Surgically Induced Corneal Astigmatism Research Articles

Effects of clear corneal incision location and morphology on corneal surgically induced astigmatism and higher-order aberrations after ICL V4c implantation

PurposeTo evaluate the effects of clear corneal incision (CCI) location and morphology on corneal surgically induced astigmatism (SIA) and higher-order aberrations (HOAs) in patients receiving implantable collamer lens (ICL V4c) implantation.MethodsThis retrospective study classified right eyes that underwent ICL implantation into two groups based on temporal or superior CCI. The Pentacam HR analyzer was used to measure the corneal astigmatism and HOAs. Analysis of the clear corneal incision (CCI) morphology, including incision width (Angle-W), incision length (IL), incision angles (Angle-En/Ex), and distance from the incision to corneal apex (Dis-En/Ex), was conducted using anterior segment optical coherence tomography (AS-OCT).ResultsThere were 75 eyes in the temporal CCI group and 47 eyes in the superior CCI group. Both groups showed satisfactory safety and efficacy postoperatively. In the temporal CCI group, Dis-En and Dis-Ex were considerably longer, whereas the superior CCI group displayed a significantly wider Angle-W. The anterior and posterior corneal SIA were comparable in both groups. Anterior corneal SIA was significantly correlated to Dis-En and Dis-Ex in the superior CCI group. Superior CCI caused a notable rise in corneal Z (3, 3), while temporal CCI led to increased Z (3, 1). CCI morphology was correlated to corneal Z (4, −4) and Z (4, 4) in the superior CCI group.ConclusionCCI locations caused slight variations in postoperative corneal SIA and HOAs following ICL implantation. Optimal postoperative visual outcomes may be better achieved with a CCI design featuring an increased distance from the corneal centroid and a decreased Angle-W.

Analysis of Posterior Corneal Surgically Induced Astigmatism Following Cataract Surgery With a 1.8-mm Temporal Clear Corneal Incision.

To determine posterior corneal surgically induced astigmatism (SIA) when using a temporal clear corneal incision and the IOLMaster 700 (Carl Zeiss Meditec AG) for biometric measurements and to determine whether posterior corneal SIA can be predicted from preoperative data. A total of 258 consecutive eyes of 258 patients underwent cataract surgery with a 1.8-mm temporal clear corneal incision. Biometry measurements were taken preoperatively and 6 weeks postoperatively using the IOLMaster 700. Using vector analysis, the SIA of the posterior cornea was calculated. The centroid of posterior corneal SIA was 0.01 diopters (D) @159 ± 0.14 D. The mean posterior corneal SIA was 0.12 D ± 0.07 D. Posterior corneal SIA magnitude was 0.25 D or less in 95% of patients. There was no correlation found between posterior corneal SIA magnitude and any preoperative measurement. The authors suggest not adjusting for posterior corneal SIA if using a small caliber, temporal incision. It was not possible to predict posterior corneal SIA from preoperative biometric measurements. [J Refract Surg. 2023;39(6):381-386.].

Changes in Vector Astigmatism After Superotemporal Versus Temporal Clear Corneal Incision Cataract Surgery.

