Effects Of L/M-cone Contrast On Accommodation-blur Sensitivity And The Relationship With Myopia

SummaryThe results of this study show that myopes have higher L-cone sensitivity when compared with emmetropes, which implies that myopes are more susceptible to a blurred image on the retina secondary to longitudinal chromatic aberration of the optical system of the eye. This study is based on chromatic theory and proposes a new point to the mechanism of the onset and development of myopia. Firstly, we conduct the research of accommodation system and blur sensitivity on the subjects who have different sensitivity of L/M cones; Secondly, the study on accommodation system and blur sensitivity was performed with the targets which can supply different L/M cone contrast, the illumination conditions of these targets are similar to the normal survival environment of human beings and avoid the shortcomings of monochromatic light which was widely used in previous research; Thirdly, we combine the L/M cone sensitivity with refractive errors and focus it on myopia.Part I:Research on different L/M-cone sensitivity between myopes and emmetropesObjective:This study was conducted to determine whether there is a difference in the L/M-cone sensitivity between myopes and emmetropes.Methods:223 optometry students in NSU participated in this study,57 emmetropes and 166 myopes. All subjects were free of ocular disease and defective color vision, with mean age 25.2±3.46 years old. A preliminary session was used to gather a case history, test color vision by Ishihara Pseudoisochromatic Plates, and measure visual acuity, subjective refraction. One eye of each subject was tested with an HMC Anomaloscope (Type 47700) for his/her red/green match value,matching range and the brightness point with the Rayleigh match program. In data analysis, the red/green match value, matching range and brightness match point between myopes and emmetropes were the dependent variables analyzed via independent-samples t-test by SPSS 13.0,P<0.05 was considered to be significant.Results:1) Mean red/green match values in myopes and emmetropes were 3851±1.73 and 40.77±1.41 respectively, statistical analysis demonstrated a significantly lower level of red/green match value in the myopic group than in the emmetropic group (P<0.001), which showed that myopes have increased L-cone sensitivity. The differences in the matching range and the brightness match point between the two groups are not significant;2) The ROC shows that the area under the ROC curve is 0.853, which supports the idea that the Rayleigh match test is valid in differentiating myopes from emmetropes, the cut-off point of red/green match value is 39.55; 3) A highly statistical significance was found in the correlation of red/green match value and refraction(P< 0.001); 4)The results demonstrate no significant difference of red/green match value,matching range,brightness point between early-onset myopia (EOM) and late-onset myopia (LOM); stable myopes (SMs) and progressing myopes (PMs); low myopia(LM), medium myopia(MM) and high myopia(HM).Conclusions:There is close relationship between refractive error status and sensitivity of L/M cones, myopes have higher L-cone sensitivity when compared with emmetropes, which means myopes have increased L-cone sensitivity and more sensitive to long wavelength light.PartⅡ:Effects of different L/M-cone contrast on accommodative response and AS/AR thresholdObjective:This study was designed to investigate the effects of different L/M-cone contrast on accommodation and blur sensitivityMethods:All the participants in this project were choosed from our last research in which we investigated the different L/M-cone sensitivity between myopes and emmetropes within 223 volunteers. Two groups of subjects involved in this part The first group consisted of 12 subjects who had red/green match value and referred to normal L-cones sensitivity group (NLSG) in this article Red/green match value of subjects in this group were around 40, mean value was 39.92±0.364. In second group, there were 12 subjects whose red/green match value were much lower than 40 but still in normal range. They had an increased L-cone sensitivity and this group was called increased L-cone sensitivity group (ILSG). The mean red/group match value was 36.06±0.728. An open field infrared autorefractor (WAM-5500) and Badal optical system were used to measure accommodation responses (AR). Targets were displayed on a black background of a high resolution RGB LCD monitor (NEC AccuSync 72vx). All the targets were 2.2 c/d vertical square wave gratings with Michelson contrast of 0.56. All stimuli had a mean luminance of 80 cd/m2 and subtended a visual field of 2°. Three illumination conditions were provided to give different L/M-cone stimulus:1, A "Yellow" condition in which the main wavelength(568nm) was near the peak wavelength of L-cones; 2, A "Green" condition in which the main wavelength(535nm) was near the peak wavelength of M-cones.3, A "White" condition (normal white light). Since all the stimuli were generated by LCD with different RGB parameters, these targets were illuminated by polychromatic light. After the AR was obtained in each condition, AR/AS slope and AS/AR threshold were calculated by statistically methods. In data analysis, the AR,AR/AS slope and AS/AR threshold were the dependent variables analyzed via two-way ANOVA by SPSS 13.0 and GB Stat, P<0.05 was considered to be significant.Results:1) In these three AS levels of 1.5D,2D and 2.5D, the change of L/M-cone contrast can not affect the AR.2) In 1.5D～2.5D's AS level, there was slight effect of different L/M-cone contrast on AR/AS slope. In NLSG,statistical analysis demonstrated a significantly lower level of AR/AS slope in yellow condition than in green condition (P<0.05); In green condition, NLSG expressed higher level of AR/AS slope than ILSG (P<0.05);3) In 2D's AS level, the change of L/M-cone contrast can obviously impact the AS/AR threshold. In yellow condition, we found a significantly higher level of AS/AR threshold in NLSG than ILSG (P<0.01); In NLSQ AS/AR threshold in yellow condition was higher than green and white condition(P<0.05, P<0.01); Contrary to NLSG, AS/AR threshold in yellow condition was lower than green and white condition in ILSG(P<0.05, P<0.01).4) In white condition, it showed no statistical difference between NLSG and ILSG in AR of three AS levels(1.5D,2D and 2.5D); also there was no statistical difference in AR/AS slope between NLSG and ILSG; whereas in 2D's AS level, AS/AR threshold in ILSG was higher than NLSG(P<0.05).Conclusions:Difference of L/M-cone contrast has no effect on accommodative response, but slightly impact the AR/AS slope, furthermore, different L/M-cone contrast has significant influence on the AS/AR threshold, which represents the blur sensitivity. Increased L-cone sensitivity might induce the onset and development of myopia by decreasing the blur sensitivity and increasing the lag of accommodation response.