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. The 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 and the 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 visual 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 (ff-ERG) rod and cone amplitudes [1,4,5]. The exclusion criteria were: (1)a history of trauma; (2)a history of vitreoretinal surgery and intravitreal therapy; (3)pathological myopia; (4)other vascular retinopathies, 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 a 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 classified as blindness; BCVA of 3/60–6/18 in the better eye was classified as low vision; and BCVA of 6/18 or more was classified as normal. The researchers did not classify visual acuity according to the visual field. Full-field electroretinogram testing was performed according to the International Society of Clinical Electrophysiology of Vision’s standards .
The lens condition was classified as clear, cataract, pseudophakic or aphakic. A specialist diagnosed glaucoma based on the presence of glaucomatous optic neuropathy and intraocular pressure over 21 mmHg, with or without the presence of iridotrabecular contact . The macular microstructure was examined with Spectral Domain OCT (SD-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. The macular abnormalities were documented as: ERM, CME, MH (including lamellar and full-thickness MH), VMT and CNVM according to the following definitions[1,13,14]:
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.
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.
Lamellar-thickness macular hole (LMH) was defined as partial thickness defects of the macular area, with an irregular foveal contour and a schisis between the inner and the outer retinal layers and without any photoreceptor layer defects. Full-thickness macular hole (FTMH) was defined as a vertical split in the neurosensory layers of the foveal region.
VMT was characterized by a vitromacular adhesion that involved the foveal region from posterior hyaloid face, causing traction and distortion of the central macular.
CNVM was defined as cystic macular edema associated with a disruption of the Bruch membrane/retinal pigment epithelium (RPE) complex, accompanied by an avascular structure emanating from the deep capillary plexus and appearing as a hyperreflective lesion connected with the subretinal pigment epithelium. Other diseases that cause macular CNVM were excluded [9,14].
Molecular diagnosis and inheritance pattern
Some patients voluntarily underwent molecular diagnosis, and inheritance patterns were categorised according to the genetic test reports: autosomic dominant (AD), autosomic recessive (AR), X-linked (X-L)or sporadic (i.e., patients with negative genetic reports or no evidence of other affected family members). RP patients’ ages were divided into four groups for statistical analysis (≤15 years, 16–44 years, 45–64 years and ≥65 years )
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, inheritance 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.