Evaluation of Posterior Astigmatism Measured With Scheimpflug Imaging

Németh, Gábor; Berta, András; Lipécz, Ágnes; Hassan, Ziad; Szalai, Eszter; Módis, László

doi:10.1097/ico.0000000000000238

Cited by 40 publications

(40 citation statements)

References 27 publications

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“…The magnitude of posterior corneal astigmatism in the high-myopia group was –0.29 ± 0.17 D, which agrees well with the values recorded in normal eyes [10,13,16]. Among the different age groups, however, the mean posterior corneal astigmatism was higher in patients aged 40–50 years (–0.40 ± 0.20 D) than in the older two age groups (–0.25 ± 0.15 D, 51–60 years; and –0.28 ± 0.17 D, ≥ 61 years).…”

Section: Discussionsupporting

confidence: 87%

“…Previous studies have reported a mean magnitude of posterior corneal astigmatism of −0.30 D [10]. Furthermore, the anterior corneal surface shifted from with-the-rule (WTR) to against-the-rule (ATR) astigmatism with age, whereas the posterior corneal surface continued to show ATR astigmatism in most cases [10–16]. Therefore, patient-specific posterior corneal astigmatism measurements are required to estimate total corneal astigmatism.…”

Section: Introductionmentioning

confidence: 99%

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Posterior Corneal Characteristics of Cataract Patients with High Myopia

et al. 2016

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PurposeTo evaluate the characteristics of the posterior corneal surface in patients with high myopia before cataract surgery.MethodsWe performed a cross-sectional study at the Eye and ENT Hospital of Fudan University, Shanghai, China. Corneal astigmatism and axial length were measured with a rotating Scheimpflug camera (Pentacam) and partial coherence interferometry (IOLMaster) in a high-myopia study group of 167 eyes (axial length ≥ 26 mm) and a control group of 150 eyes (axial length > 20 mm and < 25 mm).ResultsTotal corneal astigmatism and anterior corneal astigmatism values were higher in the high-myopia group than in the control group. There was no significant difference in posterior corneal astigmatism between the high-myopia study group and the control group. In the study group, the mean posterior corneal astigmatism (range 0 – −0.9 diopters) was –0.29 diopters (D) ± 0.17 standard deviations (SD). The steep corneal meridian was aligned vertically (60°–120°) in 87.43% of eyes for the posterior corneal surface, and did not change with increasing age. There was a significant correlation (r = 0.235, p = 0.002) between posterior corneal astigmatism and anterior corneal astigmatism, especially when the anterior corneal surface showed with-the-rule (WTR) astigmatism (r = 0.452, p = 0.000). There was a weak negative correlation between posterior corneal astigmatism and age (r = –0.15, p = 0.053) in the high-myopia group. Compared with total corneal astigmatism values, the anterior corneal measurements alone overestimated WTR astigmatism by a mean of 0.27 ± 0.18 D in 68.75% of eyes, underestimated against-the-rule (ATR) astigmatism by a mean of 0.41 ± 0.28 D in 88.89% of eyes, and underestimated oblique astigmatism by a mean of 0.24 ± 0.13 D in 63.64% of eyes.ConclusionsPosterior corneal astigmatism decreased with age and remained as ATR astigmatism in most cases of high myopia. There was a significant correlation between posterior corneal astigmatism and anterior corneal astigmatism when anterior corneal astigmatism was WTR. If posterior corneal astigmatism is not accounted for when selecting toric intraocular lenses for high-myopia patients, the use of anterior corneal astigmatism measurements alone will lead to overestimation of WTR astigmatism and underestimation of ATR and oblique astigmatism.

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Section: Discussionsupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Posterior Corneal Characteristics of Cataract Patients with High Myopia

et al. 2016

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“…Anterior corneal astigmatism (AA) is the astigmatism value arising from the anterior corneal surface alone and calculated as the difference in simulated keratometry values (calculated using the standard keratometric index (1.3375) and the radius of anterior corneal curvature) between the steepest and the flattest meridians [13–16]. …”

Section: Methodsmentioning

confidence: 99%

“…The posterior corneal astigmatism is defined as the difference in keratometry values between the flattest and steepest meridians, which were calculated using the radius of posterior corneal curvature and the refractive indices of the cornea (1.376) and aqueous humor (1.336) [13–16]. …”

