| Objective:Refractive errors are common to mankind and it is the most common eye disease.China is one of the countries of the highest prevalence rate of myopia. Myopia has become the main eye disease that influences the visual sight of teenagers. According to investigation, 60% of senior high school students occur myopia. And recent years, myopic outbreak turns toward the low age of population gradually. Myopia is corrected usually by wearing of spectacles (SP). Usually, we meet the patients who wear SP to correct refraction very well in the clinic work, but patients still feel faintness in vision. So the correction of vision acuity by the wearing of SP already can not be the objective standard for evaluation of visual quality. Therefore, how to improve the visual quality of patients with myopia is a hot topic in ophthalmology.Contrast sensitivity (CS) is a recognizing ability for the difference of two visual districts in average bright degree. CS can measure the contrast degree that human eye distinguish the different space frequency sketch. It is helpful for us to better understand the sensitation function of human eye. Generally, decline of patients' CS is prior to decrease of sight on vision chart, therefore CS can act as the guideline that more overall evaluate visual function.Less report has been seen about the study on the difference of CS between wearing SP and wearing rigid gas permeable contact lens (RGPCL) as well as the relationship between diopter and CS. The aim of this study was to investigate CS function in the population wearing SP or RGPCL for myopes and evaluate the visual quality of different fashions of refractive error correction and explore guiding significance of CS to correction way for myopic eyes.Materials and methods:Three hundreds and sixty eyes of 180 patients with myopia were collected in Henan Eye Institute from September, 2007 to February, 2009, including 89 male and 91 female. The patients were assigned to three groups according to power of refraction (low myopia group, moderate myopia group and high myopia group) and 120 eyes for each, and the patients from each group were randomly subdivided into SP wearing group and RGPCL wearing group.In SP wearing group, subjects' accurate diopter of myopes was checked with refractor for a suitable SP. OPTEC?6500 was used to detect CS in different circumstances.In RGPCL wearing group, keratometer was used to check the corneal curve at 2 directions for 3 times to offer the mean K value, and a nearest basual lens to the mean K value was selected as the trial lens. A evaluation of combination of dynamic and stationary wearing was performed under the slit-limp following the 20-minute initial wearing to lead the accommodation of basal curve and diameter of lens until the final determination. Also, OPTEC?6500 was used to detect CS at the same way to SP wearing group.Results:1. In the same circumstances, CS of myopes and visual quality declined steadily with the diopter increase. No significant differences were found between low and moderate myopia group (P>0.05). But the CS of high myopia group was lower than both low and moderate myopia group (P<0.05). Refraction and CS showed a negative correlation (r=-0.382,P=0.019) .2. Under the condition of same modality and the same contrast, the CS in dark circumstance was lower than that of bright circumstance, especially in the spatial frequencies of 12cpd and 18cpd (P<0.05), presenting significant differences (P<0.05). However, no significant difference was found in the CS of day circumstance with glare and without glare (P>0.05). 3. Compared with SP, correction of refractive error with RGPCL significantly improved the CS in various spatial frequencies ranged the day, day with glare and night circumstances and it was more prominent at the spatial frequencies of 12cpd and 18cpd (P<0.05), and it was further demonstrated that RGPCL improved the quality of visual function., The mean CS in night circumstance with glare was insignificant reduced in high myopes wearing RGPCL compared to wearing SP (P>0.05).Conclusions:In the same circumstances, the CS of myopes and visual quality decline steadily with the enhance of diopter. The change of refraction and CS has a negative correlation. With the same modality and the same contrast, the CS of da:k circumstance is lower than that of bright circumstance, especially in higher spatial frequency. The CS of dark circumstance with glare in various spatial frequencies range is lower than that of dark circumstance with no glare. While the CS of day circumstance with glare has no significant difference in comparison to day circumstance without glare.Compared with SP, refractive error correction with RGPCL significantly can improve the CS in various spatial frequencies, especially in a range of 12cpd and 18cpd. RGPCL offer a better visual quality for the patients with myopia. CS assessment is an effective approach to evaluating visual quality for myopes by different refractive correction and has a good guiding significance for alternation of methods of myopic correction. |
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