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Detecting macular disease with a biometry device using swept-source optical coherence tomography
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LETTERS
Reply : We sincerely thank Drs. Savini et al. for their interest and comments on our article. We agree that changes in the anterior-toposterior corneal radius ratio might lead to refractive errors in the SRK/T formula after myopic LASIK. Our article focuses on the use of the SRK/T formula without corrections made for the post-LASIK eye to simplify the contribution of corneal asphericity to hyperopic refractive errors. The K-readings with a refractive index of 1.3375 were used for the SRK/T formula, while the values were overestimated with the amounts of correction.1,2 Hence, the refractive error could include the contribution. For examining the contribution of the anterior-to-posterior corneal radius ratio, the keratometric refractive index after LASIK (npost) was calculated according to equation 7 in Savini et al.2 for the data set used for multiple regression analysis in our study (N Z 22). The npost calculated ranged from 1.3252 to 1.3355 (mean 1.3304) and showed a significant correlation with the refractive error (P ! .001, R2 Z 0.69, linear regression analysis). Stepwise multiple regression analysis performed by adding the npost to the original descriptive factors resulted in a significant Q-value factor (P ! .001, R2 Z 0.89) and the same regression equation. This confirmation showed that corneal asphericity had a more significant effect on the refractive error than npost. We would like to thank the authors of this letter for allowing us to confirm this. dYosai Mori, MD, Kimiya Shimizu, MD, PhD, Keiichiro Minami, PhD, Kazutaka Kamiya, MD, PhD, Nobuyuki Shoji, MD, PhD, Kazunori Miyata, MD, PhD
REFERENCES €chle M. Un1. Seitz B, Langenbucher A, Nguyen NX, Kus MM, Ku derestimation of intraocular lens power for cataract surgery after myopic photorefractive keratectomy. Ophthalmology 1999; 106:693–702 2. Savini G, Barboni P, Zanini M. Correlation between attempted correction and keratometric refractive index of the cornea after myopic excimer laser surgery. J Refract Surg 2007; 23:461–466
Detecting macular disease with a biometry device using swept-source optical coherence tomography We read with interest the article by Hirnschall et al.1 reporting that the central 1.0 mm retinal scan obtained using a biometry device (IOLMaster 700, Carl Zeiss Meditec AG) with swept-source optical coherence tomography (SS-OCT) technology provided useful information on the status of the macula, although it could not replace a macular
scan using a dedicated spectral-domain OCT (SDOCT) device. The authors reported that because of the limited scan width of the biometry device (1.0 mm), it was difficult to tell whether some scans that appeared abnormal were off-center or actually had abnormalities. A typical macular OCT scan, with a wider scan width, could potentially compensate for off-center scans as a result of poor fixation. In addition, the wider scan width would give ophthalmologists additional reference landmarks in the posterior pole to correctly identify the fovea. The authors also noted that the fovea appeared flatter compared with typical OCT scans as a result of the narrower zone. These are all relevant limitations to consider when evaluating a limited scan area, and we agree these images should not replace a dedicated macular OCT scan if there are clinical suspicions of macular pathology. The authors also suggested that the retinal scan in future versions of the biometry device could be color-coded to indicate possible abnormalities in foveal contour and retinal thickness. This is an interesting idea. However, retinal thickness in the central subfield has a range of values that would be considered normal. In earlier studies,2–4 the central subfield retinal thickness varied from 262.8 mm to 270 mm, with a range of approximately 8 mm. The foveal contour in a normal eye has also been reported to vary significantly.3 Some eyes have shallower foveal contours, while in others the fovea has a deep pit. As a result, it would be important for any color-coded output to take these variations into consideration. In summary, we agree that the retinal scan on the SS-OCT biometry device can alert clinicians to the presence of possible macular pathology and this is useful in the preoperative screening of patients scheduled for cataract surgery. Such scans, however, have to be interpreted with caution, and a full macular scan using an SD-OCT or SS-OCT device should be performed if there is clinical suspicion of retinal disease. Colin S. Tan, MB BS, MMed(Ophth), FRCSEd(Ophth) Kai Xiong Cheong, MB BS Singapore Financial Disclosure: Dr. Tan receives research funding from the National Medical Research Council Transition Award (code NMRC/TA/0039/2015) and the National Healthcare Group (Singapore) Clinician Scientist Career Scheme Grant (code CSCS/12005). Dr. Tan also receives travel conference support from Bayer (South East Asia) Pte. Ltd., Heidelberg Engineering GmbH, and Novartis (Singapore) Pte. Ltd. Dr. Cheong does not receive funding.
