Anterior Corneal Curvature Research Articles

Keratoconus staging by decades: a baseline ABCD classification of 1000 patients in the Homburg Keratoconus Center

BackgroundThis retrospective cross-sectional study aims to analyse the keratoconus (KC) stage distribution at different ages within the Homburg Keratoconus Center (HKC).Methods1917 corneae (1000 patients) were allocated to decades of age,...

Should Overnight Orthokeratology Patients Wear Their Lenses During Their Afternoon Nap?

The purpose of this study was to evaluate changes in visual acuity, corneal curvature, elevation, pachymetry, and objective quality of vision of experienced orthokeratology patients using their contact lenses during a simulated 30-min afternoon nap. Twelve patients aged 30.8±8.3 years were recruited for the study, with a history of overnight orthokeratology of 27.4±23.0 months. Patients were instructed to close their eyes for 30 min while wearing their contact lenses or without lenses. Anterior corneal curvature, elevation, and corneal pachymetry were assessed with the Pentacam Scheimpflug System at 17 predefined corneal locations, and the HD Analyzer (Terrassa, Spain) was used to measure objective quality of vision. Measurements were conducted before eye closure (baseline), immediately after eye opening/lens removal (M1), and 30 min later (M2). No statistically significant differences were found in anterior corneal curvature and elevation between baseline values and M1 or M2, with and without contact lenses. Corneal swelling at M1 was greater without contact lenses (change in central corneal thickness of 2.3%±3.1%, P=0.001) than with contact lenses (1.7%±1.3%, P<0.001). Recovery at M2 was slower when lenses were worn. A statistically significant improvement in objective quality of vision and visual acuity was found only when patients napped with their lenses. Even if no significant changes were found in corneal curvature and elevation, patients of overnight orthokeratology may benefit from using their contact lenses during their afternoon nap in terms of objective quality of vision and visual acuity.

Corneal Stromal Filler Injection as a Novel Approach to Correct Presbyopia-An Ex Vivo Pilot Study.

PurposeTo evaluate the ex vivo feasibility of corneal stromal filler injection to create bifocality to correct presbyopia by flattening the central posterior corneal surface and thus increase refractive power.MethodsFemtosecond laser-assisted corneal stromal pockets of varying diameters close to the posterior corneal curvature were cut into rabbit eyes ex vivo. Subsequently, hyaluronic acid was injected to flatten the central posterior curvature. Refractive parameters were determined using perioperatively acquired three-dimensional optical coherence tomography (OCT) scans. Using micrometer-resolution OCT, corneal endothelial cell morphology and density were evaluated.ResultsFollowing filler injection into the corneal stromal pockets, a fair volume-dependent increase of central refractive power up to 4 diopters (dpt) was observed. Unremarkable refractive changes of the peripheral posterior (3 mm, 0.20 ± 0.11 dpt; 2 mm, 0.11 ± 0.10 dpt) and the anterior corneal curvature (3 mm, 0.20 ± 0.34 dpt; 2 mm, 0.33 ± 0.31 dpt) occurred. Only negligible changes in astigmatism were observed. Different sizes of optical zones could be established. Furthermore, no alterations of corneal endothelial morphology or endothelial cell density (2831 ± 356 cells/mm2 vs. 2734 ± 292 cells/mm2; P = 0.552) due to the adjacent laser treatment were observed.ConclusionsThe ex vivo investigations proved the principle of injecting a filler material into femtosecond laser-created corneal stromal pockets close to the posterior corneal curvature as an efficacious, individually adjustable, and novel approach to correct presbyopia without ablating corneal tissue.Translational RelevanceDue to the aging population worldwide, presbyopia is an increasing problem; thus, our study may encourage further exploration to extend the treatment spectrum of clinically used femtosecond laser systems to correct presbyopia.

