Comparison of Ectasia Detection in Early Keratoconus Using Scheimpflug-Based Corneal Tomography and Biomechanical Assessments.

PURPOSE: The aim of this study was to determine the detection of keratoconus using corneal biomechanical parameters only, a corneal tomographic parameter only, and a parameter that combines corneal biomechanical and tomographic indices. METHODS: The discriminatory power of the Pentacam Random Forest Index (PRFI), Belin/Ambrósio Enhanced Ectasia Display (BAD-D) index, Corvis Biomechanical Index (CBI), and Tomographic and Biomechanical Index (TBI) to differentiate between normal eyes (n = 84), eyes with very asymmetric corneal ectasia (VAE-E, n = 21), and the fellow eyes without apparent ectasia based on normal tomography (VAE-NT, n = 21) was assessed. Statistical analyses were completed with R software using t -tests, Wilcoxon rank sum tests, and receiver operating characteristic (ROC) curves. The DeLong test was used to compare the area under the ROC curve (AUROC). RESULTS: The TBI and PRFI had the highest AUROC when distinguishing between normal and VAE-E corneas (AUROC = 1.00, 95% CI = 1.00-1.00); however, they were not statistically superior to the CBI (AUROC = 0.97, P = 0.27) or BAD-D (AUROC = 1.00, P = 0.34). The TBI (AUROC = 0.92, 95% CI = 0.86-0.98) was superior to CBI (AUROC = 0.78, P = 0.02) and BAD-D (AUROC = 0.81, P = 0.02) when distinguishing between healthy and VAE-NT corneas. At a threshold of 0.72, the TBI had 99% sensitivity, 67% specificity, and 92% accuracy in distinguishing normal and VAE-NT corneas. CONCLUSIONS: The TBI is a useful parameter for the screening of subclinical and frank keratoconus in tomographically normal eyes.

Progression of keratoconus in children and adolescents.

AIMS: To evaluate the rates of keratoconus progression and associated factors in eyes of children and adolescents. METHODS: Retrospective, cohort study of individuals ≤18 years old at the time of keratoconus diagnosis and with at least 6 months of follow-up. Corneal tomography was performed using an Orbscan tomographer (Bausch & Lomb, Rochester, New York, USA) to determine whether progression occurred. Tomographic progression of keratoconus was defined as a change in any of the investigated parameters (keratometry values, KMAX, maximum anterior or posterior elevation, central pachymetry, thinnest pachymetry) beyond the limits of repeatability. RESULTS: 148 eyes of 106 patients with a mean age of 15.2±2.5 years were studied over a mean follow-up period of 2.9±2.2 years. The overall rate of tomographic progression was 77.0% (114/148 eyes). Eyes that progressed had more advanced disease at presentation with higher anterior curvature (KMAX55.4±6.3 vs 52.2±5.4 dioptres; p<0.01), posterior elevation (108.2±40.9 vs 86.3±35.6 µm; p<0.01) and lower central pachymetry measurements (442.1±56.7 vs 454.4±47.5 µm; p=0.01). Age at presentation, gender, atopy, documented eye rubbing, ethnicity and duration of follow-up were not significantly associated with progression in the multivariate analyses. There was a higher rate of bilateral progression if at least one eye had severe keratoconus (73.9%) compared with no severe keratoconus in either eye (36.8%; p=0.03). CONCLUSIONS: A high rate of progression was identified in keratoconic eyes of children and adolescents. More advanced disease at initial presentation may increase the risk of further keratoconus progression.

Prospective one year study of corneal biomechanical changes following high intensity, accelerated cornea cross-linking in patients with keratoconus using a non-contact tonometer.

PURPOSE: To characterize corneal biomechanical properties utilizing a dynamic ultra-high-speed Scheimpflug camera equipped with a non-contact tonometer (CorVis ST, CST) in keratoconic corneas following continuous high intensity, high irradiance corneal cross-linking. DESIGN: Prospective longitudinal single-centre study at a tertiary referral center. METHODS: Corneal biomechanical properties were measured in patients with progressive keratoconus undergoing high intensity (30 mW/cm2), high irradiance (5.4 J/cm2), accelerated corneal cross-linking with continuous exposure to ultraviolet-A for 4 min. CST was used to assess corneal biomechanical properties pre-operatively and at 1, 3, 6 and 12 months post-operatively. CST output videos were further analyzed using several previously reported algorithms. RESULTS: A total of 25 eyes of 25 participants were examined. The mean age of participants was 20.9 ± 5.3 years; 56% were male and 80% were of Maori or Pacific Island origin. Energy absorbed area (mN mm), was the only significantly changed parameter compared to baseline at all time points measuring 3.61 ± 1.19 preoperatively, 2.81 ± 1.15 at 1 month (p = 0.037), 2.79 ± 0.81 (p = 0.033) at 3 months, 2.76 ± 0.95 (p = 0.028) at 6 months and 2.71 ± 1.18 (p = 0.016) at 12 months. CONCLUSIONS: The significant difference between the pre and post-operative energy absorbed area appears to reflect changes in corneal viscous properties that occur following corneal cross-linking.

