In-hospital stroke after transcatheter aortic valve implantation: A UK observational cohort analysis.

OBJECTIVES: We sought to identify baseline demographics and procedural factors that might independently predict in-hospital stroke following transcatheter aortic valve implantation (TAVI). BACKGROUND: Stroke is a recognized, albeit infrequent, complication of TAVI. Established predictors of procedure-related in-hospital stroke; however, remain poorly defined. METHODS: We conducted an observational cohort analysis of the multicenter UK TAVI registry. The primary outcome measure was the incidence of in-hospital stroke. RESULTS: A total of 8,652 TAVI procedures were performed from 2007 to 2015. There were 205 in-hospital strokes reported by participating centers equivalent to an overall stroke incidence of 2.4%. Univariate analysis showed that the implantation of balloon-expandable valves caused significantly fewer strokes (balloon-expandable 96/4,613 [2.08%] vs. self-expandable 95/3,272 [2.90%]; p = .020). After multivariable analysis, prior cerebrovascular disease (CVD) (odds ratio [OR] 1.51, 95% confidence interval [CI 1.05-2.17]; p = .03), advanced age at time of operation (OR 1.02 [0.10-1.04]; p = .05), bailout coronary stenting (OR 5.94 [2.03-17.39]; p = .008), and earlier year of procedure (OR 0.93 [0.87-1.00]; p = .04) were associated with an increased in-hospital stroke risk. There was a reduced stroke risk in those who had prior cardiac surgery (OR 0.62 [0.41-0.93]; p = .01) and a first-generation balloon-expandable valve implanted (OR 0.72 [0.53-0.97]; p = .03). In-hospital stroke significantly increased 30-day (OR 5.22 [3.49-7.81]; p < .001) and 1-year mortality (OR 3.21 [2.15-4.78]; p < .001). CONCLUSIONS: In-hospital stroke after TAVI is associated with substantially increased early and late mortality. Factors independently associated with in-hospital stroke were previous CVD, advanced age, no prior cardiac surgery, and deployment of a predominantly first-generation self-expandable transcatheter heart valve.

Survival relative to pacemaker status after transcatheter aortic valve implantation.

OBJECTIVES: To determine whether a permanent pacemaker (PPM) in situ can enhance survival after transcatheter aortic valve implantation (TAVI), in a predominantly inoperable or high risk cohort. BACKGROUND: New conduction disturbances are the most frequent complication of TAVI, often necessitating PPM implantation before hospital discharge. METHODS: We performed an observational cohort analysis of the UK TAVI registry (2007-2015). Primary and secondary endpoints were 30-day post-discharge all-cause mortality and long-term survival, respectively. RESULTS: Of 8,651 procedures, 6,815 complete datasets were analyzed. A PPM at hospital discharge, irrespective of when implantation occurred (PPM 1.68% [22/1309] vs. no PPM 1.47% [81/5506], odds ratio [OR] 1.14, 95% confidence interval [CI] 0.71-1.84; p = .58), or a PPM implanted peri- or post-TAVI only (PPM 1.44% [11/763] vs. no PPM 1.47% [81/5506], OR 0.98 [0.51-1.85]; p = .95) did not significantly reduce the primary endpoint. Patients with a PPM at discharge were older, male, had right bundle branch block at baseline, were more likely to have received a first-generation self-expandable prosthesis and had experienced more peri- and post-procedural complications including bailout valve-in-valve rescue, bleeding and acute kidney injury. A Cox proportional hazards model demonstrated significantly reduced long-term survival in all those with a PPM, irrespective of implantation timing (hazard ratio [HR] 1.14 [1.02-1.26]; p = .019) and those receiving a PPM only at the time of TAVI (HR 1.15 [1.02-1.31]; p = .032). The reasons underlying this observation warrant further investigation. CONCLUSIONS: A PPM did not confer a survival advantage in the first 30 days after hospital discharge following TAVI.

Optical Assessment of Soft Contact Lens Edge-Thickness.