To investigate vector and refractive astigmatism changes after superotemporal versus temporal clear corneal incision cataract surgery. Patients were diagnosed with age-related cataract with corneal astigmatism < 1.5 diopters (D) and were divided into two groups: superotemporal incision (R group) and temporal incision (L group). Uncorrected visual acuity, manifest refraction, corneal topography, anterior segment optical coherence tomography was performed pre- and six months postoperatively. Total ocular astigmatism, corneal astigmatism, vector of surgically induced corneal astigmatism (SICA), non-corneal ocular residual astigmatism (N-CORA), postoperative intraocular lens decentration and tilt were analyzed. Results: Thirty-eight subjects were included: 21, R group; 17, L group. After surgery, the N-CORA decreased significantly from 1.17±0.72 D to 0.73±0.47 D in all patients (P=0.001), 1.03±0.52 D to 0.70±0.40 D in the R group (P=0.005) and 1.35±0.90 D to 0.78±0.55 D in the L group (P=0.033). Significant differences between t:he R and L groups were found in the postoperative meridian of anterior corneal astigmatism (75.95±52.50 vs 116.79±47.29; P=0.017), total corneal astigmatism (51.65±42.75 vs 95.20±57.32; P=0.011), J45 change vector of SICA in the anterior cornea (-0.10±0.18 vs 0.00±0.11; P=0.048) and total cornea surface (-0.14±0.17 vs 0.03±0.12; P=0.001). Conclusion: The N-CORA decreased significantly after cataract surgery. Superotemporal and temporal incisions caused differences in the meridian components of oblique astigmatism in some patients but did not have a significant effect on the magnitude of corneal astigmatism.

Clinical observations of EVO-ICL implantation and changes in corneal astigmatism using a modified technique

BackgroundImplantable collamer lens (ICL) surgery techniques are constantly progressing. The purpose of this study was to investigate the application effect of the modified technique and its impact on the change in corneal astigmatism in EVO-ICL surgery.MethodsThe analysis of retrospective cohort data included 153 eyes of 81 patients with myopia from July 2018 to May 2020. An EVO-ICL was inserted by modified surgical skills, including a single 3.0 mm corneal incision and no ophthalmic viscosurgical device (OVD) before the insertion of the ICL (modified technique group: 41 cases, 80 eyes) and standard procedure (standard technique group: 40 cases, 73 eyes). Early postoperative intraocular pressure (IOP) was monitored at 2 and 24 h. IOP, corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), vault, and anterior chamber depth (ACD) were measured 1, 6, and 12 months following the initial examination. The corneal endothelial cell density (ECD) was monitored at 6 and 12 months after the operation. Surgically induced astigmatism (SIA) in the total, anterior, and posterior corneal surfaces was analysed 1 month after the operation.ResultsNo serious complications were detected. The two groups had no difference in visual outcomes, ICL vaults, or ACD at any time point (P > 0.05). Two hours postoperatively, IOP was significantly lower in the modified technique group (16.22 ± 2.22 vs. 18.37 ± 1.92 mmHg, P < 0.05) than in the standard technique group. IOP decreased gradually after 24 h to preoperative levels. The postoperative IOP remained stable over a 12-month period. The ECD at 6 and 12 months was not significantly different between the groups (P > 0.05). SIA in the total, anterior, and posterior corneal surfaces were assumed to have no clinically meaningful differences between groups at one month after operation (P > 0.05).ConclusionsThe modified technique is efficient and safe, producing comparable visual and structural outcomes without adversely affecting ECD, and reduces fluctuations in IOP at the early postoperative stages. The auxiliary incision in the standard technique does not increase corneal SIA, which is also a factor to consider for inexperienced surgeons.

Comparison of corneal surgically induced astigmatism calculations based on keratometry measurements made by 2 biometric devices.

