Regular and irregular astigmatism after superior versus temporal scleral incision cataract surgery

Analysis of surgically induced astigmatism of the anterior, posterior, and total cornea after implantable collamer lens implantation: a comparative study between temporal and superior clear corneal incisions

BACKGROUND

To comparatively analyze the surgically induced astigmatism (SIA) of the anterior, posterior, and total corneas of eyes undertaking implantable collamer lens (ICL) implantation with temporal or superior corneal incisions.

METHODS

One hundred and nine eyes of 109 patients who received ICL implantation were recruited: 40 eyes had temporal incisions and 69 eyes had superior incisions. Total corneal refractive power (TCRP); simulated keratometry of the anterior (Sim-KAnt) and posterior (Sim-KPost) corneal curvature; and astigmatism of the anterior (CAAnt), posterior (CAPost), and total (CATCRP) cornea were recorded through a Pentacam preoperatively and 3 months postoperatively. The SIA of the anterior, posterior, and total cornea were also compared between the two groups.

RESULTS

There were no significant intergroup differences for TCRP, Sim-KAnt, Sim-KPost, CAAnt, CAPost, or CATCRP, preoperatively. However, values of CAAnt, CAPost, and CATCRP with temporal incision were significantly higher than those parameters with superior incision postoperatively. All of the SIA of the anterior, posterior, and total cornea were significantly lower for temporal incision than those with a superior incision (p < 0.001, p = 0.006 and p = 0.001 respectively). Meanwhile, the superior incisions created against-the-rule (ATR) astigmatism, and temporal incisions always induce with-the-rule (WTR) astigmatism in total cornea.

CONCLUSIONS

A superior incision may be suitable for correcting WTR astigmatism, while a temporal incision for correcting ATR astigmatism when using a non-toric ICL. Meanwhile, temporal incision could be a better choice with little preoperative astigmatism or that preoperative astigmatism would be corrected with toric ICLs.

TRIAL REGISTRATION

Registration number: ChiCTR2100051739. Prospectively registered: 01 October 2021.

Long Term Evaluation of Surgically Induced Astigmatism and Corneal Higher-Order Aberrations After 2.2 Mm Clear Corneal Incisions in Femtosecond Laser-Assisted Cataract Surgery: Temporal versus Superior Approach

Purpose

To assess long term changes of the surgically induced astigmatism (SIA) and corneal higher-order aberrations (HOAs) after 2.2 mm clear corneal incisions (CCIs) in femtosecond laser-assisted cataract surgery and compare them between 2 types of CCIs: temporal and superior approach.

Patients and Methods

Patients received the temporal CCIs (Group A) or the superior CCIs (Group B). Outcome measures included visual acuity, manifest refraction, corneal astigmatism, SIA, flattening effect, and corneal HOAs. Correlation between postoperative corneal HOA and SIA at each follow-up were analysed.

Results

This study assessed data from 106 eyes, of which 64 in Group A and 42 in Group B. The two groups had similar postoperative visual acuity of distance, intermediate and near (all P > 0.05). SIA and corneal HOAs were significantly lower in Group A than Group B in the early postoperative period, while there was no significant difference in the late postoperative period. At 6 months after surgery, the arithmetic mean of SIA over corneal 4mm zone was 0.33 ± 0.19D for temporal incision, and 0.37 ± 0.25D for superior incision. For Group A, the correlations of HOAs and SIA persisted from 1 week to 6 months after surgery. For Group B, the changes in corneal HOAs were significantly related to the SIA at 1 week and 1 month postoperatively.

Conclusion

This study suggested the consistency of increasing and recovering process of corneal HOAs and SIA after surgery. Compared to the superior incisions, temporal incisions might induce quicker corneal recovery and less change in SIA and corneal HOAs.

Comparative Evaluation of Astigmatic Changes Induced by Superior and Temporal Corneal Incisions in Sutureless Phacoemulsification Surgery: A Case Series

Background In cataract surgery, the effect of corneal incision astigmatism has been widely recognized for many years. The incision's size, shape, and location can all impact the patient's postoperative visual outcomes. Currently, phacoemulsification is considered the most preferred surgical technique for cataract extraction. However, there is still some debate about whether temporal incisions, which are smaller and considered nearly astigmatic neutral, result in more astigmatism than other incisions. As a result, it is important to continue studying the refractive changes induced by corneal incisions made at different sites during phacoemulsification surgery. Aim and objective To compare the incidence, extent, and course of postoperative astigmatic changes associated with superior versus temporal clear corneal incisions for sutureless phacoemulsification cataract surgery. Materials and method In this prospective study, 50 patients of the civil hospital in Gujrat with cataracts who underwent sutureless, small incision (2.8 mm) phacoemulsification surgery were included. The preoperative evaluation comprised visual acuity assessment, refraction, keratometry, fundus examination, and intraocular lens (IOL) power calculation. The superior incision was made in 25 patients, and the temporal incision was made in another 25 patients. Patients were examined preoperatively on day 1, at one week (day 7), after one month (day 30), and after two months (day 60). Result Postoperatively, two months (on day 60) postoperatively, in group A (superior approach), the mean surgically induced astigmatism (SIA) was 0.39±0.34 SD diopters, and in group B (temporal approach), it was 0.5±0.42 SD diopters. A significant statistical difference was not seen between these two groups. Conclusion Surgically induced astigmatism was minimal and comparable with both superior and temporal approaches to clear corneal incisions for phacoemulsification surgery.

