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Oligocone trichromacy: a rare and unusual cone dysfunction syndrome
M Michaelides1, G E Holder, K Bradshaw
1Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK.
Aim:
To describe the phenotype of a case series of six patients with oligocone trichromacy.
Methods:
The six affected individuals underwent an ophthalmological examination, electrophysiological testing and detailed psychophysical assessment.
Results:
All six affected patients had a history of moderately reduced visual acuity (6/12 to 6/24) from infancy, not improved by full spectacle correction. They complained of mild photophobia and they were not aware of any colour vision deficiency. They had no nystagmus and fundi were normal. Electrophysiological testing revealed either absent/profoundly reduced cone flicker responses or preserved but delayed and mildly reduced flicker responses. Colour vision was found to be within normal limits, but some patients showed mildly elevated discrimination thresholds along all axes.
Conclusion:
The largest case series to date of patients with oligocone trichromacy is presented. The electrophysiological findings suggest that there may be more than one disease mechanism. The mode of inheritance is likely to be autosomal recessive, and while previous reports have suggested that this disorder is stationary, in one of these families there is clinical evidence of progression.