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Contact lenses have been around for a long time, since 1948, and are extremely popular as a means to temporarily or permanently replace glasses for over 125 million users worldwide. Contact lenses are primarily ocular prosthetic devices for vision correction but are also used for cosmetic or therapeutic reasons to change eye color. This study aims to determine if there is contrast sensitivity between clear and colored eye lenses depending on lighting conditions.
Background
There are two types of contact lenses hard and soft. The Rigid Gas Permeable (RGP) are hard and difficult to put in but are durable and clearer, but only compromise 2% of all wearers. The rest are soft lenses. There are temporary lenses, regular soft lenses that allow oxygen to pass through for short-term wear, and silicone hydrogen lenses for long-term wear, compromising a large portion of wearers. Contact lenses aim to correct refractive error, which ultimately cause the focus and vision problems. However, contact lenses are not fully safe, given the risk of microbial infection.
Much of the concepts around quality vision is based on contrast sensitivity. Contrast is converted to light scattering and light scattering is affected by contact lenses. For example, multifocal contact lenses are likely to decrease contrast sensitivity and lead to poorer quality. Studies previously indicated different results on CS for single focal lenses. Given these discrepancies, the researches aim to find out the CS and visual quality for different lenses in the respective light conditions.
Methods
For this study, 34 university students were selected. They had to pass multiple criteria including no disease or conditions. They had to pass unassisted acuity tests and fit on the different lenses. The researchers took time to ensure that vision was not influenced, so patients were given time of at least 2 hours to adjust to light or lens changes. The patients eyes were randomly selected to fit the lenses. Visual acuity was measured using a tumbling E chart at distance of 6m, while the Pelli Robson chart was utilized for CS.
Data Analysis and Considerations
Given that the study involved humans, ethical design and approval was necessary which was given by the Ethics Committee of Zahedan University of Medical Sciences. As for data analysis, ANOVA or analysis of variance is a statistical test used to separate observable variance data into different compounds. A one-way ANOVA helps to get the relationship between groups of data and variables. Therefore, given that the research aim is to determine the effect contact lenses on CS, this common statistical data analysis test is appropriate for this type of research.
Results
These are the fundamental results discovered as part of the study. Visual acuity did not change and was not expected to given that students were tested previously to being selected. So, CS did seem to decrease when contact lenses were applied. This was most evident in poor lighting conditions such as darkness and glare. However, no significant differences were ultimately found between clear and color lenses in regard to CS. Lighting conditions affected CS reduction for contact lenses in all circumstances.
Discussion
Studies of other researchers largely match Mahjoob and Heydarian (2021) in determining the CS drop attributed largely to soft contact lenses. Various factors may have an impact, but since this study excluded people with astigmatism and used temporary lenses, corneal edema is the most logical explanation given the continuous change of lenses.
One of the limitations was that not measuring the corneal thickness, as by doing so the corneal edema effect could have been understood better. Furthermore, the similar CS between clear and colored lenses could be to the large diameter of the pigment-free optical zone in the colored contact. This both suggests ineffectiveness of optical parameters but confirms active role of corneal edema. Overall, the study found that clear and colored lenses reduce CS, this has both real-world impacts and contributes to the body of literature which indicate potential influences such as edema, pupil size changes, and other elements that could the effect on visual contrast.
Reference
Mahjoob, M., & Heydarian, S. (2021). Effect of contact lenses on contrast sensitivity under various lighting conditions. Journal of Ophthalmic and Vision Research, 16(4), 538543. Web.
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