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Corneal Topography of Early Keratoconus: Reply
Correspondence
Vol. 108, No.6
appeared to be unilateral keratoconus with clinically normal fellow eyes, normal corneoscopy, and excellent visual acuity. In these probands we reported similar changes to those noted by Drs. Maguire and Bourne. Similar changes were noted in their family members who were also clinically normal and had reported excellent visual acuity. An important difference between these two studies is that all our patients had normal-appearing mires on corneoscopy. Rowsey and Reynolds" previously reported that they were able to detect early changes in keratoconus with the corneoscope. In our experience astigmatic changes in the range of 2.5 diopters or less are not readily detectable with this instrument. In this respect the Cornea Modelling System is valuable in that it not only provides information about the entire anterior corneal topography but also graphically illustrates .changes that are so subtle as to remain undetected on corneoscopy. In the article by Maguire and Bourne a "subtle cone" is illustrated in a patient who wore contact lenses. They do not state for how long he had not been wearing the lenses before the photographs were taken. This is an important concern because Wilson and associates" reported that changes similar to those noted in keratoconus can be induced by contact lens wear and can persist for up to six months after discontinuing lens wear. In their study they also illustrate a topographic map of a patient who had undergone cataract surgery, and interpret it as showing no evidence of keratoconus. It is possible that the superior topography was altered by the surgery, and that left undisturbed, only the inferior steepening would have been seen, which would have been indicative of early keratoconus. We wonder whether conclusions based upon topographies of postsurgical patients and of contact lens wearers are justified. YARON S. RABINOWITZ, M.D.
Baltimore, Maryland
PETER J. MCDONNELL, M.D.
Los Angeles, California
References 1. Rabinowitz, Y. 5., McDonnell, P. J., Caroline, P. J., and Zilge, L.: Corneal topographic analysis in family members of patients with keratoconus using a computer video photokeratoscope. ARVO abstracts. Supplement to Invest. Ophthalmol. Vis. Sci. Philadelphia, J. B. Lippincott, 1989, p. 188.
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2. Rowsey, J. J., Reynolds, A. E., and Brown, R.: Corneal topography. Corneoscope. Arch. Ophthalmol. 99:1093, 1981. 3. Wilson, S. E., Klyce, S. D., Insler, M.S., and Lind, D. T c.: Contact lens induced changes in corneal topography. ARVO abstracts. Supplement to Invest. Ophthalmol. Vis. Sci. Philadelphia, J. B. Lippincott, 1989, p. 218.
_ _ _ _ _ _ _ Reply EDITOR:
_
Drs. Dingeldein, Rabinowitz, and McDonnell raise some interesting points that we wish to clarify. The concept that keratoconus may exist before slit-lamp evidence of the condition is well established. Amsler's classic work on this subject (referenced in our article along with the work by Rowsey and Reynolds cited by Drs. Rabinowitz and McDonnell) showed that over 50% of patients with the diagnosis showed no slit-lamp evidence of the condition.! Diagnosis of early keratoconus was made by inspection of keratoscope photographs. Our article, the work by Rowsey and Reynolds, and the abstract and letter by Rabinowitz and colleagues all confirm the observation Amsler made in 1946, that keratoscopy is an important tool in the diagnosis of early keratoconus. Amsler also used keratoscopy to identify and follow cone progression. When he reexamined his patients three to five years later, in 66% of the patients without slit-lamp evidence of keratoconus, progression of the condition was demonstrated." The 48-year clinical and epidemiologic study of keratoconus performed at the Mayo Clinic, which we believe is the only population-based study of the condition, showed that the majority of patients with keratoconus have little or no slit-lamp evidence of the condition." In most cases (64 of 102 eyes) the diagnosis was based on the characteristic irregular light reflex on direct ophthalmoscopy or retinoscopy. Unilateral keratoconus was diagnosed in 41% of subjects. Of the patients initially identified as unilateral keratoconus, 23% later developed the condition in the opposite eye. We identified ours as a pilot study to determine the types of topography extant in patients likely to have subclinical keratoconus. Figure 1 of the article shows a pattern of power distribution qualitatively similar to that seen in Figures 2 and 3, an inferiorly displaced area of high power surrounded by con-
