OPTO Flashcards
(151 cards)
1
Q
Aberration
A
Distortions, related to astigmatism , that cause the inability of light rays entering the eye to converge (come together) to a single focus point on the retina.
2 Categories:
Higher-order
Lower-order.
2
Q
Ablation
A
Surgical removal of tissue, typically using a cool beam laser
3
Q
Accommodation
A
The automatic adjustment of optical power by the eye in order to maintain a clear image (focus) as objects are moved closer
4
Q
Altitudinal Visual Field Defects
A
Upper or lower half of the VF is selectively affected
- Creates a horizontal line across the VF - “respecting the horizontal meridian”
- Altitudinal defects occur in retinal vascular disease, glaucoma, and other disorders that affect the eye itself.
5
Q
Amblyopia
A
Dullness or obscurity of sight for no apparent organic reason, not correctable w/ specs or sx.
- Lazy Eye - one eye becomes dependent on the other eye to focus, usually dev’t in early childhood. Often associated with strabismus.
6
Q
AMD
A
Disease that damages the macula, the central part of the retina, leading to a loss of central vision and leaving only the peripheral or lateral vision intact.
7
Q
Ametropia
A
Refers to the broad condition of having some form of refractive error present in your eye
- ie: Myopia, Hyperopia, Astigmatism
8
Q
Angle (Drainage Angle)
A
Drainage area of the eye formed between the cornea and the iris
- Named for its angular shape
9
Q
Anisometropia
A
Eye condition: have unequal refractive power
10
Q
Anterior Chamber
A
Space between the cornea and the crystalline lens, contains aqueous humor
11
Q
Antimetabolite
A
Drugs that retards cell division and slows down healing
- In Glaucoma sx: used to prevent the drainage site from failing because of scarring.
12
Q
Antioxidants
A
Micronutrients that destroy or neutralize free radicals - molecules that stimulate abnormal cellular reproduction (cancer) and cellular destruction (aging).
13
Q
Anti-VEGF drugs
A
Drugs that block the action of Vascular Endothelial Growth Factor
- Effective in the treatment of Choroidal Neovascularisation
14
Q
Aphakia
A
Absence of the lens of the eye
15
Q
Aqueous / Aqueous Humor
A
Transparent fluid occupying the anterior chamber and maintains eye pressure
16
Q
Argon laser
A
Device used to treat glaucoma (usually open angle) and diabetic retinopathy using a thermal beam
17
Q
Asthenopia
A
Eyestrain
- Subjective symptoms of ocular fatigue, discomfort, lacrimation, and headaches arising from the use of eyes
18
Q
Astigmatic Keratotomy
A
A modified form of Radial Keratotomy (RK)
19
Q
Astigmatism
A
Structural defects of the eye in which the light rays from a viewed object do not meet in a single focal point, resulting in blurred images being sent to the brain
20
Q
Autosomal recessive
A
An inheritance pattern in which a person must inherit two copies of an abnormal gene (one from each parent) in order to develop the disease. If two individuals each carry one copy of an abnormal gene, then each child born to these two parents will have a 25% chance of receiving 2 copies of the abnormal gene and as a result, inherit the disease. Cystic fibrosis is an example of an autosomal recessive disease
21
Q
Binocular Vision
A
Focusing and fusing of the separate images seen by each eye into one single binocular image
22
Q
Biologic Therapeutic Agent
A
A group of genetically engineered antibodies which target specific molecules involved in the immune system or the system which regulates inflammation and block their action. Anti-VEGF drugs belong to this group.
23
Q
Blind Spot
A
Sightless area within the visual field of a normal eye, where the optic disc attaches the optic nerve to the eye. Caused by absence of light sensitive photoreceptors where the optic nerve enters the eye
24
Q
Cataract
A
Opacification/Clouding of the crystalline lens.