Short-Term Changes in Prediction Error after Cataract Surgery in Eyes Receiving 1 of 3 Types of Single-Piece Acrylic Intraocular Lenses

To compare short-term changes in refractive prediction error (PE) after phacoemulsification among eyes receiving different types of single-piece acrylic intraocular lenses (IOLs). Randomized clinical trial. A total of 195 eyes of 195 patients scheduled for implantation of a single-piece acrylic IOL were randomly assigned to receive 1 of 3 IOLs: 1) an Alcon model SN60WF, 2) a Hoya model XY-1, or 3) an AMO model ZCB00V. Manifest spherical equivalent (MRSE) value, PE, and changes in PE were examined at 1day and at 1 and 2months postoperatively and were compared among groups. The mean MRSE and PE significantly changed toward myopia between 1day and 2months postoperatively in all groups (P < .0001). The MRSE and PE did not differ significantly among groups at 1day and 1month postoperatively and were significantly smaller in the SN60WF group than in the XY-1 and ZCB00V groups at 2months (P ≤ .0006). The PE change between 1day and 2months postoperatively was significantly smaller in the SN60WF group than in the other groups (P= .0062). IOL type and changes in anterior chamber depth and corneal curvature independently correlated with PE changes. The MRSE and PE showed a significant myopic change for 2months postoperatively in eyes implanted with 1 of 3 types of single-piece acrylic IOLs and were significantly smaller in the SN60WF than in the XY-1 and ZCB00V groups. Changes in PE during the 2 postoperative months were smaller in the SN60WF IOLs than in the other IOLs, suggesting that postoperative refractive stability differs among single-piece acrylic IOLs.

Evaluation of Central and Peripheral Corneal Thicknesses in Patients with Systemic Lupus Erythematosus.

PurposeTo evaluate the corneal pachymetric and topographic parameters of systemic Lupus Erythematosus (SLE) patients using Dual Scheimpflug Imaging.MethodsThis observational cross-sectional controlled study included the right eye of 30 SLE patients and 30 age-matched controls. Corneal measurements were acquired by dual Scheimpflug imaging including anterior and posterior corneal curvatures, central, mid-peripheral corneal thickness (measured at the 5 mm zone) and peripheral pachymetry (measured at the 7 mm zone). SLE disease activity index (SLEDAI) was calculated and correlated with corneal pachymetry.ResultsSLE patients had significantly thicker corneal periphery than controls. Mean central corneal pachymetry was 530.4± 27.3 microns (SD) in SLE and 547.5±31.5 microns (SD) in control group, p = 0.032. The corneal periphery – except superiorly – was significantly thicker in SLE patients than controls (p ˂0.001). Nasal peripheral corneal thickness positively correlated with disease activity index SLEDAI (p=0.03).ConclusionSLE patients present with thicker corneal periphery than controls characteristically sparing the superior quadrant. Possible corneal photosensitivity leading to peripheral immune complex deposition as well as flatter posterior corneal surface at the periphery are proposed explanations for these findings.

Using the posterior to anterior corneal curvature radii ratio to minimize the risk of a postoperative hyperopic shift after Descemet membrane endothelial keratoplasty.

To evaluate different corneal parameters in identifying patients at risk of a hyperopic shift after (DMEK). This retrospective study included 92 eyes of patients with FECD after DMEK surgery. Pachymetry parameters, various tomographic parameters and densitometry values before and after DMEK were determined using a rotating Scheimpflug system (Pentacam HR, Oculus). For assessing the posterior to anterior corneal curvature relationship, we calculated the RPA (posterior to anterior corneal curvature radii ratio). The average keratometry reading of the posterior corneal surface (KmB) increased and the total corneal refractive power (TCRP) decreased significantly after surgery (P < .001). There was a significant difference between the preoperative and postoperative RPA (P < .001) and the posterior Q value (P < .001). The strongest correlation was found between the change in the KmB and the preoperative RPA (Spearman's correlation coefficient = 0.872, P < .001). In the receiver operating characteristic (ROC) analysis, the highest AUC values (for ∆KmB) among the different preoperative parameters tested were obtained for RPA and posterior Q value (Asph. QB) with AUROC (area under the ROC) values of 0.95 and 0.89, respectively. The Q value and the RPA showed the highest correlation with the change in corneal refractive power and the greatest AUC. These parameters could be used as surrogate markers to identify eyes that might be at risk of a greater postoperative hyperopic shift, which would allow more accurate setting of refractive goals.

