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Sorsby’s fundus dystrophy (SFD) is a rare but severe autosomal dominant disease. Clinically it is characterised by severe central visual loss, mainly due to submacular choroidal neovascularisation (CNV) during the fourth or fifth decade of life.1,2 Blindness therefore occurs during the patient’s most productive years of employment. We report a case of successful treatment of CNV in SFD with photodynamic therapy (PDT) and verteporfin.
A 40 year old white man (occupation photographer) presented in 1999 with sudden blurring and distortion of vision in the right eye. Visual acuity was 6/6 in the right eye, and 6/4 in the left. Funduscopy and fundus fluorescein angiogram (FFA) demonstrated a large subfoveal CNV. This was deemed unsuitable for laser photocoagulation owing to its location and size. Subsequently, acuity in the right eye deteriorated to 3/60 with the formation of a disciform macular scar. Standard flash electroretinogram (ERG) was normal, while dark adapted ERG was abnormal. Family history revealed that his mother and maternal grandmother went “blind” in their 50s. The patient’s cousin had also suffered from recent vision loss. A clinical diagnosis of SFD was made based on the patient’s age, family history, and retinal appearance. This was confirmed by molecular genetic assessment. Restriction digest analysis (using NsiI) showed that both the patient and his affected cousin were heterozygous for the Ser181Cys mutation in the tissue inhibitor of metalloproteinases-3 (TIMP3) gene.3
In 2001 the patient reported visual disturbance in his left eye. Visual acuity in the left eye had decreased to 6/36. FFA revealed a left extrafoveal, predominantly classic, CNV (Fig 1). It was known that submacular CNV in SFD responded poorly to conventional argon laser treatment,4 so we elected to undertake photodynamic therapy (PDT) with verteporfin.5 The protocol used for treatment was as previously described.6
Further PDT treatments were applied to the left macula at 3, 6, and 12 months. These supplemental treatments were prompted by fresh leakage seen on FFA. At 1 year, a small subretinal scar was seen at the site of the original CNV and some leakage was noted at the inferonasal edge of this scar (Fig 2). Further PDT treatment is planned for this. Visual acuity in his left eye improved from 6/36 to 6/12 and this has been maintained for the 1 year of follow up.
SFD was first described by Sorsby in 1949.1 Mildly affected patients suffer colour vision deficits and night blindness.2 In such patients, mid-peripheral drusen are often seen. Histologically, a confluent, lipid containing layer is seen deposited within the inner layer of Bruch’s membrane.7 Consistently, in the fourth to fifth decade of life affected patients suffer sudden, severe vision loss due to CNV. A few experience more gradual vision loss due to macular atrophy. All patients invariably progress to vision loss sufficient for blind registration.8
Despite some evidence to suggest improvement in night blindness with vitamin A supplements9 by far the most significant visual deficit in SFD relates to the complications of CNV. Effective treatment needs to be devised for this. Unlike age related macular degeneration, even if the CNV in SFD is juxtafoveal or extrafoveal, argon laser therapy is ineffective.4 Also, CNV natural history in age related macular degeneration can result in a variable final visual acuity.10 In SFD, however, visual prognosis after CNV, particularly when associated with the TIMP3 Ser181Cys mutation, is always very poor.8 It is particularly noteworthy therefore that 1 year after treatment, visual acuity has improved and has been maintained at 6/12 when acuity would be expected to have declined to 6/60 or less. Significantly, this has allowed the patient to continue in his career as a photographer.
This is the first report suggesting that treatment may limit severe visual deficit in an SFD patient and for an extended period. Photodynamic therapy with verteporfin should therefore be considered in other SFD patients when they suffer CNV.