Refraction Lecture Powerpoint Flashcards
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Presbyopia is a ____ refractive error
FALSE
Hyperopia
Far-sightedness, eyeball is too short (axial) or cornea is not curved sufficiently (curvature), corrected by a convex lens (positive power) that increases the eyes refractive power by converging the light
Myopia
Near-sightedness, eyeball is too long (axial) or cornea is excessively curved (curvature), corrected by a concave lens (negative power) that reduces the eyes refractive power by diverging the light rays
The majority of refraction is done by….
…the cornea (fine tuned by the lens)
What is the shape of the lens for distance viewing?
Flat
The lens of the eye cannot make a ___ shape but can go ____ to view distances
concave, flat
Myopia is corrected by what type of lens? What about hyperopia? Astigmatism?
Concave, convex, cylindrical
Most common cause of amblyopia and 3 other common onees
- Strabismus
- Refractive disorder
- cataract
- ptosis
Refraction
Ability of eye to bend light so image is focused on the retina
Concave lens
A lens with negative optical power that causes the dispersing of oncoming light, used in nearsighted patients
Convex lens
A lens with positive optic power that causes converging of the oncoming light, used in farsighted patients
Ametropia (refractive errors)
Optical imperfections that prevent the eye from properly focusing light causing blurred vision, including nearsightedness, farsightedness, or astigmatism, very common up to 1/3 of patients >40, worldwide common cause of poor visual acuity and blindness
Worldwide #1 cause of blindness
Cataracts
Visual acuity
Diagnosed via a snellen chart, a patient with less than 20/25 in either eye has impaired visual acuity, done by healthcare professional often in children and then annual beyond 61
Treatments of ametropia (3)
- Eye glasses
- Contact lens
- Lasik surgery (refractive surgery)
Orthoptist
Specialize in diagnosis and treatment of binocular vision problems such as strabismus
Factors influencing light focusing on the retina
- Cornea is extremely curved
- Refraction thru the aqueous humor is minimal
- Lens accommodates and can adjust accordingly
- Refraction thru vitreous humor is minimal
- Length of eyeball matters to bring focus to the
Emmetropia
When the eye is able to bring distant objects to a point of focus on the retina without a refractive aid
Presbyopia
A loss of lens elasticity preventing it from becoming as convex that causes difficulty seeing near things (rolling lens, flat lens is no problem), not considered a true refractive error
When an object is close, the lens refractive power must ____
increase (accommodate)
Elderly must read things by holding the media….
….farther away than a child would
___% of people have a refractive error (ametropia)
70%
Astigmatism
Misshapen cornea resulting in 2 or multiple focal lines that focus in front, behind, or on the retina
OD
Right eye
OS
Left eye
Sphere, cyl, axis, add
- Refers to the degree of optical error in the glasses
- corresponds to astigmatism
- corresponds to astigmatism
- Added to bifocals to adjust in presbyopia
LASIK
Laser assisted in situ keratomileusis, used for hyperopia, myopia, and astigmatism, laser alters shape of the cornea, can have complications including dry eyes, overcorrection or undercorrection, induced astigmatism, wrinkles in flap, or halos
Amblyopia
Disorder of visual development caused by optical, physical, or ocular alignment defect in childhood, brain selects better image to the eventual detriment of vision in the other eye (lack of development in the visual pathway), most common cause of uniocular vision loss in patients less than 45 years of age, if not treated before age of 7 permanent visual loss occurs
Esotropia
When the strabismis affected eye moves inward
Exotropia
when the strabismis affected eye moves outward
Cataract
Clouding of lens obstructing passing light, leading source is aging, can be congenital, traumatic, or drug induced, prevented with sun glasses, has loss of visual acuity and contrast sensitivity, as well as an absent red reflex
Cataract treatment (1)
-Surgical removal of lens and replacement with plastic lens (that can’t accommodate like the natural one but can sometimes have different optic settings)
