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Martin Klein, Paulina Mejia, Daniel Galles, David G Birch; Full-Field Stimulus Thresholds (FSTs) in Subjects with Inherited Retinal Degenerations (IRDs) – a 10 Years Review. Invest. Ophthalmol. Vis. Sci. 2018;59(9):54. doi: https://doi.org/.
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The FST is a well-established tool for testing retinal sensitivity in low-vision subjects (Roman et al. 2007; Klein M., Birch D.G. 2009, Messias et al. 2014; Collison et al. 2015; Klein et al. 2016) and an important outcome measure in gene therapy trials (Jacobson et al. 2012, Russell et al. 2017). These studies established correlations between the FST and different outcome measures on small groups of subjects or compared thresholds in subjects with specific mutations over time. Here we review results from 10 years of testing on untreated, advanced IRD subjects at the Retina Foundation.
FST thresholds were determined from 362 eyes of 362 subjects whose full-field electroretinograms and visual fields had become unreliable or non-detectable. Subjects tested were previously diagnosed with autosomal dominant RP (adRP, n=74), autosomal recessive RP (arRP, n=65), isolate RP (isoRP, n=118), x-linked RP (xlRP, n=27), Usher syndrome (Usher, n=50), and Leber Congenital Amaurosis (LCA, n=28). FST thresholds were obtained after 30 minutes of dark-adaptation on an Espion ColorDome (Diagnosys LLC, Lowell, MA). Rate of change was calculated for a subset of 45 eyes with at least one follow-up visit. Three outliers with unexplained rates of change of over 15dB/year were excluded.
All subjects had measurable thresholds (Table 1). LCA subjects were generally the youngest (23.2 y.) to be tested by FST, while adRP subjects were the oldest (54.6 y.). Mean thresholds were highest (-15.83 dB) for LCA and lowest (-24.3 dB) for adRP. Rate of change was slowest (-0.03 dB/year) in LCA and fastest in isoRP (0.91 dB/year) (Table 2).
Since the FST testing began once sensitivity of other measures was exhausted, the age at first testing reflects the natural history of visual loss. The severity of disease is also reflected in mean thresholds. Early and severe loss in LCA with stable thresholds over years of follow-up contrasts with later and faster progression in RP. The slow rates of progression in these groups suggest that the FST is a more suitable outcome measure for therapy trials seeking to improve vision rather than slowing disease progression.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Table 1: Age and FST thresholds by condition
Table 2: Average length of follow-up and rate of change per year
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