Achromatopsia

Notes

## Basic introduction

  • Achromatopsia (or “day blindness”) is a disease in which a patient has inability to see color in photopic condition
  • It can be acquired or congenital
  • There are two forms of hereditary achromatopsia:

_The rod monochromatism

_The blue cone monochromatism

  • Another form of achromatopsia include cerebral achromatopsia (associated with stroke and brain injury)

## Pathophysiology

  • The disease is caused by the dysfunction of the retinal transduction pathway
  • This results in reduced capacity of the cones to hyperpolarize in response to light
  • Abnormal color discrimination along protan, deutran and tritan axes

## Statistics

  • The prevalence of achromatopsia that is caused by the autosomal recessive gene: 1:33,000
Symptoms
  • Eccentric fixation
  • Lower visual acuity
  • Pendular nystagmus
  • Photophobia at the beginning of 6 months of life
  • Squinting
  • Hyperopia (far sightedness) in rod monochromats
  • The Flynn Phenomenon (which is a paradoxical pupilliary constriction when the patient is placed in the dark after exposure to bright light for several minutes)
Diagnosis
  • Clinical review
  • Visual Fields Testing (demonstrating small central scotoma)
  • Retinal examination
  • Dark Adaptation Testing (where there is an absence of the Kohlrausch Kink)
  • Rayleigh anomaloscope test
  • Color Vision Testing
  • Electroretinogram (ERG) test
  • Testing for CNGB3 and CNGA3 genes
Differential
  • Foveal dystrophy
  • Oligo-cone trichromasy
Prevention

None

Reference

a. Neuhann, T., Krastel, H., & Jaeger, W. (1978). Differential diagnosis of typical and atypical congenital achromatopsia. Graefe's Archive for Clinical and Experimental Ophthalmology, 209(1), 19-28.H

b. Flynn, J. T., Kazarian, E., & Barricks, M. (1981). Paradoxical pupil in congenital achromatopsia. International ophthalmology, 3(2), 91-96.

Management
  • Currently, there is no effective treatment
  • Gene therapy has been tried
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