Optical coherence elastography measures the biomechanical properties of the ex vivo porcine cornea after LASIK.

Significance: The biomechanical impact of refractive surgery has long been an area of investigation. Changes to the cornea structure cause alterations to its mechanical integrity, but few studies have examined its specific mechanical impact. Aim: To quantify how the biomechanical properties of the cornea are altered by laser assisted in situ keratomileusis (LASIK) using optical coherence elastography (OCE) in ex vivo porcine corneas. Approach: Three OCE techniques, wave-based air-coupled ultrasound (ACUS) OCE, heartbeat (Hb) OCE, and compression OCE were used to measure the mechanical properties of paired porcine corneas, where one eye of the pair was left untreated, and the fellow eye underwent LASIK. Changes in stiffness as a function of intraocular pressure (IOP) before and after LASIK were measured using each technique. Results: ACUS-OCE showed that corneal stiffness changed as a function of IOP for both the untreated and the treated groups. The elastic wave speed after LASIK was lower than before LASIK. Hb-OCE and compression OCE showed regional changes in corneal strain after LASIK, where the absolute strain difference between the cornea anterior and posterior increased after LASIK. Conclusions: The results of this study suggest that LASIK may soften the cornea and that these changes are largely localized to the region where the surgery was performed.

Effect of spherical aberration on visual acuity and depth of focus in pseudophakic eyes.

PURPOSE: To assess the performance of 4 intraocular lenses (IOLs) in various spherical aberration (SA) conditions, using the VAO adaptive optics simulator. SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas. DESIGN: Prospective case series. METHODS: Distance-corrected visual acuities at distance (CDVA), intermediate (DCIVA), and near (DCNVA) were measured in 42 dilated pseudophakic eyes at baseline and with ocular SA ranging from -0.4 to +0.4 µm in increments of 0.2 µm (6.0-mm pupil). 4 IOL types were assessed: monofocal IOLs with zero-SA, enhanced-monofocal, extended depth-of-focus (EDOF), and continuous range-of-vision. RESULTS: Compared with SA = 0 µm, significant changes (all P < .05) were: (1) zero-SA monofocal IOLs' DCNVA at high contrast improved by 0.13 logMAR with SA = -0.4 µm and worsened by 0.09 and 0.10 logMAR with SA = +0.2 and +0.4 µm, respectively. DCNVA at low contrast worsened by 0.09 logMAR with SA = +0.4 µm; and (2) with SA = -0.4 µm, the enhanced monofocal IOL lost 0.06 logMAR of CDVA at high contrast and gained 0.09 logMAR of DCNVA at low contrast. There were no significant changes from SA = 0 µm for EDOF and continuous range-of-vision IOLs. CONCLUSIONS: Zero-SA and EDOF IOLs were the most and least sensitive to SA modulation, respectively. In perfect optical systems where all the optical elements are aligned, induction of targeted amounts of negative SA improved the depth of focus of some IOL types. No benefit was found with positive SA.

Performance of IOL calculation formulas that use measured posterior corneal power in eyes following myopic laser vision correction.

PURPOSE: To compare the predictive accuracy of the biometer-embedded Barrett True-K TK and new total corneal power methods of intraocular lens (IOL) power calculation in eyes with prior laser vision correction (LVC) for myopia. SETTING: Academic clinical practice. DESIGN: Retrospective case series. METHODS: IOL power formulas were assessed using measurements from a swept-source optical coherence biometer. Refractive prediction errors were calculated for the Barrett True-K TK, EVO 2.0, Pearl-DGS, and HofferQST, which use both anterior and posterior corneal curvature measurements. These were compared with the Shammas, Haigis-L, Barrett True-K No History (NH), optical coherence tomography, and 4-formula average (AVG-4) on the ASCRS postrefractive calculator, and to the Holladay 1 and 2 with non linear axial length regressions (H1- and H2-NLR). RESULTS: The study comprised 85 eyes from 85 patients. Only the Barrett True-K TK and EVO 2.0 had mean numerical errors that were not significantly different from 0. The EVO 2.0, Barrett True-K TK, Pearl-DGS, AVG-4, H2-NLR, and Barrett True-K NH were selected for further pairwise analysis. The Barrett True-K TK and EVO 2.0 demonstrated smaller root-mean-square absolute error compared with the Pearl-DGS, and the Barrett True-K TK also had a smaller mean absolute error than the Pearl-DGS. CONCLUSIONS: The Barrett True-K TK and EVO 2.0 formulas had comparable performance to existing formulas in eyes with prior myopic LVC.

