that tend to have associated abnormal thyroid function (usually hyperthyroidism). Studies have shown a 50% prevalence of thyroid disease in patients diagnosed with SLK. The exact etiology and pathophysiology of SLK remains unclear, but the relation with hyperthyroidism and the pattern of exacerbations and remissions suggests a possible autoimmune association. It is thought that SLK occurs as a result of blink-related mechanical trauma that leads to irritation of the superior limbal region as loose conjunctival tissue rubs against the limbus during the blinking movement of the upper eyelids. Damage typically occurs to both the superior tarsal and conjunctival surfaces.

Answer 41

48 diopters At the time of birth, the approximate average refractive power of the human cornea is 48 diopters. As emmetropization occurs, the cornea will typically lose about 4 diopters of refractive power by the time a child reaches the age of 2.

Answer 42

Corneal abrasion Bandage contact lenses can be used in situations where the corneal surface requires protection from mechanical forces (such as trichiasis or entropion) or from eyelid movement over the exposed area; the bandage contact lenses can be used to promote healing and pain relief (i.e., from a corneal abrasion) and to improve vision while maintaining binocularity. In general, it is best to choose a silicone hydrogel for extended wear purposes that fits a little more steeply to reduce lens movement and mechanical friction (do not seal off the cornea-- some movement is required). A dellen is a paralimbal thinning of corneal tissue adjacent to elevated tissue. In general, a dellen can develop beside a pinguecula, pterygium, chemosis or scar tissue secondary to trauma or surgery. This condition arises from uneven tear film distribution, causing desiccation and thinning. If present for a long period of time, scar tissue may develop. Corneal arcus is commonly seen in the elderly as a bilateral yellow/white ring that encircles the cornea while maintaining a clear zone between itself and the limbus. The ring occurs due to lipid leakage from limbal blood vessels. Treatment is not generally required as vision is not affected. However, if the patient is under 50 years of age, consider systemic hyperlipidemia and refer for blood work. If the patient is under 40 years of age and presents with arcus, refer for a serum cholesterol measurement. Lastly, if the arcus is unilateral, consider carotid occlusion on the side that DOES NOT display corneal arcus. A limbal girdle of Vogt is located in the interpalpebral zone at the 3 and 9 o'clock positions of the cornea and comes in two types. The less common form leaves a clear zone between itself and the limbus and appears as a white/yellow band that remains in the peripheral cornea and is considered to be an early form of band keratopathy. The second form is contiguous with the conjunctiva and may be mistaken for a pinguecula, because there is no clear zone between itself and the limbus. The white-yellow band occurs as a result of collagen breakdown in Bowman's layer. No treatment is necessary.

Answer 43

Add a -1.00 lens and subtract 6D from the drum reading 1- if it is too much steeper --> Try +1.25 lens --> then add 8-9 D to the drum reading 2- if too much steep--> try +2.25 trial --> then add 16 D to the drum 3- if it is flat --> try -1.00 trial lens --> substract 6D from the drum When measuring the keratometry values utilizing a manual keratometer, there are certain circumstances in which the reading may be out of the range of the drum values. In these cases, one will need to add a trial lens to keratometer in order to extend the ranges (lenses are added to the patient's side of the keratometer). Cases in which the curvature is steeper than the drum reading, plus trial lenses are required, and when the reading is flatter than the drum reading, minus trial lenses are necessary. In the case of steeper curvatures, typically a +1.25 trial lens is tried first. If a measurement can be found with this lens, one will need to add about 8-9D to the drum reading in order to obtain the true value. A +1.25 lens will extend the range from about 52D to 60 or 61D. If keratometry values are even steeper (in the 60-68D range), a +2.25 trial lens can be utilized to extend the drum range even more. In these cases, about 16D is added to the drum reading to reach the true keratometry value. If the curvature is flatter than can be measured with the manual keratometer, a minus lens can be added to extend the range in the opposite direction. Typically a -1.00 trial lens will encompass a keratometry reading from about 32-38D. If a -1.00 lens is added, one will need to subtract 6D from the drum reading. This is the case for the above patient.