Regular and irregular astigmatism of bullous keratopathy using Fourier harmonic analysis with anterior segment optical coherence tomography

Bullous keratopathy (BK) is known to present with corneal edema and Descemet's folds, which can cause corneal astigmatism. However, no report quantitatively evaluated BK astigmatism by separating it into regular and irregular astigmatism. This study investigated the regular and irregular astigmatism of the anterior and posterior corneal surface with Fourier harmonic analysis and anterior segment optical coherence tomography. Preoperative data from 43 eyes of 41 BK patients who received corneal endothelial transplantation were compared with the data from 43 eyes of 43 subjects without corneal disease. Anterior and posterior cylinder power, central corneal thickness (CCT) and thinnest corneal thickness were significantly greater in BK. With Fourier harmonic analysis, BK eyes were found to have significantly larger anterior and posterior regular astigmatism, asymmetry component and higher-order irregularity. Asymmetry component and higher-order irregularity that accounted for the posterior irregular astigmatism increased as CCT increased in BK. Higher-order irregularity in the posterior cornea also positively correlated with worsening best corrected visual acuity. Subgroup analysis found significant correlations between CCT and posterior higher-order irregularity for intraocular surgery and laser iridotomy, but not Fuchs endothelial corneal dystrophy. This study has significance in that it revealed the characteristics of the corneal posterior irregular astigmatism of BK.

Comparison of corneal irregular astigmatism by the type of corneal regular astigmatism

We investigated the relation between corneal regular and irregular astigmatism in normal human eyes. In 951 eyes of 951 patients, corneal irregular astigmatism, such as asymmetry and higher-order irregularity components, was calculated using the Fourier harmonic analysis of corneal topography data within the central 3-mm zone of the anterior corneal surface. The eyes were classified by the type of corneal regular astigmatism into four groups; minimum (< 0.75 diopters), with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism. The mean age was significantly different among the four groups (P < 0.001); patients with WTR astigmatism were the youngest, followed by those with minimum, oblique, and ATR astigmatism. Significant inter-group differences were found among the four groups in asymmetry (P = 0.005) and higher-order irregularity components (P < 0.001); the largest was in eyes with oblique astigmatism, followed by ATR, WTR, and minimum astigmatism. The stepwise multiple regression analysis revealed that corneal regular astigmatism pattern significantly influenced the amount of corneal irregular astigmatism after controlling for confounding factors (P < 0.001). Corneal irregular astigmatism, such as asymmetry and higher order irregularity components, was the largest in eyes with oblique astigmatism, followed by those with ATR, WTR, and minimum astigmatism, even after adjustment for age of subjects.

The Association between Fourier Parameters and Clinical Parameters in Myopic Children Undergoing Orthokeratology

Purpose: To explore how Fourier parameters are associated with axial length growth (ALG) and clinical parameters in children who underwent orthokeratology.Materials and Methods: A total of 267 children received orthokeratology. Baseline cycloplegic autorefraction was performed. Axial length was measured at baseline and one year after the lens dispatch, and the difference was defined as ALG. Corneal topography was performed at the same two visits. Central treatment zone (CTZ) was identified from the difference between the two tangential maps, and its center distance to corneal center was defined as decentration. A relative refractive corneal power (RCRP) map was derived by subtracting the center value from every point on the one-year axial map. It was decomposed into 3 Fourier components: a mean (F0), a single-cycle sinewave (F1), and a double-cycle sinewave (F2). Linear regressions were used to reveal the association between ALG and these parameters.Results: At baseline, the age was 10.18 ± 1.48 year, spherical equivalent (SE) was - 3.10 ± 1.15D, astigmatism was 1.17 ± 0.58D, and axial length was 24.69 ± 0.81 mm. The mean ALG was 0.181 ± 0.22 mm. In multiple regression, ALG was negatively associated with F1 (p < .001), not F0 and F2. Amplitude-wise, F0 and F1 were correlated with decentration (p < .01) and SE (p < .01), and F2 was associated with astigmatism (p < .001). Direction-wise, F1 was correlated with decentration (p < .001) and F2 was associated with astigmatism (p < .001).Conclusions: Among Fourier parameters, F0 and F1 were negatively associated with ALG in myopic children undergoing orthokeratology. Their associations to SE and CTZ decentration may partially explain the effect on ALG retardation.