Comparison of Keratoconus Specific to Standard IOL Formulas in Patients With Keratoconus Undergoing Cataract Surgery.

PURPOSE: To assess the performance of multiple intraocular lens (IOL) formulas in eyes with keratoconus. METHODS: Eyes with stable keratoconus scheduled for cataract surgery with biometry measurements on the Lenstar LS900 (Haag-Streit) were included. Prediction errors were calculated using 11 different formulas, including two with keratoconus modifiers. Primary outcomes compared standard deviations, mean and median numerical errors, and percentage of eyes within diopter (D) ranges across all eyes with subgroup analysis according to anterior keratometric values. RESULTS: Sixty-eight eyes from 44 patients were identified. In eyes with keratometric values less than 50.00 D, prediction error standard deviations ranged from 0.680 to 0.857 D. Percentages of eyes within ±0.50 D of target ranged from 57.89% to 73.68% with no statistical differences among formulas. In eyes with a keratometric value of more than 50.00 D, prediction error standard deviations ranged from 1.849 to 2.349 D and were not statistically different with heteroscedastic analysis; percentages of eyes within ±0.50 D of target ranged from 0% to 18.18% with no statistical differences among formulas. Only keratoconus-specific formulas (Barrett-KC and Kane-KC) and the Wang-Koch axial length adjustment version of SRK/T resulted in median numerical errors not significantly different than 0, regardless of keratometric values. CONCLUSIONS: In keratoconic eyes, IOL formulas are less accurate than in normal eyes and result in hyperopic refractive outcomes that increase with steeper keratometric values. Using keratoconus-specific formulas and the Wang-Koch axial length adjustment version of SRK/T for axial lengths of 25.2 mm or greater improved IOL power prediction accuracy compared to other formulas. [J Refract Surg. 2023;39(4):242-248.].

Efficacy of segmented axial length and artificial intelligence approaches to intraocular lens power calculation in short eyes.

PURPOSE: In short eyes, to compare the predictive accuracy of newer intraocular lens (IOL) power calculation formulas using traditional and segmented axial length (AL) measurements. SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas and East Valley Ophthalmology, Mesa, Arizona. DESIGN: Multi-center retrospective case series. METHODS: Measurements from an optical biometer were collected in eyes with AL <22 mm. IOL power calculations were performed with 15 formulas using 2 AL values: (1) machine-reported traditional AL (Td-AL) and (2) segmented AL calculated with the Cooke-modified AL nomogram (CMAL). 1 AL method and 7 formulas were selected for pairwise analysis of mean absolute error (MAE) and root mean square absolute error (RMSAE). RESULTS: The study comprised 278 eyes. Compared with the Td-AL, the CMAL produced hyperopic shifts without differences in RMSAE. The ZEISS AI IOL Calculator (ZEISS AI), K6, Kane, Hill-RBF, Pearl-DGS, EVO, and Barrett Universal II (Barrett) formulas with Td-AL were compared pairwise. The ZEISS AI demonstrated smaller MAE and RMSAE than the Barrett, Pearl-DGS, and Kane. K6 had a smaller RMSAE than the Barrett formula. In 73 eyes with shallow anterior chamber depth, the ZEISS AI and Kane had a smaller RMSAE than the Barrett. CONCLUSIONS: ZEISS AI outperformed Barrett, Pearl-DGS, and Kane. The K6 formula outperformed some formulas in selected parameters. Across all formulas, use of a segmented AL did not improve refractive predictions.

Developmental Improvement in Children With Intellectual Disability After Photorefractive Keratectomy for Severe Isoametropia.

