Aberrations induced in wavefront-guided laser refractive surgery due to shifts between natural and dilated pupil center locations

An analysis of the factors involved in IOL decentration after phacoemulsification using CASIA 2 anterior segment optical coherence tomography

PURPOSE

To evaluate the magnitude of IOL transversal shift (ITS) after phacoemulsification and to analyse the factors contributing to IOL decentration and ITS.

METHODS

94 consecutive patients who underwent cataract surgery and IOL implantation was enrolled. Each patient underwent anterior segment optical coherence tomography with CASIA 2 (Tomey, Nagoya, Japan) to assess crystalline lens decentration, thickness and diameter seven days preoperatively and at one and sixty days postoperatively. Univariate and multivariate linear regression analysis were performed to evaluate the determinants of ITS and final decentration.

RESULTS

The preoperative crystalline lens diameter was associated with the ITS and with the IOL final decentration. A positive association between the final IOL decentration and the first post-surgical day decentration was found (p < 0.0001).

CONCLUSION

Greater crystalline lens diameter was associated with greater decentration and with greater ITS. Day-one IOL decentration seems to be the main determinant of final IOL decentration.

Repeatability of Pentacam-derived intraocular lens decentration measurements and the level of agreement with OPD-Scan III: A prospective observational case series

PURPOSE

This study aimed to assess the repeatability of intraocular lens (IOL) decentration measurements obtained through Pentacam, based on corneal topographic axis (CTA) and pupillary axis (PA), and to evaluate the level of agreement between Pentacam and OPD-Scan III devices in measuring IOL decentration.

METHODS

In this prospective observational case series, three measurements were performed with Pentacam to evaluate the repeatability of the measurements. The analysis included the calculation of the mean and standard deviations (SD), conducting a repeated measures analysis of variance (rANOVA), and determining an intraclass correlation coefficient (ICC) to assess the repeatability of the measurements. Moreover, Bland-Altman analysis was employed to assess the agreement between Pentacam and OPD-Scan III devices in measuring IOL decentration. IOL decentration measurements were obtained with respect to both CTA and PA.

RESULTS

A total of 40 eyes from 40 patients were analyzed. The rANOVA revealed no significant difference among three consecutive measurements of IOL decentration obtained with Pentacam. The mean SD of all parameters ranged from 0.04 mm to 0.07 mm. With CTA as the reference axis, the ICC values for Pentacam measurements of IOL decentration were 0.82 mm for the X-axis, 0.76 mm for the Y-axis, and 0.82 mm for spatial distance. When using PA as the reference axis, the corresponding ICC values were 0.87, 0.89, and 0.77, respectively. The 95% limits of agreement for all IOL decentration measurements were wide when comparing Pentacam and OPD-Scan III.

CONCLUSIONS

Pentacam demonstrated high repeatability in measuring IOL decentration with respect to both CTA and PA. However, due to poor agreement between Pentacam and OPD-Scan III measurements, caution should be exercised when using data interchangeably between the two devices.

Stachydrine, a Bioactive Equilibrist for Synephrine, Identified from Four Citrus Chinese Herbs

Four Chinese herbs from the Citrus genus, namely Aurantii Fructus Immaturus (Zhishi), Aurantii Fructus (Zhiqiao), Citri Reticulatae Pericarpium Viride (Qingpi) and Citri Reticulatae Pericarpium (Chenpi), are widely used for treating various cardiovascular and gastrointestinal diseases. Many ingredients have already been identified from these herbs, and their various bioactivities provide some interpretations for the pharmacological functions of these herbs. However, the complex functions of these herbs imply undisclosed cholinergic activity. To discover some ingredients with cholinergic activity and further clarify possible reasons for the complex pharmacological functions presented by these herbs, depending on the extended structure-activity relationships of cholinergic and anti-cholinergic agents, a simple method was established here for quickly discovering possible choline analogs using a specific TLC method, and then stachydrine and choline were first identified from these Citrus herb decoctions based on their NMR and HRMS data. After this, two TLC scanning (TLCS) methods were first established for the quantitative analyses of stachydrine and choline, and the contents of the two ingredients and synephrine in 39 samples were determined using the valid TLCS and HPLC methods, respectively. The results showed that the contents of stachydrine (3.04‱) were 2.4 times greater than those of synephrine (1.25‱) in Zhiqiao and about one-third to two-thirds of those of Zhishi, Qingpi and Chenpi. Simultaneously, the contents of stachydrine, choline and synephrine in these herbs present similar decreasing trends with the delay of harvest time; e.g., those of stachydrine decrease from 5.16‱ (Zhishi) to 3.04‱ (Zhike) and from 1.98‱ (Qingpi) to 1.68‱ (Chenpi). Differently, the contents of synephrine decrease the fastest, while those of stachydrine decrease the slowest. Based on these results, compared with the pharmacological activities and pharmacokinetics reported for stachydrine and synephrine, it is indicated that stachydrine can be considered as a bioactive equilibrist for synephrine, especially in the cardio-cerebrovascular protection from these citrus herbs. Additionally, the results confirmed that stachydrine plays an important role in the pharmacological functions of these citrus herbs, especially in dual-directionally regulating the uterus, and in various beneficial effects on the cardio-cerebrovascular system, kidneys and liver.

Using a smartphone app in the measurement of posture-related pupil center shift on centration during corneal refractive surgery

Purpose: Pupil center is an important anchor point in corneal refractive surgery, which may affect by body position. This study investigated the feasibility of using a smartphone application in measurement of posture-related pupil center shifts. Methods: Images of undilated eyes were captured for 25 participants (age: 18-38 years) at a distance of 40 cm in four body positions (seated, supine, right lateral, and left lateral) under controlled lighting conditions. During taking images, a smartphone application was used to guide positioning without head rotation and tilt. From the images, the location of the pupil center and pupil diameter with respect to the limbus boundary were measured. Results: According to the data obtained by the smartphone application, pupil center was located slightly nasal and superior to the limbus center in the seated position, and it shifted more nasally and superiorly (p < 0.001, OD 0.54 ± 0.11 mm, OS 0.57 ± 0.14 mm) in the supine position. When body position switched between left and right lateral positions, the pupil centers of both eyes shifted along the direction of gravity (p < 0.05), and no significant shift occurred along the longitudinal axis. Moreover, pupil constriction was observed when the body position changed from seated to supine position (p < 0.001, OD 0.64 ± 0.57 mm, OS 0.63 ± 0.58 mm). Conclusion: Posture-related pupil center shift may be larger than the error tolerance of centration in corneal refractive surgery, which might be difficult to measure by the existing instruments. An accessible application is necessary for evaluating the shift of pupil center and guiding centration during the surgery.