- Types: traumatic, congenital, age-related
25
Cecocentral Scotomas
These are visual field defects that extend from the central vision to the natural blind spot. This type of field defect usually represents an insult to the cluster of retinal ganglion cells called the papillomacular bundle
26
Central Vision
An eye’s best vision; used for reading and discriminating fine detail and color
27
Choroid
The pigmented layer of the eye between the retina and the sclera
- Contains a rich network of blood vessels
28
Choroidal Neovascular Membrane
Wet Macular Degeneration - complication of ARMD
- Network of blood vessels which originates from the choroid layer which comes to lie just under the retina, resulting in leakage of fluid or bleeding into the retina
29
Ciliary Body
A pigmented part of the eye, lying just behind the iris. One of its functions is to produce aqueous
30
Conjunctivochalasis
A redundant folds in the conjunctiva typically located between the globe and the lower eyelid. Loose bulbar conjunctiva that may become pinched between the lids and cause tearing and inflammation. Frequently age-related. Usually found along the lower lid margin. It interferes with the normal distribution of tears causing dry eye and epiphora
31
Convergence
Reflex that enables the eyes to focus on a single point in near vision
32
Cornea
Front window of the eye
- Transparent front part of the globe shaped like a slightly domed cap, covering the iris, pupil, and anterior chamber and provides most of an eye’s optical power.
33
Crystalline Lens
Transparent biconvex lens located behind the pupil; refracts light to focus images on the retina
- Natural lens inside of the eye
34
Cupping (Disk Cupping)
An enlargement of the cup or central depression in the optic nerve head
- Visible with an ophthalmoscope
- If accompanied by a notch or a small spot of bleeding is a sign of glaucoma.
- Cupping is a clinical sign that indicates that a large number of nerve fibers in the optic nerve have been lost
35
Cycloplegic
A substance which paralyses the ciliary muscle. It is usually necessary to use this to obtain an accurate measurement of refractive error in younger children
36
Descemet’s Membrane
A layer of the cornea which lies just forward of the endothelium
37
Deuteranopia / Deuteranopic
Complete color deficiency affecting the ability to see the color green
- 3 possible color vision deficits:
Red (protan)
Green (deutan)
Blue (tritan)
- The suffixes -omaly and -opia indicate partial and complete color vision deficits, respectively. Therefore, a person who has deuteranopia has a complete green color deficit.
38
Digital Surfacing
Precise surface cutting using single point turning; cutting height is controlled at all points on the lens
39
Dyschromotopsia
Colour blindness
- Heritable vision deficits:
Red (protan) - x-linked
Green (deutan) - x-linked
Blue (tritan) - autosomal recessive
- Either partial (-omaly) or complete
(-opia).
40
Electroretinogram (ERG)
A test that measures the electrical activity of the retina when exposed to flashes of light of varying intensity. Abnormalities in the electroretinogram typically occur in conditions that affect the photoreceptor cells (e.g. retinitis pigmentosa).
41
Emmetropia
Emmetropia is a term that refers to the condition of having “normal” 20/20 vision, with eyes free of refractive errors
- Sometimes called ‘normal 20/20 vision’ - images at 20ft focus sharply on the retina
42
Endophthalmitis
Infection which involves the internal structures of the eye. It usually poses a serious threat to the visual function of the eye
43
Endothelium
The layer of the cornea closest to the anterior chamber. It is a single layer of cells which does not regenerate after birth. Its function is to pump fluid out of the cornea. If it fails, the cornea becomes hazy (decompensates).
44
Epiphora
Excessive tear production or insufficient tear drainage from the eyes (usually from blockage of the lacrimal duct) causing overflow of tears onto the face.
45
Excimer laser
A type of laser which emits in the ultraviolet range of the spectrum. In ophthalmology, it is used for removing tissue from the cornea, particularly in refractive surgery
46
Fovea Centralis / Fovea
(Latin: ‘the pit/pitfall’)
- Small depression in the center of the macula region of the retina.
- Produces the sharpest focus
- High concentration of cones which aid in clear central vision
- About 1.0 mm dia. with a high concentration of cone photoreceptors
47
Foveal burn
A laser burn in the fovea, which can occur as an adverse event during retinal laser treatment
48
Foveola
The center of the fovea
- About 0.2 mm in diameter
- Only cone photoreceptors are present, very compact cones, thinner and more rod-like in appearance than cones elsewhere
- Starting at the outskirts of the fovea, however, rods gradually appear, and the absolute density of cone receptors progressively decreases.