Effect of timolol maleate (0.5%) in the management of myopic regression post laser-assisted in-situ keratomileusis: Clinical and topographical outcomes.

Purpose:The aim of this study was to analyze the effect of timolol maleate (0.5%) eye drops in the treatment of myopic regression after laser-assisted in-situ keratomileusis (LASIK).Methods:The study was conducted at a tertiary care eye hospital in north India between April 2017 & March 2018 as a prospective interventional study. Patients who underwent uneventful myopic LASIK with hansatome mechanical keratome and presented with regression were included in the study. Baseline demographic characteristics, time to presentation with regression best-corrected visual acuity (BCVA), refraction, intraocular pressure, central corneal thickness and keratometry were recorded at baseline and at each follow-up visit. The enrolled patients were prescribed timolol maleate (0.5%) eyedrops twice daily. They were followed up every month till 3 months on timolol maleate (0.5%) eyedrops and at 6 months post stopping the treatment.Results:Twenty-nine eyes of 15 patients were enrolled in the study. Mean pre LASIK spherical equivalent (SE) was – 7.48 ± 2.9 Diopters (Range-3.125 to –11.75 Diopters) and mean regression spherical equivalent was –1.02 ± 1.1 Diopters. There was a decrease in mean SE from presentation (intervention start point) up to 6 months follow-up (–1.34 ± 0.89 to –0.30 ± 0.29 Diopters). While posterior corneal curvature (K1 and K2 Back) changed significantly over treatment period (P = 0.0029, P = 0.0024 respectively), changes in anterior corneal curvature (K1 and K2 Front) were not significant (P = 0.05, P = 0.06 respectively). Central corneal thickness (CCT) and intraocular pressure (IOP) did not change significantly over treatment course.Conclusion:Timolol maleate (0.5%) eyedrop is an effective modality for the treatment of refractive regression post LASIK circumventing the need for laser re-treatment in such patients. The most probable mechanism is reversal of the anterior bowing of the cornea in response to intraocular pressure changes.

Outcomes of Descemet-Stripping Automated Endothelial Keratoplasty in Congenital Hereditary Endothelial Dystrophy.

To evaluate the outcomes and complications of Descemet-stripping automated endothelial keratoplasty (DSAEK) in children with congenital hereditary endothelial dystrophy (CHED). Eighteen eyes from 10 children with CHED who underwent standard phakic DSAEK were enrolled in this retrospective interventional case series. Medical records including slit-lamp biomicroscopy, cycloplegic refraction, visual acuity, and measurements of central corneal thickness, corneal topography, and endothelial cell density were evaluated. All complications were recorded. The mean age of cases was 8.1±4.2 (range: 3-16) years at the time of surgery. Descemet-stripping automated endothelial keratoplasty was performed successfully in all eyes, which survived in 16/18 (88.9%) of cases during a median follow-up period of 38 (range 19-64) months. In patients with clear graft, best-corrected visual acuity was improved to a range of 20/100 to 20/40 and improved to fix and follow in one younger child. Endothelial cell density decreased by an average of 42.1%, comparing baseline and 6-month follow-up and was relatively stable thereafter. A marked flattening of the anterior corneal curvature (mean change of anterior K reading: +2.56±3.14 diopters) was observed after DSAEK. The only major complication in patients with clear graft was intraocular pressure elevation in 61.1% of the eyes, which was easily controlled with one antiglaucoma medication. None of the eyes developed cataract. Descemet-stripping automated endothelial keratoplasty is a safe and successful procedure in children with an acceptable graft survival in a mid-term follow-up period. A marked hyperopic shift could occur after DSAEK in children with CHED.

Ocular biometric parameters are associated with non-contact tonometry measured intraocular pressure in non-pathologic myopic patients.

