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The effect of corneal irregularity on astigmatism measurement by automated versus ray tracing keratometry.

Roh HC, Chuck RS, Lee JK, Park CY - Medicine (Baltimore) (2015)

Bottom Line: The difference (Δ) between TCRPs and AK (ΔTCRPs-AK) was 0.43 ± 0.37 (TCRP3) and 0.39 ± 0.35 (TCRP4) diopters.Linear regression analysis revealed that age (P < 0.001), IR (P < 0.001), and AK (P < 0.001) were positively correlated with ΔTCRPs-AK.In highly irregular corneas (IR over 0.77 diopters: mean + 2 standard deviation), postoperative ORAs calculated using TCRPs were significantly lower than ORAs calculated using AK.

View Article: PubMed Central - PubMed

Affiliation: From the Department of Ophthalmology, Dongguk University, Ilsan Hospital, Goyang, Kyunggido, South Korea (HCR, CYP); and Department of Ophthalmology and Visual Sciences, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY, USA (RSC, JKL).

ABSTRACT
The aim of this study was to compare the effect of corneal irregularity on astigmatism assessment using automated keratometry (AK) (IOLMaster) versus ray tracing keratometry (Pentacam). This is an observational case series approved by the institutional review board of Dongguk University Hospital, Goyang, South Korea. A total of 207 eyes of 207 cataract patients were included. Preoperative corneal astigmatism was measured by both IOLMaster and Pentacam. Corneal irregularity index (IR) was calculated in Fourier analysis map of Pentacam. AK by IOLMaster and total corneal refractive power (TCRP, 3 mm and 4 mm zone analysis with pupil centered) by Pentacam were selected and the difference between the 2 measurements (delta Δ) was calculated using vector analysis. Ocular residual astigmatism (ORA) after cataract surgery was calculated by subtracting 6-month postoperative refractive astigmatism (RA) measurements from corresponding preoperative values (AK, TCRP3, and TCRP4). The mean irregularity index measured was 0.042 ± 0.019 mm (mean ± standard deviation) and was positively correlated with age and magnitude of corneal astigmatism (P < 0.001 and P < 0.05). The difference (Δ) between TCRPs and AK (ΔTCRPs-AK) was 0.43 ± 0.37 (TCRP3) and 0.39 ± 0.35 (TCRP4) diopters. Linear regression analysis revealed that age (P < 0.001), IR (P < 0.001), and AK (P < 0.001) were positively correlated with ΔTCRPs-AK. In highly irregular corneas (IR over 0.77 diopters: mean + 2 standard deviation), postoperative ORAs calculated using TCRPs were significantly lower than ORAs calculated using AK. Corneal irregularities significantly impact astigmatism assessment by IOLMaster (AK) and Pentacam (TCRPs). Compared with AK, TCRPs were more accurate in predicting postoperative residual astigmatism in highly irregular corneas.

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Related in: MedlinePlus

The screenshot of measurement in Pentacam. (A) The four refractive map. This map shows the anterior and posterior curvature and posterior astigmatism (red dotted area). Sagittal power, front and back elevation, and pachymetry were demonstrated in 4 separate graphics. (B) The screenshot for measurement of total corneal refractive power (TCRP). Several pupil centered zones with TCRP measurement are shown (red dotted area).
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Figure 1: The screenshot of measurement in Pentacam. (A) The four refractive map. This map shows the anterior and posterior curvature and posterior astigmatism (red dotted area). Sagittal power, front and back elevation, and pachymetry were demonstrated in 4 separate graphics. (B) The screenshot for measurement of total corneal refractive power (TCRP). Several pupil centered zones with TCRP measurement are shown (red dotted area).

Mentions: Preoperative corneal astigmatism was measured using IOLMaster (Carl Zeiss Meditec, Jena, Germany) and rotating Scheimpflug imaging (Pentacam® ver. 1.17r24; Oculus, Wetzlar, Germany). All measurements were performed in triplicate, and mean values were used for analysis. Among several keratometric values available in Pentacam, TCRP was selected and used for the analysis. Detailed information about TCRP is available at http://www.pentacam.com/sites/calc_corneal_power.php#ptop. TCRP is calculated by ray tracing, using a 3 (TCRP3) or 4-mm (TCRP4) diameter zone with the pupil center (Figure 1). AK from IOLMaster was used for analysis. Corneal irregularity index (IR) was automatically calculated in mm scale in Fourier analysis map, whereas total corneal irregular astigmatism at 4-mm zone is automatically calculated in μm scale in Cataract Pre-Op map of Pentacam. Mean anterior and posterior cornea curvature radii were measured by Pentacam at 3-mm central zone. And anterior to posterior curvature ratio was calculated. In the following, AK and TCRPs will be defined as the astigmatism obtained by their respective modalities when not otherwise specified.