Rotational Stability, Decentration, and Tilt of a New Hydrophobic Acrylic Intraocular Lens Platform

PURPOSE

To evaluate rotational stability, decentration and tilt of the monofocal intraocular lens (IOL) Nanex (NC1-SP; HOYA Surgical Optics).

DESIGN

Prospective interventional case series.

METHODS

The study was performed at the Department of Ophthalmology, Medical University of Vienna. The study population comprised 130 eyes of 68 patients with age-related cataract who underwent cataract surgery with implantation of a Nanex IOL. Baseline image for rotational stability evaluation was obtained at the end of surgery (EoS) and compared to retroillumination images taken at 1 hour, 1 week, 1 month, and 6 months after surgery. Axis alignment was assessed using nonmovable landmarks on the sclera and the optic-haptic junctions of the IOL. Anterior segment OCT images were performed to evaluate decentration and tilt. The main outcome measure was absolute rotation from EoS to 6 months postoperatively.

RESULTS

Median IOL rotation of all eyes from EoS to 6 months was 1.9° (interquartile range 0.1°-37.5°). Ten eyes (9.71%) rotated more than 5° and 2 eyes (1.94%), more than 10°. IOL rotation did not correlate with axial eye length (Spearman r = -0.042, P = .46), crystalline lens thickness (Spearman r = 0.134, P = .19), and crystalline lens equatorial diameter (Spearman r = 0.101, P = .325). IOL rotation positively correlated with anterior fibrosis severity (Spearman r = 0.321, P = .002). Preoperative decentration (0.2 ± 0.12 mm) and tilt (5.7 ± 1.6°) did not change significantly after surgery (0.22 ± 0.12 mm and 5.62 ± 1.49°, respectively).

CONCLUSION

The investigated IOL presented good rotational stability and low decentration and tilt values. Nevertheless, anterior capsule fibrosis development led to a higher tendency of IOL rotation after 1 week.

Effects of tilt and decentration of Visian Implantable Collamer Lens (ICL V4c) on visual quality: an observational study

Background

The central hole of the Visian Implantable Collamer Lens (ICL V4c) provides a reference to observe its tilt or decentration. This study aimed to investigate the tilt and decentration effects of ICL V4c on visual quality after implantation.

Methods

A total of 135 eyes from 69 patients who underwent ICL V4c implantation were included in this study. Evaluation of uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and aberrations were performed 6-months postoperatively. The anterior segment parameters were collected using CASIA2 anterior segment-optical coherence tomography, tilt and decentration of ICL V4c were analyzed using MATLAB software. All patients received questionnaires to investigate the visual quality postoperatively.

Results

The safety and effectiveness were 1.18 ± 0.17 and 1.11 ± 0.18, respectively. No significant changes were observed regarding higher-order and spherical aberrations after the operation; however, coma and trefoil significantly increased compared to preoperative values. The average total decentration and tilt was 0.21 ± 0.12 mm and 2.54 ± 1.00°, respectively. Horizontal, vertical, and total values of tilt and decentration were not significantly associated with postoperative CDVA, UDVA, and aberrations. The most common visual symptom was halo, and 97.04% of patients had a satisfaction score ≥ 8. The total or horizontal tilt was significantly positively correlated with the frequency, severity, and bothersome scores from the questionnaires.

Conclusions

ICL V4c implantation can obtain high visual quality and patient satisfaction. Although the degree of tilt and decentration after ICL V4c implantation was small, a positive effect on subjective visual quality was observed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-022-02499-4.

Clinically Significant Intraocular Lens Decentration and Tilt in Highly Myopic Eyes: A Swept-Source Optical Coherence Tomography Study

PURPOSE

To investigate the occurrence and risk factors of clinically significant intraocular lens (IOL) decentration and tilt in highly myopic eyes using swept-source anterior segment optical coherence tomography (SS-AS-OCT).

DESIGN

Cross-sectional study.

METHODS

This study included 334 participants (334 eyes) with high myopia, defined as axial length (AL) ≥26 mm, who underwent phacoemulsification with IOL implantation. Decentration and tilt of IOL were assessed by SS-AS-OCT. Clinically significant IOL decentration and tilt was defined as decentration ≥0.4 mm and tilt ≥7°. Routine preoperative and postoperative examinations included visual acuity, refraction, biometric measurement using IOLMaster 700 (Carl Zeiss Meditec), and objective visual quality evaluated by OPD-Scan III (Nidek Technologies).

RESULTS

Among the 334 highly myopic participants, 71 (21.3%) had clinically significant IOL decentration, and 26 (7.78%) had clinically significant IOL tilt. The proportion of clinically significant IOL decentration (37.1% vs 14.0%, P < .001) and tilt (16.2% vs 3.90%, P < .001) in those with AL ≥30 mm was significantly higher than in those with AL <30 mm. The multivariable logistic regression model showed only AL ≥30 mm was associated with clinically significant IOL decentration (odds ratio, 1.65; P = .002). AL ≥30 mm (odds ratio, 2.09; P = .001) was an independent risk factor for clinically significant IOL tilt after adjusting for confounders. AL ≥30.3 mm could effectively predict IOL decentration ≥0.6 mm (area under the curve, 0.802).

CONCLUSIONS

Participants with AL >30 mm have a higher risk of clinically significant IOL decentration and tilt, thus caution should be taken to implant multifocal or toric IOL for these patients.

Rotational Stability of a New Hydrophobic Acrylic IOL With Modified C-loop Haptics

PURPOSE

To assess rotational stability, axial stability, decentration, and tilt of the Rayner RAO800C single-piece hydrophobic acrylic intraocular lens (IOL) (Rayner Intraocular Lenses Ltd) from end of surgery to 4 to 7 months postoperatively.

METHODS

Surgeries were performed at the Department of Ophthalmology at the Medical University of Vienna. A total of 130 eyes of 68 patients received an aspheric hydrophobic Rayner RAO0800C IOL. IOLs were randomly implanted to the 0 ± 10, 45 ± 10, 90 ± 10, or 135 ± 10 degree axis. Baseline measurement was performed with the patient still supine on the operating table. Axis alignment after 1 hour, 1 week, 1 month, and 4 months was evaluated by retroillumination pictures. Postoperative IOL decentration, tilt, and aqueous depth at 4 months were assessed using an anterior segment swept-source optical coherence tomography.

RESULTS

Absolute median IOL rotation from end of surgery to 4 months was 2.4 degrees (range: 0.0 to 85.0 degrees). Median IOL rotation from end of surgery to 1 hour, 1 hour to 1 week, 1 week to 1 month, and 1 month to 4 months was 1.6 (range: 0.0 to 86.2), 1.1 (range: 0.0 to 28.8), 0.6 (range: 0.0 to 5.2), and 0.7 (range: 0.0 to 2.6) degrees. Respective proportions of IOLs rotating more than 5, 10, and 20 degrees from end of surgery to 4 months were 23.9%, 11.0%, and 6.4%. Horizontal and vertical decentration at 4 months was -0.09 ± 0.14 and 0.09 ± 0.14 mm, respectively. Horizontal and vertical tilt at 4 months was -4.78 ± 1.36 and -1.58 ± 1.10 degrees, respectively. A posterior axial shift of 0.052 ± 0.055 mm was observed from 1 week to 4 months.