PURPOSE: To assess the impact of refractive error correction from photorefractive keratectomy on development in children with severe isoametropia, subnormal visual acuity, and intellectual disability unable to use refraction correction. DESIGN: Prospective noncomparative interventional case series. METHODS: Before and after photorefractive keratometry (PRK), subjects who had plateaued developmentally for 18 or more months were assessed using a battery of developmental tests. The primary outcome measure was the change in the developmental quotient (DQ) 6 months after PRK. Secondary outcomes were the change in the DQ, uncorrected visual acuity, cycloplegic refraction, and corneal status 12, 24, and 36 months after PRK. RESULTS: Sixteen subjects aged 2 to 8 years were included. Twelve were highly myopic (mean, -9.69 ± 3.82 diopters [D]), 3 highly hyperopic (mean, +5.75 ± 0.59 D) and 1 highly astigmatic (mean, +3.50 D). Six months after PRK, the DQ significantly improved for expressive communication (mean, 4.51 ± 2.27 months; P = .04), interpersonal relationships (mean, 9.45 ± 4.18 months; P = .02) and coping (mean, 6.44 ± 2.10 months; P = .05). Twelve months after PRK, the DQ significantly improved for receptive communication (8.04 ± 1.80 months; P < .001), expressive communication (6.99 ± 2.27 months; P < .05), written communication (9.28 ± 3.72 months; P < .04), domestic skills (6.50 ± 2.43 months; P < .03), interpersonal relationships (10.57 ± 4.17 months; P < .02), and coping (8.41 ± 3.25 months; P < .5). CONCLUSIONS: PRK significantly improves developmental abilities of children with intellectual disability, severe isoametropia, and previously plateaued development, in addition to improving visual acuity and refractive error.

Intraocular Lens Implantation in the Absence of Zonular Support: An Outcomes and Safety Update: A Report by the American Academy of Ophthalmology.

PURPOSE: To review the published literature on the visual acuity results and complications of different surgical techniques for intraocular lens (IOL) implantation in the absence of zonular support. METHODS: Peer-reviewed literature searches were conducted last in PubMed and the Cochrane Library in July 2019. The searches yielded 734 citations of articles published in English. The panel reviewed the abstracts of these mostly retrospective case series studies, and 45 were determined to be relevant to the assessment objectives. Three articles were rated as level II evidence, and 42 articles were rated as level III evidence. RESULTS: Eight different types of IOL fixation techniques with at least 6-month follow-up were evaluated: anterior chamber IOL (ACIOL), iris-claw IOL, retropupillary iris-claw IOL, 10-0 polypropylene iris-sutured posterior chamber IOL (PCIOL), 10-0 polypropylene scleral-sutured PCIOL, 8-0 polypropylene scleral-sutured PCIOL, CV-8 polytetrafluoroethylene, and intrascleral haptic fixation (ISHF). Eight articles reported data comparing 2 techniques. The 45 studies had insufficient statistical power to compare the techniques conclusively. A qualitative analysis of similar types showed that trends in visual acuity outcomes were not inferior to those of ACIOL implantation, but the severity of preoperative pathologic features was not controlled for. Compared with ACIOL, complications of cystoid macular edema were higher in 10-0 polypropylene iris-sutured PCIOL and 8-0 polypropylene scleral-sutured PCIOL. Non-anterior chamber IOL techniques were less likely to report chronic uveitis. Chronic glaucoma was highest in the 8-0 polypropylene scleral-sutured PCIOL group. Although retinal detachment was infrequent overall, it was twice as common in both iris- and scleral-sutured PCIOLs (except CV-8 polytetrafluoroethylene suture) compared with nonsutured methods: ACIOL, iris-clipped IOL, and ISHF PCIOL. CONCLUSIONS: The evidence reviewed shows no superiority of any single IOL implantation technique in the absence of zonular support. The various techniques seem to have equivalent visual acuity outcomes and safety profiles. Each technique has its own profile of inherent risk of postoperative complications. Surgeons must educate patients on the importance of close, long-term follow-up as a result of the uncertain nature of these techniques. Large prospective studies are needed to confirm the long-term complication profiles of these various IOL implantation techniques.

Autologous Serum-Based Eye Drops for Treatment of Ocular Surface Disease: A Report by the American Academy of Ophthalmology.

