12. CVD - Monochromacy Flashcards
What is the principle of univariance?
A photoreceptor can only count the number of photons it absorbs and cannot tell the wavelength. Therefore, single cones are colour blind.
How do metamers work with just 1 photoreceptor type (considering a test wavelength with sensitivity of 10)?
- Two different wavelengths with sensitivities that
...will give a match - Different wavelength with sensitivity of
...will give a match - A wavelength with
...sensitivity can have its...cranked up to give a match - All in all, need only
...to match
How do metamers work with just 1 photoreceptor type (considering a test wavelength with sensitivity of 10)?
- Two different wavelengths with sensitivities that
add up to 10will give a match - Different wavelength with sensitivity of
10will give a match - A wavelength with
lowersensitivity can have itsintensitycranked up to give a match - All in all, need only
1 wavelengthto match
What are the three kinds of monochromacy and their Stiles’ notation?
- Typical (rod) monochromacy, π0
- ‘Blue cone’ monochromacy, π1
- Atypical monochromacy
What are the typical signs of typical monochromacy?
- Lowered
...without... -
...- blind in...without... -
...-...on the fovea, eyes move to... - Reduced sensitivity to
...- rod peak sens is...nm ...- Other
...may be affected
What are the typical signs of typical monochromacy?
- Lowered
VAwithoutobvious explanation -
Painless photophobia- blind inphotopic conditionswithoutpain -
Nystagmus-rod free regionon the fovea, eyes move tofixate constantly - Reduced sensitivity to
red light- rod peak sens is540nm Total colour blindness- Other
family membersmay be affected
Explain Larsen’s case (1918) and Holm and Lodberg’s (1940) findings about typical monochromacy.
Mikkeline Neilson had 6/... VA and ... from birth. Her luminous efficiency (Vλ) was ...; reading was best at ... and she ... in daylight. She had normal ... but did know .... ... were affects. From ....
Holm and Lodberg found that ... has ...x the global population rate due to ... (1:... rate).
Explain Larsen’s case (1918) and Holm and Lodberg’s (1940) findings about typical monochromacy.
Mikkeline Neilson had 6/60 VA and nystagmus from birth. Her luminous efficiency (Vλ) was scotopic; reading was best at dusk and she shaded eyes in daylight. She had normal dark adaptation but did know what colour was. Many siblings were affects. From Island of Fur.
Holm and Lodberg found that Island of Fur has 4000x the global population rate due to consanguinity (1:70 rate).
What were the following researchers’ findings on typical monochromacy?
Wright (1947) measured Vλ and found it to be ....
Louise Sloan (1954) studied ... cases to give more information about the characteristics.
Knut Nordby is a vision researcher with ... and studied himself.
What were the following researchers’ findings on typical monochromacy?
Wright (1947) measured Vλ and found it to be scotopic.
Louise Sloan (1954) studied 19 cases to give more information about the characteristics.
Knut Nordby is a vision researcher with typical monochromacy and studied himself.
What did the following researchers find about VA in typical monochromacy?
Hecht (1948) found logVA as a function of logretinal illumination, resulting in a VA of 6/... and no ... (... case).
Sloan (1954) studied ... cases and found VA to be 6/... to 6/... at low ... which reduces as ....
Blackwell and Blackwell (1961) studied ... cases and found VA to be 6/... and it decreases at ....
What did the following researchers find about VA in typical monochromacy?
Hecht (1948) found logVA as a function of* log*retinal illumination, resulting in a VA of 6/36 and no cone branch (1 case).
Sloan (1954) studied 19 cases and found VA to be 6/24 to 6/60 at low retinal illuminances which reduces as illuminance increases.
Blackwell and Blackwell (1961) studied 3 cases and found VA to be 6/18 and it decreases at higher illuminances.
What are the signs of photophobia in typical monochromacy?
..., ..., see better in ..., ..., ..., wears ....
Photophobia is ... but not ..., implies ... might be occurring.
What are the signs of photophobia in typical monochromacy?
