Characteristics of retinal parameters in patients with keratoconus based on OCTA

Objective  To analyze the distribution characteristics of retinal nerve fiber layer (RNFL), macular ganglion cell complex, macular retinal thickness and foveal avascular zone (FAZ) blood flow parameters in patients with keratoconus (KC) using optical coherence tomography (OCTA).

Methods  A cross-sectional study was conducted. Fifty-one patients (90 eyes) diagnosed with KC at the Department of Ophthalmology of People’s Hospital of Ningxia Hui Autonomous Region from September 2021 to November 2023 were enrolled as the KC group, and 43 individuals (86 eyes) for health examination were enrolled as the control group during the same period. According to the Amsler-Krumeich classification, 53 of 90 eyes in the KC group were stage 1, 30 were stage 2, and 7 were stage 3. OCTA was used to measure the RNFL retinal thickness, macular ganglion cell complex thickness, macular retinal thickness, and FAZ blood flow parameters. This study adhered to the Helsinki Declaration, and the research protocol was reviewed and approved by the Ethics Committee of People’s Hospital of Ningxia Hui Autonomous Region (No. [2022]-NZR-035).

Results  Compared with the control group, the RNFL thickness of KC patients showed a trend of thinning in the superonasal (SN), nasoupper (NU), nasolower (NL), inferonasal (IN), and inferotemporal (IT) regions and exhibited a trend of thickening in the temporoupper (TU) and temporolower (TL) regions. Significant differences were observed between the two groups in RNFL thickness in the NU, NL, and TU regions (Wald χ ²=25.288, 7.697, 7.983; all P<0.05). The RNFL thickness in the TU and TL regions exhibited a thinning trend with KC progression. There were significant overall differences in the RNFL thickness of the TU, TL, NU, NL, IN regions between KC patients at different stages and the control group (Wald χ ²=13.895, 27.903, 18.255, 14.782, 8.088; all P<0.05). Compared with the control group, the RNFL thickness in the NU and NL regions was significantly lower in KC patients at all stages (both P<0.05). There were no significant differences in the thickness of ganglion cell complex and retinal thickness in the macula among the different stages of KC patients or between the different stages of KC patients the control group (all P>0.05). The FAZ area and perimeter were 1.19(0.34, 1.22)mm ² and 6.44(2.66, 7.54)mm in the KC group, which were significantly larger than 0.58(0.31, 0.60)mm ² and 4.01(2.45, 4.35)mm in the control group (Wald χ ²=10.573, 12.566; both P<0.05).

Conclusions  The nasal RNFL thickness is thinner, and the FAZ area and perimeter are larger in the KC group than these in the control group. Monitoring RNFL and FAZ changes in KC patients may provide a valuable reference for evaluating disease progression and prognostic outcomes.