To compare calculated corneal surgically induced astigmatism (SIA) by means of anterior-based keratometry (K) and total keratometry (TK) measurements made by 2 biometric devices. Ophthalmology Department, Shaare Zedek Medical Center, Jerusalem, Israel. Retrospective, consecutive case series. The medical records of patients who had undergone cataract surgery through a 2.4 mm temporal clear corneal incision by a single surgeon between March 2018 and November 2020 were retrospectively reviewed. Patients for whom there were preoperative and postoperative K measurements assessed by 2 biometric devices, optical low-coherence reflectometry (OLCR) (Lenstar LS900, Haag-Streit, software v. eye suite i/9.1.0.0) and swept-source optical coherence tomography (SS-OCT) (IOLMaster700, Carl Zeiss Meditec AG, software v. 1.80.6.60340), were identified. Corneal SIA (mean vector value) was calculated by vector analysis for 3 groups: SS-OCT(K), SS-OCT(TK), and OLCR(K). Bivariate analyses were applied for comparisons. 147 eyes of 123 patients (73 right eyes and 74 left eyes) were enrolled in the study. The right eye corneal SIA values were 0.09 diopters (D) @ 136 degrees, 0.09 D @ 141 degrees, and 0.07 D @ 123 degrees for the SS-OCT(K), SS-OCT(TK), and OLCR, respectively. The corresponding left eye corneal SIA values were 0.13 D @ 120 degrees, 0.11 D @ 123 degrees, and 0.08 D @ 120 degrees. There were no statistically significant differences between the mean vector value and variance of the corneal SIA for the right (P = .78 and P = .65) and the left (P = .75 and P = .37) eyes of the 3 groups. Corneal SIA values were low (0.07 to 0.13 D) and similar for the SS-OCT and the OLCR biometric devices with standard K measurements. TK measurements yielded similar corneal SIA values compared with anterior corneal-based measurements.

Posterior Corneal Surface Changes After Pterygium Excision Surgery

To evaluate the effect of pterygium excision on the posterior corneal surface and analyze the factors associated with those changes. A prospective, interventional study including 33 eyes of 31 patients who underwent pterygium excision at the Tel Aviv Medical Center (Tel Aviv, Israel). Exclusion criteria included corneal dystrophy, pseudopterygium, corneal scarring, or previous ocular surgery in the treated eye. Data were obtained by using the Galilei dual Scheimpflug analyzer. Recorded posterior corneal data included steep keratometry, flat keratometry, mean keratometry, corneal astigmatism, best-fit sphere, and the squared eccentricity index (e). Posterior surgically induced astigmatism (SIA) was calculated to demonstrate the astigmatic effect of surgery. Anterior-segment high resolution optical coherence tomography was used to measure pterygium dimensions (depth and horizontal/vertical size). The mean age was 53.7 ± 16.7 years. Posterior corneal SIA was 0.9 ± 1.1 D (P < 0.001) and was significantly correlated with age (r = 0.568, P = 0.002), horizontal pterygium size (r = 0.387, P = 0.046), and preoperative posterior astigmatism (r = 0.688, P < 0.001). In a multivariable analysis, only age (coefficient = 0.010, P = 0.038) and preoperative posterior astigmatism (coefficient = 0.648, P = 0.002) remained significant. Pterygium dimensions were not significantly associated with SIA magnitude. Flat keratometry steepened by 0.5 ± 1.1 D (P = 0.019), mean keratometry steepened by 0.3 ±0.6 D (P = 0.035), posterior astigmatism was reduced by 0.4 ± 1.2 D (P = 0.072), and e decreased by 5.1 ± 17.3 (P = 0.021). Pterygium excision has a significant astigmatic effect on the posterior corneal surface. The astigmatic effect increases with age and with higher preoperative posterior astigmatism. Pterygium depth and size are not associated with the degree of surgical astigmatic effect.

Surgically induced astigmatism in canines following sutured dorsonasal vs dorsotemporal clear corneal incisions.

To investigate use of the Pentacam® HR for evaluation of surgically induced corneal astigmatism (SIA) in canines undergoing bilateral phacoemulsification and determine differences between dorsonasal and dorsotemporal clear corneal incisions. Client-owned canines undergoing bilateral phacoemulsification. Patients received anterior segment imaging pre-operatively, immediately post-operatively, and 2-4months post-operatively (follow-up). Total corneal refractive power was used to determine SIA. Surgically induced astigmatism was compared between right and left eyes, representing dorsotemporal and dorsonasal incisions, respectively. Repeated measures analyses were used between time points and paired t test compared SIA between eyes. Complete imaging series were obtained for seven patients. Follow-up imaging occurred at a median of 112days (range 60-132days) post-operatively. For repeated measures analyses, significant differences were found between pre- and immediate post-operative values (P<0.01), and between immediate post-operative and follow-up values (P<0.01). There was no significant difference between pre-operative and follow-up values. Surgically induced astigmatism was significantly different between right and left eyes, with values of 2.01 ± 1.24D and 3.05 ± 1.58D at 3mm radius (P < 0.05), and 2.04 ± 1.18D and 3.06 ± 1.27D at 4mm radius (P < 0.05) for dorsotemporal and dorsonasal incisions, respectively. Preliminary investigation revealed improvement of corneal SIA 2-4months post-operatively, but development of significantly more SIA in dorsonasal vs dorsotemporal incisions. This prompts consideration of patient or microscope rotation to create a more dorsotemporal incision when possible.