PURPOSE: To assess the edge shape of soft contact lenses using Gabor-Domain Optical Coherence Microscopy (GD-OCM) with a 2-µm imaging resolution in three dimensions and to generate edge-thickness profiles at different distances from the edge tip of soft contact lenses. METHODS: A high-speed custom-designed GD-OCM system was used to produce 3D images of the edge of an experimental soft contact lens (Bausch + Lomb, Rochester, NY) in four different configurations: in air, submerged into water, submerged into saline with contrast agent, and placed onto the cornea of a porcine eyeball. An algorithm to compute the edge-thickness was developed and applied to cross-sectional images. The proposed algorithm includes the accurate detection of the interfaces between the lens and the environment, and the correction of the refraction error. RESULTS: The sharply defined edge tip of a soft contact lens was visualized in 3D. Results showed precise thickness measurement of the contact lens edge profile. Fifty cross-sectional image frames for each configuration were used to test the robustness of the algorithm in evaluating the edge-thickness at any distance from the edge tip. The precision of the measurements was less than 0.2 µm. CONCLUSIONS: The results confirmed the ability of GD-OCM to provide high-definition images of soft contact lens edges. As a nondestructive, precise, and fast metrology tool for soft contact lens measurement, the integration of GD-OCM in the design and manufacturing of contact lenses will be beneficial for further improvement in edge design and quality control. In the clinical perspective, the in vivo evaluation of the lens fitted onto the cornea will advance our understanding of how the edge interacts with the ocular surface. The latter will provide insights into the impact of long-term use of contact lenses on the visual performance.

Quantitative optical inspection of contact lenses immersed in wet cell using swept source OCT.

We demonstrate swept source optical coherence tomography (OCT) imaging of contact lenses (CLs) in a wet cell and comprehensive quantitative characterization of CLs from volumetric OCT datasets. The approach is based on a technique developed for lens autopositioning and autoleveling enabled by lateral capillary interactions between the wet cell wall and the lens floating on the liquid surface. The demonstrated OCT imaging has enhanced contrast due to the application of a scattering medium and it improves visualization of both CL interfaces and edges. We also present precise and accurate three-dimensional metrology of soft and rigid CLs based on the OCT data. The accuracy and precision of the extracted lens parameters are compared with the manufacturer's specifications. The presented methodology facilitates industrial inspection methods of the CLs.

Predicting through-focus visual acuity with the eye's natural aberrations.

PURPOSE: To develop a predictive optical modeling process that utilizes individual computer eye models along with a novel through-focus image quality metric. METHODS: Individual eye models were implemented in optical design software (Zemax, Bellevue, WA) based on evaluation of ocular aberrations, pupil diameter, visual acuity, and accommodative response of 90 subjects (180 eyes; 24-63 years of age). Monocular high-contrast minimum angle of resolution (logMAR) acuity was assessed at 6 m, 2 m, 1 m, 67 cm, 50 cm, 40 cm, 33 cm, 28 cm, and 25 cm. While the subject fixated on the lowest readable line of acuity, total ocular aberrations and pupil diameter were measured three times each using the Complete Ophthalmic Analysis System (COAS HD VR) at each distance. A subset of 64 mature presbyopic eyes was used to predict the clinical logMAR acuity performance of five novel multifocal contact lens designs. To validate predictability of the design process, designs were manufactured and tested clinically on a population of 24 mature presbyopes (having at least +1.50 D spectacle add at 40 cm). Seven object distances were used in the validation study (6 m, 2 m, 1 m, 67 cm, 50 cm, 40 cm, and 25 cm) to measure monocular high-contrast logMAR acuity. RESULTS: Baseline clinical through-focus logMAR was shown to correlate highly (R² = 0.85) with predicted logMAR from individual eye models. At all object distances, each of the five multifocal lenses showed less than one line difference, on average, between predicted and clinical normalized logMAR acuity. Correlation showed R² between 0.90 and 0.97 for all multifocal designs. CONCLUSIONS: Computer-based models that account for patient's aberrations, pupil diameter changes, and accommodative amplitude can be used to predict the performance of contact lens designs. With this high correlation (R² ≥ 0.90) and high level of predictability, more design options can be explored in the computer to optimize performance before a lens is manufactured and tested clinically.

