Int Ophthalmol DOI 10.1007/s10792-014-9949-1
LETTER TO THE EDITOR
Variation of subfoveal choroidal thickness measurements with spherical equivalent Colin S. H. Tan • Kai Xiong Cheong Wei Kiong Ngo
•
Received: 24 March 2014 / Accepted: 13 April 2014 Ó Springer Science+Business Media Dordrecht 2014
We read with interest the article by Erkul et al. [1] describing subfoveal choroidal thickness in a Turkish cohort, and their analysis of the factors affecting this. This paper provides valuable information on the considerable variation of choroidal thickness reported among different populations, which is essential to our understanding of how choroidal thicknesses vary with and possibly influence different ocular diseases [2, 3]. Although the authors reported no significant correlation between spherical equivalent and subfoveal choroidal thickness in this cohort, it would be interesting to know if they observed any patterns in the variation of choroidal thickness among different groups of refractive error. As the authors have noted, several earlier studies have reported significant variation of choroidal thickness with spherical equivalent, with the choroid progressively thinning with increasing severity of myopia [2]. A possible factor influencing the findings in the current study was the relatively narrow range of spherical equivalent among their participants (mean 0.24 D, standard deviation ±1.9 D). In a study of
C. S. H. Tan K. X. Cheong W. K. Ngo Department of Ophthalmology, Tan Tock Seng Hospital, Singapore, Singapore C. S. H. Tan (&) Fundus Image Reading Center, National Healthcare Group Eye Institute, Singapore, Singapore e-mail: [email protected]
choroidal thickness among 124 normal, healthy Chinese participants with spherical equivalent ranging from -10.0 to ?0.5 D, a statistically significant variation in mean central subfield choroidal thickness was found with refractive error [2]. In that study, mean choroidal thickness was 457.4 lm among emmetropes (spherical equivalent -0.49 to ?0.50 D) and decreased significantly to 357.9 lm among low myopes (-0.50 to -2.99 D), 316.7 lm among moderate myopes (-3.00 to -5.99 D) and 253.8 lm among high myopes (B -6.0 D) [2]. This represents a difference of[200 lm between emmetropes and high myopes. Similarly, a paper by Coscas et al. [4] reported thicker choroidal measurements in emmetropes and low myopes compared to high myopes. It is possible, therefore, that inclusion of patients with a wider range of refractive errors might have allowed more accurate elucidation of the influence of spherical equivalent on choroidal thickness in the current study. We agree with the authors that point thickness measurements of the choroid have important limitations. Recent studies have demonstrated considerable topographic variation of the choroid and retina at the macula [2]. Besides assessing choroidal volumes, we believe that measuring mean choroidal thickness using the Early Treatment Diabetic Retinopathy Study (ETDRS) grid is also a useful means to provide more comprehensive information on the topographic variation of the choroid. Using this method, we have observed important variations of choroidal topography with refractive error [2].
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In summary, we congratulate the authors on their results, which add to our understanding of the factors affecting choroidal thickness among different populations.