PURPOSE: To describe the safety and effectiveness of using autologous serum-based eye drops for the treatment of severe dry eye and persistent corneal epithelial defect. METHODS: Literature searches of the PubMed and Cochrane Library databases were conducted most recently in March 2019. The searches identified 281 citations, which were reviewed in abstract form. Of these, 48 were selected for a full-text review, and 13 met the inclusion criteria and were assigned a quality-of-evidence rating by the panel methodologist. Eight of these studies were rated level II and 5 were rated level III; there were no level I studies. RESULTS: This analysis included 10 studies of the use of autologous serum-based eye drops for severe dry eye disease and 4 studies of persistent epithelial defect. Several studies showed good effectiveness, with some improvement in symptoms, signs, or both. Eight of the studies reported improved symptoms for severe dry eye disease, and all noted improvement in at least 1 clinical sign. For persistent epithelial defects, all of the studies showed improvement, with 3 of the 4 demonstrating an improvement rate of more than 90%. Adverse events were rare. CONCLUSIONS: Although autologous serum-based tears may be effective in the treatment of severe dry eye and persistent epithelial defect, conclusions are limited owing to the absence of controlled trials.

How much astigmatism to treat in cataract surgery.

PURPOSE OF REVIEW: Astigmatism correction in cataract surgery is a common surgical challenge. Although there are numerous approaches to its treatment during cataract surgery, there remains a lack of consensus on what level of postoperative astigmatism to target. We examine the literature to determine the effect of astigmatism on visual function and provide a recommendation on how much to treat in cataract surgery. RECENT FINDINGS: Distance visual acuity decreases as myopic, hyperopic, or mixed astigmatism increases. Near visual acuity decreases with hyperopic astigmatism but improves with myopic astigmatism. The effect of astigmatism is generally independent of axis; however, against-the-rule (ATR) astigmatism with mild myopia may benefit reading. A progressive ATR shift occurs with age whether or not an individual undergoes cataract surgery. In the presence of higher order aberrations, correction of astigmatism below 0.5 D shows minimal practical benefit. Presbyopia-correcting intraocular lenses (IOLs) are sensitive to astigmatism but achieve distance visual acuities similar to monofocal IOLs and reach their full near and/or intermediate potential when residual astigmatism 0.5 D or less. SUMMARY: In cataract surgery, we recommend correction to 0.5 D or less of postoperative residual astigmatism to achieve optimum visual function and patient satisfaction following cataract surgery.

Comparison of intraocular lens power calculation formulas in Chinese eyes with axial myopia.

PURPOSE: To assess the accuracy of intraocular lens (IOL) power calculation formulas in Chinese eyes with axial lengths (ALs) longer than 26.0 mm. SETTING: Department of Cataract Surgery, Shanxi Eye Hospital, China. DESIGN: Prospective case series. METHODS: This study evaluated (1) two new formulas (Barrett Universal II and Hill-RBF 2.0), (2) three vergence formulas (Haigis, Holladay 1, and SRK/T), and (3) the original and modified Wang-Koch AL adjustment formulas with Holladay 1 and SRK/T. The User Group for Laser Interference Biometry lens constants were used for IOL power calculation. The refractive prediction error was calculated by subtracting the predicted refraction from the actual refraction postoperatively. The mean numerical error (MNE), percentage of eyes with hyperopic outcomes, and mean absolute error (MAE) were determined. RESULTS: The study comprised 136 eyes. The Barrett and Hill-RBF formulas had MNEs close to zero (-0.09 D to 0.03 D), the Haigis, Holladay 1, and SRK/T produced hyperopic MNEs (0.25 to 0.70 D), and the original and modified Wang-Koch AL adjustment formulas induced myopic MNEs (-0.48 to -0.22 D). The original Wang-Koch formulas produced significantly lower percentages of eyes with hyperopic outcomes (15% to 18%) than all other formulas (28% to 91%). There were no significant differences in MAEs between the Barrett, Hill-RBF, Haigis, and original and modified Wang-Koch adjustment with the Holladay 1 (0.32 to 0.41 D). CONCLUSION: The performances of the Barrett and Hill-RBF were comparable in long eyes. The incidence of hyperopic outcome with the Wang-Koch AL adjustment formula was significantly lower than other formulas.

Corneal indices following photorefractive keratectomy in children at least 5 years after surgery.

