The effect of a Computer Lens Filter on visual performance in subjects with retinitis pigmentosa

BackgroundRetinitis pigmentosa (RP) patients uauslly complained nyctalopia and poor dark adaptation which caused their visual discomfort, in this study we aimed to explore the effects of a Computer Lens Filter (CLF) on contrast sensitivity (CS), reading speed for computer screen text and visual comfort in subjects with retinitis pigmentosa (RP), and to find wheather CLF would be helpful for RP patients . Method: Twenty-two subjects diagnosed with binocular RP participated. Bright CS using the Mars test and reading speed of screen text were measured using the spectacle corrections for best corrected visual acuity (BCVA) both with and without CLF wear. Subjective estimates of computer screen brightness and visual comfort were evaluated by questionnaire. These functions were compared for the two conditions of filter wear/non-wear. Result Mean subject age was 38.2±7.5 years and mean log MAR VA was .45± .24. Wearing a CLF neither improved bright CS (t = .452, P=.653) nor increased reading speed (t =.414, P = .683). CLF wear was judged to reduce screen brightness (t = 5.412, P<.0001) and improve visual comfort (t = 6.897, P<.0001). Conclusion CLF wear neither improved RP subjects’ CS nor reading speed for screen text but did reduce the appearance of screen brightness and improve subjects’ reported visual comfort. Improvement in comfort alone may be sufficient justification for filter use as a vision aid for RP patients during vision rehabilitation.

3 more difficult pedestrian orientation and mobility, and together with reduced VA it impairs recognition of detail and slows the reading rate [3]. Reading is the second most important near vision demand reported by low vision patients in China [4]. Our reliance on computers to execute work-related tasks has increased [5] resulting in more commonly reported visual fatigue [6] from increased blue light emissions of LED-backlit liquid crystal displays [7]compared with previous-generation cathode ray tubes. Selected wavelength filters protect the retina and other ocular tissues against sunlight glare and contribute to ocular comfort in RP low vision [8,9]. Filters improve the quality of vision by reducing recovery durations for light adaptation. They increase retinal image contrast and decrease light dispersion and chromatic aberration inside the ocular media, improving visual comfort [10].
Previous studies have shown that wearing a blue UV filter during computer use reduces glare and visual fatigue [7,11,12]. However, these studies do not indicate whether an associated improvement in visual comfort of RP patients occurs with filter wear.
We analyzed bright CS, reading speed and visual comfort of our RP subjects when reading text on a computer with and without CLF wear. We sought also to determine whether wearing a CLF improved visual comfort and warranted prescription as an effective low vision aid during vision rehabilitation.

Subjects
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 4 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.

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/m 2 . 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.

4.
The bright contrast sensitivity 5 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/m 2 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.

Questionnaire
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.

Data analysis
Results were tabulated and comparisons tested using SPSS V23.0. Statistical significance was judged to be P <0.05.

Patient characteristics
6 The average age of subjects was 38.2±7.5 years and the ratio of males to females was

Discussion
Photophobia and light-induced interference with visual comfort and performance are the main complaints of RP patients [13,14]. Discomfort is usually reported as glare, reflections, flicker and non-uniformity of illumination, all interfering with task performance [15]. Probable causes of these symptoms in RP patients are: (1)  Helsinki. Written informed consents were obtained from the patients.

Consent for publication
All authors approved the manuscript for publication, but there is not applicable of consent for the publication of identifying images or other personal or clinical details of participants that compromise anonymity.

Availability of data and materials
The datasets used during the current study available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.

Funding
This work was supported by Clinical study on mental health status of patients with low vision caused by high myopia, no. Y20160561 .This fundinghad no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.   Figure 1 The questionnaire of comfort level and brightness.

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