CLEAR - Contact lens optics.

The most fundamental aspect of a contact lens is its optics; the manner in which the refraction of light is managed to optimise vision to the clinical benefit of the lens wearer. This report presents contemporary information on the optical structure of the eye and the optical models employed to understand the correction of refractive error. The design, measurement and clinical assessment of spherical, aspheric, toric, multifocal and myopia control contact lenses are described. The complexity and variety of multifocal lenses is recognised and detailed information is provided for alternating, simultaneous, diffractive, annular, aspheric and extended depth of field lens designs. In terms of clinical assessment, a contemporary review is provided for the measurement of: visual acuity, contrast sensitivity, through focus curves, reading performance, peripheral refraction, toric displacement realignment and patient reported outcomes. Overall, the paper aims to serve as a resource for the prescribing clinician, who can optimise contact lens corrections for patients by building on the optical rationale of these devices; and also highlights future opportunities for research innovation.

ACTIVATION (PercutAneous Coronary inTervention prIor to transcatheter aortic VAlve implantaTION): A Randomized Clinical Trial.

OBJECTIVES: This study sought to determine if percutaneous coronary intervention (PCI) prior to transcatheter aortic valve replacement (TAVR) in patients with significant coronary artery disease would produce noninferior clinical results when compared with no PCI (control arm). BACKGROUND: PCI in patients undergoing TAVR is not without risk, and there are no randomized data to inform clinical practice. METHODS: Patients with severe symptomatic aortic stenosis and significant coronary artery disease with Canadian Cardiovascular Society class ≤2 angina were randomly assigned to receive PCI or no PCI prior to TAVR. The primary endpoint was a composite of all-cause death or rehospitalization at 1 year. Noninferiority testing (prespecified margin of 7.5%) was performed in the intention-to-treat population. RESULTS: At 17 centers, 235 patients underwent randomization. At 1 year, the primary composite endpoint occurred in 48 (41.5%) of the PCI arm and 47 (44.0%) of the no-PCI arm. The requirement for noninferiority was not met (difference: -2.5%; 1-sided upper 95% confidence limit: 8.5%; 1-sided noninferiority test P = 0.067). On analysis of the as-treated population, the difference was -3.7% (1-sided upper 95% confidence limit: 7.5%; P = 0.050). Mortality was 16 (13.4%) in the PCI arm and 14 (12.1%) in the no-PCI arm. At 1 year, there was no evidence of a difference in the rates of stroke, myocardial infarction, or acute kidney injury, with higher rates of any bleed in the PCI arm (P = 0.021). CONCLUSIONS: Observed rates of death and rehospitalization at 1 year were similar between PCI and no PCI prior to TAVR; however, the noninferiority margin was not met, and PCI resulted in a higher incidence of bleeding. (Assessing the Effects of Stenting in Significant Coronary Artery Disease Prior to Transcatheter Aortic Valve Implantation; ISRCTN75836930).

Transcatheter aortic valve implantation via surgical subclavian versus direct aortic access: A United Kingdom analysis.