Comparison of corneal biomechanical properties following penetrating keratoplasty and deep anterior lamellar keratoplasty for keratoconus.

IMPORTANCE: Keratoplasty is a surgical procedure to create a more regular optical surface following biomechanical weakening of the cornea in keratoconus. The ideal keratoplasty procedure should also restore corneal biomechanics to that of the healthy cornea. BACKGROUND: This study aimed to evaluate and compare the biomechanical properties of corneas following penetrating keratoplasty (PKP) and predescematic deep anterior lamellar keratoplasty (DALK) to those of healthy eyes. DESIGN: Prospective cross-sectional study. PARTICIPANTS: Two cohorts of post-keratoplasty eyes (42 eyes with PKP and 27 eyes with DALK) with each other, and with a cohort of 152 healthy eyes. METHODS: All eyes were examined by slit-lamp biomicroscopy, tomography, anterior segment-OCT and non-contact tonometry CorVis ST (CST). MAIN OUTCOME MEASURES: CST biomechanical parameters, maximum corneal deformation (MCD) and corneal energy dissipation were compared between keratoplasty techniques, and with healthy eyes. RESULTS: The mean age of participants with PKP and DALK were 35 ± 13.7 and 36.1 ± 12.6 years, respectively. None of the CST parameters were significantly different between PKP and DALK eyes. However, when compared to healthy corneas, numerous parameters were significantly different for both keratoplasty techniques. Of note, MCD was significantly higher in PKP compared to DALK and healthy corneas, after controlling for co-factors. CONCLUSIONS AND RELEVANCE: Neither type of keratoplasty technique utilized in keratoconus completely restored corneal biomechanical properties to that of healthy corneas. However, PKP resulted in a greater number of parameters significantly different to healthy corneas, compared to DALK.

Improved Refractive Outcomes of Small-Incision Extracapsular Cataract Surgery after Implementation of a Biometry Training Course.

PURPOSE: To determine whether a biometry training course could improve refractive outcomes of patients undergoing manual small-incision extracapsular cataract surgery (SICS). MATERIALS AND METHODS: This was a prospective, interventional, cohort study at the Pacific Eye Institute, Fiji. SICS refractive outcomes were evaluated before and after a structured biometry teaching course. Eyes that underwent evaluation and subsequent SICS with placement of a posterior chamber intraocular lens (IOL) were included. Axial length measurements were obtained using A-scan applanation ultrasound and keratometry with a handheld keratometer. Main outcome measures included mean absolute prediction error of IOL calculations, percentage of eyes within ±0.5 D and ±1.0 D of intended spherical equivalent, and proportion of eyes with ≥6/18 uncorrected visual acuity. RESULTS: A total of 240 eyes were analyzed: 120 eyes before and 120 eyes after the structured biometry training. The mean absolute prediction error was 50% lower following the training (1.13 ± 0.84 D pre vs. 0.56 ± 0.44 D post; P < 0.001). A higher percentage of the eyes had a postoperative spherical equivalent within ±0.5 D (26.7% pre vs. 52.5% post; P < 0.001) and ±1.0 D (55.0% pre vs. 90.0% post; P < 0.001) of the intended target. A higher proportion of the eyes achieved ≥6/18 uncorrected visual acuity (77.5% pre vs. 91.7% post, P = 0.004), while the proportion with ≥6/18 corrected visual acuity was similar (94.4% pre vs. 98.3% post; P = 0.28). CONCLUSIONS: A structured biometry training course may improve the accuracy of preoperative IOL calculations to achieve the postoperative refractive target. Ophthalmology training programs should include structured biometry teaching in their curricula.

Ex vivo evaluation of the stability, safety and antibacterial efficacy of an extemporaneous povidone-iodine preparation for ophthalmic applications.

