unit 2b Flashcards
Visual Disorders: Retina
cataract
an opacity in the lens that block light f/ reaching retina; often occurs in older age due to sunlight (UV) exposure
retinal colorblindness
inability to correctly see colors due to mutations in PR (ex; medium-length cones muted to respond like long-length cones)
Monochromacy
a form of congenital achromatopsia ( color blindness) arising f/ problems in retina
Rod monochromacy
rod monochromats are ppl whose cone PRs are present in retina but completely non-functional.
Cones can’t absorb light → patient relies only on rod vision (sees in black/white w/ low visual acuity)
Cone monochromacy
patient has 1 func. cone type.
Color vision is restricted to abt 100 colors (normal ~10million)
Blue-cone monochromacy is rare, but more common than L/M cone monochromacy.
Dichromacy
color vision disorder I which one type of cone is absent or nonfunc.
Protanopia (dichromacy)
(L) PR deficit causes Red-Green colorblindness
Deuteranopia (Dichromacy)
(M) PR deficit causes Red-Green colorblindness
Tritanopia (S)
PR deficit causes Blue-Yellow colorblindness
Red-Green colorblindness
a form of retinal colorblindness where either Green cones are missing or respond like Red cones.
More common in males
Blue-Yellow colorblindess
A form of retinal colorblindness where people confuse Blue w/ green and Yellow w/ violet.
Very rare (1/10,000)- not sex-linked
Anomalous trichromacy
Patients w/ types of anoumouls trichromacy (protanomaly, deuteranomaly, or tritanormaly) are trichromats, BUT color matches they make differ f/ normal
Protanomaly (anomoulos trichromacy)
L-cone (RED) spectrum shifted closer to M-cone (GREEN) spectrum
Deuteranomaly (Anom. Trichromacy)
M-cone (GREEN) spectrum shifted closer to L-cone (RED) spectrum
Tritanomaly (Anom. trichromacy)
Blue-yellow discrimination altered
Ishihara Plates
38 colored plates used to test those w/ red-green color blindness
Tetrachromats
women who have 4 types of cones which allows them to see abt 100 million colors (normal: 10 mill)
4th type of cone occurs when women inherits 2 diff L-cone alleles (gene subtype)- each of which codes for an l-cone photopigment w/ small mutation that makes it absorb a slightly diff wavelength of light.
Due to process: X-chromosome Inactivation (in every female cell, 1 of the X-chromosomes os randomly inactivated), each retinal L-cone cell may randomly express 1 L-cone allele or the other.
Opponency syst. can incorp. the 2 slightly diff L-cones as indiv. PR types. Brains can instead make a more complex opponent system that allows tetrachromats to see more colors.
Scotoma
An area of impaired/lost vision in the visual field.
Can arise f/ damage along the visual pathway f/ the retina to primary visual cortex (V1)
Beyond V1, more specialized types of visual disorders arise (ex: visual object agnosia)
Diff. extents of a scotoma that can occur due to very specific locations of damage:
Unilateral field loss, Hemianopsia, Bitemporal hemianopsia, Binasal hemianopsia, Homonymous hemianopsia
Homonymous hemianopsia
blindness in same hemisphere of visual field in both eyes due to damage in OPPOSITE HEMISPHERE OF CORTEX (often f/ stroke/trauma)
‘Right homonymous hemianopsia’ refers to loss of right hemifield of vision in each eye f/ damage to left V1
Binasal hemianopsia
Blindness in middle halves of visual field in BOTH eyes
Due to damage to UNCROSSED FIBERS (often due to calcification of carotid arteries; also assoc w/ hydrocephalus
Bitemporal hemianopsia
Blindness in outer halves of visual field in BOTH eyes.
Due to damage to OPTIC CHIASM (tumors often culprit)
Hemianopsia
Blindness in one half of the visual field in 1 or BOTH eyes.
Unilateral field loss
Loss of an ENTIRE eye’s vision due to tumor/trauma that results f/ DISCONNECTION OF OPTIC NERVE.