CONCLUSIONS

Although median IOL rotation appeared to be low, a significant proportion of IOLs rotated postoperatively. Decentration and tilt values were generally low. A minimal posterior optic shift was observed after 1 week. [J Refract Surg. 2021;37(2):112-118.].

Angle alpha orientation and magnitude distribution in a cataract surgery population

PURPOSE

To report normative angle alpha orientation and magnitude distribution in a cataract surgery patient population.

SETTING

U.S. academic medical center.

DESIGN

Retrospective review.

METHODS

A total of 11 871 wavefront aberrometer/corneal topographer angle alpha measurements were performed over 40 months, yielding 8773 bilateral measurements (73.9%) with zero bad wavefront datapoints. The analysis was limited to the first right-eye scan for 3382 unique patients. The angle alpha magnitudes (millimeters) and orientations (degrees) were analyzed for these unique right eyes.

RESULTS

For the 3,382 unique patients, the mean angle alpha magnitude was 0.44 ± 0.15 mm (median, 0.44 mm; 25th and 75th percentiles 0.34 mm, 0.53 mm). Angle alpha orientation was predominantly horizontal (P < .01), with a mean of 186 ± 32 degrees. The expected point of intraocular lens (IOL) centration (EPIC) based on the geometric center of the corneal limbus was temporal to the visual axis in 3212 eyes (95%), nasal in 92 eyes (2.7%), inferior in 56 eyes (1.7%), and superior in 22 eyes (0.6%). The mean angle alpha magnitude was 0.3 mm or less in 607 eyes (18%) and 0.5 mm or greater in 1089 eyes (32%).

CONCLUSIONS

Angle alpha is a predominantly horizontal phenomenon with a mean EPIC of 0.44 mm temporal to the visual axis. This information may assist in determining eligibility for patients in multifocal IOL implantation.

Theoretical Effect of Coma and Spherical Aberrations Translation on Refractive Error and Higher Order Aberrations

(1) Background: The purpose of the study is to present a simple theoretical account of the effect of translation of coma and spherical aberrations (SA) on refractive error and higher order aberrations. (2) Methods: A computer software algorithm was implemented based on previously published methods. The effect of translation (0 to +1 mm) was analyzed for SA (0 to +2 µm) and coma (0 to +2 µm) for a circular pupil of 6 mm, without any rotation or scaling effect. The relationship amongst Zernike representations of various aberrations was analyzed under the influence of translation. (3) Results: The translation of +0.40 µm of SA (C[4,0]) by +0.25 mm with a pupil diameter of 6mm resulted in induction of tilt (C[1,1]), −0.03D defocus (C[2,0]), +0.03D astigmatism (C[2,2]) and +0.21 µm coma (C[3,1]). The translation of +0.4 µm of coma (C[3,1]) by +0.25 mm with a pupil diameter of 6 mm resulted in induction of tilt (C[1,1]), −0.13D defocus (C[2,0]) and +0.13D astigmatism (C[2,2]). A theoretical quantitative relationship between SA, coma, astigmatism and defocus is presented under the influence of translation. (4) Conclusion: The results can act as a guide for the clinician, in order to readily assess theoretical impact of wavefront map translation from pupil center to the visual axis. The resultant refractive coupling has to be taken into consideration especially when treating eyes with an abnormal corneal shape and/or large pupil center to corneal vertex chord.

Pupil influence on the quality of vision in rotationally asymmetric multifocal IOLs with surface-embedded near segment

PURPOSE

To evaluate the influences of preoperative pupil parameters on the visual outcomes of the SBL-3, a rotationally asymmetric multifocal intraocular lens (IOL) with a surface-embedded near segment.

SETTING

Cathedral Eye Clinic, Belfast, Northern Ireland, United Kingdom.

DESIGN

Retrospective comparative case series.

METHODS

Postoperatively, patients divided into 4 groups according to their pupil size as follows: Group A: 2.50 to 2.99 mm, Group B: 3.00 to 3.50 mm, Group C: 3.51 to 4.00 mm, and Group D: 4.01 to 4.50 mm. The uncorrected distance (UDVA), intermediate (UIVA), and near (UNVA) visual acuities, IOL centration and tilt, and quality of vision (QoV) questionnaires were compared between the 4 groups for 18 months postoperatively.

RESULTS

The study comprised 90 patients (180 eyes). The mean preoperative pupil (photopic and mesopic) diameter was 4.3 mm ± 0.3 (SD) and 5.6 ± 1.4 mm, respectively, which decreased to 3.8 ± 0.7 mm and 4.9 ± 1.2 mm, respectively, at 18 months. Eighteen months postoperatively, both photopic and mesopic pupil groups had a statistically significant reduction in size from preoperative levels. No significant differences in UDVA, UIVA, and UNVA were found between the groups (P > .001). Significant differences in the QoV questionnaire day scores and night scores were found between the 4 groups (P < .001).

CONCLUSIONS

The rotationally asymmetric multifocal IOL provided excellent optical performance during 18-months follow-up. The preoperative photopic pupil is an important parameter for consideration of this type of IOL because smaller pupils have a significant negative subjective impact on QoV.

Effect of topical pilocarpine on refractive surgery outcomes

PURPOSE

To investigate the effect of topical pilocarpine on topical cycloplegia and on the results of refractive surgery.

METHODS

The study included 100 eyes of 100 patients who underwent laser-assisted in situ keratomileusis. Group 1 comprised patients who wanted to undergo surgery on the same day after cycloplegic examination and were applied with 2% pilocarpine hydrochloride; group 2 comprised patients whose pupils spontaneously went into the natural position. Corneal thickness, mean refractive spherical equivalent (MRSE), uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), pupil diameter, pupil center shift and high-order aberrations (HOAs) were compared between the two groups.

RESULTS

There were no statistically significant differences between the groups in respect of preoperative age, gender, corneal thickness, MRSE, UDVA and CDVA. The pupil diameter was not statistically significant between the groups. Pupil diameter after pilocarpine was not statistically significant when compared with the natural pupil diameter. There were no statistically significant differences in postoperative HOA between the two groups.

CONCLUSIONS

The pupillary dilatation and the associated pupillary shift were reduced with pilocarpine. Postoperative refractive values and aberrations showed no difference between the groups.