BACKGROUND: Povidone-iodine is used as a cost-effective broad-spectrum antiseptic in the prophylaxis and treatment of certain ocular infections. In this study, the stability, ophthalmic irritation potential and antibacterial efficacy of an extemporaneous povidone-iodine preparation was determined using established ex vivo and in vitro assays. METHODS: Extemporaneous iodine was prepared by simple dilution in normal saline. Preparation stability was evaluated by monitoring concentration and pH. Ocular safety was determined using the bovine cornea opacity and permeability assay. Efficacy was assessed by determining the minimum inhibitory and minimum bactericidal concentration of the preparation on Staphylococcus aureus and Pseudomonas aeruginosa. RESULTS: Diluted povidone-iodine maintained its stability over the 28-day evaluation. The formulation caused mild ocular irritation at the lowest prepared concentration (0.5 per cent w/v), with irritation noticeably increased at higher concentrations. The preparation showed minimum bactericidal and inhibitory concentrations of 0.078 and 0.3 per cent w/v on S. aureus and P. aeruginosa, respectively. CONCLUSIONS: This study confirms the stability and broad-spectrum antibacterial efficacy of povidone-iodine, while addressing the ocular irritation potential of this chemical.

Advanced anterior segment imaging in keratoconus: a review.

Advances in anterior segment imaging have enhanced our ability to detect keratoconus in its early stages and characterize the pathologic changes that occur. Computerized corneal tomography has elucidated the alterations in shape of the anterior and posterior corneal surfaces and alterations in thickness as the disease progresses. Automated screening indices such as the keratoconus screening index were developed to assist in detecting keratoconus in suspicious cases. In vivo assessment of keratoconic corneas has revealed that compromised corneal biomechanics can now be measured clinically. Optical coherence tomography has demonstrated alterations in corneal epithelial thickness and distribution in keratoconus, has a role in assessing Descemet's membrane detachment in acute corneal hydrops (ACH) and the depth of the demarcation line following corneal collagen cross-linking. In vivo confocal microscopy has exhibited cellular changes that occur in keratoconus and provided insight into cellular events that may be related to the development of neovascularization in ACH.

In vivo ocular biomechanical compliance in thyroid eye disease.

BACKGROUND/AIMS: To compare the ocular biomechanical properties in patients with thyroid eye disease (TED) and healthy participants using a non-contact Scheimpflug-based tonometer (CorVis ST). METHODS: All eyes were examined by slit lamp biomicroscopy, corneal tomography and the CorVis ST (CST). Patients with TED were examined by a fellowship trained oculoplastics specialist to determine status and assess severity. The outputs from CST and additionally derived parameters, including maximum orbital deformation (MOD), were compared between healthy participants and patients with TED using Student's t-test. Furthermore, a multiple linear regression analysis was used to control for various factors known to influence ocular biomechanical responses to an air pulse. RESULTS: This study included 20 patients with TED and compared them with a cohort of 152 healthy participants. The mean age of patients with TED was 46.7±19.0 years and the mean age of healthy participants was 35.9±13.8 years (p=0.03). There were no statistically significant differences in gender distributions between both groups (p>0.05). Several CST parameters were significantly different between groups (p<0.05). Of note, however, MOD was significantly lower in patients with TED (0.16±0.04 mm) compared with the healthy participants (0.25±0.05 mm, p<0.001). This dissimilarity remained even after controlling for the various cofactors. Receiver-operating characteristic analysis revealed an area under the curve of 0.91±0.04 (95% CI 0.84 to 0.98, p<0.001) for MOD. CONCLUSIONS: The in vivo ocular biomechanics as measured by the CST reflects a reduced orbital compliance. This method of ocular biomechanical assessment may aid in the categorisation of TED severity and assist in monitoring and/or diagnosing TED.

Repeatability and Agreement of Orbscan II, Pentacam HR, and Galilei Tomography Systems in Corneas With Keratoconus.

