Vision Correction Flashcards
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?
spherical lens
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?
Radial keratotomy
What is the most common surgical procedure for vision correction?
LASIK
What does LASIK stand for?
laser-assisted in situ keratomilusis
Which procedures are surface ablation procedures?
3
- photorefractive kertotoamy (PRK),
- laser epithelial keratomileusis (LASEK) and
- epitherilial laser keratomileusis (epi-LASIK)
What procedures are intracorneal procedures?
corneal inlays
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?
Refractive keratoplasty
What are three types of refractive keratoplasties?
- Keratotomies, ie corneal incisions
- Keratectomies, ie removal of corneal epithelium
- 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?
6
- Autoimmune disease
- collagen vascular disease and 3. immunodeficiency disease affect corneal healing
- Women who are pregnant or nursing have fluctuating visual acuity
- Patients with abnormal wound healing (keloids) may have abnormal corneal healing
- DM—can perform if well-controlled, without cataract or diabetic retinopathy
Specific ocular contraindications for vision correction surgery?
7
- Keratoconjunctivitis sicca (dry eye syndrome)
- Exposure keratitis
- Neurotrophic keratitis (degenerative disease caused by impaired corneal innervation)
- Lid disorder affecting the tear layer
- Patient with a h/o herpetic keratitis
- Any patient with an abnormal shaped cornea
- Sever rosacea
Why dont we use radial keratotomy anymore?
What kind of vision impairment was it used for?
Not accurate
didnt work in everyone
higher risk of infection
have to do second eye six weeks apart
incisions in periphery make central cornea flatter
myopia
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?
Nearsighted people?
Astigmatism?
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?
4
- Changes made to the cornea cannot be reversed after LASIK
- Technically complex—problems may occur when the doctor cuts the flap which can permanently affect vision
- 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) - Costs $500-$1000 per eye
Advantages of LASIK
5
- Around 90% of patients will have their desired vision
- Associated with very little pain
- Vision is corrected nearly immediately or by the day after
- No bandages or stitches
- Adjustments can be made years after to further correct vision
Potenital side affects of LASIK?
6
- Discomfort for 24-48 hrs after surgery
- Glare
- Seeing halos around images
- Difficulty driving at night
- Fluctuating vision
- Dry eyes