J CATARACT REFRACT SURG - VOL 42, OCTOBER 2016
LETTERS
REFERENCES 1. Hirnschall N, Leisser C, Radda S, Maedel S, Findl O. Macular disease detection with a swept-source optical coherence tomography-based biometry device in patients scheduled for cataract surgery. J Cataract Refract Surg 2016; 42:530–536. Available at: http://www.jcrsjournal.org/article/S0886-3350(16) 30007-4/pdf. Accessed July 7, 2016 2. Tan CSH, Cheong KX, Lim LW, Li KZ. Topographic variation of choroidal and retinal thicknesses at the macula in healthy adults. Br J Ophthalmol 2014; 98:339–344 3. Tan CSH, Lim LW, Chow VS, Chay IW, Tan S, Cheong KX, Tan GT, Sadda SR. Optical coherence tomography angiography evaluation of the parafoveal vasculature and its relation-
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ship with ocular factors. Invest Ophthalmol Vis Sci 2016; 57:224–234 4. Samara WA, Say EAT, Khoo CTL, Higgins TP, Magrath G, Ferenczy S, Shields CL. Correlation of foveal avascular zone size with foveal morphology in normal eyes using optical coherence tomography angiography. Retina 2015; 35: 2188–2195
Reply : We thank Dr. Tan et al. for their comments, which are in line with our conclusions.dNino Hirnschall, MD, PhD, Christoph Leisser, MD, Stephan Radda, MD, Oliver Findl, MD, MBA
ERRATUM
In the May 2016 article, “Management of subluxated capsular bag-fixated intraocular lenses using a capsular anchor” (J Cataract Refract Surg 2016; 42:653–658), a co-author’s name was misspelled. The correct name is Ruth Lapid-Gortzak instead of Ruth Lapid Gortzak.
J CATARACT REFRACT SURG - VOL 42, OCTOBER 2016
LETTERS
Reply : We sincerely thank Drs. Savini et al. for their interest and comments on our article. We agree that changes in the anterior-toposterior corneal radius ratio might lead to refractive errors in the SRK/T formula after myopic LASIK. Our article focuses on the use of the SRK/T formula without corrections made for the post-LASIK eye to simplify the contribution of corneal asphericity to hyperopic refractive errors. The K-readings with a refractive index of 1.3375 were used for the SRK/T formula, while the values were overestimated with the amounts of correction.1,2 Hence, the refractive error could include the contribution. For examining the contribution of the anterior-to-posterior corneal radius ratio, the keratometric refractive index after LASIK (npost) was calculated according to equation 7 in Savini et al.2 for the data set used for multiple regression analysis in our study (N Z 22). The npost calculated ranged from 1.3252 to 1.3355 (mean 1.3304) and showed a significant correlation with the refractive error (P ! .001, R2 Z 0.69, linear regression analysis). Stepwise multiple regression analysis performed by adding the npost to the original descriptive factors resulted in a significant Q-value factor (P ! .001, R2 Z 0.89) and the same regression equation. This confirmation showed that corneal asphericity had a more significant effect on the refractive error than npost. We would like to thank the authors of this letter for allowing us to confirm this. dYosai Mori, MD, Kimiya Shimizu, MD, PhD, Keiichiro Minami, PhD, Kazutaka Kamiya, MD, PhD, Nobuyuki Shoji, MD, PhD, Kazunori Miyata, MD, PhD
REFERENCES €chle M. Un1. Seitz B, Langenbucher A, Nguyen NX, Kus MM, Ku derestimation of intraocular lens power for cataract surgery after myopic photorefractive keratectomy. Ophthalmology 1999; 106:693–702 2. Savini G, Barboni P, Zanini M. Correlation between attempted correction and keratometric refractive index of the cornea after myopic excimer laser surgery. J Refract Surg 2007; 23:461–466
Detecting macular disease with a biometry device using swept-source optical coherence tomography We read with interest the article by Hirnschall et al.1 reporting that the central 1.0 mm retinal scan obtained using a biometry device (IOLMaster 700, Carl Zeiss Meditec AG) with swept-source optical coherence tomography (SS-OCT) technology provided useful information on the status of the macula, although it could not replace a macular
