The criteria for evaluating efficacy and the timing of evaluation have been a constant point of contention with the regulatory Authority in Clinical Trials and have not been changed to date in either drugs or devices for RP patients [8, 9]. Many RP cases are chronic, progress slowly, and do not progress for about one year, so clinical trials over several years are needed, but for various reasons long term clinical trials are difficult to conduct. In addition, it is difficult to expect improvement because the disease often progresses irreversibly. Even in two-arm comparative studies with placebo or sham control groups, it can be assumed that neither the control nor the treatment group will worsen or improve visual function over the course of a one- to two-year study.

Visual function includes visual acuity and visual field as well as macular sensitivity. Macular sensitivity was defined as the -MD value when tested in the central 10-degree mode of the static quantitative HFA. However, macular sensitivity is not routinely tested even in clinical practice, and it is unclear what significance it has from the patient’s perspective, and its relationship with quality of life related to conventional visual functions has been investigated in RP patients [10, 11]. Visual ADL data is needed as well as visual QOL information.

What significance it has from the patient’s perspective, and its relationship with quality of life related to conventional visual function has not been investigated. The LVFAM used in this study as a visual ADL test is a questionnaire developed from the original LVFAM for patients with low vision. Generally, low vision is defined as corrected visual acuity of less than 0.3, but even if the corrected visual acuity is 1.0, patients with RP and progressive visual field narrowing are considered to be in need of a low vision clinic, and were included in the target population. The results of the LVFAM show that in the daily life of RP patients, most difficult to see were letters on price tags and tags of products, price lists and timetables, and the appearance of people a short distance away, while the most difficult activities were going out and writing. Since LVFAM was correlated with visual acuity, the visual ADL study LVFAM may reflect visual function in RP as well. Since macular sensitivity also correlated with LVFAM, the negative MD value of 10 degrees of HFA, defined as macular sensitivity, could reflect PRO as a visual function other than corrected visual acuity.

Some ALD studies in specific situations of patients with some form of visual dysfunction are reported [12, 13]. On the other hand, using spectacle-mounted prisms for field expansion in 15 patients with retinitis pigmentosa (RP) provided visual field expansion and spatial orientation benefits [14]. However, these are different from the LVFAM used in this study, so comparisons are not applicable. Ono, Suzukamo, and colleagues in Japan collected items from domestic and international literature on ADL measurements in low vision patients and questionnaires in similar fields, and compared them with the content of the Activities’ item of the International Classification of Functional Living (ICF) to create a tentative version of the index. The LVFAM was then completed by calculating the level of difficulty and fit statistics for each item and examining the degree of fit to the Rasch model in 186 low vision patients [7]. In this paper, it was performed on all patients independent of the primary disease and included 36 RPs. However, in the final results, items characteristic of RP related to visual field were excluded from the results as they need to be further examined. Therefore, we felt that more RP cases needed to be further examined.

The LFVAM took nearly 30 min if the patient was unfamiliar with the test, but once the they had practiced and became familiar with it, the test could usually be performed within 10 min, or 15 min at the most. Those who were more cautious about individual questionnaire items tended to take longer, and the examination time varied depending on age and whether the patient came to the hospital with a family member.

The limitation of this study is that the number of cases was limited to 15, but the total score of each LVFAM was related to corrected visual acuity and macular sensitivity, and there was a trend in the evaluation index for each question. This may be expected as a breakthrough in terms of fostering an evaluation system for the development of PRO in diseases for which a cure has not yet been established.

In the development of treatments for RP, the primary endpoint is both important and not easy to set [8, 9]. This is because RP is a disease of visual field narrowing in which central visual acuity is preserved to the end. Macular sensitivity was established as a visual field that approximates central visual acuity, but its clinical significance is unknown because it has not been standardized in clinical practice. Therefore, it is necessary to confirm the relationship of macular sensitivity with visual QOL and visual ADL, which are directly related to PRO. This is one of a number of reports of cases of visual field impairment such as RP with a focus on PROs [15, 16]. Visual QOL is important in addition to visual ADL, and should be examined with various PROs. Opinions may differ because assessing the results takes much time. Furthermore, as time passes, each PRO should be updated with more appropriate PROs. Based on the results of this study, further research on LVFAM for RP is warranted in the future. It is expected that an English version of the LVFAM will be prepared in the future to investigate trends in other populations as well.