Is patient identification of ‘comfortable’ print size a useful clinical parameter for low vision reading assessment?

Abstract

Purpose:The purpose of this study was to determine what a person with vision loss considers a 'comfortable' print size to read, and examine whether this reflects any of three currently used parameters for identifying print size required for sustained reading tasks: minimum size to achieve maximum reading speed (the critical print size (CPS)); minimum size for functional reading at 80 wpm and/or a size that is double the reading acuity (representing an acuity reserve of 2:1).Methods: Forty-seven participants entering low vision rehabilitation (mean age 77 years, 24 with macular degeneration) were assessed using MNREAD charts to determine reading acuity, maximum reading speed, CPS and the minimum size allowing functional (80 wpm) reading. Comfortable print size was assessed by asking participants to identify 'the smallest print size that you would find comfortable using' on the MNREAD chart.Results: There was little difference between comfortable print size and CPS (mean difference 0.05 logMAR (SD 0.18); p = 0.08, limits of agreement ±0.35 logMAR), and no trend for the difference between values to differ across the functional range.Size for functional reading could only be assessed for 41 participants, and the difference between this and comfortable print size varied across the functional range. Comfortable print size was consistently smaller than twice the reading acuity size (mean difference 0.11 logMAR (SD 0.17); p < 0.001), with an average acuity reserve of 1.74:1. Conclusions:Asking people with visual impairment to identify a print size that is comfortable to read provides a print size similar to the CPS. This can be used as a guide in selecting magnification for sustained reading without having to undertake further analyses. Identification of perceived comfortable print size may offer a time-efficient clinical method of estimating magnification requirements, and be relevant for undertaking effective remote consultations.

Can listening provide a useful clinical estimate of low vision reading parameters?

“…Such a discrepancy seems a reasonable clinical approximation, given that CPS provides a starting point for exploring magnification requirements for sustained reading with a patient rather than a definitive prescription. For comparison, a similar difference of 0.05logMAR was observed between comfortable print size and CPS derived by inspection, 18 with CPS being the larger value in this case.…”

“…A disadvantage of the sample is that the causes of visual loss are not necessarily ‘typical’ of a group of low vision patients and does not include a large number of participants with central field loss (e.g., those with macular degeneration). However, in previous studies considering reading, 16,18,21 we have not found differences between individuals with specifically central visual loss and those with other conditions. The level of visual function has been the important discriminating factor for performance, rather than the cause of visual loss.…”

“…Whilst CPS is a valuable clinical measurement, it is inherently quite variable, given the large grading interval of 0.1 log units 18 . However, the estimates of CPS derived from listening are similar to, and no more variable than, more formal methods of assessment.…”

“…36,37 A disadvantage of the sample is that the causes of visual loss are not necessarily 'typical' of group of low vision patients and does not include a large number of participants with central field loss (e.g., those with macular degeneration). However, in previous studies considering reading, 16,18,21 we have not found differences between individuals with specifically central visual loss and those with F I G U R E 4 Maximum reading speed (MRS) in words per minute (wpm) derived by inspection compared to the first judgments of reading speed by rater 1 (blue symbols) and rater 2 (orange symbols). The solid horizontal line represents a measured MRS of 80 wpm, and the dashed line a measured MRS of 120 wpm T A B L E 2 Summary of the ability of each rater to judge whether the maximum reading speed (MRS) was 'functional' (>80 wpm) or 'nonfunctional' (<80 wpm) Note: Category options as for Table 3.…”

“…However, acuity reserve values are known to vary widely between individuals, 14,16,17 and use of a mean value may not be accurate for a given patient. A recently proposed alternative is to ask the patient to identify the print size that they find comfortable to read, 18 which has been shown to relate well to CPS values determined by inspection.…”