Effects of eye rotation and contact lens decentration on horizontal peripheral refraction

PURPOSE

Peripheral refraction is important in design of myopia control therapies. The aim was to investigate the influence of contact lens decentration associated with eye rotation on peripheral refraction in the horizontal visual field.

METHODS

Participants were 10 emmetropes and 10 myopes in good general and ocular health. Right eyes underwent cycloplegic peripheral refraction, using a Grand-Seiko WAM-5500 Autorefractor, in 5° steps to ±35° eccentricities along the horizontal visual field. Targets were fixated using eye rotation only or head rotation only. Refractions were measured without correction and with three types of contact lenses: single vision, a multifocal centre-distance aspheric with +2.50 D add and NaturalVue aspheric. Photographs of eyes during lens wear were taken for each eye rotation. Effects of visual field angle, lens type and test method (head or eye rotation) on vector components of relative peripheral refraction were evaluated using repeated measures anovas. Test method for each visual field angle/lens combination were compared via paired t-tests.

RESULTS

Horizontal decentration ranges across the visual field were 1.2 ± 0.6 mm for single vision and 1.2 ± 0.4 mm for multifocal lenses but smaller at 0.7 ± 0.4 mm for NaturalVue lenses. There were only two significant effects of test method across the visual field angle/lens type combinations (single vision: for emmetropes horizontal/vertical astigmatism component at 35° nasal with mean difference -0.38 D and for myopes spherical equivalent refraction at 20° temporal with mean difference +0.24 D).

CONCLUSION

Upon eye rotation the contact lenses decentred on the eye, but not enough to affect peripheral refraction. For the types assessed and for the horizontal visual field out to ±35° when measurements were performed with the Grand-Seiko WAM-5500 autorefractor, it is valid to use eye rotations to investigate peripheral refraction.

True rotational stability of a single-piece hydrophobic intraocular lens

BACKGROUND

To evaluate rotation and its influencing factors of an aspheric one-piece hydrophobic acrylic intraocular lens (IOL) Vivinex XY1 during 6 months after operation.

METHODS

In this institutional trial, 122 eyes of 66 patients were implanted with a non-toric aspheric IOL Vivinex XY1 (Hoya Corporation, Tokyo, Japan). IOL alignment was assessed at the end of surgery, 1 hour, 1 week, 1 month and 6 months after implantation. Confounding factors such as axial length, presence of anterior fibrosis and randomised implantation in four different intended axes (0°, 45°, 90°, 135°) were evaluated. Decentration and tilt were measured using a Purkinje metre.

RESULTS

Assessment of rotational stability was possible for 103 of 122 implanted IOLs 6 months after eye surgery. The median absolute rotation was 1.1° (range: 0°-5°). Rotation was significantly increased within the first hour after operation compared with later time-points (p<0.001). No correlation was found with axial length and rotation (Spearman's r=0.048, p=0.63). No significant difference was observed regarding different implantation axes (p=0.75). Rotation was not influenced by the presence of anterior fibrosis (p=0.98).

CONCLUSION

Assessing the true IOL position at the end of surgery is crucial for the evaluation of rotational stability of IOLs. No IOL rotation exceeding 5° could be detected 6 months after surgery.

Assessment of tilt and decentration of crystalline lens and intraocular lens relative to the corneal topographic axis using anterior segment optical coherence tomography

Purpose

To investigate the tilt and decentration of the crystalline lens and the intraocular lens (IOL) relative to the corneal topographic axis using anterior segment ocular coherence tomography (AS-OCT).

Methods

A sample set of 100 eyes from 49 subjects (41 eyes with crystalline lenses and 59 eyes with IOLs) were imaged using second generation AS-OCT (CASIA2, TOMEY) in June and July 2016 at Okayama University. Both mydriatic and non-mydriatic images were obtained, and the tilt and decentration of the crystalline lens and the IOL were quantified. The effects of pupil dilation on measurements were also assessed.

Results

The crystalline lens showed an average tilt of 5.15° towards the inferotemporal direction relative to the corneal topographic axis under non-mydriatic conditions and 5.25° under mydriatic conditions. Additionally, an average decentration of 0.11 mm towards the temporal direction was observed under non-mydriatic conditions and 0.08 mm under mydriatic conditions. The average tilt for the IOL was 4.31° towards the inferotemporal direction relative to the corneal topographic axis under non-mydriatic conditions and 4.65° in the same direction under mydriatic conditions. The average decentration was 0.05 mm towards the temporal direction under non-mydriatic conditions and 0.08 mm in the same direction under mydriatic conditions. A strong correlation was found between the average tilt and decentration values of the crystalline lens and the IOL under both non-mydriatic and mydriatic conditions (all Spearman correlation coefficients, r ≥ 0.800; all P < 0.001).

Conclusion

When measured using second generation AS-OCT, both the crystalline lens and the IOL showed an average tilt of 4–6° toward the inferotemporal direction relative to the corneal topographic axis and an average decentration of less than 0.12 mm towards the temporal direction. These results were not influenced by pupil dilation and they showed good repeatability.

Predictive factors for photic phenomena after refractive, rotationally asymmetric, multifocal intraocular lens implantation

AIM

To investigate the independent factors associated with photic phenomena in patients implanted with refractive, rotationally asymmetric, multifocal intraocular lenses (MIOLs).

METHODS

Thirty-four eyes of 34 patients who underwent unilateral cataract surgery, followed by implantation of rotationally asymmetric MIOLs were included. Distance and near visual acuity outcomes, intraocular aberrations, preferred reading distances, preoperative and postoperative refractive errors, mesopic and photopic pupil diameters, and the mesopic and photopic kappa angles were assessed. Patients were also administered a satisfaction survey. Photic phenomena were graded by questionnaire. Independent-related factors were identified by correlation and bivariate logistic regression analyses.

RESULTS

The distance from the photopic to the mesopic pupil center (pupil center shift) was significantly associated with glare/halo symptoms [odds ratio (OR)=2.065, 95% confidence interval (CI)=0.916-4.679, P=0.006] and night vision problems (OR=1.832, 95% CI=0.721-2.158, P=0.007). The preoperative photopic angle kappa was significantly associated with glare/halo symptoms (OR=2.155, 95% CI=1.065-4.362, P=0.041). The photopic angle kappa was also significantly associated with glare/halo symptoms (OR=2.155, 95% CI=1.065-4.362, P=0.041) and with night vision problems (OR=1.832, 95% CI=0.721-2.158, P=0.007) in patients implanted with rotationally asymmetric MIOLs.

CONCLUSION

A large pupil center shift and misalignment between the visual and pupillary axis (angle kappa) may play a role in the occurrence of photic phenomena after implantation of rotationally asymmetric MIOLs.

Topography-Guided Transepithelial Surface Ablation in the Treatment of Moderate to High Astigmatism

PURPOSE

To analyze the outcomes of treatment of astigmatism of 2.00 diopters (D) or greater with topography-guided transepithelial surface ablation.