The effect of suture by absorbable material on corneal astigmatism after phacoemulsification

Objectives To investigate the effect of absorbable suture on surgically-induced corneal astigmatism in 3.0-mm sclera tunnel cataract surgeries. Methods Medical records of patients who underwent phacoemulsification cataract surgery using a 3.0-mm sclera tunnel incision made by a single surgeon were reviewed. Uncorrected distant visual acuity, corneal astigmatism and surgically-induced astigmatism were measured in 56 patients' eyes that underwent sclera tunnel cataract surgery with absorbable sutures (sutured group) and in 23 patients' eyes without sutures (unsutured group). Uncorrected visual acuity, intraocular pressure, slit lamp examination, and automated keratometry were evaluated preoperatively and at 3 days, 2 weeks, 4 weeks, and 8 weeks after cataract operation. Results There were no significant differences in preoperative average uncorrected distant visual acuity of the two groups (sutured group: 0.79 ± 0.64, unsutured group: 0.68 ± 0.72, P = 0.145). Corneal astigmatism measured using keratometry in the sutured and unsutured group at postoperative day 3 were 2.27 ± 2.12 D versus 0.83 ± 0.55 D at ( P &amp;lt; 0.001), a difference which had disappeared after 4 weeks. Surgically induced astigmatism using the Holladay and Vector methods showed similar outcomes, suggesting that the sutured group exhibited higher astigmatism compared with the unsutured group until 2 weeks post-surgery. Conclusions TPatients undergoing scleral tunnel cataract surgery with absorbable sutures have greater surgically induced astigmatism, especially in the early postoperative period, compared with those without sutures. However, this surgically induced astigmatism due to absorbable sutures in scleral tunnel cataract surgery is temporary and disappears at 4 weeks post-surgery.

Improving the Toric Intraocular Lens Calculation by Considering Posterior Corneal Astigmatism and Surgically-induced Corneal Astigmatism.

PurposeTo investigate the effect of surgically induced corneal astigmatism (SICA) and total corneal astigmatism (TCA) estimation on the anterior corneal astigmatism (ACA)-based toric intraocular lens (IOL) calculation.MethodsData from preoperative and postoperative corneal astigmatism, postoperative visual acuities, and refractive outcomes were collected. The incision was superior in with the rule anterior corneal astigmatism (WTRA) eyes and temporal in against the rule anterior corneal astigmatism eyes. The following five methods of calculating the toric IOL were compared: (1) ACA only and estimated SICA; (2) ACA with a fixed posterior corneal astigmatism (PCA) and estimated SICA; (3) ACA with a fixed PCA value and actual SICA; (4) and (5) TCA derived from the regression equations of ACA and actual SICA. The residual astigmatism was simulated. The Alpins method was used to analyze the astigmatism.ResultsSixty eyes from 46 patients were enrolled. Thirty eyes had WTRA and the other thirty had against the rule anterior corneal astigmatism. The vector and arithmetic means of the difference vector decreased when the information regarding the actual SICA and PCA was added to the calculation (from 0.59 diopters [D] @ 87.5° to 0.15 D @ 48.5°, and from 0.95 ± 0.53 to 0.71 ± 0.63 D, respectively; p < 0.001). The mean difference vector across the whole sample was lowest using model 5. The correction index was significantly closest to 1.0 in the WTRA group.ConclusionsResearchers may improve the accuracy of post-implantation predictions by calculating toric IOL using exact SICA and TCA, with consideration of the PCA derived from the regression equation of ACA.

