N165 Quiz2; Unit 2b

• an opacity in the lens that blocks light from reaching the retina
• often occurs in older age due to sunlight (UV) exposure

• an inability to correctly see colors due to mutations in photoreceptors
• ex. medium-length cones mutated to respond like long-length cones

a form of congenital achromatopsia (color blindness) arising from problems in the retina

• rod monochromats are people whose cone photoreceptors are present in the retina but are completely non-functional
• the cones cannot absorb light, and therefore the patients relies only on rod vision 
• sees in black and white with low visual activity

• patient has one functioning cone type
• color vision is restricted to about 100 colors (rather than out normal ~10 million)
• blue-cone monochromacy is rare, but slightly more common than L/M-cone monochromacy

color vision disorder in which one type of cone is absent or non-functioning

• (L)
• photoreceptors deficit that causes Red-Green Colorblindness

• (M)
• photoreceptors deficit that causes Red-Green Colorblindness

• (S)
• photoreceptors deficit that causes Blue-Yellow Colorblindness

• a form of retinal colorblindness where either the green cones are missing completely or respond like red cones
• it id much more common in males than females

• a form of retinal colorblindness where people confuse blue with green and yellow with violet
• it is very rare (roughly 1/10,000) and not sex-linked

patients with types of anomalous trichromacy (protanomaly, deuteranomaly, or tritanomaly) are trichromats, but the color matches they make significantly differ from normal

L-cone (red) spectrum shifted closer to M-cone (green) spectrum

M-cone (green) spectrum shifted closer to L-cone (red) spectrum

blue-yellow discrimination altered

38 colored plates used to test those with red-green color blindness

• women who have 4 types of cones, which likely allows them to see about 100 million colors (rather than our normal ~10 million).
• The 4th type of cone occurs when one woman inherits two different L cone alleles (gene subtype), each of which codes for an L-cone photopigment with a small mutation that makes it absorb a slightly different wavelength of light than the other allele.
• Due to a process called X-chromosome inactivation (in every female cell, one of the X chromosomes is randomly inactivated), each retinal L-cone cell may randomly express one L-cone allele or the other.
• Fascinatingly, the opponency system of our color vision can incorporate the two slightly different L-cones as individual photoreceptor types.
• I would have assumed that our brain would not be able to change to accommodate the new input type, that the two L-cone types would just be grouped together as L-cone info.
• Instead, our brains can instead make a more complex opponency system that allows tetrachromats to see more colors, as L-cone type 1 now can be compared to L-cone type 2, and so on, just like L-cone vs. M-cone comparisons in trichromats (normal human vision).

• An area of impaired or lost vision in the visual field.
• A scotoma can arise from from damage anywhere along the visual pathway from the retina to primary visual cortex (V1).
• Beyond V1, more specialized types of visual disorders arise (e.g., visual object agnosia).

loss of an entire eye's vision due to tumor or trauma that results from the disconnection of the optic nerve

blindness in one half of the visual field in one or both eyes

blindness in the outer halves of the visual field in both eyes, due to damage to the optic chiasm (tumors are often the culprit)

blindness in the middle halves of the visual field in both eyes, due to damage to uncrossed fibers (often due to calcification of carotid arteries; also associated with hydrocephalus)

• blindness in the same hemisphere of the visual field in both eyes, due to damage to the opposite hemisphere of cortex (often from stroke or trauma)
• right 'homonymous hemianopsia' refers to the loss of the right hemifield of vision in each eye from damage to left V1