The effect of corneal irregularity on astigmatism measurement by automated versus ray tracing keratometry.

Roh HC, Chuck RS, Lee JK, Park CY - Medicine (Baltimore) (2015)

The screenshot of measurement in Pentacam. (A) The four refractive map. This map shows the anterior and posterior curvature and posterior astigmatism (red dotted area). Sagittal power, front and back elevation, and pachymetry were demonstrated in 4 separate graphics. (B) The screenshot for measurement of total corneal refractive power (TCRP). Several pupil centered zones with TCRP measurement are shown (red dotted area).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4554023&req=5

Figure 1: The screenshot of measurement in Pentacam. (A) The four refractive map. This map shows the anterior and posterior curvature and posterior astigmatism (red dotted area). Sagittal power, front and back elevation, and pachymetry were demonstrated in 4 separate graphics. (B) The screenshot for measurement of total corneal refractive power (TCRP). Several pupil centered zones with TCRP measurement are shown (red dotted area).
Mentions: Preoperative corneal astigmatism was measured using IOLMaster (Carl Zeiss Meditec, Jena, Germany) and rotating Scheimpflug imaging (Pentacam® ver. 1.17r24; Oculus, Wetzlar, Germany). All measurements were performed in triplicate, and mean values were used for analysis. Among several keratometric values available in Pentacam, TCRP was selected and used for the analysis. Detailed information about TCRP is available at http://www.pentacam.com/sites/calc_corneal_power.php#ptop. TCRP is calculated by ray tracing, using a 3 (TCRP3) or 4-mm (TCRP4) diameter zone with the pupil center (Figure 1). AK from IOLMaster was used for analysis. Corneal irregularity index (IR) was automatically calculated in mm scale in Fourier analysis map, whereas total corneal irregular astigmatism at 4-mm zone is automatically calculated in μm scale in Cataract Pre-Op map of Pentacam. Mean anterior and posterior cornea curvature radii were measured by Pentacam at 3-mm central zone. And anterior to posterior curvature ratio was calculated. In the following, AK and TCRPs will be defined as the astigmatism obtained by their respective modalities when not otherwise specified.

Bottom Line: The difference (Δ) between TCRPs and AK (ΔTCRPs-AK) was 0.43 ± 0.37 (TCRP3) and 0.39 ± 0.35 (TCRP4) diopters.Linear regression analysis revealed that age (P < 0.001), IR (P < 0.001), and AK (P < 0.001) were positively correlated with ΔTCRPs-AK.In highly irregular corneas (IR over 0.77 diopters: mean + 2 standard deviation), postoperative ORAs calculated using TCRPs were significantly lower than ORAs calculated using AK.

View Article: PubMed Central - PubMed

Affiliation: From the Department of Ophthalmology, Dongguk University, Ilsan Hospital, Goyang, Kyunggido, South Korea (HCR, CYP); and Department of Ophthalmology and Visual Sciences, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY, USA (RSC, JKL).

ABSTRACT
The aim of this study was to compare the effect of corneal irregularity on astigmatism assessment using automated keratometry (AK) (IOLMaster) versus ray tracing keratometry (Pentacam). This is an observational case series approved by the institutional review board of Dongguk University Hospital, Goyang, South Korea. A total of 207 eyes of 207 cataract patients were included. Preoperative corneal astigmatism was measured by both IOLMaster and Pentacam. Corneal irregularity index (IR) was calculated in Fourier analysis map of Pentacam. AK by IOLMaster and total corneal refractive power (TCRP, 3 mm and 4 mm zone analysis with pupil centered) by Pentacam were selected and the difference between the 2 measurements (delta Δ) was calculated using vector analysis. Ocular residual astigmatism (ORA) after cataract surgery was calculated by subtracting 6-month postoperative refractive astigmatism (RA) measurements from corresponding preoperative values (AK, TCRP3, and TCRP4). The mean irregularity index measured was 0.042 ± 0.019 mm (mean ± standard deviation) and was positively correlated with age and magnitude of corneal astigmatism (P < 0.001 and P < 0.05). The difference (Δ) between TCRPs and AK (ΔTCRPs-AK) was 0.43 ± 0.37 (TCRP3) and 0.39 ± 0.35 (TCRP4) diopters. Linear regression analysis revealed that age (P < 0.001), IR (P < 0.001), and AK (P < 0.001) were positively correlated with ΔTCRPs-AK. In highly irregular corneas (IR over 0.77 diopters: mean + 2 standard deviation), postoperative ORAs calculated using TCRPs were significantly lower than ORAs calculated using AK. Corneal irregularities significantly impact astigmatism assessment by IOLMaster (AK) and Pentacam (TCRPs). Compared with AK, TCRPs were more accurate in predicting postoperative residual astigmatism in highly irregular corneas.

Show MeSH
Related in: MedlinePlus