METHODS

Retrospective analysis of a series of 206 eyes divided into two groups: myopic astigmatism (153 eyes) and mixed astigmatism (53 eyes). All cases were treated with topography-guided transepithelial surface ablation. Efficacy, safety, and predictability were evaluated, and vector analysis of cylindrical correction was performed.

RESULTS

The median preoperative spherical equivalent was -2.63 and -0.63 D for the myopic and mixed astigmatism groups, respectively, with median cylinder of -2.50 D. Postoperative uncorrected distance visual acuity was 20/20 or better in 92% and 83% of eyes in the myopic and mixed astigmatism groups, respectively; the corresponding efficacy indices were 1.00 and 0.96 and residual astigmatism of 0.50 D or less was present in 82.4% and 56.7% of eyes in the myopic and mixed astigmatism groups, respectively. The arithmetic mean magnitude of the difference vector was 0.38 (myopic) and 0.65 (mixed) D. Difference vector magnitude was positively correlated with the magnitude of target induced astigmatism in both groups. The geometric mean coefficient of adjustment index was 1.04 and 1.19, representing undercorrection of 4% and 19% in the myopic and mixed astigmatism groups, respectively.

CONCLUSIONS

Topography-guided transepithelial ablation is a safe, effective, and predictable treatment for moderate to high astigmatism. [J Refract Surg. 2016;32(6):418-425.].

Higher order aberrations of the eye: Part one

This article is the first in a series of two articles that provide a comprehensive literature review of higher order aberrations (HOAs) of the eye. The present article mainly explains the general principles of such HOAs as well as HOAs of importance, and the measuring apparatus used to measure HOAs of the eye. The second article in the series discusses factors contributing to variable results in measurements of HOAs of the eye.Keywords: Higher order aberrations; wavefront aberrations; aberrometer

Time Course of Pupil Center Location after Ocular Drug Application

PURPOSE

To investigate the time course of pupil centration after application of common topical ocular drugs.

METHODS

Single drops of 2.5% phenylephrine hydrochloride, 1% tropicamide, and 2% pilocarpine hydrochloride were applied on different days to the right eyes of 12 participants. Anterior eye images were captured, at 5-min intervals for an hour, using an infrared-sensitive camera. The images were analyzed to determine pupil diameter and pupil center, the latter with respect to the limbal center. As a control, natural pupil size and pupil center were determined under different illuminances.

RESULTS

Pupil centers of natural pupils shifted temporally as pupils dilated. At common pupil sizes, drug-induced pupil centers were different from natural pupil centers. Phenylephrine produced a center shift in the nasal and inferior directions that peaked after a mean of 30 min, whereas dilation was continuing up to 60 min. Tropicamide produced transient center shifts in the nasal and inferior directions that peaked at about 10 min before reducing toward baseline values, whereas dilation reached a peak at about 25 min. Pilocarpine produced a small sustained superior shift that, like constriction, reached a peak after about 25 min.

CONCLUSIONS

Application of topical ophthalmic drugs cause shifts in pupil center that do not match those produced by natural changes in pupil size and that, in the cases of phenylephrine and tropicamide, follow a different time course than the pupil size changes.

Combined wavefront-guided laser in situ keratomileusis and aspheric ablation profile with iris registration to correct myopia

PURPOSE

To compare the effects of a combined wavefront-guided and aspheric ablation profile with an aspheric ablation profile alone to correct myopia in patients with a preoperative total higher-order aberration root mean square (HOA RMS) lower than 0.30 μm in both eyes.

SETTING

Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China.

DESIGN

Comparative case series.

METHODS

Laser in situ keratomileusis was performed, with 1 eye randomized to wavefront-guided with aspheric ablation and the fellow eye to aspheric ablation only. The uncorrected (UDVA) and corrected (CDVA) distance visual acuities, manifest subjective refraction, corneal topography, RMS value of total and grouped HOAs, and contrast sensitivity were measured preoperatively and 1 and 6 months postoperatively.

RESULTS

The study enrolled 62 eyes (31 patients). The increasing factors of total HOA RMS, 3rd-order RMS and 4th-order RMS were 2.09, 2.09, and 1.99, respectively, in the wavefront-guided with aspheric ablation group and 2.52, 2.68, and 2.51, respectively, in the aspheric ablation only group at 6 months; the aspheric ablation group had statistically significantly larger increasing factors (P=.016, P=.038, and P=.027, respectively). The reduction in contrast sensitivity log values was statistically significantly less in the wavefront-guided with aspheric ablation group than in the aspheric ablation only group except at 1.5 cycles per degree.

CONCLUSION

The wavefront-guided with aspheric ablation profile was associated with better limitation of HOAs and faster recovery of mesopic contrast sensitivity for patients with a preoperative total HOA RMS lower than 0.30 μm.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Dilute brimonidine to improve patient comfort and subconjunctival hemorrhage after LASIK

PURPOSE

To investigate whether dilute brimonidine (0.025%) reduces patient discomfort, subconjunctival hemorrhage, and injection after LASIK without a significant increase in the rate of flap complications or surgical enhancements.

METHODS

This randomized, double-blind, prospective study enrolled 180 patients (360 eyes) in a contralateral eye comparison of topical dilute brimonidine, naphazoline/pheniramine, or Systane Ultra (Alcon Laboratories, Inc., Fort Worth, TX) administered shortly before LASIK for any indication. Patients were evaluated for subconjunctival hemorrhage, injection, and flap dislocation 1 hour and 1 day postoperatively. Patient questionnaires measuring patient comfort and ocular symptoms were administered at these same follow-up visits. Patients were examined for 3 months to determine similar outcomes for standard indices of safety, predictability, efficacy, and enhancement rates.

RESULTS

Scores of patient discomfort, subconjunctival hemorrhage, and injection were significantly lower in eyes treated with dilute brimonidine at the 1 hour and 1 day postoperative examinations. Refloats for mild-flap edge wrinkling were required in 3 brimonidine eyes (2.5%), 1 naphazoline/pheniramine eye (0.8%), and no control eyes, but this difference did not reach statistical significance (P = .18). There was no significant difference between eyes at 3 months in terms of visual acuity, refractive error, corrected distance visual acuity, or rate of enhancement.

CONCLUSIONS

Use of dilute brimonidine before LASIK reduces subconjunctival hemorrhage and injection and improves patient comfort after surgery. Flap edge wrinkling requiring refloat may still be a complication with dilute brimonidine.

One-step transepithelial topography-guided ablation in the treatment of myopic astigmatism

PURPOSE

To evaluate one-step topography-guided transepithelial ablation in the treatment of low to moderate myopic astigmatism using a 1KHz excimer laser.

