High Resolution Image Analysis Reveals Changes Of Lens Thickness And Cone Density In A Cohort Of Young Myopic Patients

ObjectiveIn recent years,the emergences of high-resolution ophthalmic equipment have made it possible to understand the fine anatomy of the eye.Some studies have reported that the choroidal thickness is associated with myopia.However,there are few studies on lens thickness and cone density in myopia because of the limitations of device penetration and accuracy.To understand the changes of Eyeball biological parameters in myopia with swept source optical coherence tomography(SS-OCT)and adaptive optics(AO)fundus camera,especially lens thickness(LT)and cone photoreceptor spatial features.MethodsA prospective cross-sectional study.68 subjects included 136 eyes were recruited from Henan Provincial People’s Hospital from December 2020 to February 2021.IOL Master was used to measure axial length(AL).SS-OCT was used to quantify central corneal thickness(CCT),anterior chamber depth(ACD),LT,the thickness of retina and choroid.The built-in software in SS-OCT automatically divided retina into three layers,i.e.,the ganglion cell complex(GCC)layer,the inner nuclear layer(INL)and the outer retinal layer(ORL).Based on the ETDRS grid,a macular map with a diameter of 6 mm was built and divided the above layers into two rings: the inner ring(1-3 mm)and the outer ring(3-6 mm).The thicknesses of the inner and outer rings of each retinal layer and choroid were measured.AO was used to quantify spatial features of the cone photoreceptors,including density,spacing,dispersion and regularity.Cone density was defined as the number of cells per square millimeter,cone spacing was defined as the center-to-center spacing of adjacent cones,cone regularity was defined as the percentage of cells that had five to seven neighbor cells and cone dispersion was defined as the spread of cones,which was the coefficient of variation of the cone spacing.The cones were analyzed at 2° and 4° eccentricity from the center of the fovea along the four meridians(superior,inferior,nasal and temporal),with the 2° represented the inner region and the 4° represented the outer region.The thickness of central retinal artery wall and diameter was measured by AO.The differences between the three groups were analyzed by one-way ANOVA,and the comparison between the two groups was tested by the minimum significant difference method.The associations among the AL and CCT,ACD,LT,the thickness of retina and choroid and cone features were evaluated with liner regression.ResultsAnterior segment: There were differences in AL,ACD and LT among EM/LM,M/M and H/M groups(F = 7.889 ～ 54.534,P < 0.01).With the increase of AL,LT decreased significantly(r =-0.453,P < 0.001)and ACD increased significantly(r =-0.453,P < 0.001).Posterior segment: There were differences in the outer rings’ thickness of GCC,the inner and outer rings’ thickness of INL,ORL and choroid among EM/LM,M/M and H/M groups(F = 1.505 ～ 16.152,P < 0.05).With axial elongation,the thickness of ORL and choroid decreased significantly both in the inner ring and outer ring(r =-0.418 to-0.320,all P < 0.001),whereas the GCC and INL layers tended to decrease in the outer ring(r =-0.458 to-0.358,both P < 0.01).Further analysis of the changes in the superior,inferior,nasal and temporal directions of the retina and choroid showed that as the AL increased,the thickness of ORL and choroid decreased significantly both in the inner ring and outer ring in the four directions(r =-0.478 to-0.224,all P < 0.001),and INL layers only thinned in the outer ring of four directions(r =-0.493 to-0.314,all P < 0.001),while the inner ring of GCC increased in the nasal direction(r = 0.190,P = 0.028),the outer ring was thinner in the superior,inferior and temporal directions(r =-0.544 to-0.382,all P < 0.001).Cone spatial features: There were differences in cone density and spacing among EM/LM,M/M and H/M groups(F = 13.506 ～ 19.328,P < 0.001).With the increase of AL,cone density decreased significantly both in the inner region and outer region(r =-0.724 and 0.717,both P < 0.001),and cone spacing increased significantly both in the inner region and outer region(r = 0.726 and 0.743,both P < 0.001).We further analyzed the relationship between the cone spatial features and the layers of choroid and retinal,and found that with the decrease of the choroid/ORL thickness,the cone density decreased(r = 0.297 ～ 0.332,P < 0.01)and the spacing increased(r =-0.311 ～-0.292,P < 0.01).However,with the decrease of INL,cones were less regular(r = 0.224,P = 0.028,)and more dispersed(r =-0.228,P = 0.025).Retinal artery: There were no differences in the wall,lumen thickness and wall/lumen of the main branch of central retinal artery between EM/LM,M/M and H/M groups(all P > 0.05).With the increase of AL,the wall,lumen thickness and wall/lumen of the main branch of the central retinal artery did not change(all P >0.05).ConclusionsWe found that with the increase of myopia degree,the AL gradually increased and the LT,the thickness of ORL and cone density decreased.While decreasing of LT might imply intrinsic physical accommodation during the development of myopia,decreasing of cone density and ORL should be related to axial elongation.These results provided further morphological evidence of the pathology and a basis for further understanding myopia by new biometric data.