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Sir,

Late-onset retinal degeneration (L-ORD) is an autosomal dominant disorder characterised by onset of night vision problems in midlife and progressive loss of peripheral visual field and central vision over ensuing decades.1,2,3,4 The late onset of symptoms mimics other more common eye disorders in the elderly in this condition and can lead to misdiagnosis. We report cases of sisters with L-ORD, who were initially diagnosed as age-related macular degeneration and normal tension glaucoma.

Case reports

Case 1

A 63-year-old woman presented in 1986 with floaters in her left eye. Her best corrected visual acuity was 6/9 N5 in both eyes. Her father was blind in later life. A posterior vitreous detachment was diagnosed, but she was noted to have cupping of the right optic disc despite normal intraocular pressures. After 2 years, she had developed bilateral visual field defects. Despite ocular hypotensive treatment, her visual fields continued to deteriorate and she had bilateral trabeculectomies.

Her visual acuity then started to deteriorate and pigmentary changes at the macula were noted. This progressed to atrophy with widespread peripheral retinal degenerative changes in both eyes (Figure 1a). An electroretinogram showed no measurable scotopic or photopic responses and led to the diagnosis of L-ORD. Her vision is now hand movements in both eyes with very restricted visual fields.

Figure 1
figure 1

(a) Fundus appearance of case 1. (b) Peripheral retinal appearance of case 2.

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Case 2

A 78-year-old woman was referred in 1997 with a gradual deterioration in her vision. On examination, her visual acuity was hand movements in both eyes. Fundal examination showed atrophic maculae. A diagnosis of age-related macular degeneration was made and the patient was registered blind.

She returned to the clinic 1 year later with worsening sight. Her visual acuities remained at hand movements but she had reduced visual fields. On examination, the peripheral retina showed widespread pigmentary changes with chorioretinal atrophy (Figure 1b). She reported that her sister (case 1) had recently been registered blind and her father and grandfather had poor sight in later life. A diagnosis of L-ORD was made on this clinical picture. An electroretinogram showed unmeasureable responses.

Comment

The late onset of this disease is the defining feature of L-ORD. Initially, there can be no ophthalmoscopic abnormalities, which is unusual for most inherited dystrophies. The earliest symptoms occur in the sixth decade and after, with problems with dark adaptation1 although formal dark adaptation testing can show abnormalities a decade before symptoms.2 The first signs can be clusters of fine yellow–white dots in the mid-periphery.1,2 The disease then progresses to loss of central and peripheral vision with peripheral pigmentary retinopathy and chorioretinal atrophy. The macula usually becomes atrophic but occasionally there is a disciform scar. The optic disc becomes pale and this coupled with the visual field abnormalities may lead to the diagnosis of normal tension glaucoma. The standard ERG may be normal in the early stages. At the end stage of the disease, only a reduced amplitude, delayed cone ERG is detectable.1 There is some evidence that the early dark adaptation abnormalities are partially responsive to vitamin A therapy2 but how this affects the poor long-term prognosis is still unknown. The diagnosis of L-ORD is either based on the above clinical picture or on the pathological appearance of a thick sub-RPE deposit throughout the retina1,3,4 like that found in Sorsby's fundus dystrophy6 and sometimes in age-related macular degeneration.7 It is postulated that this deposit may act as a barrier to nutrient transport to the retina. In the later stages, there is widespread loss of RPE and photoreceptors.4

In the early stages, the disease can mimic other ophthalmic conditions as in our two cases. Our first patient was seen relatively early in the disease course but the diagnosis was not made in the patient or her sister until the peripheral retinal changes were present. Asking about night vision problems, family history and careful examination of the fundus including peripheral retina can be helpful in detecting this unusual disease. Our patients' diagnosis was further confirmed when they were found to be distantly related members of a fully investigated L-ORD family.2

These cases are important to raise awareness of L-ORD in the ophthalmic community. We often try to reassure our patients with ARM that they will not lose their peripheral vision. This rare subgroup of patients does lose this vital visual function with devastating visual results.