BACKGROUND: Surgical subclavian (SC) and direct aortic (DA) access are established alternatives to the default transfemoral route for transcatheter aortic valve implantation (TAVI). We sought to find differences in survival and procedure-related outcomes after SC- versus DA-TAVI. METHODS: We performed an observational cohort analysis of cases prospectively uploaded to the UK TAVI registry. To ensure the most contemporaneous comparison, the analysis focused on SC and DA procedures performed from 2013 to 2015. RESULTS: Between January 2013 and July 2015, 82 (37%) SC and 142 (63%) DA cases were performed that had validated 1-year life status. Multivariable regression analysis showed procedure duration was longer for SC cases (SC 193.5 ± 65.8 vs. DA 138.4 ± 57.7 min; p < .01) but length of hospital stay was shorter (SC 8.6 ± 9.5 vs. DA 11.9 ± 10.8 days; p = .03). Acute kidney injury was observed less frequently after SC cases (odds ratio [OR] 0.35, 95% confidence interval [CI 0.12-0.96]; p = .042) but vascular access site-related complications were more common (OR 9.75 [3.07-30.93]; p < .01). Procedure-related bleeding (OR 0.54 [0.24-1.25]; p = .15) and in-hospital stroke rate (SC 3.7% vs. DA 2.1%; p = .67) were similar. There were no significant differences in in-hospital (SC 2.4% vs. DA 4.9%; p = .49), 30-day (SC 2.4% vs. DA 4.2%; p = .71) or 1-year (SC 14.5% vs. DA 21.9%; p = .344) mortality. CONCLUSIONS: Surgical subclavian and direct aortic approaches can offer favourable outcomes in appropriate patients. Neither access modality conferred a survival advantage but there were significant differences in procedural metrics that might influence which approach is selected.

Effect of procedural refinement of transfemoral transcatheter aortic valve implantation on outcomes and costs: a single-centre retrospective study.

Objectives: To determine the effect of introducing several procedural refinements of transfemoral transcatheter aortic valve implantation (TAVI) on clinical outcomes and costs. Design: Retrospective analysis comparing two consecutive 1-year periods, before and after the introduction of procedural refinements. Setting: Tertiary hospital aortic valve programme. Participants: Consecutive patients undergoing transfemoral TAVI treated between April 2014 and August 2015 using the initial setup (n=70; control group) or between September 2015 and August 2016 after the introduction of procedural refinements (n=89). Interventions: Introduction of conscious sedation, percutaneous access and closure, omission of transoesophageal echocardiography during the procedure, and an early discharge procedure. Outcome measures: Procedural characteristics, complications and outcomes; length of stay in intensive care unit (ICU) and hospital; hospital-related direct costs associated with TAVI. Results: There were no statistically significant differences in the incidence of complications or mortality between the two groups. The mean length of stay in the ICU was significantly shorter in the procedural-refinement group compared with the control group (5.1 vs 57.2 hours, p<0.001), as was the mean length of hospital stay (4.7 vs 6.6 days, p<0.001). The total cost per TAVI procedure was significantly lower, by £3580, in the procedural-refinement group (p<0.001). This was largely driven by lower ICU costs. Conclusions: Among patients undergoing transfemoral TAVI, procedural refinement facilitated a shorter stay in ICU and earlier discharge from hospital and was cost saving compared with the previous setup.

Usefulness of 64-detector row computed tomography for evaluation of intracoronary stents in symptomatic patients with suspected in-stent restenosis.

To determine whether 64-slice multidetector computed tomographic coronary angiography (MDCTA) can accurately assess the coronary artery lumen in symptomatic patients with previous coronary artery stents and potential in-stent restenosis (ISR). The primary aim was to determine the accuracy of binary ISR exclusion using MDCTA compared with invasive catheter angiography (ICA). Secondary aims were comparisons of stent dimensions measured using MDCTA and variables that affect accuracy. Forty patients with previous stent placement underwent both ICA and 64-slice MDCTA after elective presentation with chest pain, and ICA quantitative coronary angiographic data were used as the reference standard. Thirty-six men and 4 women (age 64 +/- 10 years; range 44 to 83) with 103 stents (2.8 +/- 1.6 stents/patient) were comparatively evaluated (stent exclusion rate 9.6%). There were 45 bare-metal and 58 drug-eluting stents (20 +/- 18 months after implantation) with an average diameter of 3.23 +/- 0.7 mm. Overall accuracy for the detection of significant ISR showed sensitivity, specificity, and positive and negative predictive values of 85%, 86%, 61%, and 96% for proximal stents > or =3 mm, which improved to 100%, 94%, 81%, and 100%; if the visible luminal diameter on MDCTA was <1.5 mm, accuracy decreased to 40%, 84%, 29%, and 90%, respectively. In conclusion, 64-slice MDCTA assessment of symptomatic patients with suspected clinically significant ISR is a realistic alternative to ICA if reference stent diameter is > or =2.5 mm and visible lumen cross-sectional diameter is > or =1.5 mm, for which a negative MDCTA result virtually excludes the presence of significant ISR.