Wound stability and surgically induced corneal astigmatism after transconjunctival single-plane sclerocorneal incision cataract surgery.

To compare intraocular pressure (IOP) immediately after cataract surgery, and surgically induced corneal astigmatism (SIA) and corneal shape changes between eyes with transconjunctival single-plane sclerocorneal incisions (TSSIs) and eyes with clear corneal incisions (CCIs). Bilateral eyes of 64 patients undergoing phacoemulsification were randomized to undergo 2.4-mm temporal TSSI or CCI. IOP was measured preoperatively, and in the immediate postoperative periods. SIA was determined using vector analysis, and corneal shape changes and irregular astigmatism were evaluated using a videokeratography preoperatively, and in the early postoperative periods. Wound hydration was performed in 23 eyes (35.9%) of the TSSI group and in 60 (93.8%) of the CCI group (P<0.0001). Mean IOP was significantly higher in the TSSI group than in the CCI group at 30, 60, and 120min postoperatively (P≤0.0179). SIA tended to be smaller in the TSSI group than the CCI group, but the difference was not significant. The higher order irregular astigmatism was smaller in the TSSI group than in the CCI group at 2days (P=0.0312). The videokeratography revealed a wound-related flattening postoperatively in both groups; this change disappeared within 4weeks in the TSSI group, whereas it persisted until 12weeks in the CCI group. IOP was significantly higher immediately after TSSI than after CCI and required less wound hydration, suggesting better stability with TSSI. Higher order irregular astigmatism and wound-related corneal flattening were smaller after TSSI than after CCI in the early periods, suggesting that fewer corneal shape changes with TSSI.

Comparison of surgically induced astigmatism between femtosecond laser and manual clear corneal incisions for cataract surgery

To assess the surgically induced corneal astigmatism (SIA) introduced by femtosecond laser-assisted clear corneal incisions (CCIs) for cataract extraction and to compare it with the SIA of manually created CCIs. Bascom Palmer Eye Institute, Miller School of Medicine, Miami, Florida, USA. Prospective nonrandomized comparative case series. Eyes received femtosecond laser-assisted CCIs (Group 1) or manual CCIs (Group 2). The surgical plan included 1 primary and 1 secondary port; the sites of the incisions were the same in both groups and were diametrically opposed between the right eye and left eye. The SIA was assessed using the preoperative and 1-month postoperative keratometric values obtained from corneal topography examinations. This study included 72 eyes of 68 patients with a mean age of 69.0 years ± 9.87 (SD) (range 36 to 90 years). Thirty-six eyes received femtosecond laser-assisted CCIs (Group 1) and 36 received manual CCIs (Group 2). The mean preoperative topographic corneal astigmatism was -1.19 ± 0.68 diopters (D) (range 0 to 2.50 D) and -0.92 ± 0.63 D (range 0.10 to 2.45 D) for Group 1 and Group 2, respectively, whereas, 1 month after cataract surgery, it was -1.16 ± 0.63 D (range 0.20 to 2.57 D) and -0.95 ± 0.64 D (range 0.21 to 2.37 D), respectively. Multivariate vector analysis revealed no statistically significant difference between the 2 groups for preoperative astigmatism, postoperative astigmatism, and SIA (P > .05 for all comparisons between Group 1 and Group 2). Femtosecond laser-assisted and manual corneal incisions for cataract surgery did not appear to significantly alter corneal astigmatism, whereas they showed comparable SIA. Drs. Yoo and Donaldson are speakers for and consultants to Alcon Surgical, Inc., and Abbott Medical Optics, Inc. No other author has a financial or proprietary interest in any material or method mentioned.