References 1. Erkul SO, Kapran Z, Uyar OM (2014) Quantitative analysis of subfoveal choroidal thickness using enhanced depth imaging optical coherence tomography in normal eyes. Int Ophthalmol 34:35–40. doi:10.1007/s10792-013-9787-6
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2. Tan CS, Cheong KX, Lim LW, Li KZ (2014) Topographic variation of choroidal and retinal thicknesses at the macula in healthy adults. Br J Ophthalmol 98:339–344. doi:10.1136/ bjophthalmol-2013-304000 3. Tan CS, Ouyang Y, Ruiz H, Sadda SR (2012) Diurnal variation of choroidal thickness in normal, healthy subjects measured by spectral domain optical coherence tomography. Invest Ophthalmol Vis Sci 53:261–266. doi:10.1167/iovs.11-8782 4. Coscas G, Zhou Q, Coscas F, Zucchiatti I, Rispoli M, Uzzan J, De Benedetto U, Savastano MC, Soules K, Goldenberg D, Loewenstein A, Lumbroso B (2012) Choroid thickness measurement with RTVue optical coherence tomography in emmetropic eyes, mildly myopic eyes, and highly myopic eyes. Eur J Ophthalmol 22:992–1000. doi:10.5301/ejo.5000189
LETTER TO THE EDITOR
Variation of subfoveal choroidal thickness measurements with spherical equivalent Colin S. H. Tan • Kai Xiong Cheong Wei Kiong Ngo
•
Received: 24 March 2014 / Accepted: 13 April 2014 Ó Springer Science+Business Media Dordrecht 2014
We read with interest the article by Erkul et al. [1] describing subfoveal choroidal thickness in a Turkish cohort, and their analysis of the factors affecting this. This paper provides valuable information on the considerable variation of choroidal thickness reported among different populations, which is essential to our understanding of how choroidal thicknesses vary with and possibly influence different ocular diseases [2, 3]. Although the authors reported no significant correlation between spherical equivalent and subfoveal choroidal thickness in this cohort, it would be interesting to know if they observed any patterns in the variation of choroidal thickness among different groups of refractive error. As the authors have noted, several earlier studies have reported significant variation of choroidal thickness with spherical equivalent, with the choroid progressively thinning with increasing severity of myopia [2]. A possible factor influencing the findings in the current study was the relatively narrow range of spherical equivalent among their participants (mean 0.24 D, standard deviation ±1.9 D). In a study of
C. S. H. Tan K. X. Cheong W. K. Ngo Department of Ophthalmology, Tan Tock Seng Hospital, Singapore, Singapore C. S. H. Tan (&) Fundus Image Reading Center, National Healthcare Group Eye Institute, Singapore, Singapore e-mail: [email protected]
choroidal thickness among 124 normal, healthy Chinese participants with spherical equivalent ranging from -10.0 to ?0.5 D, a statistically significant variation in mean central subfield choroidal thickness was found with refractive error [2]. In that study, mean choroidal thickness was 457.4 lm among emmetropes (spherical equivalent -0.49 to ?0.50 D) and decreased significantly to 357.9 lm among low myopes (-0.50 to -2.99 D), 316.7 lm among moderate myopes (-3.00 to -5.99 D) and 253.8 lm among high myopes (B -6.0 D) [2]. This represents a difference of[200 lm between emmetropes and high myopes. Similarly, a paper by Coscas et al. [4] reported thicker choroidal measurements in emmetropes and low myopes compared to high myopes. It is possible, therefore, that inclusion of patients with a wider range of refractive errors might have allowed more accurate elucidation of the influence of spherical equivalent on choroidal thickness in the current study. We agree with the authors that point thickness measurements of the choroid have important limitations. Recent studies have demonstrated considerable topographic variation of the choroid and retina at the macula [2]. Besides assessing choroidal volumes, we believe that measuring mean choroidal thickness using the Early Treatment Diabetic Retinopathy Study (ETDRS) grid is also a useful means to provide more comprehensive information on the topographic variation of the choroid. Using this method, we have observed important variations of choroidal topography with refractive error [2].
123
Int Ophthalmol
In summary, we congratulate the authors on their results, which add to our understanding of the factors affecting choroidal thickness among different populations.
References 1. Erkul SO, Kapran Z, Uyar OM (2014) Quantitative analysis of subfoveal choroidal thickness using enhanced depth imaging optical coherence tomography in normal eyes. Int Ophthalmol 34:35–40. doi:10.1007/s10792-013-9787-6
123
2. Tan CS, Cheong KX, Lim LW, Li KZ (2014) Topographic variation of choroidal and retinal thicknesses at the macula in healthy adults. Br J Ophthalmol 98:339–344. doi:10.1136/ bjophthalmol-2013-304000 3. Tan CS, Ouyang Y, Ruiz H, Sadda SR (2012) Diurnal variation of choroidal thickness in normal, healthy subjects measured by spectral domain optical coherence tomography. Invest Ophthalmol Vis Sci 53:261–266. doi:10.1167/iovs.11-8782 4. Coscas G, Zhou Q, Coscas F, Zucchiatti I, Rispoli M, Uzzan J, De Benedetto U, Savastano MC, Soules K, Goldenberg D, Loewenstein A, Lumbroso B (2012) Choroid thickness measurement with RTVue optical coherence tomography in emmetropic eyes, mildly myopic eyes, and highly myopic eyes. Eur J Ophthalmol 22:992–1000. doi:10.5301/ejo.5000189
