Refractive outcomes of toric intra-ocular lens implantation in cases of high posterior corneal astigmatism

Purpose: To evaluate whether the toric intra?ocular lens (IOL) power calculation based on total corneal astigmatism (TCA) in eyes with high posterior corneal astigmatism (PCA) could result in a systematic over?correction or under?correction after operation. Methods: The present study included a mono?centric retrospective study design. The data were collected from 62 consecutive eyes during uncomplicated cataract surgery by a single surgeon with a measured PCA of 0.50 diopters (D) or higher. Toric IOL calculations were made using TCA measurements. The eyes were grouped as either “with?the?rule” (WTR) or “against?the?rule” (ATR) on the basis of the steep anterior corneal meridian. The post?operative refractive astigmatic prediction error was analyzed 1 month post?operatively using the vector analysis by the Alpins method and double?angle plots method. Results: The correction indexes were 1.14 ± 0.29 in the ATR eyes and 1.25 ± 0.18 for the WTR eyes, indicating a tendency toward over?correction. The mean over?correction was 0.22 ± 0.52D in the ATR group and 0.65 ± 0.60D in the WTR group. The magnitude of error (ME) values were significantly different from the ideal value of zero in both groups (ATR: P = 0.03; WTR: P = 0.00). No significant difference in mean absolute error (MAE) in predicted residual astigmatism was found between ATR and WTR groups (0.61 ± 0.42 D versus 0.64 ± 0.39 D; P = 0.54). The ATR group yielded better results, with 48% <0.50D prediction error in the main analysis. Conclusions: The results suggested that in cases of high PCA, the toric IOL calculation, which was performed using TCA, may cause a potential over?correction in the ATR and WTR eyes. For ATR eyes, over?correction led to slight disruption of post?operative visual quality because of the “with?the?rule” residual astigmatism after operation. Therefore, we suggested using TCA for toric IOL calculation in ATR eyes.

Distribution of posterior corneal astigmatism and its effect on the calculation of Toric intraocular lens / 中华实验眼科杂志

Objective To analysis the distribution of posterior corneal astigmatism (PA) and evaluate the influence of keratometric astigmatism (KA) and total corneal astigmatism (TCA) on the calculation of Toric intraocular lens (Toric IOL) in patients with age-related cataract (ARC) and high corneal astigmatism.Methods An observational study design was adopted.Pentacam was used to measure 200 eyes of 181 patients with ARC and KA＞0.75 D in Affiliated Hospital of Nantong University from August 2016 to April 2017.KA,PA,TCA and anterior corneal astigmatism (AA) were recorded.The astigmatism magnitude and axis of PA was studied.The subjects were divided into astigmatism with the rule group,astigmatism against the rule group and oblique astigmatism group according to the axis of AA.The correlations of decomposition values between PA and AA or KA and TCA in each group were analyzed by Pearson linear correlation analysis.The difference of decomposition values between KA and TCA in each group was compared by paired sample t test.The type and axis of Toric IOL were calculated by online formula according to KA and TCA.This study followed the Declaration of Helsinki and written informed consent was obtained from each patient prior to any medical examination.Results The mean astigmatic magnitudes of PA was -0.32 D×93.1°.PA exceeded 0.5 D in 22 eyes (11％).The steepest posterior corneal meridian was vertically aligned in 163 eyes (81.5％).The decomposition value KP(0) and KP (45) of PA were positively correlated with those ofAA (r=0.480,P＜0.001;r=0.251,P＜0.001).The mean astigmatic magnitudes of KA and TCA were 1.44D×89.6° and 1.32 D×89.5° in astigmatism with the rule group,1.39 D×153.4° and 1.71 D×154.4° in astigmatism against the rule group and 1.13 D× 122.0° and 1.24 D× 124.2° in oblique astigmatism group.53 eyes (69.7％) had KA higher than TCA in astigmatism with the rule group.82 eyes (87.3％) had KA lower than TCA in astigmatism against the rule group;20 eyes (66.7％) had KA lower than TCA in oblique astigmatism group.There were significant differences in KP (0) between KA and TCA in different astigmatism groups (all at P＜0.001).The calculated Toric IOL type were inconsistent in 85 eyes(42.5％) and the calculated axis were inconsistent in 176 eye s (88.2％).Conclusions In patients with high corneal astigmatism,the astigmatism type of PA is mostly astigmatism against the rule.Ignoring the PA can lead to deviation of Toric IOL type selection and axis placement in some patients.For patients who cannot measure PA or TCA,the type of Toric IOL should be adjusted appropriately.