49
Glaucoma
A condition, usually characterised by raised pressure in the eye which causes damage to the optic nerve resulting in defects in the field of vision. It is treated by reducing the pressure in the eye. Increase in intra-ocular pressure resulting, if left untreated, in an irreversible deterioration of the optical nerve and of the retina, as well as an alteration of the visual field, i.e. a reduction in visual performance, often accompanied by headaches and aching eyes. A disease of the eye characterized by increased intraocular pressure. A common cause of preventable vision loss. May be treated by prescription drugs or surgery.
50
Glaucoma (Normal/Low Tension Glau)
Glaucoma in which the intraocular pressure is normal but there is progressive optic nerve damage and visual field loss.
51
Goldmann Visual Field
Tangent screen or Goldmann field exam.
The object is usually a pin or bead on the end of a black stick that is moved by the examiner. This exam creates a map of your central 30 degrees of vision. This exam is usually used to detect brain or nerve (neurologic) problems.
52
Humphrey Visual Field
Measures the entire area of peripheral vision that can be seen while the eye is focused on a central point.
53
Hyperopia
Far-sightedness, an eye that is too short and/or insufficiently powered. The image forms behind the retina, which explains why the hyperopic subject has better eyesight in far vision than in near vision.. Corrected with plus (convex) lenses.
54
Incomplete Penetrance
The concept that even though several members of a family or population may have the same DNA mutation, not everyone with that mutation will have or develop the disease. This is in contrast to variable expressivity which means that people with the same disease have varying disease severity. Penetrance, in contrast, is more of a yes/no question. Does or does not the person have the disease.
55
Intraocular Pressure
Fluid pressure exerted inside the eyeball (ocular globe), which keeps the wall taut
56
Iris
Pigmented tissue lying behind the cornea that gives color to the eye
- Acts as a diaphragm that contracts according to the intensity of light
- Controls light by contracting and constricting the opening (pupil).
57
Lens Capsule
The eye’s lens consists of tightly packed layers of transparent protein fibres contained within an elastic capsule. During cataract surgery, the layers of lens fibres are removed, but the posterior part of the lens capsule and its supporting zonular fibres are retained to act as a support for the lens implant.
58
Lenticulation
The process of thinning the edges of a minus lens or centers of plus lenses using a carrier shape or change of curvature. It involves specifying an area of the lens as the ‘visual area’, which is the part of the lens the patient is intended to actually look through. This ‘visual area’ is also referred to as a ‘bowl’, and can be as small as 30mm. The balance of the lens has edges thinned in minus lenses and centers thinned in plus.
59
Limbus
The region where the cornea and the sclera meet.
60
Low Vision
When you’re either legally blind (you have a best corrected visual acuity of less than 20/200 or tunnel vision) or have visual acuity between 20/70 and 20/200, despite the use of glasses or contacts
61
Macula / Macula Centralis
Central part of the retina. Composed uniquely of cone cells and enables precise vision
- Part of the retina at the back of the eye
- About 5mm across, but is responsible for our central vision, most of our colour vision and the fine detail of what we see
- A healthy macula is about 250 microns (one quarter of a millimetre) thick
62
Macular Edema
The accumulation of fluid within the central area of the retina. This may occur as a complication of intraocular surgery, as a response to uveitis or as a complication of other retinal conditions such as diabetic retinopathy
- A swelling of the macula that makes it hard to see. It usually results from injury or disease.
63
Microkeratome
A device which cuts a flap of the cornea prior to removal some of the thickness of the underlying corneal stroma with the excimer laser during refractive surgery
64
Mydriatic
An eye drop or ointment which dilates the pupil
65
Mydriasis
The dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response.
Non-physiological causes of mydriasis include disease, trauma, or the use of certain types of drug. It may also be of unknown cause.
66
Myopia
Near-sightedness - an eye that is too powerful or too long. The image forms in front of the retina; a person with myopia thus sees badly in far vision but well in near vision.
- Requires a minus (concave) lens
67
Anomaloscope
- Instrument and color vision test, often used to quantify and characterize color blindness. They are expensive and require specialized knowledge to operate, but are viewed as the gold standard for color vision standards.