METHODS

Retrospective study of 117 consecutive eyes available for evaluation 12 months after surgery. Pre- and post-operative visual and refractive data as well as post-operative pain and haze were analyzed. A novel technique integrating custom refractive- and epithelial- ablation in a single uninterrupted procedure was used.

RESULTS

The mean pre-operative spherical equivalent (SE) and the mean cylinder were: -3.22 diopters (D) ±1.54 (SD) (range -0.63 to -7.25 D) and -0.77 D ±0.65 (range 0 to -4.50 D), respectively. At 12 months after surgery: no eyes lost ≥2 lines of corrected distant visual acuity (CDVA). Safety and efficacy indexes were 1.27 and 1.09, respectively. Uncorrected distant visual acuity (UDVA) was ≥20/20 in 96.6% of the eyes. Manifest refraction spherical equivalent was within ±0.5 D of the desired refraction in 93.2% of the eyes. Average root mean square (RMS) wavefront error measured at central 6 mm, increased from 0.38 pre-operatively to 0.47 µm post-operatively. Refractive stability was achieved and sustained 1 month after surgery. No visually significant haze was registered during the observation period. Post-operative pain was reported in 4.5% of patients.

CONCLUSIONS

One-step transepithelial topography-guided treatment for low to moderate myopia and astigmatism performed with a 1 KHz laser, provided safe, effective, predictable and stable results with low pain and no visually significant haze.

Effect of pupil size on residual wavefront aberration with transition zone after customized laser refractive surgery

The analysis of the change in residual wavefront aberrations after laser refractive surgery is important for the development of visual correction technology. Based on the ablation profile for wavefront-guided refractive surgery including optical zone and transition zone, the effect of pupil size on residual wavefront aberrations was studied. The research revealed that the optical zone to pupil ratio had a significant influence on the residual wavefront aberrations. The residual spherical aberration and coma were obviously larger than other individual Zernike higher-order terms when pupil diameter was larger than the optical zone size, and they increased rapidly as the pupil size increased. In addition, when the ablation zone diameter was kept constant, the residual higher-order aberrations increased rapidly as the blend coefficient increased for a 6 mm or 7 mm pupil. Furthermore, the residual higher-order aberrations with treatment decentration were distinctly larger than those without decentration. In the achievement of the best postoperative visual performance, the design of ablation profile played a crucial role in decrease of the residual wavefront aberrations after refractive surgery, especially optical zone size and the ablation pattern of transition zone.

Comparison of wavefront-guided aspheric laser in situ keratomileusis for myopia: coaxially sighted corneal-light-reflex versus line-of-sight centration

PURPOSE

To compare refractive outcomes, higher-order aberrations (HOAs), and contrast sensitivity of myopic wavefront-guided aspheric laser in situ keratomileusis centered on the coaxially sighted corneal light reflex or on the line of sight.

SETTING

Okamoto Eye Clinic, Ehime, Japan.

DESIGN

Comparative case series.

METHODS

Data at 3 months were compared based on the distance between the coaxially sighted corneal light reflex and the line of sight (P-distance) as follows: distance greater than 0.25 mm (high-distance group), distance greater than 0.15 mm and less than 0.25 mm (intermediate-distance group), and distance less than 0.15 mm (low distance group).

RESULTS

The chart review included 317 eyes in the corneal-light-reflex group and 269 eyes in the line-of-sight group. The mean postoperative manifest refraction spherical equivalent was +0.123 diopter (D) ± 0.378 (SD) and +0.187 ± 0.480 D, respectively (P = .07). The safety and efficacy indices were significantly higher in the corneal-light-reflex group, including the high-distance subgroup and eyes with a P-distance less than 0.25 mm (P<.05, all cases). The HOAs (P<.001) and coma (P = .001) were significantly higher in the line-of-sight group (P<.001 and P = .001, respectively). The line-of-sight group had a significantly greater change in contrast sensitivity (P = .026).

CONCLUSIONS

Centration on the coaxially sighted corneal light reflex resulted in better safety, effectiveness, and contrast sensitivity than line-of-sight centration. Centration on the coaxially sighted corneal light reflex was safer for myopic eyes with P-distances greater than 0.25 mm.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.

Outcomes of custom laser in situ keratomileusis: dilated wavescans versus undilated wavescans

PURPOSE

To evaluate refractive outcomes of custom laser in situ keratomileusis (LASIK) based on undilated and pharmacologically dilated wavefront aberrometry with the Visx laser system.

SETTING

Clinical refractive practice, St. Louis, Missouri, USA.

DESIGN

Comparative case series.

METHODS

Eyes that had LASIK using dilated wavescans (study group) were evaluated for the reason for use of dilated scans; age; preoperative refractive error; preoperative root mean square (RMS), coma, trefoil, and spherical aberration values; postoperative uncorrected distance visual acuity (UDVA); postoperative refractive error; percentage of iris-registration capture; and enhancement rate. The study group was compared with a control group that had LASIK using undilated wavescans.

RESULTS

The study group comprised 52 eyes (31 patients) and the control group, 104 eyes (55 patients). At 1 month, the mean postoperative UDVA was 20/21 in the study group and 20/22 in the control group and at 3 months, 20/22 and 20/20, respectively. At 1 month, the mean postoperative spherical equivalent (SE) was +0.07 diopter (D) ± 0.49 (SD) in the study group and +0.14 ± 0.30 D in the control group and at 3 months, -0.01 ± 0.44 D and +0.02 ± 0.23 D, respectively; there was no statistically significant difference between groups at either timepoint. There was no statistically significant difference in preoperative RMS or postoperative coma, trefoil, or spherical aberration between the groups. Although the study group had a slightly higher enhancement rate, the difference was not statistically significant.

CONCLUSION

Compared with custom LASIK based on undilated wavescans, use of dilated wavescans for custom LASIK resulted in comparable postoperative outcomes.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Contribution of optical zone decentration and pupil dilation on the change of optical quality after myopic photorefractive keratectomy in a cat model

PURPOSE

To simulate the simultaneous contribution of optical zone decentration and pupil dilation on retinal image quality using wavefront error data from a myopic photorefractive keratectomy (PRK) cat model.

METHODS

Wavefront error differences were obtained from five cat eyes 19+/-7 weeks (range: 12 to 24 weeks) after spherical myopic PRK for -6.00 diopters (D) (three eyes) and -10.00 D (two eyes). A computer model was used to simulate decentration of a 6-mm sub-aperture relative to the measured wavefront error difference. Changes in image quality (visual Strehl ratio based on the optical transfer function [VSOTF]) were computed for simulated decentrations from 0 to 1500 mum over pupil diameters of 3.5 to 6.0 mm in 0.5-mm steps. For each eye, a bivariate regression model was applied to calculate the simultaneous contribution of pupil dilation and decentration on the pre- to postoperative change of the log VSOTF.