Surgically induced corneal astigmatism after fornix‐based trabeculectomy

PurposeTo evaluate the degree of surgically induced corneal astigmatism (SIA) following trabeculectomy and to investigate the relation of SIA with long‐term reduction of intraocular pressure (IOP).MethodsFourty‐four eyes of 44 patients undergoing fornix‐based trabeculectomy were included in this single center, prospective trial. IOP, visual acuity (VA), corneal astigmatism, medication use and adverse events were recorded preoperatively and at 1, 3, 6 and 18 months postoperatively. Changes in corneal astigmatism were analysed using vector analysis. Pre‐ and postoperative parameters were compaired using one‐sample t‐test. Correlation between SIA and IOP were assessed using Pearson correlation coefficients.ResultsVector analysis of corneal astigmatism revealed a significant increase in with‐the‐rule corneal astigmatism, reaching a maximum at 1 month postoperatively (1.15 ± 0.8 D, P &lt; 0.001) followed by a gradual decline (0.87 ± 0.8 D, P &lt; 0.001 at month 18). SIA at 1 month showed a borderline significant correlation with IOP reduction at 3 months (r = 0.315, P = 0.051). SIA at 3, 6 and 18 months did not correlate with reduction in IOP (P &gt; 0.05). After a transient decline at 1 month after surgery, VA recovered to preoperative values at month 3 without need for adjustment of the optical correction.ConclusionsFornix‐based trabeculectomy induces statistically significant with‐the‐rule astigmatism without affecting long term VA. In our population, maximum SIA, measured at 1 month postoperatively, showed a borderline significant correlation with reduction of IOP at 3 months.

An analysis of the factors influencing the residual refractive astigmatism after cataract surgery with toric intraocular lenses.

To investigate the influence of posterior corneal astigmatism, surgically-induced corneal astigmatism (SICA), intraocular lens (IOL) orientation, and effective lens position on the refractive outcome of toric IOLs. Five models were prospectively investigated. Keratometric astigmatism and an intended SICA of 0.2 diopters (D) were entered into model 1. Total corneal astigmatism, measured by a rotating Scheimpflug camera, was used instead of keratometric astigmatism in model 2. The mean postoperative SICA, the actual postoperative IOL orientation, and the influence of the effective lens position were added, respectively, into models 3, 4, and 5. Astigmatic data were vectorially described by meridional and torsional powers. A set of equations was developed to describe the error in refractive astigmatism (ERA) as the difference between the postoperative refractive astigmatism and the target refractive astigmatism. We enrolled 40 consecutive eyes. In model 1, ERA calculations revealed significant cylinder overcorrection in with-the-rule (WTR) eyes (meridional power = -0.59 ± 0.34 D, P < 0.0001) and undercorrection in against-the-rule (ATR) eyes (0.32 ± 0.42 D, P = 0.01). When total corneal astigmatism was used instead of keratometric astigmatism (model 2), the ERA meridional power decreased in WTR (-0.13 ± 0.42 D) and ATR (0.07 ± 0.59 D) eyes, both values being not statistically significant. Models 3 to 5 did not lead to significant improvement. Posterior corneal astigmatism exerts the highest influence on the ERA after toric IOL implantation. Basing calculations on total corneal astigmatism rather than keratometric astigmatism improves the prediction of the residual refractive astigmatism.

Analysis of surgically induced astigmatism on the posterior surface of the cornea.