PURPOSE: To evaluate long-term corneal outcomes in pediatric patients who underwent photorefractive keratotomy (PRK) for the treatment of refractive amblyopia. METHODS: In this prospective interventional case series, children with refractive amblyopia underwent PRK between January 1, 2007, and December 31, 2011, at Texas Children's Hospital's Department of Ophthalmology, a single tertiary eye center, and were followed for at least 5 years after surgery. Main outcome measures were 5+ years postoperative indices of corneal thickness, keratometry, degree of corneal haze, and presence or absence of keratectasia. RESULTS: Twelve eyes of 8 subjects aged 3-9 years who underwent PRK and were followed for at least 5 years were included. The mean PRK treatment dose was 8.46 D for the myopic cohort and 4.49 D for the hyperopic cohort, which removed an average of 72 µm of corneal stromal tissue in addition to the 50 µm of corneal epithelium that was removed prior to laser ablation. The mean corneal thickness was 563 µm preoperatively, which decreased to 441 µm immediately following the PRK. The mean corneal thickness 5+ years after PRK was stable, at 498 µm, because of epithelial regrowth. None of the subjects developed visually significant corneal haze or topographic evidence of keratectasia. CONCLUSIONS: In this study cohort, there were no topographic signs of keratectasia or corneal haze in children treated with PRK for high refractive error 5 years or more after surgery.

Anterior Segment Optical Coherence Tomography of Ocular Cystinosis Confirmed by Electron Microscopy.

PURPOSE: To report a case of ocular cystinosis diagnosed by anterior segment optical coherence tomography (AS-OCT) and histopathology. METHODS: A 67-year-old man who presented with eye pain was found to have unilateral corneal crystal deposition. Ocular cystinosis was diagnosed by histopathology, AS-OCT, and lack of renal involvement of the disease. RESULTS: AS-OCT showed hyperreflective densities in the corneal epithelium. The patient underwent superficial keratectomy given irregular astigmatism prior to cataract surgery. Electron microscopy of the corneal scrapings revealed epithelial cells with intracystoplasmic membrane-bound crystals confirming the diagnosis of cystinosis. CONCLUSION: To our knowledge, this is the first reported case of ocular cystinosis involving strictly the epithelial layer of the cornea that has been imaged by AS-OCT.

Calculation of Axial Length Using a Single Group Refractive Index versus Using Different Refractive Indices for Each Ocular Segment: Theoretical Study and Refractive Outcomes.

PURPOSE: To investigate the difference between the segmented axial length (AL) and the displayed AL on an optical low-coherence reflectometry (OLCR) biometer and to compare the refractive prediction errors calculated using the segmented and displayed ALs. DESIGN: Retrospective case series. PARTICIPANTS: Four thousand nine hundred ninety-two eyes from 4992 patients in the theoretical study and 1758 eyes from 1758 patients in the refractive prediction error comparison. METHODS: First, we calculated the segmented AL as the sum of geometrical ocular segments converted from the optical path length (OPL) in each medium. To convert the OPL to a geometrical distance in each medium, we used 4 sets of group refractive indices. Then, the mean absolute prediction error (MAE) was calculated with the displayed AL and segmented AL using 6 intraocular lens power formulas: Olsen, Barrett Universal II (Barrett), Haigis, Hoffer Q, Holladay 1, and Sanders-Retzlaff-Kraff trial (SRK/T). MAIN OUTCOME MEASURES: Segmented AL, difference in AL (segmented AL minus displayed AL), MAE, and percentage of eyes within 0.5 diopter (D) of error. RESULTS: The segmented ALs were up to 0.29 mm longer in short eyes and 0.50 mm shorter in long eyes. The differences in ALs were correlated negatively with the displayed ALs (r values, -0.941 to -0.913; P < 0.001). The MAEs were significantly lower using segmented ALs for all formulas except the Olsen in both the entire group and the long eye subgroup (AL, ≥26 mm) and for the Holladay 1 and Hoffer Q in the short eye subgroup (AL, ≤ 22 mm). Use of segmented ALs produced a greater percentage of eyes within 0.5 D of error for all formulas except the Olsen and Haigis for the entire group, for long eyes, and for the Holladay 1 in short eyes. CONCLUSIONS: The segmented ALs were longer in short eyes and shorter in long eyes compared with the displayed ALs calculated with a single group refractive index for the entire eye. The refractive accuracy with segmented ALs was improved in short eyes with the Hoffer Q and Holladay 1 formulas and in long eyes with all formulas except the Olsen formula.