RESULTS

Pupil diameter and decentration explained up to 95% of the variance of VSOTF change (adjusted R(2)=0.95). Pupil diameter had a higher impact on VSOTF (median beta=-0.88, P<.001) than decentration (median beta=-0.45, P<.001). If decentration-induced lower order aberrations were corrected, the impact of decentration further decreased (beta=-0.26) compared to the influence of pupil dilation (beta=-0.95).

CONCLUSIONS

Both pupil dilation and decentration of the optical zone affected the change of retinal image quality (VSOTF) after myopic PRK with decentration exerting a lower impact on VSOTF change. Thus, under physiological conditions pupil dilation is likely to have more effect on VSOTF change after PRK than optical zone decentration.

The effect of the asphericity of myopic laser ablation profiles on the induction of wavefront aberrations

PURPOSE

To compare the effects of laser profile asphericity on the induction of wavefront aberrations, susceptibility to decentration, and depth of focus in a polymethylmethacrylate (PMMA) model.

METHODS

Four PMMA lenses received an excimer laser ablation of -6 D with a 6-mm optical zone and different amounts of primary spherical aberration (Z(4)(0)): 0, -0.346, -1.038, and -2.076 microm. The curvature of each lens was measured by using surface profilometry, and wavefront changes were computed from curvature differences. Changes in optical quality were compared by treatment simulation of 13 real myopic eyes. The influence of pupil diameter, ablation decentration, and defocus on retinal image quality was measured by using the optical transfer function-based visual Strehl ratio (VSOTF).

RESULTS

Aspheric ablation profiles induced significantly less primary but higher secondary spherical aberration (Z(6)(0)) than did the standard profile; however, Z(4)(0) compensation was incomplete. Simulated treatments with aspheric profiles resulted in significantly better retinal image quality and higher decentration tolerance than did the standard profile. Optical depth of focus was not affected with a 3-mm pupil, whereas with a 6-mm pupil, there was a small but statistically significant decrease in depth of focus.

CONCLUSIONS

Aspheric laser profiles showed theoretical optical benefits over standard ablation profiles for the treatment of myopia, including terms of decentration tolerance. However, there remained profound induction and thus, undercorrection of Z(4)(0), due to loss of laser ablation efficiency in the lens periphery.

Wavefront aberrations in eyes with decentered ablations

PURPOSE

To compare the refractive and functional outcomes and wavefront profiles in eyes with decentered ablations and eyes with well-centered ablations.

SETTING

Medical Research Foundation, Chennai, Tamil Nadu, India.

METHODS

This retrospective analysis comprised eyes with topographically diagnosed decentered ablations after laser in situ keratomileusis (LASIK). Refraction, contrast sensitivity, and ocular wavefront aberrations were measured preoperatively and 1 month postoperatively. The induced aberrations in these eyes were compared with those in eyes with well-centered ablations.

RESULTS

Forty-six eyes (38 patients) had decentered ablations and 60 eyes (32 patients), well-centered ablations. The mean decentration in the study group was 0.86 mm +/- 0.29 (SD) (range 0.35 to 1.61 mm). There was no significant correlation between decentration and attempted refractive correction. There was, however, a statistically significant (P<.05) linear correlation between the distance of decentration and the magnitude of induced tilt (r = -0.31), coma (r = -0.41), and secondary astigmatism (r = 0.36). The induced changes in tilt, oblique astigmatism, vertical coma, and spherical aberration were statistically significantly higher in eyes with decentered ablations than in eyes with well-centered ablations. A statistically significantly higher percentage of eyes (87%) with well-centered ablations than eyes with decentered ablations (70%) had a postoperative uncorrected visual acuity (UCVA) of 20/20 or better. There was no significant difference in contrast sensitivity between groups.

CONCLUSION

Eyes with decentered ablations had a significantly higher magnitude of induced aberrations and lower UCVA than eyes with well-centered ablations.

Residual higher-order aberrations caused by clinically measured cyclotorsional misalignment or decentration during wavefront-guided excimer laser corneal ablation

PURPOSE

To evaluate the impact of residual wavefront aberrations on optical image quality induced by cyclotorsional misalignment and centration error.

SETTING

Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA.

METHODS

Cyclotorsional misalignment and decentration were measured in 58 eyes of 38 patients using an iris-registration system. To calculate residual wavefront aberrations if iris registration was not engaged, each eye's preoperative wavefront map was rotated or decentered by the amounts calculated by iris registration; this wavefront was subtracted from the preoperative wavefront (6.0 mm pupil). The impact of the residual wavefront aberrations on optical quality were analyzed by (1) the root mean square of the total aberrations (2nd to 6th orders), lower-order aberrations (LOAs) (2nd order), and higher-order aberrations (HOAs) (3rd to 6th orders); (2) normalized polar Zernike coefficients; (3) polychromatic modulation transfer function (PMTF) with the Stiles-Crawford effect.

RESULTS

On average, centration error induced 4.9 times, 2.8 times, and 8.7 times higher values of total aberrations, LOAs, and HOAs, respectively, than cyclotorsional misalignment. For all Zernike terms except 2nd-order astigmatism, centration error produced significantly higher values than cyclorotational misalignment (all P<.05 with Bonferroni correction). Compared with the PMTF value with perfect alignment, cyclotorsional misalignment decreased the PMTF values slightly whereas centration error reduced the PMTF values by 31% to 66%.

CONCLUSION

Theoretically, image quality was reduced more by clinically measured decentration than by cyclotorsional misalignment.

Higher-Order Wavefront Aberrations for Populations of Young Emmetropes and Myopes

Purpose

To test the hypothesis that human eyes have a central tendency to be free of higher-order aberrations by analyzing wavefront aberrations for two young populations of respectively emmetropic and myopic subjects.

Methods

Both right and left eyes of 75 emmetropes and 196 myopes were measured for corneal wavefront aberration using a Humphrey corneal topographer and for the whole eye wavefront aberration using a WASCA wavefront sensor without pupil dilation. 35 Zernike aberration coefficients over a 6.0 mm pupil diameter were derived, and statistics of the higher-order terms (3^rd to 5^th orders) were tested.

Results

When signed Zernike aberrations of the right and left eyes were averaged together for the emmetropes, three higher-order modes (j=6, 12 and 13) were significantly different from zero in both the cornea and the whole eye (P<0.0005), and three additional terms (j=14, 15 and 17) were statistically non-zero for the whole eye. As the signs of y-axis asymmetrical terms in the left eye were flipped, three more terms in either the cornea (j=8, 18 and 19) or the whole eye (j=8, 10 and 20) became statistically non-zero. For the myopes, 8 corneal terms and 5 whole-eye terms were statistically non-zero when the two eyes were averaged together. As the signs flipped, the majority of the Zernike aberration terms were statistically different from zero.