Transapical valve-in-ring mitral valve implantation through the anterior mitral valve leaflet.

Transcatheter mitral valve implantation (TMVI) is a relatively novel intervention used to replace the mitral valve of individuals deemed too high risk or unsuitable for surgery. It is associated with a number of specific risks, including left ventricular outflow tract obstruction (LVOTO).  In this video tutorial we present the case of a 75-year-old man who was unable to undergo redo surgical repair and had a number of risk factors for LVOTO. To minimize these risks, we deployed the TMVI within the anterior mitral valve leaflet. The postoperative result was mild mitral valve regurgitation and no LVOTO.  The long-term outcome of this approach is yet to be determined but we believe this technique offers a novel method to manage a select group of patients suffering with mitral valve disease and at risk of LVOTO.

Transapical valve-in-ring mitral valve implantation through the anterior mitral valve leaflet.

Transcatheter mitral valve implantation is a relatively novel intervention that replaces the mitral valve of individuals deemed too high-risk or unsuitable for surgery. It is associated with a number of specific risks, including left ventricular outflow tract obstruction. In this report, we present the case of a 75-year-old man who was unable to undergo redo surgical repair and had a number of risk factors for left ventricular outflow tract obstruction. To minimize this risk, we deployed transcatheter mitral valve implantation within the anterior mitral valve leaflet resulting in mild mitral valve regurgitation postoperatively and no left ventricular outflow tract obstruction. Long-term durability of this approach is yet to be determined, but we believe that this intervention adds to the armamentarium of the heart team.

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.

Corneal light backscatter measured by optical coherence tomography after LASIK.

PURPOSE: To objectively quantify corneal light backscatter after LASIK using optical coherence tomography (OCT). METHODS: Twenty-eight eyes of 14 patients (mean age: 39.9 +/- 8.6 years) underwent LASIK surgery. Corneal images were taken with a custom built anterior segment OCT at 1310 nm before and 1 day, 1 week, and 1 month after surgery. Backscattered light from the epithelium and 10 equally divided corneal stromal layers of the central cornea were analyzed using custom software. Light scattering of the interface area (defined as seven image pixels [46.2 microm] in depth centered by the peak corresponding to the interface between the corneal flap and bed) was also calculated and compared to the light backscatter at an equivalent depth of the respective preoperative cornea. RESULTS: There were significant differences of light backscatter in different layers (analysis of variance [ANOVA]: F(10, 130) = 44.89, P = .0001), but no significant differences between right and left eyes preoperatively (ANOVA: F(10, 130) = 1.16, P = .32). After surgery, there were significant differences in light backscatter profiles of the central cornea (repeated measures ANOVA: F(30, 810) = 7.70, P = .0001) with significant increases at approximately 140 to 190 microm in depth from the corneal front surface at 1 day (post hoc test: P = .004) and 1 week (post hoc test: P = .001) postoperatively, compared to the baseline. One month after surgery, light backscatter increased significantly in the epithelium (post hoc test: P = .0001) and decreased significantly (post hoc test: P = .0001) at approximately 100 to 140 microm in depth. Light backscatter results of these interface areas (repeated measures ANOVA: F(3, 81) = 21.29, P = .0001) showed significant increases at 1 day and 1 week postoperatively (post hoc tests: P = .0001) compared to baseline results and 1-month postoperative results. CONCLUSIONS: Objective and quantitative analysis of corneal light backscatter from OCT demonstrated increasing comeal light scattering at the interface and subsequent recovery.