Fourier Analysis of Corneal Irregular Astigmatism Due to the Anterior Corneal Surface in Dry Eye

OBJECTIVES

To evaluate corneal irregular astigmatism due to the anterior corneal surface using Fourier harmonic analysis with a Placido ring-based corneal topographer (Placido-based topographer) and three-dimensional anterior segment optical coherence tomography (OCT) in dry eyes.

METHODS

Forty-four eyes of 44 subjects with dry eye and 20 eyes of 20 normal control subjects were enrolled. Corneal topographic data were obtained using a Placido-based topographer and OCT. Dioptric data from the central 3-mm zone of the anterior corneal surface were decomposed using Fourier harmonic analysis. Spherical, regular astigmatism, and irregular astigmatism (asymmetry and higher-order irregularity) refractive error components of the cornea from the two imaging modalities were compared.

RESULTS

Both asymmetry and higher-order irregularity values were significantly greater in dry eyes than in control eyes for both the Placido-based topographer and OCT measurements (all P<0.05). In dry eyes, measured values of asymmetry and higher-order irregularities were significantly smaller when obtained with OCT than with the Placido-based topographer (both P<0.001). By contrast, these parameters were not significantly different between the two devices in control eyes. In dry eyes, severity of superficial punctate keratopathy in the central corneal region was correlated with irregular astigmatism.

CONCLUSIONS

The amount of corneal irregular astigmatism, quantified using Fourier harmonic analysis, was significantly higher in dry eyes than in normal eyes. Measurements obtained with OCT and the Placido-based topographer differed in subjects with dry eyes. Therefore, caution should be practiced when trying to use these measurements interchangeably.

[Phacoemulsification versus manual small incision cataract surgery: Anatomic and functional results]

PURPOSE

Prospective randomised study to compare the impact of phacoemusification (PHACO) and small incision cataract surgery (SICS) on endothelial structure (cell density and morphology) and refractive results (visual acuity, induced astigmatism).

METHODS

Prospective study of 57 patients (63 eyes) over 20 months (May 2012-January 2014) undergoing surgery by 2 experienced surgeons. We included patients with senile or presenile cataracts, LOCS III class 2, 3 and 4. Patients were randomized into 2 groups based on their birth month (group 1: PHACO [33]; group 2: SICS [30]). All pre- intra- and postoperative data were collected prospectively. The minimum follow-up was 6 months. We used the SPSS 18.0 for statistical analysis. Statistical tests used included the test-t Student, the Anova test, the Mann-Witney non-parametric test and the Khi² test. A threshold of significance was set at 0.05.

RESULTS

The mean preoperative endothelial cell density was 2447.5±225 c/mm² with no significant difference between the two groups (P=0.207). The mean percentage of hexagonality was 55.5±8.2% in groups 1 and 2. The most significant cell loss was during the first immediate postoperative period for both groups. At Day 15 postoperative, the decrease in cell loss was significant (P<0.001) with a mean loss of 312.9±208.9 c/mm² (P<10^-2). Postoperatively, the mean best-corrected visual acuity was 0.057 log MAR for all of our patients (P=0.170); no patient had an acuity ≤1/10. The mean astigmatism at the conclusion of follow-up was 1.08±0.42 D in group 1 and 1.51±0.55 D in group 2, with a significant difference (P=0.001).

CONCLUSION

Both SICS and PHACO give excellent results, both anatomical and refractive. However, SICS appears to be more advantageous than PHACO in terms of speed, cost, and independence from technology, and appears to be better suited to dense cataracts and mass surgery.

The location of incision in cataract surgery and its impact on induced astigmatism

PURPOSE OF REVIEW

The purpose of the present study is a systematic review of previous studies on choosing the best incision site for the correction of astigmatism in cataract surgery and assessing the amount of surgically induced astigmatism (SIA) with each approach.

RECENT FINDINGS

Regardless of astigmatism axis, studies show that using an on-axis incision is associated with favorable results for 0.5-1.0 diopter (D) of astigmatism. In cases with more than 1.0 D astigmatism, paired on-axis incisions can be appreciably efficient in astigmatism correction and cause at least 1.5 D SIA. Considering the amount of SIA, a temporal incision is the best approach when the patient has minimal amounts of corneal astigmatism preoperatively. At higher levels of astigmatism, if no other astigmatism correction method is used simultaneously, the temporal incision is used less frequently; however, since it is associated with the least SIA, it is still the choice site when another correction method is used.

SUMMARY

The temporal incisions in cataract surgery are associated with little SIA and are appropriate choices for mild preoperative astigmatism. At higher levels of preoperative astigmatism, superior incisions are associated with better results when combined methods are not applied.