- The currently available Neitz OT and Oculus Heidelberg anomaloscopes are designed to perform in the same way as the original Nagel anomaloscope, which is no longer available.
68
Neovascular Glaucoma
A form of glaucoma which arises because of the growth of new blood vessels on the iris which close off the trabecular meshwork. It can be a complication of a number of conditions (ie: diabetic retinopathy)
69
Ocular Globe
The eyeball, about 25mm in diameter when emmetropic
70
Optical Coherence Tomography
Optical
OCT - noninvasive imaging technology used to obtain high resolution cross-sectional images of the retina
- Similar to ultrasound testing, except that imaging is performed by measuring light rather than sound
- Measures the retinal nerve fiber layer thickness in glaucoma and other diseases of the optic nerve
71
Optical Correction
Combination of the curvatures of the front and rear surfaces of a lens, measured in diopters
72
Organic/Plastic Lenses
Made from a “polymerized” resin.
73
Orthophoric
Proper alignment of the two eyes. Absence of eye deviation
74
Orthoptics
Optical specialty dealing with the diagnosis and treatment of defective eye coordination, binocular vision, and functional amblyopia by non-medical and non-surgical methods, e.g., glasses, prisms, exercises.
75
Papillomacular Bundle
A collection of retinal ganglion cells that carry the information from the macula (the central retina) to the optic nerve and on to the brain. If damaged, central visual field defects occur
76
Pars Pana
A flat, rather featureless area of the ciliary body which contains relatively few blood vessels. Instruments used in vitreoretinal surgery are inserted in this region
77
Peripapillary Atrophy
Thinning of the retina and retinal, pigment epithelium in the region immediately surrounding the optic nerve head. This can be seen in a number of pathologic and benign conditions
78
Photochromic
Variable tint lens that can darken or lighten depending on the presence of UV
79
Photophobia
Light sensitivity” and the aversion to sunlight or well-lit places
- Not a morbid fear, but an experience of discomfort or pain to the eyes due to light exposure. May be associated with excessive tearing, and can be caused by inflammation of the iris or cornea
80
Photopic
A condition of “light adaptation” that is used in retinal testing such as the electroretinogram. Light adaptation is accomplished by exposing a patients eyes to diffuse light of moderate intensity several minutes. This can be useful for determining the health of “cones,” the fine detail and color perceiving cells in the retina.
81
Polycarbonate
Lens material characterized by lightness, impact resistance, high refractive index, UV absorption.
82
Posterior Capsule Opacification
Thickening of the lens capsule following cataract surgery. This is a healing response, which in some people may be sufficient to reduce the vision and require laser treatment to make an opening in the capsule at some point after cataract surgery
83
Posterior Capsule Rupture
A break in the posterior capsule of the lens, usually as a complication of cataract surgery. It may allow vitreous to move forward into the anterior chamber of the eye
84
PAL (Progressive Addition Lens)
Progressives
Corrects presbyopia by varying optical power progressively from an upper to lower part. No demarcation lines.
85
Prostaglandin Analogue
One of the groups of eye drops used to treat glaucoma. They work by increasing the rate at which aqueous passes out of the eye.
86
Protanomaly / Protanomalous
Partial color deficiency affecting the ability to see the color red.
There are three possible color vision deficits: red (protan), green (deutan), and blue (tritan). The suffixes ?omaly and ?opia indicate partial and complete color vision deficits, respectively.
Therefore, a person who has tritanomaly will have a partial blue color vision deficit while a person who has deuteranopia will have a complete green color deficit.
87
Pupil
Central opening of the iris through which rays of light enter the eye. The diameter depends on ambient light. An opening in the center of the iris, of variable sizes, that regulates the amount of light that enters the eye
88
Refractive Error
The amount of myopia, hyperopia or astigmatism. An error in refraction of the eye. An optical defect in an unaccommodating eye in which parallel light rays do not focus sharply on the retina.
