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Occult macular dystrophy (OMD) is an inherited macular dystrophy characterised by a progressive decline of visual acuity without visible fundus abnormalities.1–3 In these patients, the fluorescein angiograms and conventional full field electroretinograms (ERGs) are normal, but the amplitudes of the focal macular ERGs and multifocal ERGs are significantly reduced but only in the central retina.1–4
The age at the onset of symptoms in OMD patients is relatively old,1–3 and the first visit to the hospital is aged 20 years or more with the youngest being 16 years in most cases. Here, we present an 11 year old boy who was diagnosed as having OMD because of the results of electrophysiological and psychophysical tests.
An 11 year old boy was referred to our hospital with a complaint of progressive decline of vision in both eyes. His corrected visual acuity was 20/25 in both eyes at 6 years of age, but had decreased to 20/33 at 10 years of age. Family history revealed no other members to have any eye diseases. At the initial examination, his visual acuity was 20/40 right eye and 20/33 left eye with −3.0 dioptres (D) in both eyes. The fundus examination and fluorescein angiograms were normal (fig 1). The peripheral visual fields were intact but a relative central scotoma was detected with the I-2 target within 10 degrees in both eyes. A moderate red-green defect was found on the Ishihara pseudoisochromatic plates, Hardy-Rand-Rittler pseudoisochromatic plates, and Farnsworth-Munsell 100 hue test.
The amplitude of full field ERGs were within the normal range for both rod and cone components (fig 2A). However, focal macular ERGs with 5, 10, and 15 degrees stimulus spots3 were severely reduced and essentially absent (fig 2B). The multifocal ERGs4 demonstrated a loss of local responses in the central retina (fig 2C).
Psychophysical rod and cone sensitivity was performed on his right eye with 31 test points across the 60 degree horizontal meridian using a previously described method.5 The cone sensitivities were severely affected in the central retina but fell within the normal range in the periphery (fig 2D). The rod sensitivities were at the lower borderline at almost all locations tested (not shown).
At present (August 2003, 13 years old), his acuity has decreased to 20/50 in both eyes, but his fundi still remain normal in both eyes.
This boy had a progressive decrease of visual acuity in both eyes, and his fundus examinations and fluorescein angiograms were completely normal. The amplitude of the conventional full field ERGs were also within the normal range for both rod and cone components. However, focal macular cone ERGs and multifocal ERGs were severely reduced in the central retina. Results of psychophysical perimetry showed a reduction of cone sensitivity but only in the central retina. These findings are consistent with the clinical characteristics of OMD which we have previously reported.1,3,4
OMD in children is very rare.1–3 In our 42 consecutive OMD patients seen at the Nagoya University Hospital from 1988 to 2003, the age at initial visit to the hospital ranged from 16 to 74 years (mean 45.8 years), and 95.2% of patients visited the hospital at 20 year old or more. To the best of our knowledge, this boy is the youngest case with OMD reported anywhere.
We would like to emphasise that OMD can be found even in children. Because the fundus examination and full field ERGs are normal in these patients, these children are apt to be misdiagnosed as optic nerve disease, central nerve disease, or psychological disorders. Focal or multifocal ERG techniques are the only key to diagnose this rare type of macular dystrophy.
Grant support: Grant in aid 13307048 (YM), 14370557 (HT), 14770952 (MK) from the Ministry of Education, Science, Sports and Culture, Japan.
Proprietary interest: None.