This research aimed to investigate effects and risk factors on non-contact tonometer (NCT) readings in healthy myopic subjects by employing cross-sectional study design. Totally, sixty otherwise healthy myopic volunteers (mean 28.4years old) with 90% female were recruited in ophthalmic clinic. The routine ophthalmic tests, refractive evaluation, examination central corneal thickness (CCT), depth of anterior chamber, axial length, corneal curvature, white-to-white and NCT were assessed at baseline. The linear-mixed model was utilized to evaluate correlation between the readings and ocular biometric parameters. For population in this study, mean spherical equivalents were - 4.85 ± 1.79 diopters in right eyes and - 4.63 ± 1.95 diopters in left eyes. Meanwhile, 28.3% of the eyes had a refractive error exceeding - 6.0 diopters. The mean NCT reading was 15.02 ± 3.02mmHg in left eyes and 15.33 ± 2.96mmHg in right eyes. Among the factors analyzed, CCT was the most significant parameter associated with NCT readings. After adjusting for the other factors, per one standard deviation increase of central corneal thickness (36.11μm) was associated a 1.14 (95% confidence interval 0.53-1.77) mmHg elevated NCT reading. The average central corneal curvature, age and spherical equivalence were also significantly and independently associated with NCT readings. Central corneal thickness, age, corneal curvature and degree of myopia were independently associated with NCT measured intraocular pressure. Central corneal thickness is one of the most influential factors.

Refractive and corneal responses of young myopic children to short-term orthokeratology treatment with different compression factors

PurposeTo evaluate changes in refractive and corneal responses in myopic children wearing orthokeratology (ortho-k) lenses with conventional compression factor (CCF, 0.75 D) and increased compression factor (ICF, 1.75 D). MethodsThis was a double-blind self-controlled study. Subjects were randomly fitted with CCF in one eye and ICF in the fellow eye. Weekly monitoring of refraction, visual acuity (VA), external ocular health, and corneal responses were performed over one month of lens wear and after discontinuation of lens wear until stabilization was achieved. ResultsTwenty-five subjects, aged 9.4 ± 1.0 years, completed one-month lens wear, of whom 23 completed the washout period. The first fit success rates for CCF and ICF were 93% and 96%, respectively. Myopia, unaided VA, central corneal thickness, anterior corneal curvatures (K), apical power (AP), and corneal resistance factor (CRF) all changed significantly during the study period (P < 0.003). Between-eye difference was significant only for myopia reduction (P = 0.001). About 4% and 8% of ICF and CCF eyes were under-corrected. The attempted target was achieved in about 80% of CCF and 60% of ICF eyes at week 4. At the end of the washout period (3 weeks), myopia, K, and AP were significantly different compared to baseline (P < 0.001). ConclusionIncreasing the compression factor did not affect the first fit success rate and external ocular health, but did allow faster correction of refractive error within one month of lens wear. Further investigation is warranted to investigate the long-term effects of ICF on myopia control compared to CCF.

Heritability of Corneal Curvature and Pentacam Topometric Indices: A Population-Based Study.

To investigate familial aggregation of anterior and posterior corneal curvature, corneal astigmatism, and some corneal topometric indices using the Pentacam. Of 3,851 eligible individuals who resided in the selected areas, 2,779 met the conditions for analysis. However, analysis was limited to families whose Pentacam measures were available for at least 2 family members (father or mother and a child), resulting in 1,383 individuals in 382 families. All selected subjects underwent a set of examinations, including refraction, uncorrected and corrected visual acuity measurement, slitlamp biomicroscopy, and Pentacam imaging. Heritability estimation was used to calculate familial aggregation. The results of our study showed a fairly high corneal curvature heritability. The heritability of K2 and K1 in the anterior surface was 58.61% (95% confidence interval [CI], 54.99-62.23) and 55.82% (95% CI, 52.66-58.98), respectively. The heritability of posterior corneal curvature was slightly higher than that of the anterior corneal curvature. The heritability of K2 and K1 in the posterior surface was 63.42% (95% CI, 60.07-66.77) and 59.67% (95% CI, 55.85-63.49), respectively. Investigation of the quantitative topographic corneal indices showed that index of surface variance (ISV), central keratoconus index, and index of vertical asymmetry (IVA) had the highest levels of heritability (81.2% [95% CI, 73.64-88.76], 75.21% [95% CI, 67.19-82.28], and 66.46% [95% CI, 61.99-70.93], respectively). However, keratometric power deviation and index of height asymmetry had the lowest heritability levels (7.48% 95% CI, [4.94-10.02] and 18.31% [95% CI, 16.07-20.55], respectively). The familial aggregation and relatively high heritability of the corneal curvature and some keratoconus-related indices, such as ISV and IVA, confirm a high correlation between these phenotypes and genetic factors and warrant further investigation of the genetic mechanisms in keratoconus.

