Stargardt’s Disease is an autossomal recessive hereditary disease included in the group of degenerative macular diseases, which consists in progressive lost of cones in fovea of both eyes, leading to variable levels of central vision loss. At fundoscopy, there’s often the presence of yellowish flecks around the macula, a condition called fundus flavimaculatus.
It usually develops in ages between 7 and 12, with an estimated incidence between 1/1660 and 1/15000, what makes this disease the largest cause of macular degeneration affecting the retinal pigment epithelium (RPE) in the first and second decades of life, and correspond to 7% of all retinian dystrophies.
This disease was first described as an autossomal recessive inherited disease, but there are some described cases of dominant pattern. The recessive pattern, which includes more than 90% of cases, is due to a defect at the chromosome 1q21-p13. The dominant pattern seems to be related to a change at chromosome 6, but some studies also reported the location on chromosome 12. The altered gene seems to be responsible for the transcription of protein that works like an outer molecular pump.
The foveal damage is possibly due to a defect on an outer molecular pump that would eliminate a specific substance from cones. This molecule builds up inside the rods, accumulating as a form of lipofuscine, which penetrates in the RPE, acting as a poisoning substance for this layer, making it susceptible to lysis. The photoreceptor layer in the fovea demands an enormous fagocytic and metabolic activity from the RPE (much greater than in periphery), what makes the atrophic changes in Stargardt’s Disease be found mainly at foveal area. Fundus Flavimaculatus happens as a consequence of the atrophic epithelium of the central area, that becomes hyperfluorescent, and the still intact epithelial cells immersed in lipofuscin, which absorbs the blue excitatory wave-lengths, making this perifoveal region hypofluorescent in pisciform shapes(corresponding to the fresh flecks at fundoscopy).
The degeneration process begin early , normally at 7 years old, being the foveal reflexes alteration with granulous aspect of RPE the first manifestation. Hardly the disease is diagnosed at this age due to low age of patients. These lesions progress with macular and perimacular atrophy of RPE. The yellowish flacks can be observed around the macula characterizing the fundus flavomaculatus .
The visual effect of disease consists in a loss of central visual responsible for visual acuity and color perception. Usually it evolutes slowly until reaches the 20/40 level, then rapidly progressing to something around the 20/200 level. It leads to variable levels of visual loss , up to a 10/200 level or less. In some cases, it can in a period of months evolute from 20/40 to 10/200 , but it do not lead to complete blindness.
The presence of a defect in green-red axis color perception and a progressing central scotoma are the other common features of affected patients.
Evaluation for Stargardt’s Disease.
You should suspect of Stargardt’s Disease in every young person presenting with a history of progressive visual acuity loss , mainly if there was a family member with the same complaints .
After a visual acuity evaluation test, the following exams should be performed :
1-Ophtalmoscopy - It will show loss of foveal reflex and granulous aspect of RPE cells. The most characteristic finding are the yellowish flecks around the macular area, the fundus flavimaculatus .
2-Fluoresceinic Angiography - Of great diagnostic value , it will show the characteristic aspect of "bull’s eye" due to a "window effect" at the level of the perifoveolar despigmentation limit. The coroidian silence, due to a mask effect in the periphery of retina, appearing as a shadow hypofluorescent caused by lipofuscine deposits in the peripheral retina . In the Diffuse form of F. flavimaculatus , the peripheral retina will appear hyperfluorescent.
Fluoresceinic Angiography: It shows a Fluoresceinic Angiography with the
characteristic aspect of "bull's eye" due to a "window effect" at the level
of the perifoveolar despigmentation limit.
3-Electric Diagnostic Tests - The Electro-oculography (EOG) is normal in early stages. As the RPE degeneration becomes more widespread, the EOG tends to show abnormality. The ERG * is normal or manifests only a slight delay in obtaining an otherwise normal maximal B-wave amplitude. Prolonged periods of dark adaptation can also be found.
There is no treatment that proved to improve the visual loss or to retard the progressing of the disease. There are a few measures that should be adopted and that will help the patients solving some of the problems that they face. There are many kinds of binocular lens, either for improving near vision or distance vision, increase the visual field, protect against the light, watching, looking at the blackboard and improving the reading of the patients; the choose of the most useful lens for each patient should be performed by the physician and the patient together. the More affected persons should learn to read in Braille, and have the other specific management for low vision conditions. A great number of the affected patients will be classified as owing legal blindness. Some doctors recommend the use of vitamins, in special A, E, C, Selenium and Betacarotene.
The level of visual acuity loss will depend on each case, starting to progress in tender ages and determining variable levels of visual defect, from discrete loss to complete lack of detail vision, with the presence of big central scotomas extending to peripheral areas. Complete blindness is a very rare event in the natural course of Stargardt’s Disease.