Tay-Sachs Disease: Cherry-red Spot
The center of the fovea appears bright red because it is surrounded by a milky halo.
This halo represents loss of retinal transparency which comes from a pile up of ganglioside in ganglion cells. The ganglioside accumulates because its catabolic enzyme (hexosaminidase A) is missing. Remember that there are no ganglion cells in the center of the fovea, so that the underlying choroid transmits its red color.
A similar metabolic cherry-red spot occurs in other lysosomal enzyme deficiences such as generalized gangliosidosis (GM 1), Sandhoff's, Gaucher's, mucolipidosis Types 1 and 2, Niemann-Pick Type A, and multiple sulfatase deficiency. Vision is usually subnormal because the ganglion cells are not working properly.
How do you distinguish a metabolic cherry-red spot from the cherry-red spot found in ? There are three ways:
- The halo is thinner in the metabolic disorders.
- Acute loss of vision does not occur in the metabolic disorders.
- The cherry-red spot is always binocular in metabolic disorders and uniocular in retinal occlusion.