Cystoid Macular Lesions in Inherited Retinal Diseases: Prevalence, Characteristics, and Genetic Associations in a Hungarian Cohort

<b>Background/Objectives</b>: Cystoid macular lesion (CML) is a treatable cause of central vision loss in inherited retinal diseases (IRDs). We aimed to determine the frequency of CML in a large Hungarian IRD cohort and examine associations with causative genes. <b>Methods</b>: This longitudinal, retrospective, monocentric study included patients with genetically confirmed IRD identified from our database. Targeted next-generation sequencing (351-gene panel) and comprehensive ophthalmic evaluation were performed, including best-corrected visual acuity (BCVA) and spectral domain optical coherence tomography (SD-OCT). CML was defined as intraretinal hyporeflective spaces with well-defined borders visible on at least two B-scans within the SD-OCT macular volume and was categorized as cystoid macular edema (CME) or non-CME. <b>Results</b>: We enrolled 430 patients with genetically confirmed IRDs. CML was detected in 93 eyes of 57 patients. Mean age at OCT was 36.6 ± 18.7 years (range, 3-76); 32 were male (56.1%). Inheritance patterns were autosomal recessive in 24 (42.1%), X-linked in 19 (33.3%), and autosomal dominant in 14 (24.6%). Frequently implicated genes were <i>RS1</i> (12/57), <i>USH2A</i> (7/57), <i>NR2E3</i> (7/57), <i>PRPF31</i> (4/57), <i>RPGR</i> (4/57), and <i>RHO</i> (4/57). CME predominated in retinitis pigmentosa (32/57, 56%), with mean BCVA 0.44 ± 0.29 (decimal) and central retinal thickness (CRT) 401 ± 181 µm. Non-CME CML occurred in 25/57 (44%)-notably in X-linked retinoschisis and enhanced S-cone syndrome-with BCVA 0.40 ± 0.23 and CRT 465 ± 258 µm. BCVA did not correlate with CRT (r_S = 0.18). <b>Conclusions</b>: CML occurred in 13.2% of patients within a large Hungarian cohort of genetically confirmed IRDs. Patients with IRD-mainly RP-are at higher risk for CML. Gene therapy is promising for retinal diseases, but CMLs can compromise effectiveness. Reducing and managing CME before gene therapy corroborates retinal stability and the functional state essential for the proper delivery and penetration of corrective genes to the target cells.