scan using a dedicated spectral-domain OCT (SDOCT) device. The authors reported that because of the limited scan width of the biometry device (1.0 mm), it was difficult to tell whether some scans that appeared abnormal were off-center or actually had abnormalities. A typical macular OCT scan, with a wider scan width, could potentially compensate for off-center scans as a result of poor fixation. In addition, the wider scan width would give ophthalmologists additional reference landmarks in the posterior pole to correctly identify the fovea. The authors also noted that the fovea appeared flatter compared with typical OCT scans as a result of the narrower zone. These are all relevant limitations to consider when evaluating a limited scan area, and we agree these images should not replace a dedicated macular OCT scan if there are clinical suspicions of macular pathology. The authors also suggested that the retinal scan in future versions of the biometry device could be color-coded to indicate possible abnormalities in foveal contour and retinal thickness. This is an interesting idea. However, retinal thickness in the central subfield has a range of values that would be considered normal. In earlier studies,2–4 the central subfield retinal thickness varied from 262.8 mm to 270 mm, with a range of approximately 8 mm. The foveal contour in a normal eye has also been reported to vary significantly.3 Some eyes have shallower foveal contours, while in others the fovea has a deep pit. As a result, it would be important for any color-coded output to take these variations into consideration. In summary, we agree that the retinal scan on the SS-OCT biometry device can alert clinicians to the presence of possible macular pathology and this is useful in the preoperative screening of patients scheduled for cataract surgery. Such scans, however, have to be interpreted with caution, and a full macular scan using an SD-OCT or SS-OCT device should be performed if there is clinical suspicion of retinal disease. Colin S. Tan, MB BS, MMed(Ophth), FRCSEd(Ophth) Kai Xiong Cheong, MB BS Singapore Financial Disclosure: Dr. Tan receives research funding from the National Medical Research Council Transition Award (code NMRC/TA/0039/2015) and the National Healthcare Group (Singapore) Clinician Scientist Career Scheme Grant (code CSCS/12005). Dr. Tan also receives travel conference support from Bayer (South East Asia) Pte. Ltd., Heidelberg Engineering GmbH, and Novartis (Singapore) Pte. Ltd. Dr. Cheong does not receive funding.
J CATARACT REFRACT SURG - VOL 42, OCTOBER 2016
LETTERS
REFERENCES 1. Hirnschall N, Leisser C, Radda S, Maedel S, Findl O. Macular disease detection with a swept-source optical coherence tomography-based biometry device in patients scheduled for cataract surgery. J Cataract Refract Surg 2016; 42:530–536. Available at: http://www.jcrsjournal.org/article/S0886-3350(16) 30007-4/pdf. Accessed July 7, 2016 2. Tan CSH, Cheong KX, Lim LW, Li KZ. Topographic variation of choroidal and retinal thicknesses at the macula in healthy adults. Br J Ophthalmol 2014; 98:339–344 3. Tan CSH, Lim LW, Chow VS, Chay IW, Tan S, Cheong KX, Tan GT, Sadda SR. Optical coherence tomography angiography evaluation of the parafoveal vasculature and its relation-
1545
ship with ocular factors. Invest Ophthalmol Vis Sci 2016; 57:224–234 4. Samara WA, Say EAT, Khoo CTL, Higgins TP, Magrath G, Ferenczy S, Shields CL. Correlation of foveal avascular zone size with foveal morphology in normal eyes using optical coherence tomography angiography. Retina 2015; 35: 2188–2195
Reply : We thank Dr. Tan et al. for their comments, which are in line with our conclusions.dNino Hirnschall, MD, PhD, Christoph Leisser, MD, Stephan Radda, MD, Oliver Findl, MD, MBA
ERRATUM
In the May 2016 article, “Management of subluxated capsular bag-fixated intraocular lenses using a capsular anchor” (J Cataract Refract Surg 2016; 42:653–658), a co-author’s name was misspelled. The correct name is Ruth Lapid-Gortzak instead of Ruth Lapid Gortzak.
J CATARACT REFRACT SURG - VOL 42, OCTOBER 2016