Topographic changes after excision surgery of primary pterygia and the effect of pterygium size on topograpic restoration

OBJECTIVE

To assess the effect of pterygium size on time-course change of corneal topography after excision surgery of primary pterygium.

METHODS

Retrospective case series included eyes that underwent excisions of primary pterygium. Pterygium size was graded according to the advancing edge position: less than one third of corneal diameter (grade 1), outside the pupil (grade 2), and within the pupillary area (grade 3). Time-course changes in corneal refractive power, astigmatism, and irregularity (surface regularity and asymmetry indices) in corneal topographies over 12 months postoperatively were compared between the pterygium size grades.

RESULTS

Pterygium excision was performed on 562 eyes, consisting of 119, 338, and 105 eyes with grades 1 to 3, respectively. Grade 1 did not change in corneal irregularity, and there was no difference between grades 1 and 2, except for corneal astigmatism at 6 months. Grade 3 showed significantly higher corneal refractive power and irregularity than grade 1 until 3 and 6 months, respectively, whereas corneal astigmatism was higher over 12 months.

CONCLUSIONS

Topographic changes after primary pterygium excision were associated with pterygium size. Pterygium advancing over the pupillary area required 6 to 12 months for corneal topography restoration, resulting in slow recovery of visual acuity.

Paired opposite clear corneal incision: time-related changes of its effect and factors on which those changes depend

PURPOSE

To assess astigmatism induced by paired opposite clear corneal incision (OCCI) compared to single incisions and to investigate factors on which its effect depends.

METHODS

The study comprised 326 eyes from 326 patients. In patients with <1.0 D corneal astigmatism, clear corneal incision was performed (CC group, n = 245), and in those with >1.0 D preoperative corneal astigmatism, a second, opposite clear corneal incision was made (OCCI group, n = 81). Both groups consisted of superior, temporal, and oblique subgroups according to the steepest meridian. Prior to the surgery, and after surgery, repeated keratometry was performed and surgically induced astigmatism (SIA) was calculated using vector analysis.

RESULTS

Two weeks after the surgery, the SIA was 0.67 ± 0.44 D in the CC group and 1.15 ± 0.65 D in the OCCI group; 9 weeks after the operation, it was 0.61 ± 0.43 D in the CC group and 0.99 ± 0.57 D in the OCCI group (p<0.001). The SIA showed no significant postoperative change in our groups.

CONCLUSIONS

Opposite clear corneal incision reliably induces about 1.0 D of corneal astigmatism on the steep meridian in proportion to the rate of preoperative astigmatism. Its magnitude is independent of the location of the incisions and its effect remains unchanged during the postoperative period.

[Cataract surgery outcomes by temporal small incision techniques with and without phacoemulsification. Results of a prospective study from Kenya]

BACKGROUND

The present outcomes of cataract surgery in Africa do not meet the recommendations of the World Health Organization. Superior manual small incision cataract surgery (SICS) is the operation of choice in many developing countries. However, there is good evidence that temporal incisions are more stable and cause less surgically induced astigmatism (SIA).

METHODS

In a prospective, non-randomized study in an anterior segment clinic in the southeastern part of Kenya, 405 eyes were operated on using either temporal phacoemulsification (n = 288) or temporal SICS (n = 117) with implantation of a rigid intraocular lens (IOL). The main outcome variables were preexisting corneal astigmatism, SIA, visual outcomes and complication rates.

RESULTS

Preoperatively, the mean astigmatism in all eyes was 1.1 diopters (D) ranging from 0 to 6.28 D. Against-the-rule astigmatism (ATR) (mean 1.18 D) was most common with 60.4%. After 8 weeks following surgery the mean SIA was 1.13 D (SD ±0.63 D) at 92° for phacoemulsification and 1.11 D (SD ±0.56 D) at 102° for SICS. Of the eyes 89.6% reached a best corrected visual acuity (BCVA)  ≥ 0.3 and 82.7% reached this visual acuity also uncorrected. The main reasons for not reaching BCVA ≥ 0.3 were ocular comorbidities.

CONCLUSIONS

In the population studied most patients had preexisting ATR astigmatism and a switch to routine temporal incisions appeared beneficial. The World Health Organization recommends that poor (BCVA below 0.1) or borderline (BCVA below 0.3) outcomes after cataract surgery should not be more than 10-20%. This goal has been achieved in this study with the techniques presented.

Cataract surgery outcome at a rural eye care hospital in India

We report the final outcomes, based on final visual acuity, of patients who underwent cataract surgery at an outreach rural ophthalmology unit and document the details of the ophthalmic examination, type of surgery, intra- and postoperative complications and the final visual acuity. Of 208 eyes (198 patients), 81.3% had small incision cataract surgery and 18.7% had phacoemulsification. We believe that, with good planning and the proper utilization of available resources, it is possible to achieve a good visual outcome in the great majority of cases.

