Cone Dystrophy

Cone Dystrophy
SYMPTOMS Progressive vision loss, Metamorphopsia, Central scotomas, Color vision deficiencies, Hemeralopia, Photophobia
Peripheral vision loss and Nyctalopia occurs later on in the course of the disease as rods are eventually involved as well
SIGNS Bilateral
Early signs: Fundus can look anywhere from normal to diffuse RPE pigment granularity or stippling throughout the posterior pole.
Late signs: RPE proliferation at the macula, RPE atrophy at the macula in a “bulls-eye” pattern, RPE hyperpigmentation/atrophy in the peripheral retina, Retinal arteriolar attenuation, Temporal optic nerve pallor
With the presence of late signs, vision is anywhere from 20/200 to Counting Fingers
WORK-UP Pupils (decrease in direct light response in the presence of optic nerve pallor and/or presence of an APD if optic nerve pallor is asymmetric), Color vision (dyschromatopsia), Full eye exam with dilated retinal exam, Visual field (presence of central scotomas in the early stage with involvement of the peripheral visual field in the late stage), OCT analysis of the macula, OCT-Angiography, Fundus Autofluorescence, Fluorescein Angiography, Fundus photos, Infrared photos, Electrodiagnostic testing (ERG: Abnormal in photopic conditions but normal in scotopic conditions. As the dystrophy progresses, the ERG will also be abnormal in scotopic conditions), Dark adaptation (abnormal), Watzke-Allen test, Macular photostress test, Amsler grid
TREATMENT Give take home Amsler grid in order to monitor for change
Recommend AREDS II vitamins
Recommend genetic counseling for other family members
Monitor. No treatment is effective
If the patient develops poor vision, refer to low vision
FOLLOW-UP Patient should be seen back every 6 months
ETIOLOGY Typically an autosomal dominant progressive dystrophy (can also be autosomal recessive or x-linked)
Mutation in CRX and GUCY2D genes are involved with autosomal dominant cone dystrophies / Mutation in ABCA4 gene is involved with autosomal recessive cone dystrophies / Mutation in RPGR gene is involved with x-linked cone dystrophies
DIFFERENTIAL DX Stargardt disease, Plaquenil maculopathy, Leber congenital amaurosis, Rod dystrophy
NOTES There are two types of cone dystrophies (Stationary: Typically starts in early childhood but the symptoms and signs typically remain the same throughout the patient’s life / Progressive: Typically starts in early adulthood with progression of symptoms and signs throughout the patient’s life)
The vision loss tends to be more severe in cases where the cone dystrophy started at an earlier age
With cone dystrophies, legal blindness is typically seen before the patient turns 40 years old
Typically rods will become involved as well, especially in the later course of the dystrophy