To measure surgically induced astigmatism (SIA) on the posterior surface of the cornea using Scheimpflug-based keratometry on eyes with with-the-rule astigmatism. Repeated Scheimpflug-based keratometry was obtained preoperatively and a mean of 8.65 weeks postoperatively following superior clear corneal incisions. Differences in the keratometric values and SIA were determined on the anterior and posterior surfaces separately and the data were analyzed. The study included 88 eyes of 88 patients (age range: 46.4 to 87.5 years), with the steepest total corneal meridian between 75° and 105°. Preoperatively, the magnitude of the anterior and posterior corneal astigmatism was 0.74 ± 0.44 and 0.29 ± 0.14 diopters (D), respectively, which was greater than 0.5 D in 10 eyes (11.36%). The difference between preoperative and postoperative keratometric data on the posterior surface was significant, as was the difference between the preoperative and postoperative posterior astigmatism. The mean magnitude of posterior corneal SIA was 0.32 ± 0.29 D, which was 0.5 D or greater in 22 eyes (25.00%). A statistically significant correlation was observed between the diopter of the preoperatively measured posterior corneal astigmatism and the postoperative SIA on the posterior surface (r = 0.34, P = .001). The correlation was not significant between SIA on the anterior and posterior surfaces (r = 0.10, P = .36). SIA on the posterior surface of the cornea may have a significant role, especially in cases of toric intraocular lens implantation. Posterior corneal astigmatism and SIA may have a significant clinical impact on more precise planning of cataract surgeries.

Influence of corneal biomechanical properties on surgically induced astigmatism in cataract surgery

To perform an overall follow-up of the morphologic, optical, and biomechanical properties of the cornea to determine new parameters influencing the refractive outcomes of cataract surgery. Clinical study. Patients scheduled for cataract surgery were assessed for surgically induced corneal astigmatism (SIA) and higher-order aberrations, (HOAs) using a Scheimpflug rotating camera (Pentacam) together with corneal imaging by optical coherence tomography (Spectralis) and biomechanical analysis by the Ocular Response Analyzer preoperatively and 1, 7, and 30 days postoperatively. The central and peripheral corneal thicknesses; incision width, length, and architecture; corneal hysteresis (CH); and corneal resistance factor (CRF) were computed to identify new parameters influencing corneal optical changes that determine the final refractive result. The study enrolled 40 patients (40 eyes). The SIA and HOAs were significantly lower after microincision surgery (≤ 2.2 mm) than after small-incision surgery (2.75 mm) (both P<.01). The CRF was significantly reduced with a direct corneal incision compared with a constructed incision (P<.01). Multivariate analysis showed that SIA was correlated not only with incision width (P<.05) but also with preoperative CH (P<.01). Corneal 3rd-order trefoil depended on incision width (P<.01). In addition to the well-known influence of incision size on SIA, CH also modulates optical changes. The biomechanical features of the cornea should be taken into account preoperatively to better predict the refractive outcomes of cataract surgery.

Vector Analysis of Corneal and Refractive Astigmatism Changes Following Toric Pseudophakic and Toric Phakic IOL Implantation

To determine the efficacy of the astigmatism correction following toric intraocular lens (IOL) and toric phakic IOL (pIOL) implantation in eyes with no previous ocular surgery and in postkeratoplasty (PKP) eyes. In addition, changes in corneal astigmatism were determined. Astigmatism was analyzed in 35 eyes with an AcrySof toric IOL, 35 eyes with an Artiflex toric pIOL, 50 eyes with an Artisan toric pIOL, and 40 PKP eyes with an Artisan toric pIOL. Refractive astigmatism was analyzed by using Alpins method. Surgically induced corneal astigmatism (SICA) was determined following a superior 2.2-mm, 3.4-mm, or 5.4-mm incision. Follow-up was 12 months. Following toric IOL implantation, the index of success was 0.14 and overall residual astigmatism, 0.37 diopter (D). Following toric pIOL implantation, the index of success was 0.32 (Artiflex) and 0.18 (Artisan), and overall residual astigmatism was approximately 0.60 D. In PKP eyes, Artisan pIOLs resulted in an index of success of 0.28 and overall residual astigmatism of 1.56 D. The SICA, following 2.2-mm, 3.4-mm, 5.4-mm (normal eyes), and 5.4-mm (PKP eyes) incisions, was -0.25 ± 0.42 D (P = 0.108), -0.31 ± 0.43 D (P < 0.001), -0.48 ± 0.55 D (P < 0.001), and -0.49 ± 1.48 D (P = 0.035), respectively. Toric IOLs and pIOLs provide an effective astigmatism correction. Incorporating the SICA into the toric IOL power calculation may further increase their effectiveness. Therefore, incorporation of 0 D, -0.30 D, or -0.50 D of SICA for a 2.2-, 3.4-, or 5.4-mm superior incision, respectively, is recommended.