Visual outcome of manual small-incision cataract surgery: comparison of modified Blumenthal and Ruit techniques

AIM

To compare the efficacy and visual results of the modified Blumenthal and Ruit techniques for manual small-incision cataract surgery (MSICS).

METHODS

This was a prospective, non-randomized comparison of 129 patients with senile cataracts scheduled to undergo routine cataract surgery via either a superior scleral tunnel incision, i.e., the Blumenthal technique (group 1, n=64) or a temporal scleral tunnel incision, i.e., the Ruit technique (group 2, n=65). MSICS and intraocular lens implantation were performed through an unsutured 6.5- to 7.0-mm scleral tunnel incision. Uncorrected and corrected visual acuity, intraoperative and postoperative complications, and surgically induced astigmatism calculated by simple subtraction were compared. Patients were examined at 1 day, 1 week, 1 month, and 3 months after surgery.

RESULTS

Both groups achieved good visual outcome with minor complications. Three months after surgery, the corrected visual acuity was 0.73 in the Blumenthal group and 0.69 in the Ruit group (P=0.29). The average (SD) postoperative astigmatism was 0.87 (0.62) diopter (D) for the Blumenthal group and 0.86 (0.62) D for the Ruit group. The mean (SD) surgically induced astigmatism was 0.55 (0.45) D and 0.50 (0.44) D for the Blumenthal and Ruit groups, respectively (P=0.52). Common complications were minimal hyphema and corneal edema. There was no statistically significant difference in the complication rate between the groups (P>0.05).

CONCLUSION

In MSICS, both the Blumenthal and Ruit techniques achieved good visual outcomes, with low complication rates.

Assessment and statistics of surgically induced astigmatism

The aim of the thesis was to develop methods for assessment of surgically induced astigmatism (SIA) in individual eyes, and in groups of eyes. The thesis is based on 12 peer-reviewed publications, published over a period of 16 years. In these publications older and contemporary literature was reviewed(1). A new method (the polar system) for analysis of SIA was developed. Multivariate statistical analysis of refractive data was described(2-4). Clinical validation studies were performed. The description of a cylinder surface with polar values and differential geometry was compared. The main results were: refractive data in the form of sphere, cylinder and axis may define an individual patient or data set, but are unsuited for mathematical and statistical analyses(1). The polar value system converts net astigmatisms to orthonormal components in dioptric space. A polar value is the difference in meridional power between two orthogonal meridians(5,6). Any pair of polar values, separated by an arch of 45 degrees, characterizes a net astigmatism completely(7). The two polar values represent the net curvital and net torsional power over the chosen meridian(8). The spherical component is described by the spherical equivalent power. Several clinical studies demonstrated the efficiency of multivariate statistical analysis of refractive data(4,9-11). Polar values and formal differential geometry describe astigmatic surfaces with similar concepts and mathematical functions(8). Other contemporary methods, such as Long's power matrix, Holladay's and Alpins' methods, Zernike(12) and Fourier analyses(8), are correlated to the polar value system. In conclusion, analysis of SIA should be performed with polar values or other contemporary component systems. The study was supported by Statens Sundhedsvidenskabeligt Forskningsråd, Cykelhandler P. Th. Rasmussen og Hustrus Mindelegat, Hotelejer Carl Larsen og Hustru Nicoline Larsens Mindelegat, Landsforeningen til Vaern om Synet, Forskningsinitiativet for Arhus Amt, Alcon Denmark, and Desirée and Niels Ydes Fond.

Change in astigmatism after temporal clear corneal cataract extraction in the pediatric population

Purpose:

To evaluate the early postoperative change in astigmatism in pediatric patients having cataract extraction with intraocular lens implantation using sutured temporal clear corneal incision. Methods: A retrospective chart review was performed on all pediatric patients who underwent clear corneal cataract surgery with intraocular lens implantation between 12/01/2005 and 11/30/2006. Results: A total of 31 eyes of 22 patients who underwent temporal clear corneal cataract surgery and intraocular lens implantation were included. The mean patient age at surgery was 6.05 years (range 1.5 months to 17 years). Mean postoperative refractive astigmatism the first day after surgery was 2.35±1.37 diopters (D). There was a statistically significant decrease in mean postoperative astigmatism by postoperative week 1 to 1.45 ± 0.79 D. Mean astigmatism was 1.48 ± 0.98 D by postoperative months 2-4, which was not a statistically significant change from postoperative day 1. Conclusions: Postoperative astigmatism can be expected after sutured temporal clear corneal surgery in pediatric patients and decreases over time without removal of sutures. The amount of postoperative astigmatism in children requires close follow-up after pediatric cataract surgery.

Long-term refractive stability following combined astigmatic keratotomy and phakoemulsification

BACKGROUND

To determine whether combined astigmatic keratotomy and cataract surgery induces a sustained reduction in astigmatism.

