Flashcards in Vision Correction Deck (42):
What is refraction?
bending of light rays as they pass from one transparent medium through another of different density
What is normal refraction?
light that is reflected from an object is refracted through the cornea and lens directly onto the retina
When does myopia occur?
the refracting power of the eye is too strong
THe contact lens for myopia is shaped how?
minus and divergent
When does hyperopia occur?
the refracting power of the eye is weak
If contact lens for hyperopia is shaped how?
plus and convergent
What kind of lens is astigmatism corrected with?
(toric- a lens with different optical power and focal length in two orientations perpendicular to each other)
So for myopia and astigmatism what will the lens look like?
spherical and divergent
What is an incisional procedure that corrects vision?
What is the most common surgical procedure for vision correction?
What does LASIK stand for?
laser-assisted in situ keratomilusis
Which procedures are surface ablation procedures?
1. photorefractive kertotoamy (PRK),
2. laser epithelial keratomileusis (LASEK) and
3. epitherilial laser keratomileusis (epi-LASIK)
What procedures are intracorneal procedures?
Name a generic term, which includes all surgical procedures on the cornea to improve vision by changing the shape, and thus the refractive index of the corneal surface?
What are three types of refractive keratoplasties?
1. Keratotomies, ie corneal incisions
2. Keratectomies, ie removal of corneal epithelium
3. Keratomileusis, ie reshaping a stromal layer of the cornea
What are some precautions for patient selection for vision correction surgery?
patients with presbyopia in patietns 60-69 (higher retreatment rates)
Contraindications for vision correction surgery?
1. Autoimmune disease
2. collagen vascular disease and 3. immunodeficiency disease affect corneal healing
4. Women who are pregnant or nursing have fluctuating visual acuity
5. Patients with abnormal wound healing (keloids) may have abnormal corneal healing
6. DM—can perform if well-controlled, without cataract or diabetic retinopathy
Specific ocular contraindications for vision correction surgery?
1. Keratoconjunctivitis sicca (dry eye syndrome)
2. Exposure keratitis
3. Neurotrophic keratitis (degenerative disease caused by impaired corneal innervation)
4. Lid disorder affecting the tear layer
5. Patient with a h/o herpetic keratitis
6. Any patient with an abnormal shaped cornea
7. Sever rosacea
Why dont we use radial keratotomy anymore?
What kind of vision impairment was it used for?
didnt work in everyone
higher risk of infection
have to do second eye six weeks apart
incisions in periphery make central cornea flatter
Describe HE Excimer laser surgery
Emits an ultraviolet beam with sufficient energy to break intermolecular bonds with the cornea (“photoablation”)
Using UV beam to break bonds in cornea removing discrete volumes of cornea stroma
In LASIK surgery what is our goal in farsighted people?
to flatten the too steep cornea
to steepen the too flat cornea
smoothing irregular cornea into a more normal shape
What are the disadvantages of LASIK?
1. Changes made to the cornea cannot be reversed after LASIK
2. Technically complex—problems may occur when the doctor cuts the flap which can permanently affect vision
3. Can sometimes bt rarely cause a loss of “best” vision
(Your best vision is the highest degree of vision that you achieved while wearing your contacts or eyeglasses)
4. Costs $500-$1000 per eye
Advantages of LASIK
1. Around 90% of patients will have their desired vision
2. Associated with very little pain
3. Vision is corrected nearly immediately or by the day after
4. No bandages or stitches
5. Adjustments can be made years after to further correct vision
Potenital side affects of LASIK?
1. Discomfort for 24-48 hrs after surgery
3. Seeing halos around images
4. Difficulty driving at night
5. Fluctuating vision
6. Dry eyes
In Photorefractive Keratectomy (PRK) where is corneal tissue removed in myopia?
myopia- is removed in its center
hyperopia- removed in its periphery
What takes longer to heal LASIK, RK or PRK?
PRK is the longest
and has a greater potential for scarring
dont see results as quick
Describe LASEK vision correction
A very thin corneal flap is made (70 microns)
A few drops of a 20% alcohol solution are instilled and left on the cornea for 30 seconds that washed with water and dried
The eximer laser treats the stroma just like in LASIK
Uses alcohol, LASIK doesnt
Advantages of LASEK?
1. Thinner corneal flap may avoid corneal ectasia (cornea bows anteriorly)
2. LASIK requires more complicated equipment
3. Risks of infection are easier to manage with a thinner flap
Disadvantages of LASEK?
1. The thin corneal flap may dislodge postop causing greater pain
2. Slower optical recovery time
3. Can cause stromal haze in treated myopic patients
What kind of vision can crystalens affect?
hyperopia or presbyopia
What does the crystalens proceddure consist of?
The natural lens of the eye is removed and replaced with a plastic lens
Replacing the natural lens of the eye with crystalens eliminates the chance of what?
Non surgical procedure by which a special contact lenses are worn at nighttime that slowly reshape the cornea over time to correct myopia
What is vitamin A help with in the eye?
2 other things too not associated with the eye
Necessary for night vision,
wound healing and proper functioning of the immune system.
What vitamin helps reduce chronic inflammation and prevents homocysteine in the blood associated with vascular problems of the retina?
Vitamin B complex
What vitamin could help reduce the risk of macular degeneration and help in the treatment of uveitis?
How does vitamin C help the eye?
Potent antioxidant associated with reduced risk of cataracts
How does vitamin D help the eye?
Associated with lower risk of macular degeneration
How does vitamin E help the eye?
Associated with lower risk of cataracts
How does Omega 3s help the eye?
reduces risk of dry eye
What are some photochemical antioxidents?
ginkgo, biloba and bilberry which may provide protection form oxidative stress in the eyes