Colorblindness-Achromatopsia 2

Clinical Characteristics
Ocular Features: 

Patients with this congenital, nonprogressive condition often have nystagmus as infants which may improve later. Eccentric fixation secondary to a small central scotoma is often present.  Visual acuity is 20/200 or worse.  Hyperopia is common.  Photophobia is extreme and vision under daylight conditions improves in dim light.  Patients are unable to distinguish any colors.  However, there is considerable variability in symptoms and some individuals retain some color perception and have better visual acuity (sometimes 20/80) than others suggesting some residual cone function.  The term ‘incomplete achromatopsia’ is sometimes applied to such cases but the molecular basis for this variation is unknown.  Optical coherence tomography reveals the central retina to be thinner than in normal controls.  The fundus appearance is normal, however.

ERG responses indicate an absence of cone function with no photopic responses. 

Systemic Features: 

There are no associated systemic abnormalities. 

Genetics

Mutations in CNGA3 account for approximately 25% of cases of achromatopsia.  ACHM2 is an autosomal recessive disorder caused by mutations in CNGA3 (2q11).  Mutations in this gene also have been found in rare patients with progressive cone dystrophies.  A clinically similar but genetically distinct disorder, ACHM3, results from mutations in CNGB3 (262300).  Mutations in GNAT2 (ACHM4; 139340) and PDE6C (ACHM5; 613093) also cause achromatopsia. 

Treatment
Treatment Options: 

There is no treatment for the underlying condition but darkly tinted lenses can help in bright light.  Red contact lenses can alleviate photophobia and improve vision as well.  Low vision aids and vocational training can be of great benefit.  In spite of the poor vision, some patients may find that correction of the hyperopia enables them to see better. 

References
Article Title: 

References

Varsanyi B, Somfai GM, Lesch B, Vamos R, Farkas A. Optical coherence tomography of the macula in congenital achromatopsia. Invest Ophthalmol Vis Sci. 2007 May;48(5):2249-53.

PubMedID: 17460287

Holopigian K, Greenstein VC, Seiple W, Hood DC, Carr RE. Rod and cone photoreceptor function in patients with cone dystrophy. Invest Ophthalmol Vis Sci. 2004 Jan;45(1):275-81.

PubMedID: 14691184

Park WL, Sunness JS. Red contact lenses for alleviation of photophobia in patients with cone disorders. Am J Ophthalmol. 2004 Apr;137(4):774-5.

PubMedID: 15059731