METHODS

Patients who had previously undergone combined cataract surgery and astigmatic keratotomy for naturally occurring astigmatism were identified and their notes reviewed. Mean final follow-up was 34 months (30-42 months). Fourteen eyes of 11 patients were eligible for study. Arcuate corneal incisions had been employed using the Buzard nomogram. Using power vector analysis, the post-operative refractive change at 6 months and final follow-up was determined.

RESULTS

The mean preoperative manifest cylindrical refractive error was 2.88 D (1.50-5.50 D). The mean postoperative manifest cylindrical refractive error was 1.89 and 1.79 D at 6 months and final follow-up, respectively. Power vector analysis demonstrated a significant postoperative reduction in refractive blur at 6 months and final follow-up (P = 0.006, P = 0.004, respectively): mean preoperative blur strength was 2.90 D and mean postoperative blur strength was 1.33 and 1.25 D at 6 months and final follow-up, respectively. Sustained postoperative reduction in astigmatism was noted in 12 of 14 eyes at final follow-up.

CONCLUSIONS

Astigmatic keratotomy is a well-established treatment for astigmatism. In this series, the refractive benefit from combined astigmatic keratotomy and cataract surgery is maintained for several years. No surgical complications were observed.

Torque and flattening effects of clear corneal temporal and on-axis incisions for phacoemulsification

PURPOSE

To compare the torque and flattening effect induced by temporal or on-axis clear corneal incisions (CCIs) for phacoemulsification.

SETTING

Moorfields Eye Hospital, London, United Kingdom.

METHODS

Randomized controlled clinical trial on 62 eyes with cataract and mild to moderate corneal astigmatism (<2.60 diopters [D]) having phacoemulsification with a temporal CCI (temporal group) or on-axis CCI (on-axis group). Corneal astigmatism was assessed by corneal topography preoperatively and 3 weeks after surgery. The meridian of the incisions was marked on the cornea before local anesthesia was given to avoid anesthesia-related cyclotorsion. The surgically induced astigmatism (SIA) vector, torque, flattening effect, and accuracy of incision placement were analyzed in the 2 groups and compared with a paired t test.

RESULTS

Three weeks after surgery, the on-axis CCI induced slightly more flattening of the meridian of the incision (mean -0.63 +/- 0.57 D [SD]) than the temporal CCI (mean -0.50 +/- 0.44 D); however, the differences were not statistically significant (P = .31). Simple algebraic difference showed a mean increase in astigmatism magnitude of 0.12 +/- 0.52 D in the temporal group and a mean reduction of 0.21 +/- 0.53 D in the on-axis group (P = .02). The mean absolute torque was 0.28 +/- 0.27 D and 0.53 +/- 0.37 D, respectively (P<.005). The absolute angle of error of incision placement (alpha) was greater after on-axis CCIs (mean 25.9 +/- 20.1 degrees) than after temporal CCIs (mean 14.5 +/- 14.3 degrees) (P = .01).

CONCLUSIONS

In eyes with preoperative astigmatism less than 2.60 D, on-axis CCI phacoemulsification induced slightly more flattening along the incision meridian than temporal CCI phacoemulsification, although the differences were not significant. The on-axis CCI was associated with significantly greater absolute torque and angle of error than the temporal CCI. These factors could limit the benefit of placing the incision on axis when the aim is to reduce preoperative astigmatism in phacoemulsification.

Surgically induced astigmatism after phacoemulsification in eyes with mild to moderate corneal astigmatism

PURPOSE

To determine whether there is a difference in surgically induced astigmatism (SIA) and postoperative uncorrected visual acuity (UCVA) and best corrected visual acuity (BCVA) between 2 types of clear corneal incisions used in phacoemulsification: the temporal and the on-axis (ie, on the steeper corneal meridian) clear corneal incision (CCTI and CCOI, respectively).

SETTING

Moorfields Eye Hospital, London, United Kingdom.

METHODS

In a prospective randomized controlled trial (pilot study), 61 eyes with cataract and mild to moderate corneal astigmatism (<2.58 diopters [D] on corneal topography) having phacoemulsification (single surgeon, 3.2 mm incision) were randomized to receive CCTI or CCOI. Main outcome measures included postoperative BCVA and corneal astigmatism and SIA (calculated using the Holladay vector analysis formula). Measurements were repeated postoperatively at 3 weeks in all eyes, whereas only 46 eyes made it to the final assessment at 8 weeks. Continuous variables between groups were compared by Student t test. The power of the study was calculated.

RESULTS

At the first follow-up, the difference in SIA between the 2 incision types was 0.15 D and it was not statistically significant (0.65 D in CCOI; 0.50 D in CCTI). At the second follow-up, the difference was 0.29 D and it was statistically significant (0.63 D in CCOI; 0.34 D in CCTI; P = .0004). There was no statistically significant difference in the final postoperative visual acuity. The power of the pilot study was 72%.

