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LETTER TO EDITOR
Year : 2006  |  Volume : 54  |  Issue : 4  |  Page : 289-290

Defective vision due to oligocone trichromacy in a young adult


Aravind Eye hospital and Postgraduate Institute of Ophthalmology, Madurai, Tamilnadu, India

Correspondence Address:
Vasumathy Vedantham
Aravind Eye hospital and Postgraduate Institute of Ophthalmology, Madurai, Tamilnadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0301-4738.27968

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How to cite this article:
Vedantham V, Kanungo S. Defective vision due to oligocone trichromacy in a young adult. Indian J Ophthalmol 2006;54:289-90

How to cite this URL:
Vedantham V, Kanungo S. Defective vision due to oligocone trichromacy in a young adult. Indian J Ophthalmol [serial online] 2006 [cited 2020 Dec 5];54:289-90. Available from: https://www.ijo.in/text.asp?2006/54/4/289/27968

Dear Editor,

Cone dysfunction syndromes are hereditary conditions characterized by bilateral visual dysfunction, abnormal color vision, photophobia, central scotomata and abnormal photopic responses in full-field electroretinography (ERG).[1] We report a very rare type of cone dysfunction syndrome known as oligocone trichromacy characterized by normal color vision and abnormal photopic ERG.

A 26-year-old male patient presented to the retina-vitreous service of our tertiary eye care hospital with complaints of defective vision since infancy, with photophobia. Ocular examination revealed 20/80, N18 vision in both eyes with normal anterior segment. Fundus examination revealed normal maculae with a ring of retinal pigment epithelial atrophy starting from the peripapillary region and continuing along the arcades in both the eyes [Figure - 1], top right and left. There was posterior staphyloma in both eyes. ERG (UTAS 3000, LKC Technologies) showed normal scotopic and extinguished photopic responses in both the eyes [Figure - 1], bottom right and left. A provisional diagnosis of cone dystrophy was made in both the eyes. However, to our surprise, color vision as tested by Ishihara's pseudoisochromatic plates was normal in both the eyes. This was against the diagnosis of cone dystrophy. A diagnosis of oligocone trichromacy was made (Prof. Graham Holder, Director of Electrophysiology, Moorfields Eye Hospital, personal communication).The family members of the patient were not available for examination. The patient was referred to the low visual aids department for appropriate visual aids.

Oligocone trichromacy is a rare cone dysfunction syndrome, first described by Van Lith.[2] These patients have reduced number of normal functioning cones (hence the term, oligocone), which is corroborated by normal color vision but extinguished photopic ERG.[3] It appears to be a form of stationary cone dysfunction with trichromacy. It is similar to cone dystrophy except for absence of bull's eye maculopathy and normal color vision. The mode of inheritance is said to be autosomal recessive but there is a lot of genetic heterogeneity.[3] It might result due to mutations within the genes currently identified in achromatopsia.[3] It is characterized by reduced visual acuity, photophobia, normal fundus, preservation of color vision and abnormal photopic ERG, all of which were seen in our patient as well except for a complete normal fundus. We are reporting this case in order to highlight this very rare disorder as a cause of central visual dysfunction with normal color vision.


  Acknowledgment Top


The authors would like to acknowledge the expert guidance of Prof. Graham Holder, Director of Electrophysiology, Moorfields Eye Hospital, in diagnosing this case.



 
  References Top

1.
Michaelides M, Hunt DM, Moore AT. The cone dysfunction syndromes. Br J Ophthalmol 2004;88:291-7.  Back to cited text no. 1
    
2.
van Lith GH. General cone dysfunction without achromatopsia. In : Pearlman JT, editors. 10th ISCERG Symposium: Doc Ophthalmol Proc Ser; 1973. p. 175-80.  Back to cited text no. 2
    
3.
Michaelides M, Holder GE, Bradshaw K, Hunt DM, Mollon JD, Moore AT. Oligocone trichromacy: A rare and unusual cone dysfunction syndrome. Br J Ophthalmol 2004;88:497-500.  Back to cited text no. 3
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