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Show f. Clin. Neuro-ophthalmol. 3: 152, 1983. Achromatopsia and Congenital Nystagmus To the Editor: The extremely informative paper by O'Connor et al. on Achromatopsia l contained some misconceptions which require clarification. Quoting Pierce/ the authors stated that congenital nystagmus (CN) is a cause of blindness. One of us has already published a review of Pierce's paper3 which can be briefly summarized as being poorly written and ill-conceived; 20% of the so-called "blind" patients had acuities better than 20/100 in at least one eye, and 90% of the remaining patients had abnormal foveas. Whereas CN may be responsible for lowering the acuity a few lines on the Snellen chart, in some patients, it is never a primary cause of blindness. In fact, we have recorded many patients with CN who have had 20/20 vision. O'Connor et al. stated that their six patients with achromatopsia were all initially "misdiagnosed as congenital nystagmus." Although one cannot be certain whether these patients had true CN rather than manifest latent nystagmus (another congenital form of nystagmus4 ), they probably all had a congenital form of nystagmus and were not "misdiagnosed." Unless the authors prove that the nystagmus was absent in infancy and developed later in childhood (presumably secondary to the visual distrubance), the nystagmus was, in fact, "congenital." Congenital nystagmus is often associated genetically with a primary afferent disturbance. It is this afferent disturbance which may markedly impair vision, not the nystagmus. Therefore, that which was "initially misdiagnosed" was the achromatopsia and not the CN. The tenacious misconception that there are two types of CN, "sensory" and "motor," lingers despite the fact that this has been disproved by many ocular motor studies performed in different labo- 152 ratories over the past 10 years. 5 This concept, which ascribes a simple cause and effect relationship to variables which are often associated but not causally related, was based upon clinical observations that have not survived the scrutiny of contemporary oculography. In summary, the paper by O'Connor et at properly makes the point that patients with CN are at risk for achromatopsia and describes a method for determining whether achromatopsia is present. The paper errs in the assumptions that achromatopsia is a cause of CN and that CN can be a cause of blindness. Louis F. Dell'Osso, PhD. Robert B. Darof£, MD. Cleveland, Ohio References 1. O'Connor, PS, Tredici, TJ., Ivan, D.J., Mumma, J,V., and Shacklett, D.E.: Achromatopsia. Clinical diagnosis and treatment. f. Clin. Neuro-ophthalmol. 2: 219-226, 1982. 2. Pierce, W.G.: Causes of blindness in children. 1046 cases registered with the Canadian National Institute for the Blind, 1970-1973. Can. f. Ophthalmol. 10: 469-472, 1975. 3. DelrOsso, LF.: Nystagmus and ocular motor oscillations. In Neuro-Ophthalmology 1980, Vol. 1, S. Lessell and J,TW. van Dalen, Eds. Excerpta Medica, Amsterdam, 1982, p. 151. 4. DelrOsso, LF., Schmidt, D., and Daroff, RB.: latent, manifest latent and congenital nystagmus. Arch. Ophthalmol. 97: 1877-1885, 1979. 5. Daroff, R.B.: Summary of clinical presentations. In Basic Mechanisms ofOcular Motility and their Clinical Implications, G. Lennerstrand and P. Bach-yrita, Eds. Pergamon Press, Oxford, 1975, pp. 435443. Journal of Clinical Neuro-ophthalmolog |