748
AMERICAN JOURNAL OF OPHTHALMOLOGY
centric rings of progressively lower power. Few would argue that the contour maps shown in Figures 2 and 3 are consistent with keratoconus. We have observed slit-lamp evidence of keratoconus in other patients with topographic patterns almost identical to those seen in Figures 2 and 3. The opposite eye of the patient shown in Figure 1 was such a case in point. We think the topography shown in Figure 1 is consistent with keratoconus but respect the opinion of those who argue otherwise. As stated in the discussion of the original article, we hope to reproduce the results of our pilot study in a larger series and identify other patients like that shown in Figure 1. These patients will be asked to return at regular intervals for reexamination. If we can document progression of keratoconus from a pattern as shown in Figure 1 to the pattern shown in Figures 2 and 3 in a subset of the group, the controversy will be resolved. We have read with interest Dr. Dingeldein's excellent article on the topography of normal corneas.' It is referenced in our article. Unfortunately we find no figure in that work that simulates any figure in our own. Our patient with a "subtle cone," Patient 7, had a history of soft contact lens wear, discontinued one year before our examination. Patient 1 had discontinued contact lens wear more than one year before entry into our study. We believed it reasonable to include these eyes in our study. Drs. Rabinowitz and McDonnell suggest the patient with a history of cataract extraction in the right eye 17 years before topographic examination may have keratoconus. They may be correct, but insufficient evidence is provided by the color map. This patient was included in the study because his fellow eye was thought to have keratoconus. We added a footnote to the Table to alert the reader to the history of surgery in the eye in question. LEO J. MAGUIRE, M.D. WILLIAM M. BOURNE, M.D. Rochester, Minnesota
References 1. Amsler, M.: Keratocone classique et keratocone fruste. Arguments unitaires. Ophthalmologica 111:96,1946.
December, 1989
2. - - : Quelques donnees du problerne du keratocone. Bull. Soc. Beige Ophtalmol. 129:33, 1962. 3. Kennedy, R. H., Bourne, W. M., and Dyer, J. A.: A 48-year clinical and epidemiologic study of keratoconus. Am. J. Ophthalmol. 101:267, 1986. 4. Dingeldein, S. A., and Klyce, S. D.: Computer assisted corneal topography of normal corneas. Arch. Ophthalmol. 107:512, 1989.
Increase of the Short-Term Fluctuation of the Differential Light Threshold Around a Physiologic Scotoma EDITOR:
In the article, "Increase of the short-term fluctuation of the differential light threshold around a physiologic scotoma," by 1. O. Haefliger and J. Flammer (Am. J. Ophthalmol. 107:417, April 1989), the authors found an increase of the short-term fluctuation at the border of the blind spot of normal subjects and concluded that this increase "is not necessarily only a consequence of a pathologic alteration of the visual field but may indicate simply the presence of a depression in the island of vision." In our opinion the blind spot cannot be entirely compared to a pathologic scotoma, principally because of the physiologic angioscotomas, which could occasion the great fluctuation found by the authors using a O.S-degree resolution test. Moreover, high values of short-term fluctuation can be easily foreseen by testing points close to an absolute scotoma of any type. We studied the shortterm fluctuation in the pericecal area, taking into account points within S degrees of the blind spot borders, but not connected to the absolute scotoma.' In a group of 32 normal subjects, examined with a 60-point threshold grid custom test, the pericecal mean shortterm fluctuation was 1.92 dB. This value is comparable to that obtained within 30 degrees by Brenton and Phelps" with the same automatic perimeter. In an another study, the pericecal short-term fluctuation showed a slight increase, even if not significant, from the normal individuals, patients with suspected glaucoma, and those with early open-angle glaucoma (unpublished data). This could mean that the increase of short-term fluctuation in glaucoma has a real importance and is not completely correlated with a depression
