ND - Colour Vision Disorders III - Week 7 Flashcards

1
Q

What do photoreceptors truly do? What does this mean about how they interpret colour?

A

It can only count the number of photons it absorbs, it cannot tell wavelength
Single cones are colour blind
Multiple cones with different sensitivities are needed

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2
Q

When colour matching, how many wavelengths do monochromats need?

A

Only one wavelength, and adjusting intensity

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3
Q

What are the three kinds of monochromacy?

A

Typical (rod) monochromacy
Blue cone monochromacy
Atypical monochromacy

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4
Q

Is typical monochromacy easy to diagnose? List 6 things to look out for.

A

Easy to diagnose
Lowered VA with no obvious explanation
Painless photophobia
Nystagmus
Reduced sensitivity to red light
Total colour blindness
Other affected family members

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5
Q

What is VA like in typical monochromacy?

A

Equivalent to rod VA

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6
Q

Consider a typical monochromat. Would their VA increase with increasing illiminances?

A

Up to a point, but will start decreasing again due to saturation

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7
Q

List 5 characteristics of typical monochromcy photophobia.

A

Painless
Aversion to light
See better in dim light
Blink/squint/sunglasses
Photophobia is common but not invariable

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8
Q

Is nystagmus universal in typical monochromacy? Explain.

A

No, it is common but not universal
Younger subjects seem to show it, but not older

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9
Q

Are there any retinal changes with typical monochromacy?

A

None apparent

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10
Q

What is the association between typical monochromacy and myopia?

A

Early reports of squinting and decreased viewing distance (to increase angular size of near work) erroneously lead to the notion of association wth myopia (there is no association)

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11
Q

How do typical monochromats perform on pseudo-isochromatic plates?

A

Fail but irregular responses

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12
Q

How do typical monochromats perform on Farnsworth D15?

A

On average, arrange in order of scotopic reflectance

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13
Q

How do typical monochromats perform on Nagel anomaloscopes??

A

Full range but setting with increasing red because of scotopic spectral sensitivity

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14
Q

What is the mode of inheritance for typical monochromacy?

A

Autosomal recessive

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15
Q

List 5 findings for the mechanisms of typical monochromacy and list 2 implications of these findings.

A

Scotopic spectral sensitivity
Lowered VA
Preference for dim light
Nystagmus
-due to scotoma at rod free foveal area
-not a motor anomaly
These findings suggest:
-absence of cones
-cones not functioning

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16
Q

What causes the nystagmus in monochromacy?

A

Scotoma at rod free foveal area

17
Q

What does anatomical evidence of monochromatic eyes suggest of the pure rod theory or rod only theory?

A

One consistency is the presence of morphologically intact cones, dismissing the pure rod theory

18
Q

Is a central scotoma found in all cases of monochromacy?

A

No

19
Q

Is there a rod-cone break in the following tests of monochromatic eyes?
Dark adaptation
Increment threshold
Critical fusion frequency
Directional sensitivity
What does this suggest about the cones functionally?

A

Yes to all, there was a break
This suggests that the cones are present, but contain rhodopsin or a pigment with a spectrum indistinguishable from rhodopsin

20
Q

How is blue cone monochromacy inherited?

A

X-linked recessive

21
Q

How does blue cone monochromacy compare to typical monochromacy?

A

Similar in all aspects including VA, nystagmus, and reduced red light sensitivity

22
Q

Do blue cone monochromats have some level of dichromacy?

A

Yes, but only rudimentary levels at mesopic levels

23
Q

Describe the characteristics of atypical (cone) monochromacy (3).

A

Normal VA
No photophobia
No nystagmus
Colour blind

24
Q

What could be a possible cause for atypical monochromacy?

A

A failure of the neural network rather than receptor dysfunction