Painless, aversion to light, see better in dim light, blinking, squints, wears sunglasses.
Photophobia is common but not invariable, implies adaptation might be occurring.
What are the signs of nystagmus in typical monochromacy?
It’s ... but not .... ... patients seem to show it but not ...; seems to indicate ... as they might ....
What are the signs of nystagmus in typical monochromacy?
It’s common but not universal. Younger patients seem to show it but not older; seems to indicate adaptation as they might choose a new part of the retina to fixate with.
Is myopia associated with typical monochromacy?
No. Early reports implied an association based on squinting and preference for near work.
Colour vision in monochromats.
... pseudo-isochromatic plates; give ... responses.
Seem to order colours in the Farnsworth D15 ...; they place them in order of ....
Nagel Anomaloscope gives a ... for monochromats (on yellow vs red-green match graph), implying ... is even less ... in monochromats than ....
Colour vision in monochromats.
Fail pseudo-isochromatic plates; give irregular responses.
Seem to order colours in the Farnsworth D15 randomly; they place them in order of scotopic reflectance.
Nagel Anomaloscope gives a steeper gradient for monochromats (on yellow vs red-green match graph), implying red is even less effective in monochromats than protanopes.
Inheritance pattern of typical rod monochromacy
Both sexes are affected ... and an affected person ... transmits the disorder to their offspring. Incidence is about 1:.... It follows an ... inheritance pattern.
Inheritance pattern of typical rod monochromacy
Both sexes are affected equally and an affected person rarely transmits the disorder to their offspring. Incidence is about 1:30,000. It follows an autosomal recessive inheritance pattern.
What are the two main mechanisms suggested for typical monochromacy?
Absence of cones/pure rod theory
Cones not functioning/rod only theory
What do each of these studies suggest about the anatomical changes in typical monochromacy?
Larsen’s case (1921) found that ... were present in the retina and the ... was normal; suggesting the ... theory is incorrect.
Harrison, Hoffnagel, and Hayward (1960) found ... in a 19year old male achromat’s eyes.
Falls, Wolter, and Alpern’s (1965) case found ..., a decrease in ..., and an ... in a woman’s enucleated eye dye to ...; which may have made changes to the retina.
Glickstein and Heath’s (1975) case found no ... and only ...-...% of the normal ... throughout the retina. ... had abnormal shape near fovea.
What do each of these studies suggest about the anatomical changes in typical monochromacy?
Larsen’s case (1921) found that cones were present in the retina and the ratio of rods:cones was normal; suggesting the pure rod theory is incorrect.
Harrison, Hoffnagel, and Hayward (1960) found imperfectly shaped squat cone-like units in a 19year old male achromat’s eyes.
Falls, Wolter, and Alpern’s (1965) case found few but well developed cones, a decrease in number of extra-foveal cones, and an abnormal cone shape in a woman’s enucleated eye dye to glaucoma; which may have made changes to the retina.
Glickstein and Heath’s (1975) case found no photoreceptors and only 5-10% of the normal cones throughout the retina. Cones had abnormal shape near fovea.
Are cones present but not functioning in typical monochromacy?
- Difficult to find
...in all cases - VA is too high for
...- expect a VA of 6/...-6/...but getting 6/...-6/... - Dark adaptation shows
...in some cases - Increment threshold data suggests
... - CFF data shows
... -
.../...evident -...are not...
All of this suggests that cones are present but outer segments contain ... or a ....
Are cones present but not functioning in typical monochromacy?
- Difficult to find
central scotomain all cases - VA is too high for
pure rod function- expect a VA of 6/36-6/60but getting 6/18-6/60 - Dark adaptation shows
rod-cone breakin some cases - Increment threshold data suggests
rod-cone break - CFF data shows
rod-cone break -
Stiles-Crawford/direction sensitivityevident -rodsare notdirection sensitive
All of this suggests that cones are present but outer segments contain rhodopsin or a visual pigment which has an action spectrum that is indistinguishable from rhodopsin.