Evaluation of the Repeatability and Reproducibility of Corneal Epithelial Thickness Mapping for a 9-mm Zone Using Optical Coherence Tomography.

PURPOSE: To evaluate the repeatability and between-machine/operator reproducibility of optical coherence tomography (RTVue-XR) for mapping corneal epithelial thickness (ET) and corneal thickness (CT) over a 9-mm zone. METHODS: In 5 groups of eyes (normal, contact lens, dry eye, post-LASIK/PRK, and keratoconus), corneal ET and CT were evaluated in 25 areas in the following 4 regions: 1) 1 central zone within 0 to 2.0 mm diameter, 2) 8 paracentral zones from 2.0 to 5.0 mm diameter, 3) 8 midperipheral zones from 5.0 to 7.0 mm diameter, and 4) 8 peripheral zones from 7.0 to 9.0 mm diameter. Three devices with designated operators were used to obtain 3 scans per device for each eye. The repeatability, reproducibility, and coefficient of variation were calculated. RESULTS: For all areas up to 9 mm diameter, in normal eyes, contact lens eyes, dry eyes, post- LASIK/PRK eyes, and keratoconic eyes, repeatability and reproducibility ranged from 0.7 to 1.5, 1.0 to 2.6, 0.9 to 2.0, 0.7 to 2.5, and 1.1 to 2.3 µm for ET and 1.5 to 8.3, 2.3 to 12.1, 1.7 to 14.2, 1.4 to 13.7, and 6.9 to 18.9 µm for CT, respectively. The ranges of coefficient of variation values were 1.2% to 3.0%, 1.9% to 5.5%, 1.8% to 4.3%, 1.3% to 5.2%, and 2.2% to 4.5% for ET and 0.3% to 1.2%, 0.4% to 1.8%, 0.4% to 2.1%, 0.3% to 2.0%, and 1.2% to 3.0% for CT, respectively. CONCLUSIONS: Optical coherence tomography produced excellent repeatability and reproducibility for corneal ET and CT measurements up to a 9-mm zone in normal eyes and eyes with different corneal conditions. The CT measurements in keratoconic eyes were more variable than those in eyes with other corneal conditions.

Evaluation of crystalline lens and intraocular lens tilt using a swept-source optical coherence tomography biometer.

PURPOSE: To evaluate crystalline lens and intraocular lens (IOL) tilt using a swept-source optical coherence tomography (SS-OCT) biometer (IOLMaster 700). SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. DESIGN: Retrospective case series. METHODS: The study patients were evaluated for 1) repeatability of the crystalline lens tilt measurement, 2) preoperative crystalline lens and postoperative IOL tilt in right eyes, 3) mirror symmetry between right eyes and left eyes, 4) the correlation between preoperative crystalline lens and postoperative IOL tilt, and 5) the correlation between the magnitude of lens tilt and ocular parameters. RESULTS: The study comprised 333 patients. The repeatability was 0.1 degrees for tilt magnitude and 3.0 degrees for tilt direction. Both the crystalline lens and IOL had anterior tilt of the nasal portion with mean tilt magnitudes of 3.7 degrees ± 1.1 (SD) (range 0.4 to 6.9 degrees) for the crystalline lens and 4.9 ± 1.8 degrees (range 1.6 to 10.7 degrees) for the IOL. There was mirror symmetry between right eyes and left eyes. The mean IOL tilt magnitude exceeded crystalline lens tilt by 1.2 ± 1.1 degrees (range -3.2 to 4.0 degrees), and the 2 values were significantly correlated (all P < .01). The magnitude of crystalline lens tilt significantly increased with decreasing axial length and with increasing angle α (all P < .05). CONCLUSIONS: The repeatability of crystalline lens tilt measurements using the SS-OCT biometer was excellent. There was mirror symmetry between the right eyes and left eyes. Preoperative crystalline lens tilt could be used to predict the postoperative IOL tilt. The lens tilt magnitude was greater in short eyes and in eyes with larger angle α.