ObjectiveTo determine the retinal nerve fiber layer thickness (RNFLT) of chronic progressive external ophthalmoplegia (CPEO) and kearns-sayre syndrome (KSS) patients using spectral-domain optical coherence tomography (SD-OCT) and to analyze the potential influence factors for RNFLT of these patients. Methods18 CPEO and 4 KSS (CPEO with retinitis pigmentosa and cardiac block) patients, all were muscle biopsy confirmed, were included in this study. There were 7 males and 15 females, the average age was (29.09±13.40) years, the average onset age was (16.4±10.7) years and the average disease duration was (11.30±7.30) years. All the patients underwent SD-OCT examination for the left eye, the peripapillary RNFL thickness was measured using the Spectralis 3.45 mm circle scan protocol. 8 quadrants were scanned including superior temporal (ST), temporal upper (TU), temporal lower (TL), inferior temporal (IT), inferior nasal (IN), nasal lower (NL), nasal upper (NU) and superior nasal (SN). The relationship between RNFLT and onset time, disease duration was analyzed by Pearson correlation analysis. ResultsThe average RNFLT of ST, TU, TL, IT, IN, NL, NU, SN in the 22 patients were (136.3±24.1), (85.4±25.7), (68.2±11.7), (128.2±28.7), (127.3±29.5), (66.7±16.8), (70.1±17.6) μm, respectively. The circumferential average RNFLT was (101.5±14.4) μm. There was no significant difference between the KSS group and CPEO group (P>0.05). The decrease of the circumferential RNFLT had no relationship with the onset age (r=-0.306, P=0.11), but a negative relationship with the disease course (r=-0.518, P=0.03). There were negative relationships between the disease course and RNFLT of 4 nasal quadrants (IN:r=-0.555, P=0.01, NL: r=-0.630, P=0.00, NU: r=-0.559, P=0.01, SN: r=-0.557, P=0.01). ConclusionThere is no difference in RNFLT of patients with CPEO and KSS. There is a negative relation between RNFLT (especially RNFLT of 4 nasal quadrants) and disease course.