89
Refractive Index
Characterizes the way a transparent optical material bends or refracts light
90
Relative Afferent Pupillary Defect (RAPD)
An indication of damage to the visual system which is greater on one side than the other. The presence of a relative afferent pupillary defect (RAPD) means that the pupils constrict less when a light is directed into the affected eye than they do when the same light is directed into the normal (or less affected) eye . The presence of an RAPD usually indicates damage to the retina or optic nerve that results in diminished light impulses being transmitted from the eye to the brain on the affected side.f
91
Retinal Ganglion Cells
These cells transmit the information from the other layers of the retina to the brain. The axons of these cells make up the optic nerve. Retinal ganglion cells comprise the most superficial cell layer in retina and are susceptible to damage in a number of disease entities, including glaucoma
92
Retinitis Pigmentosa
A group of genetic eye conditions leading to chronic retinal degeneration, accompanied by abnormal deposits of pigment
- Causes a progressive decrease in peripheral or side vision
- Associated with night blindness, loss of peripheral vision, tunnel vision, decreased acuity, lack of depth perception, retinal scarring, and photophobia
Any of a group of retina conditions you can inherit. Each causes you to lose sight over time. Typically a decrease in night vision may be the first sign followed by your vision tunneling down to just what you see straight ahead. Eventually, your central vision may decrease
93
Schlemm’s Canal
A small channel near the root of the iris which extends round the circumference of the eye. The trabecular meshwork filters aqueous into it, and from it the aqueous drains into veins which leave the eye
94
Sclera
The white of the eye. It forms the wall of the eye, except in the region of the cornea.
95
Scotoma
The medical term for a visual field abnormality, or a blind spot
96
Scotopic
A condition of “dark adaptation” that is used in retinal testing such as the electroretinogram. Dark adaptation is accomplished by placing black goggles over the patient’s eyes for a predetermined period of time (usually about 30 minutes). This can be useful for determining health of “rods,” or the dim light-detecting cells in the retina
97
Septo-Optic Dysplasia (SOD)
- A developmental disease present at birth. It causes underdevelopment of your optic nerve, pituitary gland and certain parts of your brain
- 60-90% of these patients present with blindness or symptoms of visual impairment. Signs related to visual loss include absent fixation, searching nystagmus, visual inattentiveness and strabismus.
98
Strabismus
Strabismus (misaligned eyes) is a condition in which one eye is turned in a direction that's different from the other eye
- Usually found in children, but can also happen in adults. Treatment may include glasses, patching, eye exercises, medication or surgery
- Greek ‘strabismos’ = squinting
99
Stroma
The central layer of the cornea between the epithelium and endothelium. It makes up the majority of the thickness of the cornea.
100
Trabecular Meshwork
A network of drainage channels located at the periphery of the anterior chamber of the eye, through which aqueous drains from the eye into the circulation
101
Trabeculectomy
A surgical procedure to allow aqueous to flow from the anterior chamber of the eye to a space under the conjunctiva in a controlled fashion, in order to reduce the pressure in the eye.
102
Trifocal
An ophthalmic lens that incorporates three lenses of different powers
- The main portion is usually focused for distance (20 ft.)
- The center segment for about 2 ft.
- The lower segment for near (40 cm, or 16 inches)
103
Tritanopia
A form of color blindness exhibiting loss of the blue receptor, inherited in an autosomal recessive fashion
104
Uveitis
Inflammation involving the pigmented layers of the eye (the iris, ciliary body and choroid).
105
Variable Expressivity
The idea that individuals with a particular disease process will not each experience the same severity of disease.
- For instance, one person may have a milder form of the disease while another person with the same disease has a more severe manifestation of the disease.
- This is in contrast to incomplete penetrance
106
Vascular Endothelial Growth Factor (VEGF)
A protein which induces the growth of new blood vessels and is usually produced in response to impaired oxygen flow to tissues. It may be produced in increased quantity in diabetic retinopathy and age-related macular degeneration
107
Vasculitis
- Plural: vasculitides
- A group of conditions characterised by the inflammation of blood vessel walls
108
Vision Rehabilitation
Process of restoring functional ability and improving quality of life and independence in an individual who has lost visual function through illness or injury
- Most rehab services are focused on Low Vision - a visual impairment that cannot be fully corrected by regular eyeglasses, contact lenses, medication, or surgery.