Answer 44

Lymphadenopathy in gonococcal infections is typically prominent Gonorrheal infections typically have the following characteristics: - Profuse conjunctival purulent discharge - Eyelid tenderness and edema - Severe conjunctival chemosis and hyperemia - Pseudomembrane formation can occur - Lymphadenopathy is typically prominent - N. gonorrhoeae can invade an intact epithelium; therefore peripheral corneal ulceration can occur if conjunctivitis is not treated properly - In severe cases, the ulceration can extend centrally, and eventual corneal perforation and endophthalmitis is possible - Gram staining will reveal a Gram-negative organism with a kidney-shaped diplococcic appearance

Answer 45

A slight hyperopic shift in vision Diffuse lamellar keratitis is a non-infectious inflammation at the interface between the corneal flap and the stroma in patients who have undergone a LASIK procedure. As the inflammation advances, the stromal tissue melts resulting in a flattening of the cornea and a hyperopic shift. DLK does not result in corneal epithelial defects and usually does not result in high levels of irregular astigmatism

Answer 46

14 days Epidemic keratoconjunctivitis typically runs a common clinical course that begins with characteristic signs and symptoms following an 8-10 day incubation period. Initially, patients will usually complain of eyelid edema, pain, photophobia, and lacrimation. Early conjunctival clinical signs include a mixed papillary and follicular response, hyperemia, chemosis, and subconjunctival hemorrhages that typically last for 7-21 days. In more severe cases, the development of a conjunctival membrane or pseudomembrane is possible. Corneal involvement in patients with EKC is variable, but most patients develop diffuse, fine, superficial keratitis within the first week of the onset of the disease. After about 6-13 days, focal punctate epithelial lesions that appear elevated and stain with sodium fluorescein often occur, and by day 14, subepithelial opacities develop under these focal lesions in about 20% of patients. These subepithelial infiltrates may affect vision and can persist for months to years but typically will eventually resolve without scarring or neovascularization.

Answer 47

Vogt's striae will often disappear when external pressure is applied to the globe Vogt's striae are fine vertical lines deep within the stroma Vogt's striae are thin, fine, parallel, vertical lines that are commonly observed in patients with keratoconus. They are typically found radiating through the center of the cone, and represent stressed collagen lamellae deep within the corneal stroma. These striae will usually disappear when external pressure is applied to the globe. Vogt's striae can also be present in patients with pellucid marginal degeneration but are most commonly found in cases of keratoconus.

Answer 48

Munson's sign Patients with moderate to severe corneal thinning and steep ectasia may exhibit a noticeable protrusion of the lower eyelid on downgaze. This is known as Munson's sign. Mild presentations will not produce significant displacement of the lower lid, as corneal protrusion is more subtle. Von Graefe's sign is lagging of the upper eyelid on downward rotation of the globe and is associated with Grave's disease. Hutchinson's sign refers to a skin lesion on the tip of the nose that commonly precedes the development of herpes zoster ophthalmicus. Uhthoff's sign is a worsening of neurologic symptoms associated with multiple sclerosis when the body's temperature is elevated. Shafer's sign is the presence of fine retinal pigment epithelial cells in the anterior vitreous that are highly indicative of a retinal tear.

Answer 49

Conductive keratoplasty In cases where the corneal curvature must be steepened in order to correct for refractive error (hyperopia or presbyopia), conductive keratoplasty (CK) is a viable surgical option. Although this surgical procedure was used more often in earlier years, it is not currently as widely used as laser-assisted in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). In comparison to CK, LASIK and PRK tend to be safe, have long-standing results, and more predictable outcomes. The CK technique involves using a radiofrequency probe to create burns in either one or two concentric rings in the mid-peripheral region of the cornea. These thermal laser burns cause subsequent stromal shrinkage, which results in an increase in the curvature of the cornea. This change in curvature typically decays over time, but the procedure can be repeated. Radial keratotomy is also an older surgical procedure in which a diamond blade is used to create several radial corneal incisions (the number and depth of the incisions depends on the refractive error) in order to flatten the corneal curvature in patients with myopic refractive errors. Limbal relaxation incisions are similar in that arcuate incisions are made on opposite sides of the corneal periphery in the meridian of the "plus" cylinder axis in order to create flattening of the steep corneal curvature (with some smaller steepening of the flat meridian) in an attempt to reduce the amount of corneal astigmatism. Photorefractive keratotomy (PRK) and laser-assisted in-situ keratomileusis (LASIK) are refractive surgery techniques that use an excimer laser to ablate corneal tissue to a certain depth in either the central cornea (to correct myopia) or peripherally (to correct hyperopia).

Answer 50

None-this layer is acellular Bowman's layer is roughly 12 microns thick and serves as a smooth support for the epithelial cells that lay anteriorly. This layer does not contain cells but is comprised of collagen fibrils arranged in a random fashion.

Answer 51

Vessel penetration in excess of 1.5mm The FDA has deemed that vessel penetration into the cornea in excess of 1.5 mm is considered to be of significance. A small amount of neovascularization (especially with soft contact lens wear) is to be expected, but if the vessels penetrate too far into the cornea, it is likely a sign of hypoxia and should be dealt with accordingly.

