The Effect Of Posterior Capsule Opacification On Visual Function

PURPOSE:To investigate the correlation between visual acuity,contrast sensitivity,glare sensitivity,and the degree of posterior capsule opacification(PCO)in different morphology.Ascertain accurate and practical quantification system of PCO assessment and to be able to predict outcomes following Nd:YAG laser capsulotomy.METHODS:One hundred and ninety pseudophakic eyes of 151 patients were recruited in this study,40 eyes without PCO as control,150 eyes with PCO of varying intensity and morphologic.The eyes were examined with a slit-lamp and direct ophthalmoscope. Intraocular pressure,visual acuity,contrast sensitivity and glare sensitivity were measured,Reflected-light and retroillumination digital images of the PCO was acquired after mydriasis.Sixty-seven eyes of 58 patients were re-examined 1 week after Nd:YAG laser capsulotomy.As main outcome measures,best corrected distant visual acuity was examined using logarithmic charts and and converted to a logarithm of minimal angle of resolution(log MAR)scale.Contrast thresholds with or without glare were measured using contrast glare tester(CGT-1000;Takagi Seiko,Japan).Contrast sensitivity as well as glare sensitivity was calculated as inverse value of the contrast threshold.Reflected-light and retroillumination digital images of the PCO were taken using a SONY DXC-990D 3CCD colour digital camera system based on TOPCON SL-8Z slit-lamp and saving into IMAGEnet 2000 softwarePCO was grade according Odrich's method based on slit-lamp and direct ophthalmoscopic evaluation,density value was measured using Evaluation of Posterior Capsule Opacification(EPCO,M.R.Tetz,Ch.Nimsgern,Humboldt-niversity, Germany)and 23 eyes using Objective System Capsule Analysis(OSCA,T.M.Aslam Edinburgh-University,UK)with retroillumination digital images.After full mydriasis,67 eyes underwent Nd:YAG laser posterior capsulotomy with a Q-switched ZEISS VISULAS YAGⅡlaser.An approximately 3-mm or 4-mm diameter area of the central posterior capsule was then cleared by emitting laser energy on the capsule.1.Comparison of 3 methods for analysis of posterior capsule opacification:To compare the results of PCO severity and correlation between the measurement of PCO severity and visual function testing in 23 eyes.2.The effect of Posterior Capsule Opacification on visual function:Compare the correlation between visual acuity,contrast sensitivity,glare sensitivity,and the degree of posterior capsule opacification(PCO)in different morphologic.3.The improvement in visual function after Nd:YAG laser posterior capsulotomy:Compare the improvement in visual function before and after Nd:YAG laser posterior capsulotomy in different extents and the influence of two different diameter of posterior capsulotomy:RESULTS:1 Comparison of 3 methods for analysis of posterior capsule opacification:1.1 To compare the EPCO scores,OSCA scores and clinical PCO severity,EPCO scores and OSCA score showed a significant correlation(r=0.508,P＜0.05),and EPCO scores showed a better correlation with clinical PCO severity and IogMAR (r=0.711,r=0.669,P＜0.01)than OSCA score(r=0.415,r=0.512,P＜0.05),also logCS,logGS showed a best orrelation with EPCO scores.1.2 Correlation between the EPCO area and total scores measured by 3 independent observers using a library of 30 retroillumination images ranging from clear posterior capsules to very severe PCO.Correlations between EPCO area of 3 clinicians are significant(r=0.864,0.878,0.832 P＜.001),between EPCO scores are more significant (r=0.977,0.977,0.965 P＜.001). 2 The effect of Posterior Capsule Opacification on visual function:2.1 Mild PCO is classified into 3 morphologys as clouding(or trace)6 eyes,fibrosis 21 eyes,thin layer 35 eyes.The visual acuity impaired in patients with thin layer and preserved in the others,but it is impaired in high frequency contrast sensitivity of clouding and intermediate frequency glare sensitivity of fibrosis.2.2 Moderate PCO is classified into 3 morphologys as fibrosis 6 eyes,thick layer 27 eyes,pearl 26 eyes.No difference on visual acuity each other,but it is significant different on contrast sensitivity and glare sensitivity.Patients with pearl-type PCO had lower contrast sensitivity and glare sensitivity than those with fibrosis-type PCO, thick layer was in the middle of the two types and approach to pearl-type.2.3 A strong correlation existed between the EPCO scores and visual function with pearl-type PCO,logcs2.5°= 1.94—0.48epco(r:0.-632,p＜0.01)loggs2.5°= 2.04—0.60 epco(r:-0.676,p＜0.01),a weak and significant correlation with layer-type PCO,no significant correlation with clouding and fibrosis types.3 The improvement in visual function after Nd:YAG laser posterior capsulotomy3.1 Classified 67 eyes underwent Nd:YAG laser posterior capsulotomy into 4 groups according EPCO scores,EPCO＜1,1≤EPCO＜2,2＜EPCO＜3,EPCO≥3.There is no difference on visual function between groups after Nd:YAG laser posterior capsulotomy.No improvement on visual function after capsulotomy in group EPCO＜1,but significant improvement in the other 3groups.3.2 Nd:YAG laser posterior capsulotomy in different diameter of capsulotomy 3-mm 24 eyes and 4-mm 43 eyes,no difference on visual function between groups after capsulotomy,but compared to no PCO patients,it was impaired at low to intermediate frequencies contrast sensitivity and all spatial frequencies glare sensitivity.CONCLUSION:1 EPCO is a accurate and practical quantification system of PCO assessment,it is good correlation with completely objective OSCA,and showed a better correlation with clinical PCO severity and visual function.It was successfully used to calculate the severity of PCO.And the assessment is simple,the individual difference of the Examiner is slight and reproductive well.2 Contrast sensitivity and glare sensitivity has a strong association with PCO than does visual acuity and therefor should be considered to reflect most accurately the degree of PCO.The effect of PCO on visual function is different in varing morphology.Pearl -type PCO impaired visual function severely,clouding and fibrosis types PCO effect slight,thick layer-type PCO approach to pearl-type.3 The EPCO will be able to predict outcomes following Nd:YAG laser capsulotomy.If EPCO＜1,the patient is not proper to be treatment,and EPCO≥1 the patient underwent capsulotomy can improve visual function significant.No significant difference in 3mm or 4mm diameter capsulotomy on visual function.But the opacification at periphery of posterior capsule considered impaired contrast sensitivity and glare sensitivity particularly.