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Clinical research on a new mobility assessment tool for RPE65-associated retinal dystrophy.

Clinical researchers based at the UCL Institute of Ophthalmology, University College London and Moorfields Eye Hospital, have published a new study that identifies how mobility and navigation are managed by visually impaired patients and not visually impaired. RPE65-associated retinal dystrophy patients have a congenital or early onset form of non-syndromic retinal disease characterised by severe retinal dystrophy, vision loss, nystagmus, and an abnormal pupil response.  Given the challenges for the traditional visual acuity test, researchers have aimed to test and validate a novel vision-guided mobility assessment providing a valuable real-world assay.  The mobility course, designed by University College London, was termed as the “Pedestrian Accessibility Movement Environment Laboratory (PAMELA), previously replicated and improved. 


The PAMELA course provides a simulated “sidewalk” environment, where light levels are controlled over a range from 1 to 15,000 lux. The dimension for PAMELA course was a 10.8 m X 7.2 m platform, with a 10m straight-line walk, a 13 m maze in the middle section (“maze”) and another 10 m straight-line walk with two foam blocks to simulate sidewalk kerbs (“kerb”).  There are a number of previous types of mobility assay issuing smaller and larger types of assessment, including one that used an entire city block (Palo Alto, California).  Recruiting of subjects included ten (10) unaffected individuals (five adults and five children) and nineteen (19) molecularly confirmed recessive RPE65-RD–affected individuals (10 adults and 9 children), all of which undertook the mobility assessment and assessments of visual function.  Researchers also outlined that the course length (meters) was divided by time to complete the course (seconds) to give walking speed (meters/second; m/s). The results of the study showed that walking speed through the maze assessment best discriminated between RPE65-RD and normally-sighted subjects, with both convergent and discriminant validity.  Researchers reported that walking speed also approached statistical significance when assessed for criterion validity (P = 0.052). Subjects with RPE65-RD had quantifiably poorer mobility at lower illumination levels. A relatively small mean difference (−0.09 m/s) was identified in comparison to a relatively large repeatability coefficient (1.10 m/s).


In summary, the authors of the study describe a novel, quantifiable, repeatable, and valid assessment of mobility designed specifically for subjects with RPE65-RD. The assessment is sensitive to the visual impairment of individuals with RPE65-RD in low illumination, identifies the known phenotypic heterogeneity and will furthermore provide an important outcome measure for RPE65-RD. In essence, the PAMELA assay was “validated in a dedicated cohort of subjects with RPE65-RD” and this then provide a relevant and quantifiable outcome measure for RPE65-RD.  It is expected that this may be used in future trials for this and potential other retinal degenerative disorders.