- Low vision interferes with the ability to perform everyday activities
- Visual impairment is caused by factors including brain damage, vision loss, and others
- Of the vision rehabilitation techniques available, most center on neurological and physical approaches
109
Vision Rehabilitation Aids
Also known as Low Vision Aids
- Devices such as magnifiers and closed circuit television sets that can help people with sub-normal vision see more and function better in day to day activities
(CCTV system or video magnifier, uses a stand-mounted or handheld video camera to project a magnified image onto a video monitor, a television (TV) screen, or a computer monitor. Cameras with zoom lenses provide variable magnification
110
Visual Acuity
A measure of the ability of the eye to distinguish shapes and the details of objects at a given distance
- The standard definition of normal visual acuity (20/20 vision) is the ability to resolve a spatial pattern separated by a visual angle of one minute of arc. Since one degree contains sixty minutes, a visual angle of one minute of arc is 1/60 of a degree.
- A normal average eye an angle of one minute of arc (1/60th degree). (usually 20 ft. or 16 in.) and letter height (8.87mm).
111
Visual Field
Your entire range of sight, including peripheral vision
112
Vitrectomy
A surgical procedure to remove vitreous from the eye
113
Vitreous
A transparent substance with the consistency of egg-white which occupies the space inside the eye behind the lens
The clear gel-like substance in the center of your eyeball
114
Vitreo-Retinal Surgery
Surgical procedures involving the vitreous or the retina
115
Zonular Fibres
The natural lens is suspended within the eye by elastic fibres around its circumference. These, and the lens capsule are retained during the cataract surgery to allow the lens implant to be supported in the position that the original lens occupied
116
Diabetic Retinopathy
Common complication of diabetes and the leading cause of blindness in American adults
- Characterized by progressive damage to the blood vessels of the retina, the light-sensitive tissue at the back of the eye that is necessary for good vision.
- Later Symptoms: Loss of central vision, blurry or wavy areas in the central vision, drusen
- The risks of DR are reduced through disease management that includes good control of blood sugar, blood pressure, and lipid abnormalities. Early diagnosis and timely treatment reduce the risk of vision loss
117
Achromatopsia
A lack of certain receptors in your retinas. Your vision won’t be sharp, and you could be nearly or completely colourblind
- An inherited condition
118
Alpha-2 Agonists
Medications used to treat glaucoma
- They help aqueous humor drain out of your eye and stop your eye from making too much of it
- Lower pressure inside your eye
119
Beta-Blockers
Medicated eye drops that treat glaucoma
- Causes eyes to make less aqueous humour, and lowers pressure inside it
120
Carbonic Anhydrase Inhibitors
Medications that treat glaucoma
- Causes eye to make less aqueous humour, which lowers pressure
121
Choroiditis
A form of uveitis, or inflammation of the uvea, the eye's middle layer
- Causes the layer beneath retina to become inflamed
122
Conjunctivitis
Inflammation of the conjunctiva, also called Pink Eye
- Highly contagious, could be caused by:
• Viruses, including the kind that causes the common cold
•Bacteria
•Irritants such as shampoos, dirt, smoke, and pool chlorine
•A reaction to eye drops
•An allergic reaction to things like pollen, dust, or smoke
•Contact lenses
•Fungi, amoebas, and parasites
123
Cryotherapy
Surgery that freezes and destroys abnormal cells
124
Cyclitis
A form of uveitis that inflames the middle portion of the eye
- Can also affect the muscle that focuses the lens, called the ciliary body
- May come on suddenly and last several months
125
Retinoblastoma
A malignant tumor that forms on the retina
- Most often happens in children under the age of 5, can affect one or both eyes
126
Tunnel Vision
Loss of peripheral vision
- Can be caused by conditions like retinitis and untreated glaucoma
127
Vitrectomy
Surgical procedure where the vitreous humor is removed from the eyeball and replaced with a clear salt solution or temporarily with a gas bubble
- Can help when scars or blood in the vitreous blocks the vision
128
Automated Field Measurement
An examination to determine the viability of the nerve fiber layer of the retina and its effect on the field of vision of an individual
129
Antimetropia
