We recruited 22 patients who attended the Low Vision Rehabilitation Center in the Eye Hospital of Wenzhou Medical University from October to December in 2017 to participate. All had been diagnosed with binocular retinitis pigmentosa. The study was conducted in compliance with good clinical practice guidelines, institutional review board regulations and the tenets of the Declaration of Helsinki. All subjects were given a written explanation of the study and consented in writing to participate. Our consent form explained that enrolment in this study did not imply any risk to ocular health and provided the right of withdrawal from the study at any time.
Inclusion criteria were: 1) both eyes were diagnosed with retinitis pigmentosa, and 2) VA with best spectacle correction was better than 20/400.
Exclusion criteria were: 1) the presence of other diseases that affected VA, such as corneal ulcer, pterygium and cataract; 2) a history of eye surgery, such as laser surgery and cataract surgery; 3) other ocular fundus diseases, such as diabetic retinopathy, glaucoma, optic nerve disease, etc; 4) congenital color blindness, mental handicap, illiteracy, and 5) refusal to answer the questionnaire.
Material and methods
- Computer Lens Filter
We used a commercially available CLF from Fitovers (Jonathan Paul Eyewear Pty Limited) as blue-light blocking spectacle lenses. Information provided by the manufacturer are transmission spectrum (Figure 1) and specific filter parameters (Table 1).
- The computer display
Our computer was a Lenovo Small New 700, with a 15.6 inch screen, a display resolution of and maximum screen illumination of 200 cd/m2. Text was presented at the maximum illumination level.
- The reading content
We selected reading content from the Chinese Reading Visual Acuity Chart written by Wang Chenxiao, This chart contains three similar sentences, each with 30 characters, as shown in figure 2. Each subject chose a font size consistent with their VA demand for clear and comfortable reading at their habitual screen distance.
- The bright contrast sensitivity
CS at near was measured monocularly on the basis of corrected VA using the Mars Numeral Contrast Sensitivity test, measured first without CLF, then with the filter. Illuminance of the examination room was 85 cd/m2 and the test distance was 0.5 m. Examination commenced with the MARS first visual target and subjects were asked to identify targets one by one until two continuous errors occurred, at which stage the test was stopped and the result recorded.
- Reading speed test on computer
RP subjects sat in front of the computer at their habitual reading distance. Using page E as the reading example, subjects adjusted font size until they could read clearly and comfortably. Reading test speeds were recorded by presenting Pages A and B both with and without the CLF but in random sequence. Words that subjects did not know or could not identify were skipped. Subjects were given a 5 minutes break between each test.
Any subjective perception of change in visual comfort and brightness of the computer before and after wearing the CLF were recorded using a questionnaire. At the end of each reading test we asked subjects to grade comfort level and perception of screen brightness on linear scales from +10 to -10. ‘Zero’ was defined as the base line score for comfort level without the CLF. The higher the score, the more comfortable the task and brighter the screen text. Questionnaire scales are shown in figure 3.
Results were tabulated and comparisons tested using SPSS V23.0. Statistical significance was judged to be P <0.05.