Analysis of related factors of the anterior corneal astigmatism axis and total corneal astigmatism axis in cataract patients / 国际眼科杂志(Guoji Yanke Zazhi)

AIM: To investigate the difference between anterior corneal astigmatism axis and total corneal astigmatism axis, and the related factors.?METHODS: The anterior corneal astigmatism axis and total corneal astigmatism axis in 789 patients(1141 eyes) of China Medical University Eye Hospital were detected by Petacam and recorded the corresponding age, value of astigmatism, anterior chamber depth, corneal thickness, refraction of cornea and anylized statistically.?RESULTS:We found age was positively correlated with the difference of the anterior corneal astigmatism axis and total corneal astigmatism axis(r=0. 139, P<0. 001). The value of astigmatism was negatively correlated with the difference of the anterior corneal astigmatism axis and total corneal astigmatism axis(r=-0. 293, P<0. 05). The anterior chamber depth was negatively correlated with the difference of the anterior corneal astigmatism axis and total corneal astigmatism axis ( r=-0. 067, P<0. 05). And the corneal thickness, refraction of cornea was not significantly correlated with the difference of the anterior corneal astigmatism axis and total corneal astigmatism axis.?CONCLUSION: There is significant difference in the anterior corneal astigmatism axis and total corneal astigmatism axis, and is positively correlated with age, and is negatively correlated with value of astigmatism and the depth of anterior chamber.

Comparison of Anterior, Posterior, and Total Corneal Astigmatism Measured Using a Single Scheimpflug Camera in Healthy and Keratoconus Eyes

PURPOSE: To compare the effect of posterior corneal astigmatism on the estimation of total corneal astigmatism using anterior corneal measurements (simulated keratometry [K]) between eyes with keratoconus and healthy eyes. METHODS: Thirty-three eyes of 33 patients with keratoconus of grade I or II and 33 eyes of 33 age- and sex-matched healthy control subjects were enrolled. Anterior, posterior, and total corneal cylinder powers and flat meridians measured by a single Scheimpflug camera were analyzed. The difference in corneal astigmatism between the simulated K and total cornea was evaluated. RESULTS: The mean anterior, posterior, and total corneal cylinder powers of the keratoconus group (4.37 ± 1.73, 0.95 ± 0.39, and 4.36 ± 1.74 cylinder diopters [CD], respectively) were significantly greater than those of the control group (1.10 ± 0.68, 0.39 ± 0.18, and 0.97 ± 0.63 CD, respectively). The cylinder power difference between the simulated K and total cornea was positively correlated with the posterior corneal cylinder power and negatively correlated with the absolute flat meridian difference between the simulated K and total cornea in both groups. The mean magnitude of the vector difference between the astigmatism of the simulated K and total cornea of the keratoconus group (0.67 ± 0.67 CD) was significantly larger than that of the control group (0.28 ± 0.12 CD). CONCLUSIONS: Eyes with keratoconus had greater estimation errors of total corneal astigmatism based on anterior corneal measurement than did healthy eyes. Posterior corneal surface measurement should be more emphasized to determine the total corneal astigmatism in eyes with keratoconus.

The Change in Corneal Astigmatism after Cataract Surgery in Patients with Small Amount of Astigmatism

PURPOSE: To analyze the change in posterior corneal astigmatism and total corneal astigmatism in patients with anterior corneal astigmatism less than 1.0 diopter (D). METHODS: In the present study we evaluated 52 eyes with anterior corneal astigmatism less than 1.0 D. Patients were divided into 2 groups according to steep axis: Group 1 included 33 eyes with within-the-rule (WTR) astigmatism and Group 2 included 19 eyes with against-the-rule (ATR) astigmatism. Anterior, posterior and total corneal astigmatism were measured using Scheimpflug imaging (Pentacam(R)). RESULTS: In Group 1, preoperative anterior astigmatism, posterior astigmatism and total astigmatism were 0.55 +/- 0.44 D, 0.31 +/- 0.14 D and 0.30 +/- 0.72 D, respectively. At postoperative 2 months, anterior astigmatism, posterior astigmatism and total astigmatism were 0.51 +/- 0.67 D, 0.31 +/- 0.15 D and 0.35 +/- 0.81 D, respectively. There was no statistically significant difference between preoperative and postoperative anterior, posterior and total corneal astigmatism in Group 1. In Group 2, preoperative anterior astigmatism, posterior astigmatism and total astigmatism were -0.48 +/- 0.46 D, 0.26 +/- 0.09 D and -0.51 +/- 0.65 D, respectively. At postoperative 2 months, anterior astigmatism, posterior astigmatism and total astigmatism were -0.17 +/- 0.68 D, 0.25 +/- 0.13 D and -0.30 +/- 0.55 D, respectively. There was no statistically significant difference between preoperative and postoperative anterior, posterior and total corneal astigmatism in the 2 groups. There was no statistical correlation between preoperative posterior corneal astigmatism and postoperative 2 months total corneal astigmatism. After vector analysis, surgically induced astigmatism (SIA) of the anterior and total astigmatism in Group 1 were 0.03 D @ 30degrees and 0.07 D @ 74degrees, respectively, and in Group 2 were 0.27 D @ 100degrees and 0.36 D @ 86degrees, respectively. CONCLUSIONS: In patients with preoperative total corneal astigmatism less than 1.0 D, posterior corneal astigmatism had a small effect on postoperative total corneal astigmatism.