PURPOSE: To assess the repeatability and agreement of keratometry and pachymetry measurements obtained using 3 tomographers in eyes with keratoconus. DESIGN: Reliability analysis. METHODS: setting: Institutional. STUDY POPULATION: Fifty eyes of 50 participants with keratoconus. observational procedure: Steep keratometry, flat keratometry, central corneal thickness (CCT), and thinnest corneal thickness (TCT) measurements using Galilei, Orbscan II, and Pentacam HR. MAIN OUTCOME MEASURES: Repeatability was assessed using within-subject standard deviation (SW), coefficient of variation (CV), and intraclass correlation coefficient (ICC). Bland-Altman plots and 95% limits of agreement (LoA) were used to evaluate agreement between device pairs. RESULTS: For all studied parameters, ICC was >0.97 with the least repeatable measurements obtained using Orbscan II. Mean steep keratometry values were similar while mean flat keratometry values were significantly different between all devices. The Galilei and Pentacam HR had the lowest 95% LoA for both CCT and TCT. There were no significant differences in mean CCT between Galilei and Pentacam HR. Mean Orbscan II CCT measurements were not significantly different overall but had wide 95% LoA with Pentacam HR (-47.95 to 58.09 µm) and Galilei (-43.70 to 53.91 µm). Mean Orbscan II CCT measurements were significantly lower when an acoustic factor of 0.92 was applied (-33.6 µm vs Pentacam HR, P < .001; -33.6 µm vs Galilei; P < .001). CONCLUSIONS: Keratometric and pachymetric measurements of keratoconic eyes obtained by Galilei, Orbscan II, and Pentacam were disparate. Measurements were less repeatable with Orbscan II compared with Pentacam HR and Galilei, although overall repeatability was high for all instruments.

Quantitative Analysis of Corneal Energy Dissipation and Corneal and Orbital Deformation in Response to an Air-Pulse in Healthy Eyes.

PURPOSE: To examine and evaluate ocular biomechanical metrics and additionally derived corneal and orbital components using a noncontact Scheimpflug-based tonometer (CorVis ST) in a population of healthy eyes. METHODS: A total of 152 eyes of 152 participants were examined by slit-lamp biomicroscopy, corneal tomography, and the CorVis ST (CST). This determined the distribution of outputs from the CST, such as deformation amplitude (DA), and additionally derived parameters, including maximum corneal deformation (MCD), maximum orbital deformation (MOD), and corneal energy dissipation (CED). RESULTS: The mean age of participants was 35.88 ± 13.8 years. Deformation amplitude significantly correlated with age (r = 0.24, P = 0.002) but not sex or ethnicity (P > 0.05). Multiple linear regression analysis revealed significant correlations between DA and age (r = 0.19, P = 0.006) and DA and IOP (r = -0.59, P < 0.001). Age correlated with MCD (r = 0.20, P = 0.01), MOD (r = 0.18, P = 0.03), and CED (r = 0.39, P < 0.001). Males had a lower MOD than females (0.24 vs. 0.26 mm, respectively, P = 0.01); however, there were no differences in MCD or CED between sexes (P > 0.05). There were no significant differences between ethnicities for MCD, MOD, and CED (P > 0.05). Multiple linear regression analysis revealed significant correlations between MCD and IOP (r = -0.65, P < 0.001), CED and age (r = 0.41, P < 0.001), CED and IOP (r = 0.28, P = 0.001), and between CED and central corneal thickness (CCT) (r = -0.36, P < 0.001). CONCLUSIONS: The isolation of the corneal component (MCD) should be used when analyzing deformation characteristics in diseases that only affect the cornea. This study establishes a baseline for a population of healthy eyes. Future publications will identify differences in MCD, MOD, and CED between healthy and diseased populations.

Biomechanical properties of the keratoconic cornea: a review.

There has been a recent surge of interest in assessing corneal biomechanical properties due to potential clinical applications, particularly in the early detection of keratoconus (KC). This review discusses the effects of keratoconus on the biomechanical properties of the cornea and the current techniques used to detect these changes both in the laboratory and clinical setting. Specific structural changes occurring in the corneal stroma as part of the disease process can be linked to alterations in the viscous and elastic properties of the cornea in keratoconus. Although there are extensive ex vivo studies using techniques such as extensometry and inflation testing to analyse the biomechanical properties of the normal cornea, few have investigated the keratoconic cornea using the same methods. There are a number of ex vivo studies that confirm the effectiveness of collagen cross-linking in increasing Young's modulus in healthy corneas. Recently, research has focussed on measuring corneal biomechanical parameters in vivo using two commercially available instruments: the Ocular Response Analyser (ORA) and the CorVis ST (CST). Both instruments analyse the dynamic behaviour of the cornea, when temporarily deformed by an air puff; however, the outputs of these instruments are not directly comparable due to differences in the characteristics of the air puff and output parameters. Studies using these instruments have reported significant differences between keratoconic and healthy corneas; however, neither instrument can currently be used in isolation to reliably diagnose keratoconus. Further research analysing the outputs of these instruments may enhance their diagnostic capabilities.