Tomographic analysis of anterior and posterior surgically induced astigmatism after 2.2 mm temporal clear corneal incisions in femtosecond laser–assisted cataract surgery

To evaluate surgically induced astigmatism (SIA) of temporal clear corneal incisions (CCIs) on anterior and posterior corneal curvature after femtosecond laser-assisted cataract surgery (FLACS) using Scheimpflug tomographic measurements. Department of Ophthalmology, Goethe University, Frankfurt am Main, Germany. Prospective interventional case series. This study enrolled patients who underwent FLACS from June 2013 to July 2014. All eyes were measured with a Pentacam HR preoperatively and at 1month and 3months postoperatively, had preoperative total corneal refractive power (TCRP) astigmatism (CATCRP) of 0.50 diopters (D) or less, and received a temporal 2.2mm incision at 0 degrees and 180 degrees. Vector analysis, using the Holladay-Cravy-Koch formula and the Alpins method, determined astigmatic changes in anterior corneal astigmatism (CAant), posterior corneal astigmatism (CApost), and CATCRP. Student t and Wilcoxon tests were performed. A P value less than 0.05 was considered statistically significant. This study comprised 53 eyes of 38 patients. At 3months postoperatively, the CAant, CApost, and CATCRP were significantly higher compared with the preoperative values (P=.015, P=.007, P=.008, respectively); however, CApost and CATCRP were significantly lower compared with the limit of 0.50 D (P<.001, P=.01, respectively), whereas CAant was not (P=.11). The mean SIA of CAant, CApost, and CATCRP was 0.25 D ± 0.15 (SD), 0.16±0.11 D, and 0.28±0.17 D, respectively. The angle of error was high (-1.98±52.95 degrees, 1.64±51.27 degrees, and -1.72±48.79 degrees, respectively). Femtosecond laser temporal CCIs induce minimal astigmatism in CAant, CApost, and CATCRP, but can be evaluated statistically as astigmatically neutral.

Comparison of corneal curvature parameters obtained from two different instruments-Pentacam and VX120.

To explore whether the same corneal curvature parameters and anterior chamber depth measured by Pentacam and VX120 have a good consistency and can replace each other. This study enrolled 140 eyes of 70 patients ranging in age from 19 to 53y. All eyes underwent a comprehensive ophthalmologic examination including an anterior segment analysis with the VX120 system (Visionix-Luneau Technologies, Chartres, France) and Pentacam (Oculus Optikgerate GmbH) respectively. The comparison on corneal curvature parameters was done between Pentacam and VX120 using clustered signed rank test; the interclass correlation coefficients (ICC) with 95% confidence intervals (CI) was calculated for each parameter between Pentacam and VX120; the Bland-Altman plot of each parameter was supplemented. The anterior corneal curvature measured by VX120 was Ks: 44.00±1.78 D, KsAt: 89.45±22.18, Kf: 42.84±1.58 D, KfAt: 93.91±79.34; which measured by Pentacam was Ks: 43.80±1.82 D, KsAt: 91.17±21.40, Kf: 42.61±1.64 D, KfAt: 91.16±78.69. There was statistical difference between Pentacam and VX120 for anterior corneal curvature parameter (P<0.001). The posterior corneal curvature measured by VX120 was Ks: -6.42±1.23 D, KsAt: 91.00±23.45, Kf: -5.85±1.24 D, KfAt: 95.93±79.11; which measured by Pentacam was Ks: -6.44±0.32 D, KsAt: 92.24±11.75, Kf: -6.01±1.05 D, KfAt: 74.43±80.64. There was statistical difference between Pentacam and VX120 for posterior corneal curvature parameters (P<0.001). Anterior chamber depth (ACD) measured by Pentacam and VX120 was statistically different. Pentacam and VX120 achieved high consistency only on corneal anterior surface, including Ks and Kf. The ICCs were 0.96 (95%CI: 0.95, 0.97) and 0.95 (95%CI: 0.94, 0.97) respectively. For other corneal surface curvature parameters, all ICCs of between Pentacam and VX120 were below 0.87. Bland-Altman plots indicated of low consistency of corneal surface curvature parameters measured by Pentacam and VX120. The corneal curvature parameters and anterior chamber depth measured by Pentacam and VX120 were statistically different. Data measured by Pentacam and VX120 is not suggested to replace each other, mixing data measured by Pentacam and VX120 together is not suggested either.

