Transcript Achromatopsia or Achromatopia

Achromatopsia or
Achromatopia
Achromatopia or Dyschromatopia
James T. Fulton
VISION CONCEPTS
[email protected]
3 July 2008
Nat. Fed. Blind--Dallas, Texas
Achromatopsia or
Achromatopia
Achromatopia or Dyschromatopia
James T. Fulton
VISION CONCEPTS
[email protected]
Achromatopsia
(with or without an S)
•
•
•
•
•
•
Terminology
History of color vision abnormalities
How visual system operates
Simple tests
Analysis of survey
Conclusions
AchromatopSia
(with or without an S)
•
•
•
•
•
Past clinical practice was indiscriminate
Term seldom used in academic circles
Oliver Sacks popularized term with an S
Futterman used term with an S
Used here to indicate Syndrome
Achromatopia
(without an S!)
• A simple concept in academia
– Achromat--(n. Latin; without color)
– Achromatope– A person lacking color vision
– Achromatopia– A “one symptom disease”
– Dyschromatopia-- (Latin; with abnormal color)
– Unilateral Achromatopia– No color in one eye
– Monochromat– Has only one type of receptor
AchromatopSia
(with an S!)
• A Syndrome rather than a single symptom
– Hemeralopia– Abnormal sensitivity to light
– Nystagmus– Uncontrolled wandering eye(s)
– Dyschromatopia– Abnormal color vision
– Amblyopia– Low visual acuity (with correction)
– Strabismus– Abnormal convergence of eyes
History of Abnormalities
• Dyschromatopia, an ancient disease
– Protanopia– Lack of Red sensitivity
– Deuteranopia– No Red/Green discrimination
– Tetartanopia– No Blue/Green discrimination
History of Color Vision
• Day vs Night vision-- ancient observation
#1– Photopic vision-- A wide color spectrum
#2– Scotopic vision– Lacking in color
Long described as a rod/cone dichotomy
Actually due to operation of red channel
Rods not required, or found in modern theory
How Vision Operates
• Failure in
–
–
–
–
–
–
–
–
–
2 or 5B
3 or 5C
4 or 5D
6B
6C
7
8
9
10
Result
Tritanopia (rare)
Pentanopia (rarer)
Protanopia
Blue/Green achrom. (tetartanopia)
Red/Green achrom. (deuteranopia
Right hemiachromatopia
Left hemiachromatopia
Achromatopia
Nystagmus, Strabismus a/o Amblyopia
How Vision Operates
• Saturation
Result
5B, 5C and 5D
AchromatopSia-- nystagmus
6B and/or 6C Dyschromatopia-- no nystagmus
Human Visual Spectrum
Saturation in Vision Channels
Analysis of Survey
• Terminology is a problem
– “Rod monochromacy” is obsolete
– AchromatopSia separate from Achromatopia
– Atypical or incomplete  dyschromatopia
• Most office diagnoses are incomplete
– Spectral exam critical to diagnoses
Analysis of Survey
• Most office diagnoses are incomplete
– Reliance on Ishahara Plates & History
– Reliance on acuity measurements
– No spectral measurements
• ERG (if performed) at only two levels
– A mid-level ERG can substitute for a spectra
– A level of 10% of the maximum is suggested
• Only one respondent with genetic testing
On Genetic Testing
• Only one respondent tested genetically
– Exhibits all symptoms of achromatopSia
– CNGB3 mutation “in both copies”
– BUT, spectrum appears to be normal
• # failure modes EXCEEDS # gene mutat.
• Need greater specificity among patients
Analysis of Survey
• 25 Participants
Diagnosis
2 Total Achromats
2 Total Achromatopsia
12 Achromatopsia
3 Incompl. Achro-opsia
3 Cone dystrophy
1 Rod Monochromat
1 no diagnosis
•
•
•
•
•
•
•
•
Alternate
2 AchromatopSia
10 Achromatopia
12 Dyschromatopia
?? Hemeralopia
0 Cone dystrophy
0 Rod Monchromats
1 Tetrachromat 
Recommendations
• Achromatopsia.org provide guidelines
– For categorizing people with abnormal color
• Individuals suggest their doctors
– Perform a 3-level ERG or
– Perform a spectral evaluation (@ 10nm resol.)
– Review this presentation if appropriate
• Do not expect quick results from genetics
– # of failure modes exceed the # of mutations
Stimulus-response graphs
Rods/Cones vs
Photoreceptors
• Two Classes: Rods and Cones
– Have been defined based on light sensitivity
– Have been defined based on spectral selectiv.
– Have been defined on Outer Segment shape
– Have been defined on Inner Segment shape
– Have been defined versus location in retina
• None of these have stood the test of time
– The spectra of a rod matches the blue and
green spectra combined.
Where are the Rods
• Baylor team, 1987
– Found “red-rods” & “green-rods,” no “rods!”
• Stockman & Sharpe have
– taken 100’s of hi-resolution pix of the retina
– Only one report claimed to locate rods
o
• Folklore says rod density highest at 10
• Data of Freiding et al. (2007)
– Show same spectrum on-axis & at 10
o
Where are the rods?
o
• Roorda & Williams (1999), 1 nasal eccen.
Recent attempts to identify
Rods/Cones
• Osterberg (1962)