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Corneal Topography of Early Keratoconus
746
December, 1989
AMERICAN JOURNAL OF OPHTHALMOLOGY
We have demonstrated that squinting can cause a significant reduction in the pattern electroretinogram amplitude. A reflex artifact induced by ocular movement (photomyoclonic reflex) has produced variability in the flash electroretinogram waveform." Because squinting and associated electrical response from the orbicularis oculi may mask the inner retinal layer's response, it is important to instruct patients to keep both eyes open to minimize the effect of ocular muscle tremor on the pattern electroretinogram.
References 1. Maffei, L., and Fiorentini, A.: Electroretinographic responses to alternating gratings before and after section of the optic nerve. Science 211:953, 1981. 2. Arden, G. B., Vaegen, and Hogg, C. R.: Clinical experimental evidence that the pattern electroretinogram (PERG) is generated in more proximal retinal layers than the focal electroretinogram (FERG). Ann. N.Y. Acad. Sci. 388:580, 1982. 3. Holopigian, K., Snow, J., Seiple, W., and Siegel,!.: Variability of the pattern electroretinogram. Doc. Ophthalmol. 70:103, 1988. 4. Dawson, W., Trick, G., and Maida, c. Evaluation of DTL corneal electrode. Doc. Ophthalmol. Proc. Ser. 31:81, 1982. 5. Johnson, M. A., and Massof, R. W.: The photomyoclonic reflex. An artifact in the clinical electroretinogram. Br. J. Ophthalmol. 66:368, 1982.
Correspondence Correspondence concerning recent articles or other material published in THE JOURNAL should be submitted within six weeks of publication. Correspondence must be typed double-spaced, on 8Y2 x ll-inch bond paper with 1Y2-inch margins on all four sides and should be no more than two typewritten pages in length. Every effort will be made to resolve controversies between the correspondents and the authors of the article before publication.
Corneal Topography of Early Keratoconus EDITOR:
In the article, "Corneal topography of early keratoconus" by 1. J. Maguire and W.
M. Bourne (Am. J. Ophthalmol. 108:107, August 1989), the authors identified topographic features of keratoconus in seven of nine eyes with no slit-lamp evidence of the condition. However, it is not clear what criteria were used to determine that topographic evidence of keratoconus was present. For example, I think it is difficult to determine whether Figure 1 represents a cornea with early keratoconus or whether it shows normal corneal topography, given that the dioptric spread in Figure 1 is only 3 diopters. This sort of distribution of corneal topography may also be seen in emmetropia.' What is clearly needed and not provided is a more objective way of determining the presence of keratoconus from corneal topographic data.! Until such methods are available and proven, I caution against diagnosing early keratoconus based on subjective interpretation of topographic data. This article represents supportive evidence of what many ophthalmologists believe, that is, keratoconus may be present before any slip-lamp evidence is manifest. I congratulate the authors on adding to our knowledge about this condition. STEVEN A. DINGELDEIN, M.D.
Burlington, North Carolina
References 1. Dingeldein, S. A., and Klyce, S. D.: The topography of normal corneas. Arch. Ophthalmol. 107:512, 1989. 2. Dingeldein, S. A., Pittman, S. D., Wang, J., and Klyce, S. D.: Analysis of corneal topographic data. ARVO abstracts. Supplement to Invest. Ophthalmol. Vis. Sci. Philadelphia, J. B. Lippincott, 1988, p. 389. EDITOR:
We are pleased to note that Drs. Maguire and Bourne in their article, "Corneal topography of early keratoconus" (Am. J. Ophthalmol. 108:107, August 1989), have confirmed our findings! that the Corneal Modelling System is an excellent means of detecting early keratoconus. We examined newly referred patients with keratoconus whose topography had not been distorted by contact lenses or surgery and identified three parameters which were statistically significantly different from a normal control group. Similar findings, less severe than those with overt disease, were detected in family members of patients with obvious keratoconus. Two of the probands in this study had what
December, 1989
AMERICAN JOURNAL OF OPHTHALMOLOGY
We have demonstrated that squinting can cause a significant reduction in the pattern electroretinogram amplitude. A reflex artifact induced by ocular movement (photomyoclonic reflex) has produced variability in the flash electroretinogram waveform." Because squinting and associated electrical response from the orbicularis oculi may mask the inner retinal layer's response, it is important to instruct patients to keep both eyes open to minimize the effect of ocular muscle tremor on the pattern electroretinogram.
