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Pediatric photoscreening
Ophthalmology Volume 107, Number 7, July 2000 their 40s. Approximately 94% of the data obtained were from patients who had not yet experienced bifocal correction. We believed that because the number of presbyopes in the study was so small and divided equally among the two groups, we had no reason to exclude their contribution to the study. Unfortunately, we did not question our patients to see whether they participated in activities requiring sustained eccentric gaze. We are unsure of how one would objectively measure this, but it is a valid point. We are pleased that our work stimulates comments and that our practices allow us, on occasion, to measure such patients. Of interest was the recent measurement of a 26year-old white woman wearing a prescription, right eye, ⫺1-25 ⫺0.75 ⫻ 010/left eye, ⫺5.00 ⫺0.75 ⫻ 170 for 16 years. Her vertical fusional amplitudes were measured to be 12 prism diopters, lending further support to our supposition. STEPHEN GRIEBEL, MD GREGORY S. KOSMORSKY, DO CHRISTOPHER RIEMANN, MD Cleveland, Ohio
Pediatric Photoscreening Dear Editor: In reading the article, “Pediatric Photoscreening for Strabismus and Refractive Error in a High-risk Population” (Ophthalmology 1999;106:1073– 80) by Drs. Simmons & Flynn, I was concerned regarding the data analysis and had questions that were not fully answered in the article. The authors mentioned that the “number of photographs required for a picture of adequate quality, was recorded for each patient,” but these data were not reported in the article. As a masked reader of the photographs, I was struck by the high numbers of eccentric fixation that were present in the photographs. Although it has been over a year since I read them, my recollection was that at least 10% to 15% of the photographs had eccentric fixation. Did the authors correlate the accuracy of strabismus evaluation in the presence of eccentric fixation in photographs with photographs that had no evidence of eccentric fixation? A small degree of eccentric fixation will cause a brightening of the red reflex and make it difficult to accurately determine whether strabismus is present, as was shown elegantly by Joe Miller, MD, in his paper presented at AAPOS this year. As well, Dr. Miller demonstrated that eccentric fixation can induce abnormal crescent sizes, which can compromise the sensitivity and specificity in reading refractive errors. Was this factor taken into account when the authors determined sensitivity and specificity? Was any correlation between crescent size and pupil size done in the analysis? It is well known that for each pupil size, crescent size varies. The MTI failure criteria are set for a pupil size of 5 mm. Did the authors use the “MTI criteria” for all crescent/pupil sizes or vary the analysis depending on pupil size? I have known for years that for pupils smaller or larger
Dr. Freedman has a financial interest in the MTI camera.
1216
than 5 mm, it is necessary to use a different criteria for crescent size to determine the proper degree of refractive error. In fact, many scientists who are doing community photoscreening are using a series of nomograms for pupil size and crescent size of different degrees. This allows more accurate interpretation of refractive errors using the MTI Photo Screener. I did not know whether the authors were aware of this or took this into account in their analysis. If they did not account for this, their measurements of sensitivity and specificity are in error. In the authors discussion of the “economics of false referrals,” I was wondering whether any comparison was made to the sensitivity and specificity of routine vision screening as currently practiced in the United States? There are many children that are falsely referred for abnormal vision screening at schools, when there are no abnormalities found in the pediatric ophthalmology office. How much are we currently spending now on false referrals for vision screening and what is the true sensitivity and specificity of vision screening as it is practiced in the school system? To my knowledge there are no good data on this. This is one of the major concerns I have when people try to assess the costs of screening when we do not really know what are the current sensitivity, specificity, and costs of our current vision screening system. HOWARD L. FREEDMAN, MD, FAAP Redmond, Washington Author’s reply Dear Editor: Dr. Freedman expresses concern that perhaps too many children required multiple photos for proper analysis. However, the mean number of photos per patient was 1.5 (SD ⫽ 0.75), and the median number of photos per patient was 1. Sixty-two patients required only one photo, 23 required two, 12 needed three, and only one patient had four photos taken; the information was unavailable for two subjects. Thus, in more than 85% of subjects, one or two images were sufficient for adequate analysis. Dr. Freedman asked us to comment on the accuracy of strabismus evaluation in subjects with and without “eccentric fixation” on the photographic images. Because the MTI camera has a built-in flash that is slightly off-center to the camera aperture, technically speaking, all photographic images of subjects display eccentric fixation. For this use, a better term is probably “improper fixation.” We did not include this parameter in determination of sensitivity and specificity in our article. To date, no data on the effects of improper fixation during photoscreening have been published in the peer-reviewed literature. (Related data were presented by Miller et al at the Association for Research in Vision and Ophthalmology annual meeting, but after the completion of our study). At this time, there is no reproducible evidence that improper fixation is a frequent, easily identifiable, or important occurrence in pediatric photoscreening. If future studies identify this as a common source of error, then all photoscreening devices will need to be reevaluated with this in mind. Dr. Freedman also requested information regarding the
