Achromatopsia

Main Features

  • Reduced vision due to lack of functioning cones
    • Vision usually 20/200 with complete color blindness in complete forms
    • Incomplete forms may have better vision and some color vision
  • Nystagmus that may improve with age
  • Central relative scotoma with normal peripheral visual fields
  • Complete and Incomplete forms
  • Usually stable but some see slow worsening of visual acuity and macular atrophy

Distinguishing Features

  • Photophobia at birth or early infancy
  • Better vision in dim illumination
  • Sluggish pupil responses with paradoxical constriction in the dark
  • Usually normal fundus appearance
    • OCT may show ellipsoid zone disruption or absence, outer retinal atrophy and RPE loss
  • ERG
    • lack of cone function- 30 Hz flicker and single flash photoptic waveform is small and delayed
    • normal ROD function- normal dark adapted dim and bright flash waveforms

Differential Dx

Pathogenesis

  • 1 in 30,000 live births
  • Recessively inherited mutation in a gene that codes for a part of the cone phototransduction pathway.
  • 70-80% from mutations in the following genes: CNGA3 and CNGB3
  • 1-2% from mutations in GNAT2, PDE6C, PDE6H, ATF6

Treatment

  • Supportive care
  • Sunglasses

Resources

  1. Taylor and Hoyt Textbook article
  2. Hirji N. et al. Achromatopsia: clinical features, molecular genetics, animal models and theraputic options. Ophthalmic Genetics 2018;39(2):149-157 _
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