The Sensitivity Of Accommodative System To Retinal Defocus In Myopia

PartⅠThe effect of the visual field of retinal defocus on the accommodative stimulus response curvePurpose:To investigate whether the visual field of retinal defocus has impact on the steady-state accommodative stimulus response curve and whether this impact differs in different refractive error groups.Methods:Ten emmetropes(EMM),10 stable myopes(SM)and 10 progressive myopes(PM),aged from 21 years to 37 years,participated in the experiment.Soft contact lenses were used to correct the refractive error of the subjects within±0.25 D. We compared their accommodative stimulus response curves(ASRCs)when a high contrast Maltese Cross was viewed with three visual fields(2°×2°,8°×6°,and 44°×23°).The target was presented by a portable DVD player(Accurian,US)placed 0.19 m to the trial lens.The order of the three visual fields was randomized.Six levels of accommodative stimuli ranging from 0.26 D to 4.90 D were provided by reducing the positive trial lenses.The subjects were instructed to look at the target and keep it clear.Accommodative responses to each accommodative stimulus were measured with open-field infrared Canon Autoref R-1.Linear fitting and third order polynomial curve fitting were conducted with the data.Repeated measures ANOVA were conducted to analyze the accommodative response data.If significant difference was found,the post hoc Tukey's HSD and Fisher's LSD tests were conducted.Results:Accommodative responses at six accommodative stimuli were not significantly different either between the three visual fields or between the three refractive error groups(p＞0.05).There was no difference in ASRC gradients, intercepts and third order polynomial coefficients either between the visual fields or between the refractive error groups(p＞0.05).In visual field of 2°×2°,the gradient of accommodative stimulus response curve was related to refractive error in myopes (r~2=0.3,P=0.007).Conclusion:Visual field does not alter the overall steady-state accommodative responses.The central retinal plays a dominant role in inducing accommodative response.The accommodative system and visual perceptual system might detect the retinal defocus via two different mechanisms.PartⅡThe correlation between the objective depth-of-focus and the magnitude of accommodative microfluctuations in myopesPurpose:To investigate the correlation between the objective depth-of-focus(DOF) of accommodative system and the magnitude of accommodative microfluctuations and whether the correlation is affected by the level of accommodative stimulus.Methods:Fifteen stable myopes,aged from 23 years to 30 years,participated in the experiment.They have refractive error ranging from-1.13 D to-5.63 D.Soft contact lenses were used to correct the refractive error of the subjects within±0.25 D. Objective DOF was determined by the least dioptric vergence that could cause a statistically detectable change in the accommodative response(AR).A 3×3 array of high contrast Snellen Eletters with spatial frequency of 12 c/deg was used as fixation target.The accommodative stimulus(AS)was presented using a Badal stimulator and the AR was measured using an open-field infrared autorefractor(Grand Seiko WAM 5500)at a sampling rate of 5 Hz.At 1 D and 4 D AS levels,the AS was changed by 0.1 D step using Badal system while the AR was continuously recorded. The accommodative microfluctuations were measured at 0,1,2,3,4 D AS levels. The AR was continuously recorded for 20 seconds at each AS level.The root mean square value(r.m.s.)was calculated to represent the magnitude of accommodative microfluctuations.One way ANOVA was conducted to analyze the r.m.s.values at five AS levels.Paired t test was conducted to compare the objective DOF at 1 D and 4 D AS levels.Pearson correlation analysis was conducted between the r.m.s.value and objective DOF.Results:Objective DOF at 4 D AS level was significantly larger than that at 1 D AS level(±0.092±0.023 D vs.±0.055±0.018 D,p＜0.001).Across 1 D and 4 D AS levels,the objective DOF showed a strong correlation with the r.m.s.value of the accommodative microfluctuations(r=0.811,p＜0.01).The correlation was higher at 4 D AS level than that at 1 D AS level(4 D AS level:r=0.717,p＜0.01;1 D AS level:r=0.527,p＜0.05).There was a significant increase in r.m.s.value with increasing AS level(p＜0.001).The r.m.s.value of the accommodative microfluctuations and objective DOF were both correlated to the accommodative error(p＜0.01).The objective DOF was not correlated to the spherical equivalent of the refractive error(p＞0.05).Conclusion:Statistic analysis can be used as a new method to measure the objective depth-of-focus.The objective depth-of-focus is affected by the accommodative stimulus level and correlates to the magnitude of accommodative microfluctuations.The blur sensitivity of accommodative system might regulate the magnitude of accommodative microfluctuations and thus contributes to the stability of accommodative functions.PartⅢThe effect of blur adaptation on the objective depth-of-focus and accommodative response in myopesPurpose:To investigate whether blur adaptation has impact on the objective depth-of-focus and whether this impact differs in different refractive error groups. Methods:Twelve emmetropes(EMM),12 stable myopes(SM)and 12 progressing myopes(PM),aged from 19 years to 36 years,participated in the study.Soft contact lenses were used to correct the refractive error of the subjects within±0.25 D.The subjects were instructed to watch a movie at a distance of 4 meters for 30 minutes. A+2.0 D lens was imposed on the trial frame to provide blurry image.Visual acuity, accommodative stimulus response curve and objective depth-of-focus(DOF)were measured before and immediately after the blur vision task.Visual acuity through+ 2.0 D lens was measured using an ETDRS vision chart.The accommodative stimulus(AS)was presented using a Badal stimulator and the accommodative response(AR)was measured using an open-field infrared autorefractor(Grand Seiko WAM 5500)at a sampling rate of 5 Hz.Objective DOF was determined by the least dioptric vergence that could cause a statistically detectable change in AR at 1 D and 4 D AS levels.In a control experiment,the subjects repeated above procedures except that they only wore their normal distant correction of refractive error.A learning effect control test was conducted in 6 subjects randomly chosen from each group. The visual acuity with+2.0 D lens were measured before and after 30 minutes of their daily visual expierence.Repeated measures ANOVA were conducted to analyze the accommodative response data.If significant difference was found,the post hoc Tukey's HSDand Fisher's LSD would be conducted.Paired t test was conducted to compare the visual acuity in learning effect control test.Results:All subjects exhibited blur adaptation with a mean improvement in visual acuity of 0.17 logMAR after watching the movie in blurry vision.At 4 D AS level, objective DOF decreased in SMs(±0.082±0.020 D vs.±0.064±0.015 D,pre-vs. post-adaptation,p＜0.05)and increased in PMs(±0.093±0.019 D vs.±0.144±0.036 D,pre-vs.post-adaptation,p＜0.01).No significant difference in DOF was found in EMMs(±0.096±0.024 D vs.±0.082±0.025 D,pre-vs.post-adaptation, p＞0.05).At 1 D level,PMs showed increased DOF after blur adaptation(±0.060±0.016 D vs.±0.079±0.023 D,p＜0.01).The DOF in other groups didn't show significant change(p＞0.05).Compared with pre-adaptation value,no constant difference in AR at six levels was found after blur adaptation(p＞0.05).Control tests showed no significant change in visual acuity,objective DOF or accommodative stimulus response curve in all groups after watching the movie with clear vision for 30 minutes(p＞0.05).Conclusions:Blur adaptation alters the blur sensitivity of the accommodative system in different directions in SMs versus in PMs.The increase of DOF in PMs observed in this study suggests that the PMs are more susceptible to blur image than other refractive error groups.