Pediatric Photoscreening Dear Editor: In reading the article, “Pediatric Photoscreening for Strabismus and Refractive Error in a High-risk Population” (Ophthalmology 1999;106:1073– 80) by Drs. Simmons & Flynn, I was concerned regarding the data analysis and had questions that were not fully answered in the article. The authors mentioned that the “number of photographs required for a picture of adequate quality, was recorded for each patient,” but these data were not reported in the article. As a masked reader of the photographs, I was struck by the high numbers of eccentric fixation that were present in the photographs. Although it has been over a year since I read them, my recollection was that at least 10% to 15% of the photographs had eccentric fixation. Did the authors correlate the accuracy of strabismus evaluation in the presence of eccentric fixation in photographs with photographs that had no evidence of eccentric fixation? A small degree of eccentric fixation will cause a brightening of the red reflex and make it difficult to accurately determine whether strabismus is present, as was shown elegantly by Joe Miller, MD, in his paper presented at AAPOS this year. As well, Dr. Miller demonstrated that eccentric fixation can induce abnormal crescent sizes, which can compromise the sensitivity and specificity in reading refractive errors. Was this factor taken into account when the authors determined sensitivity and specificity? Was any correlation between crescent size and pupil size done in the analysis? It is well known that for each pupil size, crescent size varies. The MTI failure criteria are set for a pupil size of 5 mm. Did the authors use the “MTI criteria” for all crescent/pupil sizes or vary the analysis depending on pupil size? I have known for years that for pupils smaller or larger
Dr. Freedman has a financial interest in the MTI camera.
1216
than 5 mm, it is necessary to use a different criteria for crescent size to determine the proper degree of refractive error. In fact, many scientists who are doing community photoscreening are using a series of nomograms for pupil size and crescent size of different degrees. This allows more accurate interpretation of refractive errors using the MTI Photo Screener. I did not know whether the authors were aware of this or took this into account in their analysis. If they did not account for this, their measurements of sensitivity and specificity are in error. In the authors discussion of the “economics of false referrals,” I was wondering whether any comparison was made to the sensitivity and specificity of routine vision screening as currently practiced in the United States? There are many children that are falsely referred for abnormal vision screening at schools, when there are no abnormalities found in the pediatric ophthalmology office. How much are we currently spending now on false referrals for vision screening and what is the true sensitivity and specificity of vision screening as it is practiced in the school system? To my knowledge there are no good data on this. This is one of the major concerns I have when people try to assess the costs of screening when we do not really know what are the current sensitivity, specificity, and costs of our current vision screening system. HOWARD L. FREEDMAN, MD, FAAP Redmond, Washington Author’s reply Dear Editor: Dr. Freedman expresses concern that perhaps too many children required multiple photos for proper analysis. However, the mean number of photos per patient was 1.5 (SD ⫽ 0.75), and the median number of photos per patient was 1. Sixty-two patients required only one photo, 23 required two, 12 needed three, and only one patient had four photos taken; the information was unavailable for two subjects. Thus, in more than 85% of subjects, one or two images were sufficient for adequate analysis. Dr. Freedman asked us to comment on the accuracy of strabismus evaluation in subjects with and without “eccentric fixation” on the photographic images. Because the MTI camera has a built-in flash that is slightly off-center to the camera aperture, technically speaking, all photographic images of subjects display eccentric fixation. For this use, a better term is probably “improper fixation.” We did not include this parameter in determination of sensitivity and specificity in our article. To date, no data on the effects of improper fixation during photoscreening have been published in the peer-reviewed literature. (Related data were presented by Miller et al at the Association for Research in Vision and Ophthalmology annual meeting, but after the completion of our study). At this time, there is no reproducible evidence that improper fixation is a frequent, easily identifiable, or important occurrence in pediatric photoscreening. If future studies identify this as a common source of error, then all photoscreening devices will need to be reevaluated with this in mind. Dr. Freedman also requested information regarding the