Corneo-pterygium total area measurements utilising image analysis method

PurposeTo describe an objective method to accurately quantify corneo-pterygium total area (CPTA) by utilising image analysis method and to evaluate its association with corneal astigmatism (CA). Methods120 primary pterygium participants were selected from patients who visited an ophthalmology clinic. We adopted image analysis software in calculating the size of invading pterygium to the cornea. The marking of the calculated area was done manually, and the total area size was measured in pixel. The computed area is defined as the area from the apex of pterygium to the limbal-corneal border. Then, from the pixel, it was transformed into a percentage (%), which represents the CPTA relative to the entire corneal surface area. Intra- and inter-observer reliability testing were performed by repeating the tracing process twice with a different sequence of images at least one (1) month apart. Intraclass correlation (ICC) and scatter plot were used to describe the reliability of measurement. ResultsThe overall mean (N=120) of CPTA was 45.26±13.51% (CI: 42.38–48.36). Reliability for region of interest (ROI) demarcation of CPTA were excellent with intra and inter-agreement of 0.995 (95% CI, 0.994–0.998; P<0.001) and 0.994 (95% CI, 0.992–0.997; P<0.001) respectively. The new method was positively associated with corneal astigmatism (P<0.01). This method was able to predict 37% of the variance in CA compared to 21% using standard method. ConclusionsImage analysis method is useful, reliable and practical in the clinical setting to objectively quantify actual pterygium size, shapes and its effects on the anterior corneal curvature.

Corneal Tomography Changes and Refractive Outcomes After Descemet Stripping Without Endothelial Keratoplasty.

To investigate corneal tomography changes and refractive outcomes after Descemetorhexis without endothelial keratoplasty (DWEK). Retrospective chart review of 25 eyes from 16 patients with Fuchs corneal endothelial dystrophy that underwent successful DWEK combined with cataract surgery. There was no significant change in anterior corneal curvature on tomography maps. However, all tomography maps demonstrated an increase in central posterior float and all but one demonstrated a decrease in pachymetry after DWEK. Only 7 of 25 eyes had increased irregular astigmatism on tomography after DWEK, of which 57% had preexisting irregular astigmatism before the procedure. The mean difference between the targeted and outcome refraction was +0.65 diopters (D) at the time of corneal clearance, but this improved to +0.38 D 1 month after corneal clearance. Postoperative refraction was within 1 D of target refraction for 92% of cases (23 eyes) but within 0.5 D of target refraction for only 48% of cases (12 eyes). The differences between expected and actual refractive outcomes were correlated with change in posterior corneal curvature and pachymetry. DWEK induces an increased central posterior float localized to the site of Descemet membrane stripping, confirming the need for centralized stripping. Irregular astigmatism can occur after DWEK but is typically minimal and occurs more commonly in the setting of preoperative irregular astigmatism. DWEK induces about a 0.5 D hyperopic shift, which should be considered when determining intraocular lens power with simultaneous surgery.

Correlation between body mass index and ocular parameters.

