Sunday, July 24, 2011

Congenital Stationary Nyctalopia

Congenital stationary nyctalopia is a rare X-linked non-progressive retinal condition. Patients suffering from this disorder typically have difficulty seeing in low light (night blindness). They also have other vision problems, such as reduced acuity, severe nearsightedness, and eyes that do not look in the same direction (strabismus). Congenital stationary nyctalopia has two forms, complete, also known as type-1, and incomplete, also known as type-2, depending on severity. In the complete form, there is no measurable rod cell response to light, whereas this response is measurable in the incomplete form. Patients with this disorder have difficulty adapting to low light situations due to impaired photoreceptor transmission. These patients also often have reduced visual acuity, myopia, nystagmus, and strabismus. The type-1 cogenital stationary nyctalopia is caused by mutations in the gene NYX, which encodes a protein involved in retinal synapse formation or synaptic transmission. The type-2 is caused by mutations in the gene CACNA1F, which encodes a voltage-gated calcium channel CaV1.4.

Congenital stationary nyctalopia, or night blindness disorder, is primarily rod dystrophies presenting early with symptoms of nightblindness and relative sparing of central vision. Nystagmus and photophobia are usually not features. Dyschromatopsia and loss of central acuity can develop later as the cones eventually become dysfunctional as well but these symptoms are much less severe than those seen in cone-rod dystrophies. The amount of pigmentary retinopathy is highly variable. Cone function is impacted to some degree as well in type-2, or incomplete.