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. 2020 Apr 1:2020:1916369.
doi: 10.1155/2020/1916369. eCollection 2020.

Calculation of the Real Corneal Refractive Power after Photorefractive Keratectomy Using Pentacam, When Only the Preoperative Refractive Error is Known

Maddalena De Bernardo  1 , Maria Borrelli  2 , Roberto Imparato  1 , Nicola Rosa  1
Affiliations

Calculation of the Real Corneal Refractive Power after Photorefractive Keratectomy Using Pentacam, When Only the Preoperative Refractive Error is Known

Maddalena De Bernardo et al. J Ophthalmol. .

Abstract

Purpose: To check if a regression formula, IOLMaster-derived, to calculate the real corneal power after photorefractive keratectomy (PRK), can give reliable results utilizing the Pentacam.

Methods: Pre- and postoperative IOLMaster, Km, and Pentacam K readings were measured. Patients who had myopic PRK were divided into two groups: the first group (108 eyes) was utilized to check which of the preop Pentacam K readings (P-Kpre) better fitted with the preop IOLMaster measurements; in the second group (120 eyes), the real K (Kr), obtained adding the effective treatment to the P-Kpre, were compared with the K readings calculated with the IOLMaster-derived formula (Kc). Moreover, an attempt to find a different formula utilizing the P-Kpre was made.

Results: In group 1, the best correlation was found between IOLMaster Km and Pentacam equivalent K readings (r2 0.9519). In group 2, the comparison between Kr and Pentacam postop Km showed 69 eyes (57%) with differences >0.5 D and 38 eyes (31%) with differences >1 D, (P < 0.001). The comparison between Kr and Kc showed 55 eyes (45%) with differences >0.5 D and 22 eyes (18%) with differences >1 D, (P < 0.001). Moreover, a regression formula K = EKR - [ETcp + (0.8114 ∗ ETcp - 0.2031)] was obtained in order to calculate the K readings to be used with the Pentacam in the IOL power calculation in case the effective treatment is known.

Conclusions: K calculated with the new formula could be used in patients that underwent refractive corneal surgery in case a Pentacam device is used, pending further studies conducted in clinical practice to establish its accuracy and effectiveness. This study further proves that data obtained from different machines cannot be used interchangeably.

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Conflict of interest statement

The authors report no conflicts of interest and have no proprietary interest in any of the materials mentioned in this article.

Figures

Figure 1
Figure 1
Scatterplot showing correlation between the preoperative IOLMaster mean keratometry (Km) and P-Kpre (preoperative Pentacam equivalent K reading) in diopters (D). Solid = correlation line and dashed = bisector.
Figure 2
Figure 2
(a) Scatterplot showing correlation between 6 months postoperative Pentacam equivalent K readings (EKR) and real Km (Kr) in diopters (D). Solid = correlation line and dashed = bisector. (b) Bland and Altman plot showing correlation between 6 months postoperative Pentacam equivalent K readings (EKR) and real Km (Kr) in diopters (D), with 95% LoA (range: −1.96 sd to +1.96 sd).
Figure 3
Figure 3
(a) Scatterplot showing correlation between real Km (Kr) and K readings calculated with the previously published formula (Kc) in diopters (D). Solid = correlation line and dashed = bisector. (b) Bland and Altman plot showing correlation between real Km (Kr) and K readings calculated with the previously published formula (Kc) in diopters (D), with 95% LoA (range: −1.96 sd to +1.96 sd).
Figure 4
Figure 4
Scatterplot showing correlation between effective treatment at the corneal plane and keratometric difference (Δ) in equivalent K readings at 6 months follow-up, in diopters (D). Solid = correlation line and dashed = bisector.
See this image and copyright information in PMC

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