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

PURPOSE: To determine the aberrations induced in wavefront-guided laser refractive surgery due to shifts in pupil center location from when aberrations are measured preoperatively (over a dilated pupil) to when they are corrected surgically (over a natural pupil). SETTING: Center for Visual Science and Department of Ophthalmology, University of Rochester, Rochester, New York, USA. METHODS: Shifts in pupil center were measured between dilated phenylephrine hydrochloride (Neo-Synephrine [2.5%]) and nonpharmacological mesopic conditions in 65 myopic eyes treated with wavefront-guided laser in situ keratomileusis (Technolas 217z, Bausch & Lomb). Each patient's preoperative and 6-month postoperative wave aberrations were measured over the dilated pupil. Aberrations theoretically induced by decentration of a wavefront-guided ablation were calculated and compared with those measured 6 months postoperatively (6.0 mm pupil). RESULTS: The mean magnitude of pupil center shift was 0.29 mm +/- 0.141 (SD) and usually occurred in the inferonasal direction as the pupil dilated. Depending on the magnitude of shift, the fraction of the higher-order postoperative root-mean-square wavefront error that could be due theoretically to pupil center decentrations was highly variable (mean 0.26 +/- 0.20 mm). There was little correlation between the calculated and 6-month postoperative wavefronts, most likely because pupil center decentrations are only 1 of several potential sources of postoperative aberrations. CONCLUSIONS: Measuring aberrations over a Neo-Synephrine-dilated pupil and treating them over an undilated pupil typically resulted in a shift of the wavefront-guided ablation in the superotemporal direction and an induction of higher-order aberrations. Methods referencing the aberration measurement and treatment with respect to a fixed feature on the eye will reduce the potential for inducing aberrations due to shifts in pupil center.

Higher-order aberrations in eyes with irregular corneas after laser refractive surgery.

PURPOSE: To investigate the distribution of the eye's higher-order aberrations in postoperative laser refractive surgery patients with visual complaints and highly irregular corneal shapes. DESIGN: Retrospective case-control study. PARTICIPANTS: Thirty-three symptomatic postoperative LASIK and/or photorefractive keratectomy eyes with subjective visual complaints not corrected by spectacles more than 6 months after surgery are compared with 46 normal preoperative and 46 asymptomatic successful postoperative conventional LASIK eyes. METHODS: Postoperative wave aberrations were measured for each patient using a Shack-Hartmann wavefront sensor (Zywave, Bausch & Lomb, Rochester, NY) over a 6-mm pupil. These measurements were averaged across patients with similar corneal topographic diagnoses (central islands, decentered ablations, a new group termed baby bowties, and irregularly irregular corneas). MAIN OUTCOME MEASURES: Higher-order aberrations and corneal topography. RESULTS: The average (+/-1 standard deviation) higher-order root-mean-square (rms) wavefront error values (third, fourth, and fifth orders) for the symptomatic patients was 1.31+/-0.58 microm. This was an average of 3.46 times greater than the average magnitude of normal preoperative eyes (mean rms, 0.38+/-0.14 microm), and an average of 2.3 times greater than the average magnitude of asymptomatic successful postoperative conventional LASIK eyes (mean rms, 0.58+/-0.21 microm) over a 6-mm pupil. Higher-order rms wavefront error increased with pupil size, roughly doubling for every millimeter of increasing pupil diameter. On average, eyes with central islands (n = 6) had the most vertical coma (Z3(-1); mean, -1.35+/-0.43 microm). Eyes with central islands and decentered ablations (n = 2) also had elevated amounts of spherical aberration (Z4(0); means of 0.83+/-0.11 microm and 0.69+/-0.29 microm, respectively) compared with successful postoperative LASIK eyes (mean of 0.42+/-0.20 microm). Eyes with a topographic central baby bowtie demonstrated the most secondary astigmatism (Z4(2) and Z4(-2); mean rms, 0.56+/-0.17 microm; n = 3), despite the lowest average higher-order rms (mean, 0.84+/-0.05 microm) among symptomatic topographic subgroups. Eyes with irregularly irregular corneas had a mean higher-order rms of 1.10+/-0.39 mum. CONCLUSIONS: Symptomatic postoperative laser refractive surgery patients with irregular corneas have higher-order aberrations that are 2.3 to 3.5 times greater than asymptomatic postoperative LASIK and normal preoperative eyes, respectively. The higher-order aberrations seem to correlate with corneal topography.

