Hereditary retinal dystrophies

It is a congenital and non-progressive disease that consists of a vision anomaly because of which only the colours white, black, gray and all their shades are perceived. The disease is caused by an alteration in the colour-sensitive photoreceptor cells of the retina, which are the cones.

In addition to the lack of capacity to perceive colours, there is a significant loss of visual acuity, great difficulty seeing in high light conditions, for example in the middle of the day, photophobia, and nystagmus from birth.

Achromatopsia is sometimes called “day blindness” because these children see better in dimly lit environments. Children with complete achromatopsia have reduced vision (20/200 or less) due to an abnormality in their retina. Children who have partial achromatopsia may have better vision (20/120 to 20/80). These patients usually do not present total blindness, although in some cases they may have legal blindness.

The estimated prevalence worldwide is 1/30,000 - 1/50,000.

The diagnosis of achromatopsia is based on a clinical ophthalmological examination, psychophysical tests (on colour vision) and electrophysiological tests (electroretinography/ERG), in which loss of photopic response but normal scotopic response are observed. Optical coherence tomography shows progressive interruption and/or loss of junction between the inner/outer photoreceptor segments, and attenuation of the retinal pigment epithelium (RPE) in the macular region. Diagnosis is verified by molecular genetic analysis of the causative genes.

Differential diagnoses include blue cone monochromatism (BCM), Leber congenital amaurosis, other types of cone dystrophy (see these terms), and cerebral achromatopsia.

Prenatal diagnosis is possible when there is a family history. The disease is transmitted by autosomal recessive inheritance. Once the disease-causing mutations have been identified in the family, it is therefore possible to test members at risk of being carriers of these mutations. In addition, genetic counseling should be offered to couples at risk (where both individuals are carriers of a disease-causing mutation) to inform them that they have a 25% chance of having an affected child.

Achromatopsia is often stationary, although it can cause macular degeneration.