Estimation accuracy of surgically induced astigmatism on the cornea when neglecting the posterior corneal surface measurement

To evaluate the accuracy of corneal surgically induced astigmatism (SIA) estimation when neglecting the posterior corneal surface measurement. Fifty right eyes undergoing phacoemulsification were measured with a rotating Scheimpflug camera (Pentacam; Oculus Inc., Wetzlar, Germany) both before and after surgery. Clear corneal incisions with one suture were used in the phacoemulsification surgery. The keratometric corneal SIA (KSIA) was derived using the anterior corneal surface measurement and the keratometric index (1.3375) while neglecting the posterior corneal surface measurement. The Pentacam-derived total corneal SIA (PSIA) was derived by vergence tracing and polar value analysis [KP(135) and KP(180)] of the measurements on both corneal surfaces. The mean arithmetic estimation errors of the KSIA for the PSIA were 0.16 ± 0.32 (-0.52 to 1.14) D for the KP(135), and -0.02 ± 0.30 (-0.75 to 1.29) D for the KP(180). There was a significant difference between the KP(135) components of the KSIA and PSIA. Bivariate analysis revealed a statistically significant difference between the combined means of the KSIA and PSIA. Overall, 24% had either a KP(135) component of the KSIA that differed by > 0.50 D from that of the PSIA or a KP(180) component of the KSIA that differed by > 0.50 D from that of the PSIA. The blurring strength caused by neglecting the posterior corneal measurement was > 0.50 D in 24% of eyes. Neglecting the posterior corneal surface measurement may lead to significant deviation in the corneal SIA estimation after phacoemulsification in a proportion of eyes.

Factors influencing the accuracy of the SRK formula in the intraocular less power calculation.

Several intraocular lens (IOL) power calculation formulas (either theoretical or empirical) are used to determine the emmetropic IOL power) The Sanders-Retzlaff-Kraff (SRK) linear regression formula is among the most widely recognized empirical ones. In the present study intraocular lens power calculation aiming at emmetropia was performed, using SRK formula, in 145 cataractous eyes undergoing lens implantation. The final refraction was evaluated at 8 to 12 months after surgery. The purpose of this study was the identification and quantitative evaluation of the factors which influence significantly the accuracy of SRK in the intraocular lens power calculation. The following factors were studied: (1) the error in preoperative biometry with regard to the difference between post and preoperative axial length measurements, (2) the position of the implantation of the intraocular lens (anterior versus posterior chamber), (3) the intraocular lens style, (4) the intraocular lens power level, (5) the preoperative corneal astigmatism, (6) the surgically induced corneal astigmatism, and (7) the postoperative astigmatism. Multiple regression and stepwise regression analysis showed a strong correlation (R2 = 0.65; p < 0.001) between postoperative refractive error (Rf) and error in preoperative biometry (delta AL), surgically induced corneal astigmatism (SIA) and postoperative astigmatism (Ap) only. This correlation is expressed by the following equation: Rf = 0.07 -2.55 delta AL -0.42 SIA + 0.34 Ap. This equation indicates the quantitative effect of each factor on the accuracy of the SRK formula, by defining the pattern of the fluctuations of the amount or state (myopic or hyperopic) of refractive error induced by changes of variables delta AL, SIA and Ap.