3 July 2008 Nat. Fed. Blind--Dallas, Texas
Achromatopsia or Achromatopia
Achromatopia or Dyschromatopia
James T. FultonVISION CONCEPTS
Achromatopsia or Achromatopia
Achromatopia or Dyschromatopia
James T. FultonVISION CONCEPTS
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 Result– 2 or 5B Tritanopia (rare)– 3 or 5C Pentanopia (rarer)– 4 or 5D Protanopia– 6B Blue/Green achrom. (tetartanopia)– 6C Red/Green achrom. (deuteranopia– 7 Right hemiachromatopia– 8 Left hemiachromatopia– 9 Achromatopia– 10 Nystagmus, Strabismus a/o Amblyopia
How Vision Operates
• Saturation Result5B, 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• Terminology is a problem– “Rod monochromacy” is obsolete– AchromatopSia separate from Achromatopia– Atypical or incomplete dyschromatopia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 ParticipantsDiagnosis
2 Total Achromats2 Total Achromatopsia12 Achromatopsia3 Incompl. Achro-opsia3 Cone dystrophy1 Rod Monochromat1 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
• Folklore says rod density highest at 10o
• Data of Freiding et al. (2007)– Show same spectrum on-axis & at 10o
Where are the rods?
• Roorda & Williams (1999), 1o nasal eccen.
Recent attempts to identify Rods/Cones
• Osterberg (1962)