Test-retest Variability of a Standardized Low Vision Lighting Assessment

Systematic lighting assessments should be part of low vision evaluations. The LuxIQ has gained popularity as an assessment tool, but its reliability has not been examined independently and is necessary for evidence-based vision rehabilitation.

Besides magnification, improved lighting levels are a common intervention in reading rehabilitation for individuals with low vision. Determining the appropriate lighting can be a complex and time-consuming task. The LuxIQ is a portable lighting assessment tool that can be used to systematically measure lighting preferences; however, there is little independent evidence to support its reliability in low vision rehabilitation.

One hundred nine control subjects (age, 18 to 85 years) and 64 individuals with low vision (age, 27 to 99 years) adjusted both the luminance and color temperature parameters on the LuxIQ while viewing a sentence on the MNREAD at their preferred print size for continuous reading. After 30 minutes, they were asked to repeat the same measurements.

Using Bland-Altman plots, test-retest variability was calculated using the limits of agreement (LOAs). For illuminance, the LOA width was 2806 lux for control subjects and 2657 lux for visually impaired participants. For color temperature, the LOA width was 2807 K for control subjects and 2364 K for those with a visual impairment. Difference scores were centered near zero, indicating overall accuracy.

The measurement of lighting preference lacks the precision necessary for clinical utility, given that the LOA for luminance ranged more than 2600 lux, with normally sighted and low vision participants. Such variability translates into a range of approximately ±40 or 50 W in an incandescent light bulb, depending on the luminance level, making it clinically difficult to narrow down the options for evidence-based lighting recommendations. Next steps are to examine whether the reading behavior of low vision clients is positively affected by interventions that are based on LuxIQ recommendations.