Use of multifocal ERG and OCT for diagnosing Stargardt's disease.

Stargardt’s disease (Stargardt’s macular dystrophy, juvenile macular degeneration) was originally described by Stargardt in the early 1900s and is known as the most common congenital macular dystrophy, with an incidence of one in every 10,000. Stargardt’s disease (STGD) is characterised as a widespread lipofusin storage disease of the retinal pigment epithelium (RPE). Typically, it presents between the first to third decades of life and is associated with a progressive, bilateral decrease in visual acuity leading to legal blindness and central visual acuity of 6/60 to 6/120. Though it is typically associated with an autosomal recessive (AR) inheritance pattern, autosomal dominant (AD) cases have been reported with later onset and less severe acuity loss. Classic findings include bilateral macular changes that begin as granular mottling with progression toward a ‘beaten bronze’ maculopathy. The late stage of the disease is associated with macular atrophic degeneration. Yellow-white flecks in the posterior pole may be noted; they are described as tri-radiating ‘fish tail’ (pisciform) flecks. Traditionally, Stargardt’s disease has been diagnosed through clinical evaluation and fluorescein angiography (IVFA), which demonstrates a dark or ‘silent’ choroid due to the blockage of the fluorescein by the lipofusin deposition in the RPE. Though fluorescein angiography has been considered the ‘gold standard’ in verifying the presence of the disease, the characteristic dark choroid pattern is seen in only 85 per cent of patients with Stargardt’s disease. There have been reports of patients with autosomal dominant inheritance pattern who fail to demonstrate this classic fluorescein angiography finding. Newer and minimally invasive procedures, such as the multifocal electroretinogram (mfERG) and optical coherence tomography (OCT), may aid in diagnosing and managing patients with the disease. These ancillary tests may be used in the event that fluorescein angiography cannot be performed or used in conjunction with traditional fluorescein angiography as a complementary procedure. Multifocal electroretinography (mfERG) is a minimally invasive procedure that has been shown to be helpful in the diagnosis of Stargardt’s disease. Unlike traditional flash electroretinography (fERG), this technology has proved extremely reliable in diagnosing and monitoring various forms of macular dystrophy. In the case of Stargardt’s disease, the patient presents with significant variation in presentation; from normal to reduced acuity, minimal to significant fundus findings and normal to slightly reduced full field flash electrophysiological findings. Regardless of the presentation, Stargardt’s patients typically have a significant reduction of the foveal response and central approximately 10 degrees in both eyes on mfERG, even early in the disease process with relatively good visual acuity and minimal fundus findings. In addition to electrophysiology, retinal imaging technology such as OCT has proved effective in correlating structural damage with functional visual loss. The OCT findings of patients with Stargardt’s disease include decreased thickness of the retina, most notably in the foveola. The OCT also reveals photoreceptor loss and external nuclear layer changes, as well as abnormalities in the retinal pigment epithelium.