Division of Optometry, Department of Health and Wellbeing, University of the West of England, Bristol, UK.
School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK.
Clin Exp Optom. 2023 Jul;106(5):476-483. doi: 10.1080/08164622.2022.2067470. Epub 2022 May 25.
Inter-instrument variation in anterior corneal shape (ACS) measurement has a consequence for ocular clinical practice.
To consider inter-instrument variability in keratometry measurements across the ACS and to explore instrument protocols for determining ACS keratometric analogues (KAs).
Mean keratometry/KAs of the right eye were recorded using Javal-Schiøtz keratometer (J-S), Orbscan IIz and Pentacam from 124 subjects (78 females; mean ± SD age: 24.71 ± 6.61 years). Mean radii of curvature were obtained for 1-mm wide annular zones extending up to 6 mm (horizontally) and 4 mm (vertically) from the apex for Orbscan and Pentacam. Zonal mean radius of curvature was calculated by averaging keratometry values for all measured points within the zone.
KA (mean ± SD): Horizontal: Orbscan (7.80 ± 0.31 mm) and J-S (7.82 ± 0.29 mm) were not significantly different (p = 0.072). Pentacam (7.86 ± 0.29 mm) was significantly flatter than J-S (p < 0.001) and Orbscan (p < 0.001). Vertical: Orbscan (7.64 ± 0.31 mm) was significantly steeper than J-S (7.67 ± 0.29 mm, p < 0.005) and Pentacam (7.70 ± 0.29 mm, p < 0.001). Pentacam was significantly flatter than J-S (p < 0.001) and significant flatter than Orbscan across the entire profile (1-4 mm zones horizontal and vertical, p < 0.001). LoAs (CI): J-S/Orbscan: ±0.75 mm (0.05-0.18); J-S/Pentacam: ±0.72 mm (0.01-0.12); Pentacam/Orbscan: ±0.16 mm (0.04-0.08). There was a +0.03 mm positive bias for Orbscan compared to J-S, +0.06 mm positive bias for Orbscan compared to Pentacam and -0.03 mm negative bias for Pentacam compared to J-S.
Algorithms used by Orbscan and Pentacam to solve the peripheral paraxial ray problem produce significantly different KAs. Instrument-specific KAs cannot be used inter-changeably between instruments. Differences in KA between instruments are not significant for ocular surgery, but may influence rigid contact lens fitting. Pentacam measures flatter than Orbscan and J-S.
角膜前表面（ACS）形状测量中的仪器间差异对眼科临床实践有影响。
考虑角膜曲率计测量在 ACS 中的仪器间可变性，并探索用于确定 ACS 角膜曲率模拟值（KA）的仪器方案。
对 124 名受试者（78 名女性；平均年龄 ± SD：24.71 ± 6.61 岁）的右眼进行了杰法-施托茨角膜曲率计（J-S）、Orbscan IIz 和 Pentacam 的平均角膜曲率计/KA 记录。对于 Orbscan 和 Pentacam，从顶点水平延伸至 6mm 和垂直延伸至 4mm 的 1mm 宽环形区域，获得平均曲率半径。通过在区域内所有测量点的角膜曲率计值的平均值计算角膜曲率模拟值的区域平均曲率半径。
KA（平均值 ± SD）：水平方向：Orbscan（7.80 ± 0.31mm）和 J-S（7.82 ± 0.29mm）之间无显著差异（p=0.072）。Pentacam（7.86 ± 0.29mm）比 J-S（p<0.001）和 Orbscan（p<0.001）更平坦。垂直方向：Orbscan（7.64 ± 0.31mm）比 J-S（7.67 ± 0.29mm，p<0.005）和 Pentacam（7.70 ± 0.29mm，p<0.001）更陡峭。Pentacam 比 J-S（p<0.001）和 Orbscan（p<0.001）在整个角膜形态（水平和垂直 1-4mm 区域）都更平坦。
LoAs（CI）：J-S/Orbscan：±0.75mm（0.05-0.18）；J-S/Pentacam：±0.72mm（0.01-0.12）；Pentacam/Orbscan：±0.16mm（0.04-0.08）。与 J-S 相比，Orbscan 有+0.03mm 的正偏倚，与 Pentacam 相比，Orbscan 有+0.06mm 的正偏倚，与 J-S 相比，Pentacam 有-0.03mm 的负偏倚。
Orbscan 和 Pentacam 用于解决周边近轴光线问题的算法产生了明显不同的 KA。仪器特定的 KA 不能在仪器之间互换使用。仪器之间 KA 的差异对眼科手术没有显著影响，但可能会影响硬性隐形眼镜的适配。Pentacam 的测量结果比 Orbscan 和 J-S 更平坦。
