J Korean Ophthalmol Soc.  2016 Jan;57(1):25-35. 10.3341/jkos.2016.57.1.25.

Analysis of Changes in Anterior, Posterior and Total Corneal Astigmatism after On-Axis Cataract Surgery

• Lee KI
• Park YL
• Kim HS

• KMID: 2213832
• DOI: http://doi.org/10.3341/jkos.2016.57.1.25

Abstract

PURPOSE
To assess the changes in anterior, posterior, and total corneal astigmatism after cataract surgery with on-axis clear corneal incision cataract surgery.
METHODS
This study included 48 eyes (24 eyes with 'with-the-rule [WTR]' and 24 eyes with 'against-the-rule [ATR]') that underwent phacoemulsification and intraocular lens insertion through on-axis clear corneal incision. The ATR group with vertically steep axis of posterior corneal astigmatism was divided into subgroups 1 and 2 for the opposite axis. Autorefraction, uncorrected and best-corrected visual acuities were measured. Corneal astigmatism (anterior, posterior and total) was measured using Pentacam(R) preoperatively and 1 week, 1 month, and 2 months postoperatively.
RESULTS
Multivariate linear regression analysis of preoperative data showed positive correlations among anterior, posterior and total astigmatism. Anterior corneal astigmatism showed a significant decrease in both WTR and ATR groups in all measured points (all p < 0.05). Posterior corneal astigmatism showed no statistical difference in the WTR group and ATR subgroup 2 (p > 0.05) and significant decrease in the ATR subgroup 1 (p < 0.05) at 2 months postoperatively. Total corneal astigmatism showed significant decrease 2 months after surgery in the WTR group and ATR subgroup 1 (all p < 0.05), but not in the ATR subgroup 2 (p > 0.05). According to correlation analysis based on trend line equations, 1.7 diopters of anterior astigmatism could expect 0.3 diopters of posterior astigmatism and 0.5 diopters of total astigmatism for the WTR group and 0.4 diopters of anterior astigmatism could expect 0.2 diopters of posterior astigmatism and 0.4 diopters of total astigmatism for the ATR group.
CONCLUSIONS
Considering the majority of cataract patients have vertically steep posterior corneal astigmatism, temporal incision for ATR patients is generally effective. Moreover, for patients with WTR astigmatism of more than 1.7 diopters or ATR astigmatism greater than 0.8 diopters, additional preoperative correction based on posterior astigmatism is needed for more precise prediction of postoperative total corneal astigmatism.

Keyword

Against-the-rule (ATR); On-axis incision; Posterior corneal astigmatism; With-the-rule (WTR)

MeSH Terms

Astigmatism*
Axis, Cervical Vertebra
Cataract*
Humans
Lenses, Intraocular
Linear Models
Phacoemulsification
Visual Acuity

Figure

• 

  Figure 1. Location of steep meridian on anterior and posterior corneal astigmatism. * Vertical alignment of the steep corneal meridian was seen in 50.0% for the anterior cornea; † Vertical alignment of the steep corneal meridian was seen in 83.3% for the posterior cornea.

• 

  Figure 2. Double-angle plots of corneal astigmatism and SIA using Pentacam® (Oculus, Wetzlar, Germany) from WTR group. Red dots denote for mean values of the amount and axis of corneal astigmatism for each group in (A) to (C). (A) Preoperative anterior (left), posterior (middle) and total (right) corneal astigmatism. (B) Postoperative 2 months anterior (left), posterior (middle) and total (right) corneal astigmatism. (C) SIA in anterior (left), posterior (middle) and total (right) corneal astigmatism. SIA = surgically in-duced astigmatism; WTR = with-the-rule.

• 

  Figure 3. Double-angle plots of corneal astigmatism and SIA using Pentacam® (Oculus, Wetzlar, Germany) from ATR subgroup 1. Red dots denote for mean values of the amount and axis of corneal astigmatism for each group in (A) to (C). (A) Preoperative ante-rior (left), posterior (middle) and total (right) corneal astigmatism. (B) Postoperative 2 months anterior (left), posterior (middle) and total (right) corneal astigmatism. (C) SIA in anterior (left), posterior (middle) and total (right) corneal astigmatism. SIA = surgi-cally induced astigmatism; ATR = against-the-rule.

• 

  Figure 4. Estimated cut-off value for preoperative consideration of posterior astigmatism in WTR group. (A) Trend line equation was calculated with preop.‘A’ and ‘P’. (B) Trend line equation was calculated with preop. ‘P’ and postop ‘T’ corneal astigmatism. WTR = with-the-rule; A = anterior; P = posterior; T = total; preop = preoperative; postop = postoperative; Post. = posterior astigmatism.

• 

  Figure 5. Correlations of magnitude of the ‘A’, ‘P’ and ‘T’ corneal astigmatism in WTR group. (A) Correlations of magnitude of preop ‘A’ and ‘T’ corneal astigmatism. (B) Correlations of magnitude of preop ‘A’ and postop ‘T’ corneal astigmatism. (C) Correlations of magnitude of preop ‘T’ and ‘P’ corneal astigmatism. Trend line equations for each correlation were calculated. WTR = with-the-rule; A = anterior; P = posterior; T = total; preop = preoperative; postop = postoperative.

• 

  Figure 6. Estimated cut-off value for preoperative consideration of posterior astigmatism in WTR group. (A) Trend line equation was calculated with preop. ‘A’ and ‘P’. (B) Trend line equation was calculated with preop. ‘P’ and postop ‘T’ corneal astigmatism. WTR = with-the-rule; A = anterior; P = posterior; T = total; preop = preoperative; postop = postoperative; Post. = posterior astigmatism; ATR = against-the-rule.

• 

  Figure 7. Correlations of magnitude of the ‘A’, ‘P’ and ‘T’ corneal astigmatism in WTR group. (A) Correlations of magnitude of preop ‘A’ and ‘T’ corneal astigmatism. (B) Correlations of magnitude of preop ‘A’ and postop ‘T’ corneal astigmatism. (C) Correlations of magnitude of preop ‘T’ and ‘P’ corneal astigmatism. Trend line equations for each correlation were calculated. WTR = with-the-rule; A = anterior; P = posterior; T = total; preop = preoperative; postop = postoperative.

Reference

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