Advanced Retinitis Pigmentosa Can Benefit From Full-Field Stimulus Threshold Testing

Significant correlations exist between the full-field stimulus thresholds (FST) and conventional functional and anatomical outcome measures in patients with advanced retinitis pigmentosa (RP), according to research published in the American Journal of Ophthalmology. These findings highlight the potential of FST as an adjunct outcome measure, researchers report.

Investigators conducted a cross-sectional, single-center, retrospective, chart review of consecutive patients who had retinal electrophysiology testing performed at the Columbia University Irving Medical Center, New York, between October 2021 and March 2022. They compared FST threshold values to conventional functional and anatomical measures commonly used in clinical practice for advanced RP.

A total of 42 eyes of 21 patients (mean age, 36.3±23.3 years; 71.4% men and 28.6% women) were included in the study.  Among functional measures, patients had a mean best corrected visual acuity of 0.60±0.76 logarithm of the minimum angle of resolution (logMAR, range, 0-2.70), mean light-adapted 3.0 flicker electroretinogram (ERM) amplitude of 3.4±3.3 microvolts (μV, range, 0.2-11.1 μV), and mean implicit time of 35.3±6.2 milliseconds (ms, range, 25-50 ms). 

Patients had mean FST values of -22.5±15.5 decibels (dB) for the blue stimulus, -17.6±11.5 dB for the white stimulus, and -12.7±6.0 dB for the red stimulus. These threshold values were strongly correlated with light-adapted 3.0 Candela per square meter (cd·s/m²⁾ per 30 hertz (Hz) flicker amplitude and EZ band length measured on optical coherence tomography (OCT). 

These correlations between FST and other clinical outcome measures suggest the test’s potential as an adjunct outcome measure in monitoring for RP, according to the researchers. This is particularly the case when other functional and anatomical measures cannot be applied due to degeneration or loss of rod and cone photoreceptors.

The researchers also examined potential correlations between FST and anatomical outcome measures, including the length of the intact ellipsoid zone (EZ) band, the thickness of the foveal outer nuclear layer (ONL) on OCT, and the vertical and horizontal diameter of the hyper autofluorescent ring on short-wavelength autofluorescence (SW-AF).

Among anatomical measures, patients had a mean length of the intact EZ band of 2422±1913 μm (range, 0-6527 µm), mean thickness of the foveal ONL of 83±38 μm (range, 0-134 µm), and mean vertical and horizontal diameters of the hyper autofluorescence ring of 2765±1771 μm (range, 0-7704 µm) and 2951±1752 μm (range, 0-7441 µm), respectively. 

The blue and white stimulus values on FST were predictive of EZ band length (R²=0.579 and 0.491, respectively) and the vertical (R²=0.694 and 0.532, respectively) and horizontal (R²=0.626 and 0.400, respectively) diameters of the hyper autofluorescence ring, the study shows.

“In patients with advanced RP, it may not be possible to obtain accurate measurements of BCVA and perimetry; the results of these tests may lack the ability to discriminate and detect further disease progression,” the researchers explain. “Thus, other functional tests such as FST may be useful in advanced stages of RP. FST has the advantage that it is fast, simple, and does not require stable fixation. FST has also been shown to be measurable in patients with non-detectable ERG.”

Limitations of the study included the retrospective design and relatively small sample size. 

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.  

Reference

Ngo WK, Jenny LA, Kim AH, Kolesnikova M, Greenstein VC, Tsang SH. Correlations of full-field stimulus threshold with functional and anatomical outcome measurements in advanced retinitis pigmentosa. Am J Ophthalmol. Published online July 20, 2022.  doi:10.1016/j.ajo.2022.07.010