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Randomized Controlled Trial
. 2016 Jan-Mar;9(1):13-21.
doi: 10.1016/j.optom.2015.10.003. Epub 2015 Nov 11.

Longitudinal changes in corneal curvature and its relationship to axial length in the Correction of Myopia Evaluation Trial (COMET) cohort

Mitchell Scheiman  1 , Jane Gwiazda  2 , Qinghua Zhang  2 , Li Deng  2 , Karen Fern  2 , Ruth E Manny  2 , Erik Weissberg  2 , Leslie Hyman  2 ; COMET Group
Affiliations
Randomized Controlled Trial

Longitudinal changes in corneal curvature and its relationship to axial length in the Correction of Myopia Evaluation Trial (COMET) cohort

Mitchell Scheiman et al. J Optom. 2016 Jan-Mar.

Abstract
in English, Spanish

Purpose: To describe longitudinal changes in corneal curvature (CC) and axial length (AL) over 14 years, and to explore the relationship between AL and CC, and the axial length/corneal radius (AL/CR) ratio.

Methods: In total 469, 6 to <12-year-old, children were enrolled in COMET. Measurements of refractive error, CC (D), CR (mm), and ocular component dimensions including AL were gathered annually. Linear mixed models were used to evaluate longitudinal changes adjusting for covariates (gender, ethnicity, lens type, baseline age and baseline refraction). The Pearson correlation coefficient between AL and CC was computed at each visit.

Results: There was a slight but significant (p<0.0001) flattening in CC over 14 years. At all visits females had significantly steeper CC than males (overall difference=0.53 D, p<0.0001). Caucasians had the steepest CC, and Hispanics the flattest (p=0.001). The correlation between AL and CC was -0.70 (p<0.0001) at baseline (mean age=9.3 years) and decreased to -0.53 (p<0.0001) at the 14-year visit (mean age=24.1 years). The average AL/CR ratio was 3.15 at baseline and increased to 3.31 at the 14-year visit. The correlation between the magnitude of myopia and AL/CR ratio was significantly higher (p<0.0001) at each visit than the correlation between myopia and AL alone.

Conclusions: Differences in average corneal curvature by age, gender, and ethnicity observed in early childhood remain consistent as myopia progresses and stabilizes. This study also demonstrates increases in the AL/CR ratio as myopia progresses and then stabilizes, supporting observations from previous cross-sectional data.

Objetivo: Describir los cambios longitudinales en la curvatura de la córnea (CC) y la longitud axial (LA) durante un periodo de catorce años, y explorar la relación entre dichos valores y el ratio longitud axial/radio de la córnea (LA/RC).

Métodos: Se incluyó en el estudio COMET a cuatrocientos sesenta y nueve niños, de edades comprendidas entre 6 y <12 años. Se realizaron anualmente las mediciones del error refractivo, CC (D), RC (mm), y las dimensiones de los componentes oculares. Se utilizaron modelos lineales mixtos para evaluar los cambios longitudinales, ajustando las covariables (sexo, etnia, tipo de lente, edad inicial y refracción inicial). Se calculó el coeficiente de correlación de Pearson entre LA y CC en cada visita.

Resultados: Se observó un aplanamiento ligero, aunque significativo (p<0,0001) de la CC a lo largo de los 14 años. En todas las visitas, las mujeres reflejaron una CC considerablemente más curva que los varones (diferencia general = 0,53 D, p<0,0001). La raza caucásica reflejó una CC más cerrada, y la hispana reflejó un aplanamiento superior (p=0,001). La correlación entre LA y CC fue de -0,70 (p<0,0001) en la visita inicial (edad media = 9,3 años), descendiendo a -0,53 (p<0,0001) transcurridos catorce años (edad media= 24,1 años). El ratio medio LA/RC fue de 3,15 en la visita inicial, incrementándose a 3,31 transcurridos catorce años. En cada visita, la correlación entre la magnitud de la miopía y el ratio LA/RC fue considerablemente superior (p <0,0001) que la correlación entre miopía y LA, únicamente.

Conclusiones: Las diferencias en la curvatura media de la córnea por edad, sexo y etnia, observadas en la infancia, son consistentes a medida que la miopía va progresando y estabilizándose. Este estudio demuestra también los incrementos en el ratio LA/RC a medida que la miopía progresa y se estabiliza, lo que respalda las observaciones de los datos transversales previos.

Keywords: AL/CR ratio; Axial length; Corneal curvature; Corneal radius; Curvatura de la córnea; Estudio sobre miopía COMET; Longitud axial; Myopia COMET study; Radio de la córnea; Ratio LA/RC.

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Figures

Figure 1
Figure 1
(A) Corneal curvature, steepest meridian and flattest meridian by visit. Corneal curvature is the mean of two meridians. (B) Corneal curvature by visit and gender. (C) Corneal curvature by visit and ethnicity. (D) Corneal curvature by visit and baseline age.
Figure 2
Figure 2
AL/CR ratio by visit.
Figure 3
Figure 3
Baseline AL/CR ratio vs. myopia progression at 5-year visit.
See this image and copyright information in PMC

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