Section: Methodsmentioning

confidence: 99%

Changes in Anterior, Posterior, and Total Corneal Astigmatism after Descemet Membrane Endothelial Keratoplasty

Alnawaiseh

Zumhagen

Rosentreter

et al. 2017

Journal of Ophthalmology

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Purpose. To evaluate changes in anterior, posterior, and total corneal astigmatism in patients after Descemet membrane endothelial keratoplasty (DMEK). Methods. We retrospectively included 29 eyes of 23 patients (age 67.6 ± 9.8 years, 13 female, 10 male) after DMEK surgery. The magnitude and axis orientation of anterior, posterior, and total corneal astigmatism before and after DMEK were determined using a rotating Scheimpflug system (Pentacam HR, Oculus). Results. The magnitude of anterior, posterior, and total corneal astigmatism in the central cornea did not change significantly after surgery. Before surgery, we found a significant correlation between the magnitudes of anterior and posterior corneal astigmatism (Spearman's correlation coefficient (rS) = 0.526, P = 0.003), while after surgery this correlation was no longer significant (rS = 0.038, P = 0.843). There was a significant correlation between the vector difference between preoperative and postoperative posterior astigmatism and the change in corneal pachymetry (rP = 0.47, P = 0.010). Conclusions. Posterior corneal astigmatism (especially the orientation) and therefore the relationship between anterior and total corneal astigmatism may change after DMEK. This should be considered to improve the accuracy of toric IOL power calculations following phakic DMEK or in combined procedures.

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“…[19] Bastig does not perfectly match the back element of TCPR4astig because Bastig is the back keratometric, not refractive, measurement on a ring of 15°, not 4 mm, around the corneal apex. [7,8] Although TCRP4astig and Bastig are calculated using different methods, ray tracing and the paraxial formula, respectively, such differences do not have much effect in normal eyes. [26] However, paraxial formula would be invalid compared with ray tracing if the posterior surface profile of the cornea were altered by refractive surgery.…”

Section: Discussionmentioning

confidence: 99%

Calculations of actual corneal astigmatism using total corneal refractive power before and after myopic keratorefractive surgery

Seo

Yang²,

Kim

et al. 2017

PLoS ONE

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PurposeTo calculate actual corneal astigmatism using the total corneal refractive astigmatism for the 4-mm apex zone of the Pentacam (TCRP4astig) and keratometric astigmatism (Kastig) before and after photorefractive keratectomy or laser in situ keratomileusisMethodsUncomplicated 56 eyes after more than 6 months from the surgery were recruited by chart review. Various corneal astigmatisms were measured using the Pentacam and autokeratometer before and after surgery. Three eyes were excluded and 53 eyes of 38 subjects with with-the-rule astigmatism (WTR) were finally included. The astigmatisms were investigated using polar value analysis. When TCRP4astig was set as an actual astigmatism, the efficacy of arithmetic or coefficient adjustment of Kastig was evaluated using bivariate analysis.ResultsThe difference between the simulated keratometer astigmatism of the Pentacam (SimKastig) and Kastig was strongly correlated with the difference between TCRP4astig and Kastig. TCRP4astig was different from Kastig in magnitude rather than meridian before and after surgery; the preoperative difference was due to the posterior cornea only; however, the postoperative difference was observed in both anterior and posterior parts. For arithmetic adjustment, 0.28 D and 0.27 D were subtracted from the preoperative and postoperative magnitudes of Kastig, respectively. For coefficient adjustment, the preoperative and postoperative magnitudes of Kastig were multiplied by 0.80 and 0.66, respectively. By arithmetic or coefficient adjustment, the difference between TCRP4astig and adjusted Kastig would be less than 0.75 D in magnitude for 95% of cases.ConclusionsKastig was successfully adjusted to TCPR4astig before and after myopic keratorefractive surgery in cases of WTR. For use of TCRP4astig directly, SimKastig and Kastig should be matched.

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Evaluation of Posterior Astigmatism Measured With Scheimpflug Imaging

Cited by 40 publications

References 27 publications

Posterior Corneal Characteristics of Cataract Patients with High Myopia

Posterior Corneal Characteristics of Cataract Patients with High Myopia

Changes in Anterior, Posterior, and Total Corneal Astigmatism after Descemet Membrane Endothelial Keratoplasty

Calculations of actual corneal astigmatism using total corneal refractive power before and after myopic keratorefractive surgery

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