Study design and subjects recruitment
The authors retrospectively extracted medical records of patients diagnosed with RP between January 2014 and January 2019 at Southwest Hospital/ Southwest Eye Hospital, Third Military Medical University (Army Medical University), Chongqing, China. These records included information on each patient’s age, gender, medical and surgical history, family history, complaints, best corrected visual acuity (BCVA), intraocular pressure, lens status, slit-lamp anterior segment and dilated fundus examination from the first clinical presentation. RP diagnosis was based on: (1) presence of night blindness or blurred vision and peripheral vision field restriction; (2) characteristic fundus changes, such as pale optic disc, attenuated vessels and bone-spicule-like pigmentation deposits in the mid- or far-periphery; and (3) reduced or non-detectable full-field electroretinogram (ffERG) rod and cone amplitudes [1,4,5]. Systemic syndrome RP patients were included in the study. The exclusion criteria were: (1) trauma history; (2) vitreoretinal surgery and intravitreal therapy history; (3) pathological myopia; (4) other vascular retinopathy, such as hypertensive retinopathy, diabetic retinopathy, retinal periphlebitis, etc.; (5) age-related macular degeneration; (6) atypical RP, such as unilateral pigmentary retinopathy or sectorial pigmentary retinopathy; (7) secondary retinal pigmentosa; and (8) severe systemic diseases. The study was performed according to the Declaration of Helsinki and approved by the Ethics and Research Committee of Southwest Hospital, Army Medical University (KY2020096).
Age of onset and functional examination
The age of onset (that is, of symptoms) was defined as the patient’s age subtracted from the year with positive disease history. BCVA was measured with a Tumbling E chart and converted into the logarithm of the minimum angle of resolution (logMAR) value for analysis . BCVA was classified according to the World Health Organization’s (WHO) category of vision as follows : BCVA worse than 3/60 in the better eye was considered blindness; BCVA of 3/60–6/18 in the better eye was considered low vision; and BCVA of 6/18 or more was considered normal. The researchers did not classify visual acuity according to vision field. ffERG testing was performed according to the International Society of Clinical Electrophysiology of Vision (ISCEV) standards .
Lens condition was classified as clear, cataract, pseudophakic and aphakic. A specialist diagnosed glaucoma based on the presence of glaucomatous optic neuropathy, intraocular pressure over 21 mmHg, with or without the presence of iridotrabecular contact . The macular microstructure in RP patients was examined with either Spectral Domain OCT (Cirrus HD-OCT, Carl Zeiss Meditec, Dublin California, USA) or Heidelberg Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany). Two experienced ophthalmologists independently evaluated the images. If the results differed, a third ophthalmologist re-evaluated them. Macular abnormalities were documented as follows: ERM, CME, MH (including lamellar and full-thickness MH), VMT and CNVM [1,13,14]:
CME was defined as the presence of cystoid spaces, appearing like small hypo-reflective lacunae with well-defined boundaries on two or more consecutive views of the radial scan in the macular area.
ERM was diagnosed with the presence of as avascular, fibrocellular membrane on the inner surface of the retina, often resulting from proliferative changes at the vitro-retinal interface.
VMT was characterized by a vitro-macular adhesion that involved the foveal region from posterior hyaloid face causing traction and distortion of the central macular.
LMH was defined as partial thickness defects of the macualar area, with an irregular foveal contour and a schisis between inner and outer retinal layers, and without any photoreceptor layer defects. FTMH was defined as a vertical split in the neurosensory layers of foveal region.
CNVM was defined as cystic macular edema associated with a disruption of the Bruch membrane/retinal pigment epithelium complex, accompanied by an avascular structure emanating from the deep capillary plexus appearing as a hyper-reflective lesion connected with the subretinal pigment epithelium. And other diseases that cause macular CNV were excluded [9,14].
Molecular diagnosis and inheritance pattern
Some patients voluntarily underwent molecular diagnosis, and inherence patterns were categorised according to genetic test reports: autosomic dominant (AD), autosomic recessive (AR), X-linked (X-L) and sporadic cases (i.e., patients showing negative genetic reports or no evidence of other affected family members). RP patients’ ages were divided into four groups (≤15 years, 16–44, 45–64 and ≥65) for statistical analysis, according to the International Classification of Disease.
SPSS 22.0 was used to conduct analyses. Continuous variables, such as counselling age, age of onset and BCVA (logMAR), were expressed as means±standard deviation (SD) and were compared with independent sample t-tests. Categorical variables (gender, complaints, inherence pattern, age group, lens condition and macular abnormalities) were presented as counts and percentages and compared with Chi-squared or Fisher’s exact tests. Multiple linear regression investigated the relationship between BCVA (logMAR) and macular abnormalities. Coefficients of the estimated regression (β), the corresponding statistical significance (P), the exponential parameter and its confidence interval were presented for each factor. A P-value of <0.05 was considered statistically significant.