Vol. 108, No.6
appeared to be unilateral keratoconus with clinically normal fellow eyes, normal corneoscopy, and excellent visual acuity. In these probands we reported similar changes to those noted by Drs. Maguire and Bourne. Similar changes were noted in their family members who were also clinically normal and had reported excellent visual acuity. An important difference between these two studies is that all our patients had normal-appearing mires on corneoscopy. Rowsey and Reynolds" previously reported that they were able to detect early changes in keratoconus with the corneoscope. In our experience astigmatic changes in the range of 2.5 diopters or less are not readily detectable with this instrument. In this respect the Cornea Modelling System is valuable in that it not only provides information about the entire anterior corneal topography but also graphically illustrates .changes that are so subtle as to remain undetected on corneoscopy. In the article by Maguire and Bourne a "subtle cone" is illustrated in a patient who wore contact lenses. They do not state for how long he had not been wearing the lenses before the photographs were taken. This is an important concern because Wilson and associates" reported that changes similar to those noted in keratoconus can be induced by contact lens wear and can persist for up to six months after discontinuing lens wear. In their study they also illustrate a topographic map of a patient who had undergone cataract surgery, and interpret it as showing no evidence of keratoconus. It is possible that the superior topography was altered by the surgery, and that left undisturbed, only the inferior steepening would have been seen, which would have been indicative of early keratoconus. We wonder whether conclusions based upon topographies of postsurgical patients and of contact lens wearers are justified. YARON S. RABINOWITZ, M.D.
Baltimore, Maryland
PETER J. MCDONNELL, M.D.
Los Angeles, California
References 1. Rabinowitz, Y. 5., McDonnell, P. J., Caroline, P. J., and Zilge, L.: Corneal topographic analysis in family members of patients with keratoconus using a computer video photokeratoscope. ARVO abstracts. Supplement to Invest. Ophthalmol. Vis. Sci. Philadelphia, J. B. Lippincott, 1989, p. 188.
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2. Rowsey, J. J., Reynolds, A. E., and Brown, R.: Corneal topography. Corneoscope. Arch. Ophthalmol. 99:1093, 1981. 3. Wilson, S. E., Klyce, S. D., Insler, M.S., and Lind, D. T c.: Contact lens induced changes in corneal topography. ARVO abstracts. Supplement to Invest. Ophthalmol. Vis. Sci. Philadelphia, J. B. Lippincott, 1989, p. 218.
_ _ _ _ _ _ _ Reply EDITOR:
_
Drs. Dingeldein, Rabinowitz, and McDonnell raise some interesting points that we wish to clarify. The concept that keratoconus may exist before slit-lamp evidence of the condition is well established. Amsler's classic work on this subject (referenced in our article along with the work by Rowsey and Reynolds cited by Drs. Rabinowitz and McDonnell) showed that over 50% of patients with the diagnosis showed no slit-lamp evidence of the condition.! Diagnosis of early keratoconus was made by inspection of keratoscope photographs. Our article, the work by Rowsey and Reynolds, and the abstract and letter by Rabinowitz and colleagues all confirm the observation Amsler made in 1946, that keratoscopy is an important tool in the diagnosis of early keratoconus. Amsler also used keratoscopy to identify and follow cone progression. When he reexamined his patients three to five years later, in 66% of the patients without slit-lamp evidence of keratoconus, progression of the condition was demonstrated." The 48-year clinical and epidemiologic study of keratoconus performed at the Mayo Clinic, which we believe is the only population-based study of the condition, showed that the majority of patients with keratoconus have little or no slit-lamp evidence of the condition." In most cases (64 of 102 eyes) the diagnosis was based on the characteristic irregular light reflex on direct ophthalmoscopy or retinoscopy. Unilateral keratoconus was diagnosed in 41% of subjects. Of the patients initially identified as unilateral keratoconus, 23% later developed the condition in the opposite eye. We identified ours as a pilot study to determine the types of topography extant in patients likely to have subclinical keratoconus. Figure 1 of the article shows a pattern of power distribution qualitatively similar to that seen in Figures 2 and 3, an inferiorly displaced area of high power surrounded by con-