Causes of spherical aberration induced by laser refractive surgery.

PURPOSE: To develop a corneal model to better explain how refractive surgery procedures induce spherical aberration. SETTING: Department of Ophthalmology and Center for Visual Science, University of Rochester, Rochester, New York, USA. METHODS: The preoperative cornea was modeled as a rotationally symmetric surface with various radii of curvature and asphericities. The postoperative cornea was defined as the difference between the preoperative cornea and an ablation thickness profile computed based on the Munnerlyn equation. A ray-tracing program and Zernike polynomial fitting were used to calculate the induced amount of spherical aberration assuming a fixed ablation depth per pulse or a variable ablation depth depending on the incidence angle of each pulse on the cornea. A biological eye model of the corneal surface change after laser refractive surgery was also developed to explain the induced spherical aberrations after myopic and hyperopic treatments. RESULTS: The clinical data showed that positive spherical aberration was induced after myopic correction and negative spherical aberration increased after hyperopic correction. In contrast, assuming a fixed ablation depth per pulse, the theoretical prediction was that negative spherical aberration with myopic treatment and positive spherical aberration with hyperopic treatment would increase. However, when assuming a variable ablation depth per pulse caused by non-normal incidence of laser spot on the cornea, the theoretically predicted induction of spherical aberration tends to fit better with the myopic and hyperopic clinical data. The effect of a variable ablation depth accounted for approximately half the clinically observed amount of spherical aberration. The biological model of the corneal surface change used to explain this remaining discrepancy showed the magnitude of the biological response in myopic correction is 3 times smaller than in hyperopic correction and that the direction of the biological response in hyperopic treatment is opposite that in myopic treatment. CONCLUSIONS: This nontoric eye model, which separates the effects of differences in ablation efficiency and biological corneal surface change quantitatively, explains how spherical aberration is induced after myopic and hyperopic laser refractive surgery. With the corneal topographic data, this model can be incorporated into the ablation algorithm to decrease induced spherical aberrations, improving the outcomes of conventional and customized treatments.

Surgeon offsets and dynamic eye movements in laser refractive surgery.

PURPOSE: To determine the amount of static and dynamic pupil decentrations that occur during laser refractive surgery. SETTING: The Center of Visual Science and the Department of Ophthalmology, University of Rochester, Rochester, New York, USA. METHODS: The surgeon's accuracy in aligning the pupil center with the laser center axis was measured when engaging the eye-tracker in 17 eyes receiving conventional laser in situ keratomileusis (LASIK) procedures (Technolas 217z; Bausch & Lomb). Eye movements were measured subsequently during the treatment in 10 eyes using a pupil camera operating at 50 Hz. Temporal power spectra were calculated from the eye movement measurements. RESULTS: The mean pupil misalignment by the surgeon at the beginning of the procedure was 206.1 microm +/- 80.99 (SD) (with respect to the laser center). The laser center was typically misaligned below (inferiorly) and to the left (nasally and temporally in left and right eyes, respectively) of the pupil [corrected] center. Small amounts of cyclotorsion were observed during the ablation (<2 degrees). The mean magnitude of dynamic pupil decentration from the laser center during treatment was 227.0 +/- 44.07 microm. The mean standard deviation of eye movements was 65.7 +/- 25.64 microm. Temporal power spectra calculated from the horizontal and vertical changes in eye position during the ablation were similar. Ninety-five percent of the total power of the eye movements was contained in temporal frequencies up to 1 Hz, on average, in both directions. CONCLUSIONS: Most eye movements during LASIK are slow drifts in fixation. An eye-tracker with a 1.4 Hz closed-loop bandwidth could compensate for most eye movements in conventional or customized ablations.