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A 19-month-old girl with nystagmus, paradoxical pupillary response and low vision
Digital Journal of Ophthalmology 2008
Volume 14, Number 6
February 25, 2008
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Sandra Rocio Montezuma, M.D. | Massachusetts Eye and Ear Infirmary
Diagnosis and Discussion
This patient’s ocular features of infantile nystagmus, paradoxical pupillary constriction to darkness, hyperopia and normal appearance of the retinas on ophthalmoscopy along with the ERG results make achromatopsia the most likely diagnosis.

Achromatopsia ("a-", lack of; "-chroma-", color; "-opsia", vision), also called rod monochromacy is a stationary autosomal recessive condition that affects 8,500 persons in the US (1 in 33,000). It is characterized by reduced visual acuity, nystagmus, deficits in color discrimination, normal fundus appearance and paradoxical pupillary constriction to dark.(1,2) Hyperopia is common in individuals with achromatopsia, although a broad distribution of refractive errors has been reported.(3) Patients with achromatopsia are usually photophobic (light sensitive). Our patient does not appear to be photophobic, but she is not yet ambulatory. Some children with achromatopsia do not have photophobia until walking on their own outdoors.

Achromatopsia is caused by a channelopathy of the photoreceptors.(4) The most frequent molecular cause are mutations in the cGMP-gated cation channel genes CNGA3 (Chrom 2) and CNGB3 (Chrom 8) (5,6) and less commonly, a mutation in the transducin protein GNAT2.(7) As a result, cone and cone-driven ERG responses to full-field stimuli are markedly attenuated or non-detectable, but rod and rod-driven responses are normal or mildly decreased.(8,9)

In our patient although achromatopsia is the most likely diagnosis, a progressive retinal disorder cannot be ruled out completely. For this reason regular ophthalmic follow-up is recommended.

Treatment and Recommendations:

Patients should be prescribed glasses if there is a significant refractive error. Our patient was given +5.50 spherical refraction in both eyes. In our patient no additional treatment was offered at this point since she was not light sensitive and she is not ambulatory yet. She needs a follow up examination and the vision should be monitored with special tests that include measurement of the dark-adapted visual threshold and mapping of the visual fields. Other recommendations for patients with Achromatopsia include: Red/dark central contact lenses; sun filters to be worn outdoors to decrease light sensitivity and low vision aids including the use of large print materials, sitting in the classroom away from the windows and closing blinds to decrease glare on the board.

Acknowledgements
I would like to thank Anne Fulton, M.D. for her assistance in the preparation of this manuscript.
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