748
AMERICAN JOURNAL OF OPHTHALMOLOGY
centric rings of progressively lower power. Few would argue that the contour maps shown in Figures 2 and 3 are consistent with keratoconus. We have observed slit-lamp evidence of keratoconus in other patients with topographic patterns almost identical to those seen in Figures 2 and 3. The opposite eye of the patient shown in Figure 1 was such a case in point. We think the topography shown in Figure 1 is consistent with keratoconus but respect the opinion of those who argue otherwise. As stated in the discussion of the original article, we hope to reproduce the results of our pilot study in a larger series and identify other patients like that shown in Figure 1. These patients will be asked to return at regular intervals for reexamination. If we can document progression of keratoconus from a pattern as shown in Figure 1 to the pattern shown in Figures 2 and 3 in a subset of the group, the controversy will be resolved. We have read with interest Dr. Dingeldein's excellent article on the topography of normal corneas.' It is referenced in our article. Unfortunately we find no figure in that work that simulates any figure in our own. Our patient with a "subtle cone," Patient 7, had a history of soft contact lens wear, discontinued one year before our examination. Patient 1 had discontinued contact lens wear more than one year before entry into our study. We believed it reasonable to include these eyes in our study. Drs. Rabinowitz and McDonnell suggest the patient with a history of cataract extraction in the right eye 17 years before topographic examination may have keratoconus. They may be correct, but insufficient evidence is provided by the color map. This patient was included in the study because his fellow eye was thought to have keratoconus. We added a footnote to the Table to alert the reader to the history of surgery in the eye in question. LEO J. MAGUIRE, M.D. WILLIAM M. BOURNE, M.D. Rochester, Minnesota
References 1. Amsler, M.: Keratocone classique et keratocone fruste. Arguments unitaires. Ophthalmologica 111:96,1946.
December, 1989
2. - - : Quelques donnees du problerne du keratocone. Bull. Soc. Beige Ophtalmol. 129:33, 1962. 3. Kennedy, R. H., Bourne, W. M., and Dyer, J. A.: A 48-year clinical and epidemiologic study of keratoconus. Am. J. Ophthalmol. 101:267, 1986. 4. Dingeldein, S. A., and Klyce, S. D.: Computer assisted corneal topography of normal corneas. Arch. Ophthalmol. 107:512, 1989.
Increase of the Short-Term Fluctuation of the Differential Light Threshold Around a Physiologic Scotoma EDITOR:
In the article, "Increase of the short-term fluctuation of the differential light threshold around a physiologic scotoma," by 1. O. Haefliger and J. Flammer (Am. J. Ophthalmol. 107:417, April 1989), the authors found an increase of the short-term fluctuation at the border of the blind spot of normal subjects and concluded that this increase "is not necessarily only a consequence of a pathologic alteration of the visual field but may indicate simply the presence of a depression in the island of vision." In our opinion the blind spot cannot be entirely compared to a pathologic scotoma, principally because of the physiologic angioscotomas, which could occasion the great fluctuation found by the authors using a O.S-degree resolution test. Moreover, high values of short-term fluctuation can be easily foreseen by testing points close to an absolute scotoma of any type. We studied the shortterm fluctuation in the pericecal area, taking into account points within S degrees of the blind spot borders, but not connected to the absolute scotoma.' In a group of 32 normal subjects, examined with a 60-point threshold grid custom test, the pericecal mean shortterm fluctuation was 1.92 dB. This value is comparable to that obtained within 30 degrees by Brenton and Phelps" with the same automatic perimeter. In an another study, the pericecal short-term fluctuation showed a slight increase, even if not significant, from the normal individuals, patients with suspected glaucoma, and those with early open-angle glaucoma (unpublished data). This could mean that the increase of short-term fluctuation in glaucoma has a real importance and is not completely correlated with a depression