Director of Research and Surgery, Black Mammoth Surgical, Medellín, Colombia.
Department of Ophthalmology, Universidad Pontificia Bolivariana, Medellín, Colombia.
Indian J Ophthalmol. 2023 Jan;71(1):63-68. doi: 10.4103/ijo.IJO_1121_22.
Corneal densitometry analysis provides an objective measurement of corneal transparency in patients undergoing photorefractive keratectomy (PRK). To date, no study that focuses on determining the reliability and smallest real difference (SRD), specifically in PRK candidates, has been published.
The study was conducted at Clínica de Oftalmología Sandiego, Medellín, Colombia. This was a prospective and analytical study. Refractive surgery candidates underwent Pentacam measurements twice with five minutes of difference. Repeatability of measurements was evaluated for every area using Wilcoxon signed-rank test, Spearman's rank-order correlation, and the intraclass correlation coefficient, followed by a within-subjects factor (S) finishing with a determination of the SRD for all areas. Bland-Altman plots were created and analyzed.
A total of 110 eyes were included. The mean total densitometry was 18.67 ± 1.56 grayscale units (GSU) and 18.65 ± 1.49 GSU for the first and second measurements, respectively. Wilcoxon was non-significant (P > 0.05) while the intraclass correlation coefficient demonstrated an excellent agreement. SRD ranged from 0.21 GSU (posterior × 6-10 mm) to 1.79 GSU (total × 10-12 mm). Anterior depths and 10-12 mm annulus had consistently more variability and greater (worse) SRD. The 10-12 mm annulus showed great dispersion on the Bland-Altman plots.
Corneal densitometry has an excellent repeatability in refractive surgery candidates for areas below 10 mm. Any densitometry change ≥1.0 GSU in areas under 10 mm should be considered as well above measurement noise and corresponding to a real change in measured parameters. The 10-12 mm area does not seem to be reliable enough in refractive surgery candidates to warrant surveillance after corneal-based surgery.
角膜密度测量分析可提供接受光折射性角膜切削术（PRK）治疗的患者角膜透明度的客观测量结果。迄今为止，尚无专门针对 PRK 患者的可靠性和最小实际差异（SRD）的研究。
该研究在哥伦比亚麦德林的 Clínica de Oftalmología Sandiego 进行。这是一项前瞻性分析研究。屈光手术候选者相隔 5 分钟接受 Pentacam 测量两次。使用 Wilcoxon 符号秩检验、Spearman 等级相关系数和组内相关系数评估每个区域的测量重复性，然后进行受试者内因素（S）分析，最后确定所有区域的 SRD。创建并分析 Bland-Altman 图。
共纳入 110 只眼。总平均密度分别为 18.67 ± 1.56 灰度单位（GSU）和 18.65 ± 1.49 GSU，分别为第一次和第二次测量结果。Wilcoxon 检验无统计学意义（P > 0.05），而组内相关系数显示出极好的一致性。SRD 范围为 0.21 GSU（后 × 6-10mm）至 1.79 GSU（总 × 10-12mm）。前深度和 10-12mm 环带的变异性更大（更差），SRD 也更大。10-12mm 环带的 Bland-Altman 图显示出很大的离散度。
在屈光手术候选者中，角膜密度在 10mm 以下区域具有极好的可重复性。任何 10mm 以下区域的密度变化≥1.0 GSU 都应被视为明显高于测量噪声，并且与所测参数的实际变化相对应。在屈光手术候选者中，10-12mm 区域似乎不够可靠，无需在角膜手术后进行监测。