References 1. Maffei, L., and Fiorentini, A.: Electroretinographic responses to alternating gratings before and after section of the optic nerve. Science 211:953, 1981. 2. Arden, G. B., Vaegen, and Hogg, C. R.: Clinical experimental evidence that the pattern electroretinogram (PERG) is generated in more proximal retinal layers than the focal electroretinogram (FERG). Ann. N.Y. Acad. Sci. 388:580, 1982. 3. Holopigian, K., Snow, J., Seiple, W., and Siegel,!.: Variability of the pattern electroretinogram. Doc. Ophthalmol. 70:103, 1988. 4. Dawson, W., Trick, G., and Maida, c. Evaluation of DTL corneal electrode. Doc. Ophthalmol. Proc. Ser. 31:81, 1982. 5. Johnson, M. A., and Massof, R. W.: The photomyoclonic reflex. An artifact in the clinical electroretinogram. Br. J. Ophthalmol. 66:368, 1982.
Correspondence Correspondence concerning recent articles or other material published in THE JOURNAL should be submitted within six weeks of publication. Correspondence must be typed double-spaced, on 8Y2 x ll-inch bond paper with 1Y2-inch margins on all four sides and should be no more than two typewritten pages in length. Every effort will be made to resolve controversies between the correspondents and the authors of the article before publication.
Corneal Topography of Early Keratoconus EDITOR:
In the article, "Corneal topography of early keratoconus" by 1. J. Maguire and W.
M. Bourne (Am. J. Ophthalmol. 108:107, August 1989), the authors identified topographic features of keratoconus in seven of nine eyes with no slit-lamp evidence of the condition. However, it is not clear what criteria were used to determine that topographic evidence of keratoconus was present. For example, I think it is difficult to determine whether Figure 1 represents a cornea with early keratoconus or whether it shows normal corneal topography, given that the dioptric spread in Figure 1 is only 3 diopters. This sort of distribution of corneal topography may also be seen in emmetropia.' What is clearly needed and not provided is a more objective way of determining the presence of keratoconus from corneal topographic data.! Until such methods are available and proven, I caution against diagnosing early keratoconus based on subjective interpretation of topographic data. This article represents supportive evidence of what many ophthalmologists believe, that is, keratoconus may be present before any slip-lamp evidence is manifest. I congratulate the authors on adding to our knowledge about this condition. STEVEN A. DINGELDEIN, M.D.
Burlington, North Carolina
References 1. Dingeldein, S. A., and Klyce, S. D.: The topography of normal corneas. Arch. Ophthalmol. 107:512, 1989. 2. Dingeldein, S. A., Pittman, S. D., Wang, J., and Klyce, S. D.: Analysis of corneal topographic data. ARVO abstracts. Supplement to Invest. Ophthalmol. Vis. Sci. Philadelphia, J. B. Lippincott, 1988, p. 389. EDITOR:
We are pleased to note that Drs. Maguire and Bourne in their article, "Corneal topography of early keratoconus" (Am. J. Ophthalmol. 108:107, August 1989), have confirmed our findings! that the Corneal Modelling System is an excellent means of detecting early keratoconus. We examined newly referred patients with keratoconus whose topography had not been distorted by contact lenses or surgery and identified three parameters which were statistically significantly different from a normal control group. Similar findings, less severe than those with overt disease, were detected in family members of patients with obvious keratoconus. Two of the probands in this study had what