Term
| Understand the anatomic basis for bitemporal hemianopsia, homonymous hemianopsia, upper homonymous hemianopsia, loss of peripheral vision, and uniocular blindness. |
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Definition
bitemporal hemianopsia: lesion at the optic chiasm causing bitemporal vision loss
homonymous hemianopsia: lesions occuring behind the optic chiasm leading to bilateral symmetric vision losses
upper homonymous hemianopsia: lesion in the temporal lobe (behind the optic chiasm) leading to the symmetric "pie-in-the-sky-visual loss"
loss of peripheral vision: primary open-angle glaucoma
uniocular blindness: pre-chiasmal lesions of the 2nd cranial nerve: optic neuritis and optic atrophy |
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Term
| Differentiate between hyperopia and myopia in terms of type of vision deficit, relationship between the axial length of the eye and the refractive power of the cornea and lens, type of lens used to correct the vision (positive or negative diopter). |
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Definition
hyperopia (far sightedness): axial length is too short for the refractive power of the lens, light focuses behind the eye, needs positive diopter to fix
myopia (near sightedness): axial length is too long for the refractive power of the lens, light focuses in front of the eye, needs negative diopter to fix |
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Term
| By what mechanism does having a patient look through a pinhole correct refractive error? |
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Definition
| The pinhole selects for only axial rays of light to pass through the central part of the cornea and lens, minimizing the effects of uncorrected refractive error. |
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Term
| Know the anatomic basis for astigmatism and what kind off visual impairment results. |
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Definition
Astigmatism occurs when no point image is formed by the refractive structures of the eye; oval-shaped cornea, causing blurred vision at multiple distances
corrected with cyylindrical lens |
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Term
| Understand the anatomic basis for presbyopia and descrbie the characteristics of the visual impairment that results. |
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Definition
presbyopia - blurred near (reading) vision, due to an inability of the lens to accommodate (thicken) for focus on near objects
Patients present by age 40. |
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Term
| What is anisometropia and what complication may result? |
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Definition
Anisometropia - patient's two eyes have markedly different refractive errors
Can result in refractive amblyopia -- unilateral defective vision, not correctable with glasses -- leading to suppressed connections between the ey with the worse refractive error and the visual cortex
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Term
| What is the significance of the red reflex? |
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Definition
Obsured red reflex are indicative of cataracts.
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Term
| What is the most common cause of central vision loss in the elderly? |
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Definition
| The most common cause of central vision loss in the elderly is macular degeneration causing central visual loss. |
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Term
| What is the anatomic basis for amblyopia? Describe the 3 most common mechanisms repsonsible for producing amblyopia. |
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Definition
Cortical unresponsiveness to visual stimuli is called amblyopia--unilateral defective vision, not correctable with glasses, in an otherwise normal eye.
The 3 most common causes are...
(1) Strabismus - developmental misalignment of the eye. Most common cause; two different messages reach the visual cortex simulatenously, one is suppressed.
(2) Refractive error - in the absence of ocular misalignment, refractive amblyopia develops whenever there is a marked difference in the refractive error between the two eyes early in childhood. Connections in the eye with the worse refractive error and visual cortex will be suppressed.
(3) Occlusive amblyopia - congenital cataract or retinal tumor (retinoblastoma) prevents adequate retinal stimulation to initiate cortical connections |
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Term
| On physical exam, describe tests that screen for strabismus. |
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Definition
(a) corneal reflection test - screens for strabismus - does the reflection off the cornea line up on each eyeball?
(b) cover test - when covering one eye, and then quickly covering the other eye, is their motion of either eye? more sensitive than corenal reflection test. |
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Term
| Differentiate between a phoria and a tropia. What is the significance of noncomitant strabismus? |
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Definition
phoria - misalignment in the eyes that becomes apparent when one eye is covered
tropia - misalignement of the eyes that becomes apparent when both eyes are open and looking forward (during binocular vision)
Noncomitant strabismus - exists whe nthe angle of misalignment between the eyes varies with the direction of gaze, indicative of cranial nerve palsies
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Term
| How is visual acuity measured and at what point is a patient considered legally blind? |
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Definition
| Visual acuity is measured by determining the smallest object a person can see at a given distance while comparing the patient's performance to an agreed upon standard, e.g. reading the bottom line of a Snellen chart. Legally blind occurs at 20/200, where the patient can reconize something at 20 feet what a person with a standar acuity can recognize at 80 feet. |
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