CONCLUSION

Seven weeks after small-incision phacoemulsification, the CCTI induced less SIA than the CCOI; however, there were no significant differences in the final UCVA and BCVA.

Long-term changes in corneal surface configuration after penetrating keratoplasty

PURPOSE

To examine the long-term longitudinal changes in corneal surface configuration as determined by Fourier series harmonic analysis of videokeratography data and of visual acuity and refraction after penetrating keratoplasty (PK).

DESIGN

Interventional case series.

METHODS

One hundred thirty eyes of 130 consecutive patients who were scheduled for PK using 16 interrupted 10-0 nylon sutures were recruited. Spherical equivalent power, regular astigmatism component, irregular astigmatism (asymmetry and higher-order irregularity) component of the central cornea as determined by Fourier analysis of videokeragraphic data, spectacle-corrected visual acuity, and spherical equivalent were examined at 1 week, and at 1, 3, 6, 9, 12, 18, and 24 months after PK.

RESULTS

Spherical equivalent power increased considerably for up to 1 month after PK, but thereafter showed no further appreciable change up to the final follow-up at 24 months. The regular astigmatism component decreased markedly for up to 6 months after PK, while the total irregular astigmatism (sum of the asymmetry and higher-order irregularity) component decreased considerably up to approximately 3 months, and then these showed no further relevant change for up to 24 months. Spectacle-corrected visual acuity also improved markedly until approximately 3 months after PK, after which it was virtually stable. Furthermore, important correlations were found between regular and irregular astigmatism and the spectacle-corrected visual acuity.

CONCLUSIONS

Corneal surface configuration after PK appears to be stable by approximately 6 months after PK, concurrent with postkeratoplasty stabilization of visual acuity.

Corneal irregular astigmatism after hyperopic laser in situ keratomileusis

PURPOSE

To evaluate the changes in irregular astigmatism after hyperopic laser in situ keratomileusis (LASIK).

METHODS

In a prospective case series, 15 eyes of 12 patients who had hyperopic LASIK were evaluated. Corneal topography was obtained before and after hyperopic LASIK. Corneal irregular astigmatism (asymmetry and higher-order irregularity) was calculated using Fourier harmonic analysis of the topography data.

RESULTS

Hyperopic LASIK significantly increased the asymmetry component at 3 (P = 0.0085) and 6 months (P = 0.0307) postoperatively. The mean higher-order irregularity was not significantly changed at any postoperative time-point (P = 0.222). The achieved change in the spherical equivalent was significantly correlated with the post/preoperative ratio of asymmetry (R = 0.695, P = 0.0030).

CONCLUSION

Hyperopic LASIK significantly increases the asymmetry component of the cornea, which is correlated with the achieved change in the spherical equivalent.

Paired opposite clear corneal incisions to correct preexisting astigmatism in cataract patients

PURPOSE

To evaluate the astigmatic correcting effect of paired opposite clear corneal incisions on steep axis in cataract patients.

SETTING

Sligo General Hospital, Sligo, Ireland.

METHODS

Fifteen eyes of 14 cataract patients with a mean age of 78.4 years +/- 6.38 (SD) (range 69 to 90 years) were recruited for the study. Inclusion criterion was topographic astigmatism of more than 2 diopters (D) in the cataractous eye. Preoperative refraction, autokeratometry, and topography were performed. The steep axis was marked before sub-Tenon's anesthesia was given. Paired 3-step self-sealing opposite clear corneal incisions were made 1 mm anterior to limbus on the steep axis with a 3.2 mm keratome. One incision was used for standard phacoemulsification, and the other was left unused for astigmatic correction. All the patients had day-case surgery. The first follow-up was at 1 month. Postoperative topography, keratometry, and refraction were performed on all patients.

RESULTS

Mean preoperative and postoperative topographic corneal astigmatism were 3.26 +/- 1.03 D (range 2.30 to 5.80 D) and 2.02 +/- 1.04 D (range 0.20 to 4.00 D), respectively. Mean astigmatic correction was 1.23 +/- 0.49 D (range 0.30 to 2.20 D). Mean surgically induced astigmatism by vector analysis was 2.10 +/- 0.79 D (range 0.80 to 3.36 D). There were no incision-related complications.

CONCLUSION

Paired opposite clear corneal incisions on the steep axis is a useful way to correct astigmatism in cataract patients, requiring no extra skill or instrumentation.

Visual acuity measurements using Fourier series harmonic analysis of videokeratography data in eyes after penetrating keratoplasty

PURPOSE

Fourier harmonic analysis can decompose videokeratography data into spherical power, regular astigmatism, and irregular astigmatism (asymmetry and higher-order irregularity). The aim of this study was to evaluate whether determination of cylinder power by Fourier analysis facilitates measurements of visual acuity and refraction in eyes after penetrating keratoplasty.

