Retinopathy of prematurity: Risk factors in a five-year cohort of critically III premature neonates

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1988

CURRENTOPHTHALMOLOGY

patient in their published series with see-saw nystagmus was similarly benefitted (Currie JN, Matsuo V: The use of clonazepam in the Treatment of Nystagmus - induced oscillopsia. Ophthalmolog,v93:924-932, 1986). The disturbing oscillopsia in these patients may be ameliorated by such therapy, although the mode of action remains uncertain. MYLES M. BEHRENS, M.D. NEW YORK, NEW YORK

Tobacco-Induced Primary-Position Upbeat Nystagmus, by P.A. Sibony, C. Evinger, and K.A.

Manning.

Ann Neural 21:53-58,

1987

The effects of tobacco smoke on the eye movements of normal human subjects were studied using directTobacco induced a transient primary current electro-oculography and magnetic search coil technique. position upbeat nystagmus in the dark which was suppressed by visual fixation. It obeyed Alexander’s law, and was associated with oblique upward fast phases that alternated from side to side. Tobacco-induced nystagmus exhibited a latency of onset at 40-90 seconds and a duration of 10-20 minutes. There was a maximum slow phase velocity at 2-3 minutes. The authors suggest that tobacco induces primary-position upbeat nystagmus through the excitatory effects of nicotine on central vestibular pathways that can be inhibited by visual fixation. (Author’s address: Dr. Sibony, Department of Neurology and Ophthalmology, State University of New York at Stony Brook, Stony Brook, NY 11794.)

Comment The impetus for this study arose from the examination of a patient with traumatic cortical blindness. After smoking a cigarette, the patient would develop primary-position upbeat nystagmus. This led the authors to wonder whether the tobacco-induced nystagmus that occurred in their patient was in part due to loss of visual input. By testing normal subjects smoking in the dark, the authors determined that this was indeed the case. The nystagmus was analyzed with eye-movement recordings and was noted to exhibit a linear slow phase and a slow phase velocity that increased in upgaze. The findings are consistent with a central form of vestibular nystagmus. This article represents the best in clinical research. The authors observed a finding in an individual patient and were astute enough to recognize its general implications. They then designed and carried out the anpropriate study to test their theories. II

1

WALTER M. ,JAY, M.D. LITTLE ROCK, ARKANSAS

Retinopathy of Prematurity: Risk Factors in a Five-Year Cohort of Critically III Premature Neonates, by D.R. Brown, J.R. Milley, U.J. Ripepi, and A.W Biglan. Am J Dis Child 141: 154-160, 1987 Scarring retinopathy of prematurity remains an important source of serious morbidity for survivors of neonatal intensive care. It has been estimated to cause blindness in approximately 2% of surviving neonates with a birth weight less than 1500 grams. The authors studied the importance of exposure to an elevated partial pressure of carbon dioxide in the development of scarring retinopathy of prematurity in a cohort of 92 neonates with chronic lung disease. Of these, 3 1 patients had scarring retinopathy of prematurity. This cohort was chosen to avoid confounding prolonged respiratory failure with the presence of scarring retinopathy of prematurity, and because such a cohort was expected to contain approximately 85% of all patients with

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scarring retinopathy of prematurity. Patients with scarring retinopathy of prematurity had a lower pressure of carbon dioxide and spent more time on a respirator at higher respiratory pressures during the first 70 days of life. In addition, infants with scarring retinopathy of prematurity had a lower mean arterial pressure and had a higher prevalence of seizures and intraventricular hemorrhage. The authors conclude that elevated carbon dioxide levels are not associated with scarring of retinopathy of prematurity in this group of critically premature neonates, but the presence of a seizure disorder or an intraventricular hemorrhage is strongly associated with the development of scarring retinopathy of prematurity. (Author’s address: Dr. Brown, Department of Pediatrics, McGee Women’s Hospital, Forbes Avenue and Halket St.. Pittsburgh. P.4 15213.)

Comment that this is a As our experience with retinopathy of prematurity has grown, it has become apparent multifactorial disease. Thus, the ability to identify risk factors becomes increasingly more important. Two of these, prematurity and gestational age at birth, have been repeatedly identified (James S, Lanman JT: History ofoxygen therapy and retrolental fibroplasia. Pediatrics Sr7:591-642, 1976; Tasman W, et al: Cryotherof the apy for active retinopathy of prematurity. Ophthalmology 93:58&585, 1986). I n addition the publication International Classification of Retinopathy of Prematurity in 1984 added dramatically to our ability to identify high risk eyes that were likely to progress to significant scarring retinopathy of prematurity or even retinal detachment and blindness (The Committee for the Classification of Retinopathy of Prematurity: ,4n International Classification of Retinopathy of Prematurity. Arch Ophthalmol 102: 1130-l 134, 1984). This report by Brown et al describes a study designed to test the hypothesis that exposure to an elevated PC,,, is necessary for the development of scarring retinopathy of prematurity. In the course of the study, eyes were examined with indirect ophthalmoscopy and were categorized in a five-stage system which predates the International Classification since the study was performed between January of 1979 and December of 1983. Nonetheless, I think the results presented here add a significant parameter to our understanding of retinopathy of prematurity. Although they concluded that an elevated Pro2 is not associated with scarring retinopathy of prematurity in a group of critically ill premature neonates, there was a striking occurrence of seizures in 97% of the patients with scarring retinopathy of prematurity versus only 43% of controls. Less dramatic was the 52% incidence of intraventricular hemorrhage in neonates with scarring retinopathy of prematurity versus only 26% of controls. Both the neonates with scarring retinopathy of prematurity and those without had similar mean birth weights, although the neonates with scarring retinopathy ofprematurity had a statistically lower gestational age. Thus, it would appear that a markedly abbreviated gestational age makes infants not only more susceptible to intraventricular hemorrhage and seizure disorder, but perhaps scarring retinopathy of prematurity as well. WII.I.IA.\I T.zs.\I.\N, M.D. PHII.~ZI)F,I.PHI.~. PKNNSYI.V.XNIA

Characteristics of the Capillary-Free Zone in the Normal Human Macula, by L. Wu, Z. Huang, D. Wu, and E. Chan. Jpn J OphthaZmoZ29:4Of.%411, 1985 The diameter of the fovea1 avascular zone (FAZ) in the normal human eye has been measured by various investigators and values have ranged from 0.16 to 0.73 mm. A considerable individual variation in the diameter has been reported to exist. Furthermore, enlargement of this area has been known to occur in various diseases, including diabetic retinopathy, sickle cell retinopathy, talc embolic retinopathy, and branch vein occlusion. Using fluorescein angiotrams and a digital image processing system, the authors determined the FAZ in 45 normal subjects, 25 men and 20 women. The shape of the FAZ was usually irregular and showed considerable individual variations. The mean longest diameter was 0.88 mm. The horizontal diameter was 0.73 mm, vertical diameter was .7 mm, and the average 0.43 mm. The area of the FAZ and the age of the subject showed a statistically significant positive correlation. The enlargement of the FAZ with advancing age may be related