Answer 52

Epithelium Neovascularization associated with soft contact lens wear is generally located superficially and presents as an extension of vessels from the superficial marginal arcade beyond the limbus into the cornea. Most commonly, neovascularization is the result of over-wear from a contact lens that possesses a low Dk/t. Stromal neovascularization can occur with contact lens wear but this is not the norm. Most stromal neovascularization is typically the result of infections such as chronic blepharoconjunctivitis, keratitis, phlyctenulosis, trachoma, or graft rejection.

Answer 53

No, neither eye should undergo LASIK Unfortunately, this patient is not a good candidate as his high prescription falls outside the specified parameters for LASIK. Reportedly, LASIK can be used to correct up to 12.00 D of myopia, 6.00 D of astigmatism, and 6.00 D of hyperopia. The right eye of our patient has 14.00 D of myopia in the vertical meridian (when in doubt, always place the prescription on an optical cross). His left eye possesses a high amount of astigmatism which also falls outside the range of current approval for LASIK.

Answer 54

Diffuse lamellar keratitis Diffuse lamellar keratitis (DLK), sometimes referred to as the Sands of Sahara, typically occurs two to five days post-LASIK. Initially the patient will note a progressive decrease in visual acuity. Biomicroscopy will reveal diffuse inflammatory infiltrates located across the periphery of the surgical interface but do not penetrate into the stroma nor do they extend into the flap. Very early cases will display infiltrates along the edge of the flap. Generally there will be little to no injection of the conjunctiva, the corneal surface will remain intact and there will be no reaction in the anterior chamber. The patient usually does not notice any discomfort. As the condition progresses, the patient will continue to notice a decrease in acuity. The subjective refraction will become hyperopic with astigmatism. The number of granular infiltrates will increase and diffusely cover the flap interface and a central haze will develop. With time, the central haze will become more condensed and may appear wave-like. Stromal folds may develop but some believe that this is actually not related to DLK but some other variant and thusly should not be classified as DLK. Either way, treatment is aggressive and consists of topical steroid drops every hour. If the infiltrates are severely condensed, the flap may have to lifted, the interface debrided and the flap refloated to remove them. If this condition is not detected and treated early, stromal melt along with severe scarring and poor visual acuity could ensue. It is important to be able to distinguish between microbial keratitis and DLK, as the treatments differ for each. If you treat microbial keratitis with a steroid, you are only increasing the risk of infection as the steroid will suppress the body's ability to fight infectious organisms. Remember, in general, infections will cause redness and usually will not limit themselves to the surgical interface. Some form of discharge will likely be present, and the patient will generally note some type of discomfort or irritation. Dry eye syndrome may present with mild injection of the conjunctiva and superficial punctate keratitis but infiltrates in general will not occur with this condition. The patient may report a foreign body sensation along with burning and stinging of the eyes. Epithelial ingrowth tends to develop several days to weeks post-LASIK and initially presents along the flap edge interface. Ingrowth generally progresses at a slower rate than DLK and most likely will not present diffusely throughout the flap-stromal incision sites at such a rapid rate.

Answer 55

Atmospheric oxygen Tears absorb oxygen from the air which then diffuses into the cornea. Oxygen is required by the endothelium and the epithelium because they are metabolically active. A small amount of oxygen is also supplied by the limbal blood vessels and by diffusion from the aqueous. However, due to the large amount of oxygen required by the cornea, most of the oxygen during periods of wakefulness is derived from the tears. For this reason, it is important that contact lens patients be fitted with lenses that offer high oxygen permeability.

Answer 56

r 0.50Eccentricity is the measurement of the asphericity of a curved surface. In the case of the human cornea, it indicates the way in which the cornea changes from a more curved central portion to a flatter periphery (also known as a prolate shape). Normal corneal eccentricity values (e values) range between +0.50 and +0.60 in humans. A higher corneal eccentricity value indicates that the cornea flattens more rapidly in the periphery; a lower eccentricity measurement would occur in a patient whose cornea flattened more slowly in the periphery. Another way to think of eccentricity is that the 'e' value designates that amount by which the cornea deviates from a perfect sphere (which has an eccentricity value of 0). A parabola has an eccentricity value of 1; a prolate ellipse (as in the normal cornea) will have an eccentricity between 0.1 and 0.9 depending on how fast the peripheral flattening occurs. Lastly, an oblate ellipsoid (as in some post myopic refractive surgical corneas) will have an eccentricity value of between -0.1 and -0.9, depending on how fast the curvature steepens in the periphery.

Conj and cornea and refractive error Flashcards

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