DESIGN

Cross-sectional study.

PARTICIPANTS

Sixty-six eyes of 56 subjects who had undergone penetrating keratoplasty.

METHODS

Spectacle-corrected visual acuity was measured in 2 ways: by the conventional and the Fourier methods. In the conventional method, the refraction was determined subjectively by reference to the measurement results of the autokeratometer and autorefractometer. In the Fourier method, the magnitude and axis of regular astigmatism were calculated by Fourier analysis of the videokeratography data, and spherical lenses were adjusted until best spectacle-corrected visual acuity was attained.

MAIN OUTCOME MEASURES

Logarithm of the minimum angle of resolution (logMAR) visual acuity and refraction used for correction.

RESULTS

The spectacle-corrected visual acuity obtained with the Fourier method (logMAR, 0.23+/-0.32; Snellen equivalent, 20/34) was significantly better than that attained with the conventional method (logMAR, 0.31+/-0.29; Snellen equivalent, 20/41; P<0.001, paired t test). The cylinder power used for spectacle-corrected visual acuity measurements was significantly lower with the Fourier method (-2.41+/-1.26 diopters [D]) than with the conventional method (-3.53+/-1.64 D; P<0.001). The spherical equivalent at the final refraction was not different between groups (P = 0.207).

CONCLUSIONS

Fourier analysis of videokeratography data significantly facilitates determination of refraction and measurement of best spectacle-corrected visual acuity in eyes with corneal irregular astigmatism, such as eyes that have undergone penetrating keratoplasty.

Quantitative Assessment of Videokeratography Data Using Fourier Series Harmonic Analysis

PURPOSE

To describe a method of mathematically decomposing videokeratography data using Fourier series harmonic analysis and present examples of its clinical application.

METHODS

Videokeratography data were decomposed by Fourier analysis into spherical component, regular astigmatism, asymmetry (decentration or skewness), and higher-order irregular astigmatism. These 4 Fourier components were analyzed in both normal and pathologic eyes. Color-coded maps were generated to present the 4 Fourier components.

RESULTS

Color-coded mapping of the results of Fourier analysis of videokeratography data facilitated visual and instant interpretation of complex corneal topographic information. By using Fourier components, time course of changes in corneal topography following penetrating keratoplasty and influence of suture removal were quantitatively evaluated. The Fourier analysis method was successfully applied to determine the most appropriate correction lenses in eyes after penetrating keratoplasty.

CONCLUSIONS

Fourier analysis of videokeratography data allows mathematical separation of regular and irregular astigmatism and is useful in the quantitative assessment of corneal optics in eyes with both pathologic and postsurgical conditions.

Optical aberrations of intraocular lenses measured in vivo and in vitro

Corneal and ocular aberrations were measured in a group of eyes before and after cataract surgery with spherical intraocular lens (IOL) implantation by use of well-tested techniques developed in our laboratory. By subtraction of corneal from total aberration maps, we also estimated the optical quality of the intraocular lens in vivo. We found that aberrations in pseudophakic eyes are not significantly different from aberrations in eyes before cataract surgery or from previously reported aberrations in healthy eyes of the same age. However, aberrations in pseudophakic eyes are significantly higher than in young eyes. We found a slight increase of corneal aberrations after surgery. The aberrations of the IOL and the lack of balance of the corneal spherical aberrations by the spherical aberrations of the intraocular lens also degraded the optical quality in pseudophakic eyes. We also measured the aberrations of the IOL in vitro, using an eye cell model, and simulated the aberrations of the IOL on the basis of the IOL's physical parameters. We found a good agreement among in vivo, in vitro, and simulated measures of spherical aberration: Unlike the spherical aberration of the young crystalline lens, which tends to be negative, the spherical aberration of the IOL is positive and increases with lens power. Computer simulations and in vitro measurements show that tilts and decentrations might be contributors to the increased third-order aberrations in vivo in comparison with in vitro measurements.

Fourier series harmonic analysis of corneal topography following suture removal after penetrating keratoplasty

PURPOSE

To evaluate quantitatively the influence of suture removal after penetrating keratoplasty on corneal refraction including irregular astigmatism.

METHODS

Subjects were 42 eyes of 39 patients with clear corneal grafts who underwent suture removal after penetrating keratoplasty. Videokeratography data taken before and after suture removal were decomposed using Fourier harmonic analysis into spherical power, regular astigmatism, and irregular astigmatism (asymmetry and higher order irregularity).

RESULTS

On average, spherical power significantly increased after suture removal (p < 0.0001, paired t test), and regular astigmatism did not change significantly (p = 0.247). Suture removal significantly decreased asymmetry (p < 0.0001) and higher order irregularity (p < 0.0001).

CONCLUSIONS

Suture removal after penetrating keratoplasty induces myopic shift and reduction in irregular astigmatism of the cornea.