Purpose: To investigate the relationship between BMI and selected ocular parameters.Subjects and methods: Fifty-three left eyes of normal weight subjects and 67 age-sex matched overweight subjects were studied. Inclusion criteria for the normal weight and overweight groups included BMI between 18.5–22.9 and 23.0–29.9 kg/m2, respectively. Subjects with a history of systemic disease, ocular disease or surgery, or disability were excluded. All subjects underwent a medical history interview, arterial blood pressure, height, weight, waist circumference and hip circumference measurements, and BMI and waist-hip ratio calculation. The intraocular pressure (IOP) and anterior corneal curvature were measured by non-contact tonometry and corneal topography, respectively. Measurement of anterior and posterior segment parameters of the eye, including central corneal thickness, anterior chamber depth (ACD), anterior chamber angle, macular thickness (MT), ganglion cell thickness (GCT), retinal nerve fiber layer thickness, cup to disc ratio, and choroidal thickness was performed by enhanced depth-imaging optical coherence tomography.Results: There was a positive correlation between ACD and BMI (Univariate analysis; β =0.198, P=0.030, Multivariate analysis; β =0.410, P=0.005) and between BMI and IOP (Univariate analysis; β =0.269, P=0.003). The IOP of the overweight group was found to be significantly higher than of the normal weight group (12.80±3.40 and 11.86±2.12 mm Hg, respectively, P=0.002). Also, there was a significant difference found between the GCT and the MT of the two groups (P=0.036 and 0.009, respectively).Conclusion: It was found that BMI strongly correlated with ACD and IOP. Also, the degree of obesity was found to be a significant factor; therefore, the relationship between these ocular parameters and the severity of obesity should be further investigated.

Anterior Corneal Curvature and Aberration Changes After Scleral Lens Wear in Keratoconus Patients With and Without Ring Segments.

To evaluate changes in the anterior corneal curvature and aberrometry after scleral contact lens wear in keratoconus (KC) subjects with and without intracorneal ring segments (ICRS). Twenty-six subjects diagnosed with keratoconus were selected to participate in the study. Subjects were divided into 2 groups, those with ICRS (KC-ICRS group) and those without ICRS (KC group). Subjects were instructed to wear 16.5-mm scleral lenses for 8 hours. Topographic and aberrometric parameters were evaluated before lens wear and immediately after lens removal. Anterior corneal curvature was evaluated at corneal diameters of 2, 4, 6, and 8 mm, and corneal aberrations were measured at 4-, 6-, and 8-mm pupil diameters. The mean age of subjects was 36.95±8.95 years. In KC group, there was a statistically significant flattening of the central corneal curvature, from 6.98 to 7.09 mm (P<0.05). No changes were found in the central corneal curvature in the KC-ICRS group. The KC group showed anterior corneal curvature flattening, mainly in the nasal quadrant. The KC-ICRS group showed flattening primarily in the inferior hemisphere. In the KC group, spherical aberration for 6-mm pupil increased significantly. In the KC-ICRS group, changes in aberrations were significant for high-order root mean square at 4- and 6-mm pupil diameters (P<0.05), for oblique astigmatism for 4 mm and 6 mm, and for vertical coma for 4-mm pupil (P<0.05). Short-term scleral lens wear showed flattening of the anterior corneal surface in all subjects. In the KC group, the flattening was more pronounced in the nasal quadrant while changes were more pronounced inferiorly in KC-ICRS group.

Anterior segment parameters in normal dogs using the Pentacam® HR Scheimpflug system.

To describe and compare normative anterior segment parameters between canine age groups using the Pentacam® HR Scheimpflug camera (Pentacam). Thirty-six sedated dogs (60 eyes) of varying ages and breeds were imaged with the Pentacam; only nondiseased anterior segments were included. Dogs were divided into three age groups: Group 1 (1-5years), Group 2 (6-10years), and Group 3 (11-15years). Values assessed included central corneal thickness (CCT), anterior and posterior corneal elevation (ACE/PCE), anterior and posterior corneal curvature metrics, corneal volume (CV), anterior and posterior corneal astigmatism (AA/PA), anterior chamber depth (ACD), anterior chamber volume (ACV), and anterior chamber angle (ACA). Tukey-adjusted pairwise comparisons were performed. Overall CCT (mean±SD) was 631.07±59.91µm. Central corneal thickness was 608.60±48.63µm for Group 1, 648.57±51.06µm for Group 2, and 635.37±73.71µm for Group 3. Anterior corneal elevation (ACE) measured 9.08±0.58mm, PCE measured 8.04±0.50mm, and CV was 58.13±5.39mm3 . Astigmatism values were 1.34±0.94D for AA and 0.46±0.44D for PA. Anterior chamber values were 3.76±0.56mm for ACD, 383.68±66.24mm3 for ACV, and 23.62±29.33˚ for ACA. Significant differences were found between Groups 1 and 2 for CV (55.08±4.08mm3 and 60.32±4.19mm3 , respectively), (P=0.02). Corneal volume significantly increased between Group 1 and Group 2. Central corneal thickness increased from Group 1 to Group 3, but was not significant with the current sample size. There were no other differences between age groups.

