- cornea --> aqueous humor --> anterior chamber

-->lens --> vitreous humor --> retina

Route of light

- corresponding visual field of the lower nasal quadrant of the retina

- images are upside down and reversed right to left

Upper temporal visual field

- fibers for this half of the visual field crosses at the optic chasm

Nasal fibers

- lesions in this region rarely affect visual acuity

Post-chiasm

- pressure from this structure causes bitemporal hemianopia (lateral visual field)

Optic chiasm from above (pituitary)

- axial length of eye is too short

- light focuses behind the retina

- corrected by convex, converging or positive diopter (shorter focal length) lens

Hyperopia (far-sightedness)

- a diopter is this distance

39"

Myopia (near-sightedness)

- presence of a refractive error

Ametropia

- a difference in the refractive power of the two eyes

Anisometropia

- can coexist with myopia and hyperopia

- curvature of cornea is ovular and several focal planes exist at once

- no point image is formed

- a cylindrical lens is used for correction

Astigmatism

- blurred near (reading) vision

- occurs with aging

- due to an inability of the lens to accommodate (thicken)

- begins in most people by 40 yrs

Presbyopia

- opacification or clouding of the lens that causes visual impairment

- obscures the red reflex

- most common cause of visual impairment

- caused by UV exposure, glucocorticoid use, diabetes mellitus, smoking

Cataracts

- from 12" away w/ an ophthalmoscope light reflected off the fundus makes the pupil look red

Red Reflex

- cataracts that occur in the center of the lens

- can cause myopic shift in refraction to allow elderly pt's the ability to read without glasses again

- glare at night becomes a problem

Nuclear cataracts

- when nuclear cataracts causes a myopic shift in reaction resulting in elderly pt's regaining the ability to read without glasses

Second Sight

- occurs in the most posterior portion of the lens

- causes a decrease in near vision

- associated with chronic steroid use or radiation therapy

Posterior subcapsular cataracts

- occur at the periphery of the lens

- vision is not affected until they extend centrally

Cortical cataracts

- cataracts do not respond to this tool that usually improves visual acuity

Looking through a pinhole

- functional center of the retina

- approximately 2 disk diameters temporal to optic disk

- degeneration causes irreversible central visual loss

- more common in older white females who smoke

Macula

- cortical unresponsiveness to visual stimuli

- unilateral defective vision, not correctable with glasses, in an otherwise normal eye

- caused by inadequate or conflicting visual information during first 3-4 months

- 3 types

Amblyopia

- normal visual acuity is achieved by this age

3 yrs

- most common cause for ambylopia

- two different messages reach the visual cortex simultaneously, 1 suppressed to avoid diplopia

- screened with corneal reflection test

- either comitant or noncomitant

Strabismus ambylopia

- pt looks at a penlight about 3 feet away

- reflection of the light off the patient's eyes should come from approximately the same point on each cornea

- tests for strabismus (works for <6 months)

Corneal Reflection Test

- more sensitive than corneal reflection test

- pt looks at light 3 feet away with one eye covered

- move cover from one eye to the other, if eye that was just uncovered moves, its positive

- esotrophia (nasal movement) is most common

- used for pts >6 months

Cover test for strabismus

- misalignment of the eyes that becomes apparent only when binocular vision is interrupted (covering one eye)

- small degree is normal, but larger degrees are strabismus

Heterophoria

- misalignment of the eyes during binocular vision

Heterotropia

- exotropia and exophoria refer to this direction deviation

Temporal (outward) deviation

- most cases of childhood strabismus

- angle of misalignment for eyes is the same in all directions of gaze

Comitant strabismus

- angle of misalignment between the eyes varies with direction of gaze

- characteristic of underlying neurologic disease (cranial nerve palsies)

Noncomitant strabismus

- before this age, most strabismus can be corrected before amblyopia occurs

5 years (max 10)

- occurs when there is marked difference in the refractive error between the two eyes early in childhood

- bad eye is suppressed

Refractive amblyopia

- caused by congenital cataracts or retinal tumor (retinoblastoma) that prohibits adequate retinal stimulation to initiate cortical connections

Occlusive amblyopia

- this many errors can be made to successfully read a line on the snellen chart

2 or less

- level that is legal blindness in the US

20/200

- most common color blindness

- more common in men

- usually hereditary

Red/green

Causes of non hereditary color blindness