One eye nearsighted; the other far- sighted
130
Blended Bifocal
Eliminates the tell-tale ledge found on standard bifocals
- Generally speaking, bifocals only correct vision for two distinct fields of vision, while progressive lenses offer clear vision at all distances
131
Blended Bifocal
Eliminates the tell-tale ledge found on standard bifocals
- Generally speaking, bifocals only correct vision for two distinct fields of vision, while progressive lenses offer clear vision at all distances
132
Blended Myodisc
A lenticular lens used in the correction of high myopia, having a concave central corrective area 20 to 30mm in diameter, with a flat, non-corrective periphery
- Myodiscs are not a preferred lens type, but are the least expensive option among available lenses fitted for minus powers beyond -12 diopters. They are cheap to produce but cause scotoma, a ringed blind spot. As a result, most practitioners encourage using other lens styles
133
Case Harden
Heat treatment of a glass lens for impact resistance
134
Cellulose Acetate
A thermoplastic which is not easily flammable, used as the material for spectacle frames
- Safety plastic
135
Cellulose Nitrate
A highly flammable thermoplastic, which was formerly used as the material for spectacle, frames
- Also known as celluloid, xylonite or zylonite/zyl
136
Optical Center
The central point of the lens through which a ray of light passes without suffering any deviation
- Also known as the ‘pole’
137
Blended Bifocal
Eliminates the tell-tale ledge found on standard bifocals
138
Chromatic Aberration
Also known as color fringing
- A color distortion that creates an outline of unwanted color along the edges of objects
- A dispersion of colors arising from unequal refraction of light of the different wavelengths of the spectrum
- This defect of an optical system causes the image to be surrounded by a halo of colours
- Corrected in an achromatic lens system.
139
Achromatic Lenses
Brings colors into focus at the same point, allowing users to fully focus an image
- Compared to non-corrected singlet lenses, achromats produce much clearer images, which make for easier viewing and a more accurate perception
140
Cilium / Cilia
Eyelash / Eyelashes
141
Decentration
In ophthalmic optics, the term “decentration” refers to the shift of the crystalline lens, an intraocular lens (IOL), a corneal refractive treatment, a contact lens, or the lens in a frame relatively to the visual axis
- The act of placing the optical axis of a lens in a different position than the geometric center of a spectacle lens
- The unit of measurement of the displacement is prism diopters
- Lens power in diopters x decentration in cm = prism diopters.
142
Didymium
Frequently recommended for use in flameworking and glassblowing as they are effective for blocking the bright yellow sodium flare that occurs when a torch flame is used to heat glass
143
Deuteranopia / Deuteranomaly
The most common type of red-green color vision deficiency
- Makes certain shades of green look more red
- Mild and doesn't usually get in the way of normal activities. Protanomaly makes certain shades of red look more green and less bright
144
Tritanomaly
Rare form of colour blindness
- Malfunctioning blue cones
- Makes it HARD to tell the diff. bet: blue & green, and yellow & red
- (Vs Tritanopia - unable to tell the diff…)
145
Tritanopia
Rare form of colour blindness
- Makes someone UNABLE to tell the diff. bet: blue & green, purple & red, and yellow & pink
- It also makes colors look less bright
(Vs Tritanomaly - HARD to tell the diff…)
146
Extraocular Muscles
6 muscles which cause movement of the eye:
- Internal and external recti
- Superior and inferior recti
- Superior and inferior oblique.
147
Filtration Angle
The angle formed by the cornea meeting the iris
148
Fundus / Fundus Oculi
The inside, back surface of the eye, made up of:
- Retina
- Macula
- Optic Disc
- Fovea
- Blood vessels
Fundus photography: special camera points through the pupil to the back of the eye and takes pictures
149
Gonioscope / Gonioscopy
An eye test that checks for signs of glaucoma
- Uses a special lens and slit lamp to evaluate eye’s drainage angle (anterior chamber angle) - if drainage angle is blocked or closed, you may have glaucoma
- One of many tests needed if you are at risk for glaucoma and to help determine which type of glaucoma you have and guides treatment decisions
150
Hyperopia
Farsighted - difficulty seeing up close
151
Hyperphoria
Tendency of one eye to deviate upward