15-Month Visual Outcomes and Corneal Power Changes of SMILE in Treating High Myopia With Maximum Myopic Meridian Exceeding 10.00 D.

To evaluate the long-term visual and refractive outcomes, optical quality, and stability of the cornea and axial length after small incision lenticule extraction (SMILE) for the correction of high myopia with a maximum myopic meridian exceeding 10.00 diopters (D). Via a prospective cohort study, 53 eyes (53 patients) with a maximum myopic meridian exceeding 10.00 D were corrected with a VisuMax femtosecond laser (version 3.0; Carl Zeiss Meditec AG, Jena, Germany) at the Zhongshan Ophthalmic Center of Sun Yat-sen University. Refractive outcomes, aberrations, axial length, and corneal curvature were evaluated preoperatively and at 1, 3, and 15 months postoperatively. At 15 months postoperatively, the efficacy and safety indexes were 0.91 ± 0.25 and 1.15 ± 0.18, respectively. A total of 72% of eyes were within ±0.50 D and 89% were within ±1.00 D of the attempted spherical equivalent, respectively. From 1 to 15 months postoperatively, the significant regression was -0.24 ± 0.28 D (P < .001) on manifest refraction and -0.43 ± 0.54 D (P < .001) on anterior corneal curvature. In addition, a significant increase of 0.20 µm (P = .016) was observed in the spherical aberration. No significant change was observed in posterior corneal curvature (P > .999), including mean keratometry or astigmatism, or in the ocular axis length from 1 to 15 months postoperatively (26.82 ± 0.93 and 26.82 ± 0.95 mm, respectively, P > .99). SMILE had long-term safety, efficacy, and predictability when treating high myopia with a maximum myopic meridian exceeding 10.00 D. Both a manifest refraction regression of -0.24 D and a significant spherical aberration increase of 0.20 µm were observed between 1 and 15 months postoperatively, due to the increased anterior corneal curvature. [J Refract Surg. 2019;35(1):31-39.].

Effect of corneal curvature on optical zone decentration and its impact on astigmatism and higher-order aberrations in SMILE and LASIK.

To determine the association between anterior corneal curvature and optical zone centration as well as its impact on aberration profiles in small-incision lenticule extraction (SMILE) and laser in situ keratomileusis (LASIK). Seventy-eight eyes of 78 patients treated with SMILE (45 eyes) and LASIK (33 eyes) were included. The centration of the optical zone was evaluated on the instantaneous curvature difference map between the preoperative and 3-month postoperative scans using a superimposed set of concentric circles. The correlation between optical zone decentration and anterior keratometry values was evaluated. The effect of optical zone decentration on vector components of astigmatic correction and induction of higher-order aberrations (HOA) was assessed. The mean decentration distance was 0.21 ± 0.11mm for SMILE and 0.20 ± 0.09mm for LASIK (p = 0.808). There was a significant correlation between anterior keratometric astigmatism and decentration distance (r = 0.653, p < 0.001) for SMILE but not for LASIK (r = - 0.264, p = 0.138). Astigmatic correction was performed in 67 eyes. Optical zone decentration and the vector components of astigmatic correction were not correlated (p ≥ 0.420). Significant correlation was demonstrated between the decentration distance and the induced total coma (SMILE: r = 0.384, p = 0.009; LASIK: r = 0.553, p = 0.001) as well as the induced total HOA (SMILE: r = 0.498, p = 0.001; LASIK: r = 0.555, p = 0.001). Anterior cornea astigmatism affected the treatment centration in SMILE but not LASIK. Subclinical decentration was associated with the induction of total coma and total HOA, but it did not affect the lower-order astigmatic correction.