3 july 2008nat. fed. blind--dallas, texas achromatopsia or achromatopia achromatopia or...

3 July 2008 Nat. Fed. Blind--Dallas, Texas

Achromatopsia or Achromatopia

Achromatopia or Dyschromatopia

James T. FultonVISION CONCEPTS

jtfulton@sightresearch.net

Achromatopsia or Achromatopia

Achromatopia or Dyschromatopia

James T. FultonVISION CONCEPTS

jtfulton@sightresearch.net

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• Terminology is a problem– “Rod monochromacy” is obsolete– AchromatopSia separate from Achromatopia– Atypical or incomplete dyschromatopia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)