Comparative Analysis of Functional and Structural Decline in Retinitis Pigmentosas

Nonlinear Reduction in Hyperautofluorescent Ring Area in Retinitis Pigmentosa

PURPOSE

To report baseline dimension of the autofluorescent (AF) ring in a large cohort of retinitis pigmentosa (RP) patients and to evaluate models of ring progression.

DESIGN

Cohort study.

PARTICIPANTS

Four hundred and forty-five eyes of 224 patients with clinical diagnosis of RP.

METHODS

Autofluorescent rings from near-infrared AF (NIRAF) and short-wavelength AF (SWAF) imaging modalities in RP eyes were segmented with ring area and horizontal extent extracted from each image for cross-sectional and longitudinal analyses. In longitudinal analysis, for each eye, ring area, horizontal extent, and natural logarithm of the ring area were assessed as the best dependent variable for linear regression by evaluating R2 values. Linear mixed-effects modeling was utilized to account for intereye correlation.

MAIN OUTCOME MEASURES

Autofluorescent ring size characteristics at baseline and ring progression rates.

RESULTS

A total of 439 eyes had SWAF imaging at baseline with the AF ring observed in 206 (46.9%) eyes. Mean (95% confidence interval) of ring area and horizontal extent were 7.85 (6.60 to 9.11) mm2 and 3.35 (3.10 to 3.60) mm, respectively. In NIRAF, the mean ring area and horizontal extent were 7.74 (6.60 to 8.89) mm2 and 3.26 (3.02 to 3.50) mm, respectively in 251 out of 432 eyes. Longitudinal analysis showed mean progression rates of -0.57 mm2/year and -0.12 mm/year in SWAF using area and horizontal extent as the dependent variable, respectively. When ln(Area) was analyzed as the dependent variable, mean progression was -0.07 ln(mm2)/year, which equated to 6.80% decrease in ring area per year. Similar rates were found in NIRAF (area: -0.59 mm2/year, horizontal extent: -0.12 mm/year and ln(Area): -0.08 ln(mm2)/year, equated to 7.75% decrease in area per year). Analysis of R2 showed that the dependent variable ln(Area) provided the best linear model for ring progression in both imaging modalities, especially in eyes with large overall area change.

CONCLUSIONS

Our data suggest that using an exponential model to estimate progression of the AF ring area in RP is more appropriate than the models assuming linear decrease. Hence, the progression estimates provided in this study should provide more accurate reference points in designing clinical trials in RP patients.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

The Use of Optical Coherence Tomography in Evaluation of Retinitis Pigmentosa

Optical coherence tomography (OCT) is a noninvasive imaging technology that has gained widespread use in the evaluation of multiple retinal pathologies, including retinitis pigmentosa (RP). OCT allows for visualization of distinct retinal layers and the choroid and facilitates study of morphological features associated with RP. OCT can be used to detect and to track progression of RP, as well as to correlate structural findings with functional manifestations of the disease. This chapter provides a basic overview of OCT technology and details elements of importance in the use of OCT for diagnosis and assessment of progression of RP.

Investigating Biomarkers for USH2A Retinopathy Using Multimodal Retinal Imaging

Pathogenic mutations in USH2A are a leading cause of visual loss secondary to non-syndromic or Usher syndrome-associated retinitis pigmentosa (RP). With an increasing number of RP-targeted clinical trials in progress, we sought to evaluate the photoreceptor topography underlying patterns of loss observed on clinical retinal imaging to guide surrogate endpoint selection in USH2A retinopathy. In this prospective cross-sectional study, twenty-five patients with molecularly confirmed USH2A-RP underwent fundus autofluorescence (FAF), spectral-domain optical coherence tomography (SD-OCT) and adaptive optics scanning laser ophthalmoscopy (AOSLO) retinal imaging. Analysis comprised measurement of FAF horizontal inner (IR) and outer (OR) hyperautofluorescent ring diameter; SD-OCT ellipsoid zone (EZ) and external limiting membrane (ELM) width, normalised EZ reflectance; AOSLO foveal cone density and intact macular photoreceptor mosaic (IMPM) diameter. Thirty-two eyes from 16 patients (mean age ± SD, 36.0 ± 14.2 years) with USH2A-associated Usher syndrome type 2 (n = 14) or non-syndromic RP (n = 2) met the inclusion criteria. Spatial alignment was observed between IR-EZ and OR-ELM diameters/widths (p < 0.001). The IMPM border occurred just lateral to EZ loss (p < 0.001), although sparser intact photoreceptor inner segments were detected until ELM disruption. EZ width and IR diameter displayed a biphasic relationship with cone density whereby slow cone loss occurred until retinal degeneration reached ~1350 μm from the fovea, beyond which greater reduction in cone density followed. Normalised EZ reflectance and cone density were significantly associated (p < 0.001). As the strongest correlate of cone density (p < 0.001) and best-corrected visual acuity (p < 0.001), EZ width is the most sensitive biomarker of structural and functional decline in USH2A retinopathy, rendering it a promising trial endpoint.

New criteria for evaluation of electroretinogram in patients with retinitis pigmentosa

BACKGROUND

Electroretinogram (ERG) plays an essential role in the diagnosis of retinal disease. Choosing appropriate methods could extract valuable information from ERG. In this study, a new criterion based on time-frequency domain analysis was proposed to investigate the retina in retinitis pigmentosa (RP) patients.

MATERIALS AND METHODS

The total number of 16 eyes from eight RP patients and 20 eyes from age-matched healthy subjects were assessed. The signals included photopic and scotopic ERGs. Continuous wavelet transform was applied to ERGs. Dominant frequencies were extracted, and the contours related to these dominant frequencies were selected. As a new criterion, the areas related to dominant frequency contours were considered a feature to differentiate the RP and normal groups. To better evaluate the proposed criterion results, the time-domain analysis characteristics of ERG were also considered.

RESULTS

The results showed an increase in implicit time and reduced amplitude in RP patients (P < 0.05). A significant decrease of dominant frequencies and increasing their occurrence time were seen in ERG of RP patients. Also, in RP patients, the third dominant frequency was disappeared from the three main frequencies observed in photopic ERGs of normal subjects. The area criterion showed a significant decrease in RP groups (P < 0.05).

CONCLUSION

RP can cause changes in the time and time-frequency components of the ERG. The area index could represent a new view of the characteristics of the ERG in the time-frequency domain. This criterion can help the ophthalmologist to have a better evaluation of retinal disease.