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Symptoms ⬇

Slowly progressive visual loss, photophobia, and poor color vision, with onset during the first 3 decades of life. Vision is worse in bright than dim light.

Signs ⬆ ⬇

Critical

  • Early: Essentially normal fundus examination, even with poor visual acuity. Abnormal cone function on ERG (e.g., a reduced single-flash photopic response and a reduced flicker response).
  • Late: Bull’s eye macular appearance or central geographic atrophy of the RPE and choriocapillaris.

Other

Nystagmus, temporal pallor of the optic disc, spotty pigment clumping in the macular area, tapetal-like retinal sheen. Rarely rod degeneration may ensue, leading to an RP-like picture (e.g., a cone–rod degeneration, which may have an autosomal dominant inheritance pattern).

Inheritance

Usually sporadic. Hereditary forms are usually autosomal dominant or less often X-linked.

Differential Diagnosis ⬆ ⬇

Work Up ⬆ ⬇

Workup
  1. Family history.
  2. Complete ophthalmic examination, including formal assessment for dyschromatopsia (e.g., Farnsworth–Munsell 100-hue test).
  3. Formal visual field test.
  4. Full-field ERG: abnormal photopic response with normal rod-isolated response.
  5. OCT can show disruption of outer retinal layers but may be normal even in patients with electrophysical abnormalities.
  6. FAF can be useful in the diagnosis (particularly sensitive to disturbances in the RPE), as well as for monitoring these diseases.

Treatment ⬆ ⬇

There is no proven cure for cone dystrophy. The following measures may be palliative:

  1. Heavily tinted glasses or contact lenses may help maximize vision.
  2. Miotic drops (e.g., pilocarpine 0.5% to 1% q.i.d.) are occasionally tried to improve vision and reduce photophobia.
  3. Genetic counseling.
  4. Low-vision aids as needed.

Follow Up ⬆

Yearly.