Conclusions

Human eyes have systematical higher order aberrations in population, and factors that cause bilateral symmetry of wavefront aberrations between the right and left eyes made important contribution to the systematical aberrations.

Patient satisfaction and visual symptoms after wavefront-guided and wavefront-optimized LASIK with the WaveLight platform

PURPOSE

To investigate patient satisfaction and visual symptoms after wavefront-guided LASIK.

METHODS

A prospective, randomized, double-masked, controlled study comprised 200 eyes of 100 young patients who underwent LASIK for myopia and astigmatism. Patients were randomly divided into two different treatment groups: standard ablation using wavefront-optimized profiles (wavefront-optimized group) and aberration customized aspheric treatment ablation (customized group) using the WaveLight ALLEGRETTO platform. Patients were asked to complete questionnaires regarding reasons for surgery, satisfaction, and visual symptoms. Patients were followed for 6 months.

RESULTS

The most frequent motivating factor for surgery was to improve uncorrected visual acuity (UCVA) in the wavefront-optimized and customized groups (both 100%), followed by freedom from spectacles (86.9% vs 96.3%). At 6 months postoperatively, over 95% of patients in both groups reported their UCVA was as good as anticipated and they were satisfied with the surgery and would recommend the operation to a friend or family member. Satisfaction was not correlated with age, attempted refractive error, residual refractive error, postoperative UCVA, or root-mean-square higher order aberration. The rate of postoperative overall visual symptoms was reduced and the mean analog scores of the symptoms in both groups did not change significantly postoperatively (P > .05). The rate of visual symptoms such as glare (8.7% vs 7.4%), halo (0% vs 7.4%), and night driving difficulty (8.7% vs 3.7%) decreased after LASIK at 6 months postoperatively in the wavefront-optimized and customized groups, respectively.

CONCLUSIONS

Patient satisfaction was achieved in young myopic patients who underwent wavefront-guided and standard ("wavefront-optimized") LASIK. The rate of visual symptoms such as glare, halo, and night driving difficulty decreased postoperatively after both treatment protocols.

The effect of optical zone decentration on lower- and higher-order aberrations after photorefractive keratectomy in a cat model

PURPOSE

To simulate the effects of decentration on lower- and higher-order aberrations (LOAs and HOAs) and optical quality, by using measured wavefront error (WFE) data from a cat photorefractive keratectomy (PRK) model.

METHODS

WFE differences were obtained from five cats' eyes 19 +/-7 weeks after spherical myopic PRK for -6 D (three eyes) and -10 D (two eyes). Ablation-centered WFEs were computed for a 9.0 mm pupil. A computer model was used to simulate decentration of a 6-mm subaperture in 100-microm steps over a circular area of 3000 microm diameter, relative to the measured WFE difference. Changes in LOA, HOA, and image quality (visual Strehl ratio based on the optical transfer function; VSOTF) were computed for simulated decentrations over 3.5 and 6.0 mm.

RESULTS

Decentration resulted in undercorrection of sphere and induction of astigmatism; among the HOAs, decentration mainly induced coma. Decentration effects were distributed asymmetrically. Decentrations >1000 microm led to an undercorrection of sphere and cylinder of >0.5 D. Computational simulation of LOA/HOA interaction did not alter threshold values. For image quality (decrease of best-corrected VSOTF by >0.2 log units), the corresponding thresholds were lower. The amount of spherical aberration induced by the centered treatment significantly influenced the decentration tolerance of LOAs and log best corrected VSOTF.

CONCLUSIONS

Modeling decentration with real WFE changes showed irregularities of decentration effects for rotationally symmetric treatments. The main aberrations induced by decentration were defocus, astigmatism, and coma. Treatments that induced more spherical aberration were less tolerant of decentration.

Wellenfrontaberrationen und subjektive optische Qualität nach wellenfrontgeführter LASIK

PURPOSE

To investigate the clinical impact of the postoperative ocular wavefront error (WFE) on subjective quality of vision (SQV) after LASIK.

METHOD

Forty-one myopic eyes of 21 patients underwent uneventful LASIK (median -4.63 D). Preoperatively and 1 month postoperatively, WFE measurements were performed and overall SQV was assessed for two lighting conditions (photopic and mesopic) with a questionnaire. Three different WFE representations were computed for a pupil diameter of 6 mm: (1) the visual quality metric VSOTF (visual Strehl ratio based on the optical transfer function), (2) RMS (root mean square) values of the Zernike orders 2-5, and (3) individual Zernike coefficient for orders 2-5. The impact of the postoperative WFE on SQV was calculated using linear regression analysis.

RESULTS

For photopic conditions R(2) was 0.24 for model 1 (VSOTF), 0.31 for model 2 (RMS values), and 0.29 for model 3 (Zernike coefficients). Second-and fifth-order aberrations had significant influence on SQV. For mesopic conditions, results were similar.

CONCLUSION

Subjective quality of vision after wavefront-guided LASIK could be explained partially by the ocular WFE.

Photorefractive keratectomy in the cat eye: biological and optical outcomes

PURPOSE

To quantify optical and biomechanical properties of the feline cornea before and after photorefractive keratectomy (PRK) and assess the relative contribution of different biological factors to refractive outcome.

SETTING

Department of Ophthalmology, University of Rochester, Rochester, New York, USA.

METHODS

Adult cats had 6.0 diopter (D) myopic or 4.0 D hyperopic PRK over 6.0 or 8.0 mm optical zones (OZ). Preoperative and postoperative wavefront aberrations were measured, as were intraocular pressure (IOP), corneal hysteresis, the corneal resistance factor, axial length, corneal thickness, and radii of curvature. Finally, postmortem immunohistochemistry for vimentin and alpha-smooth muscle actin was performed.

RESULTS

Photorefractive keratectomy changed ocular defocus, increased higher-order aberrations, and induced myofibroblast differentiation in cats. However, the intended defocus corrections were only achieved with 8.0 mm OZs. Long-term flattening of the epithelial and stromal surfaces was noted after myopic, but not after hyperopic, PRK. The IOP was unaltered by PRK; however, corneal hysteresis and the corneal resistance factor decreased. Over the ensuing 6 months, ocular aberrations and the IOP remained stable, while central corneal thickness, corneal hysteresis, and the corneal resistance factor increased toward normal levels.

CONCLUSIONS

Cat corneas exhibited optical, histological, and biomechanical reactions to PRK that resembled those previously described in humans, especially when the OZ size was normalized to the total corneal area. However, cats exhibited significant stromal regeneration, causing a return to preoperative corneal thickness, corneal hysteresis and the corneal resistance factor without significant regression of optical changes induced by the surgery. Thus, the principal effects of laser refractive surgery on ocular wavefront aberrations can be achieved despite clear interspecies differences in corneal biology.