Comparison of the corneal volume and the anterior chamber volume using Pentacam in individuals with healthy, subclinical and early keratoconus eyes

AIM: To compare the anterior chamber volume and corneal volume using Pentacam in people with early keratoconus, subclinical keratoconus, and healthy subjects. METHODS: This epidemiologic study was performed on 63 patients who were candidates for refractive surgery. We classified our patients into three groups as normal, subclinical keratoconus, and early keratoconus according to the Amsler-Krumeich criteria. We collected demographic information, including age and sex, and obtained a full medical history of the patients. Complete visual examination was performed for all patients. Then, using Pentacam, corneal volume and anterior chamber volume were measured among three groups. RESULTS: Corneal volume in the control group was significantly higher than the subclinical keratoconus and early keratoconus groups (P<0.05), but the anterior chamber volume was not significantly different between the groups (P>0.05). CONCLUSION: Measuring the corneal volume can help to distinguish the eyes with subclinical keratoconus and early keratoconus from normal eyes. The chamber volume might not differ remarkably among people with subclinical keratoconus, early keratoconus, and those with normal eyes.

A multicenter study of interocular symmetry of corneal biometrics in Chinese myopic patients

It is essential to know the normal range of the interocular symmetry of the cornea (ISC) for keratoconus diagnosis and corneal substitutes design. In the present study we investigated the interocular symmetry of corneal biometrics in 6,644 Chinese myopic patients from multiple ophthalmic centers. Corneal biometrics of both eyes were exported from the Pentacam instrument. Interocular symmetry of the corneal biometrics was analyzed by Spearman’s correlation test, intraclass correlation coefficient (ICC) analysis and Bland–Altman plot. Significantly strong interocular correlations were found in anterior and posterior corneal curvatures, corneal diameter, corneal thickness, corneal volume, corneal eccentricity, and corneal asphericity (r = 0.87–0.98, all P < 0.001). Moderate interocular correlations were observed in whole corneal astigmatism (r = 0.78) and posterior corneal astigmatism (r = 0.73). ICC between the right and left eyes was 0.94–0.98 for anterior and posterior corneal curvatures, corneal diameter, corneal thickness and corneal volume, 0.80–0.88 for corneal eccentricity and asphericity, and 0.73–0.79 for corneal astigmatism (all P < 0.001). Bland–Altman plot showed that the 95% limit of agreement between both eyes was narrow and symmetric in most of the corneal biometrics, suggesting strong interocular agreements in these corneal biometrics. In conclusion, significant interocular symmetry of corneal biometrics is observed in Chinese myopia patients. Extra attention should be paid to patients with interocular corneal asymmetry.

A Multicenter Study of the Correlations of Anterior and Posterior Corneal Parameters in Chinese Myopic Patients

In this observational cross-sectional study consisting of 8365 Chinese myopic patients from five different ophthalmic centers, we investigated the correlations between anterior and posterior corneal parameters. Strongly negative anterior-posterior correlations of the mean corneal curvature were observed, with similar correlation coefficients in all myopic groups (R: -0.85 to -0.88). The anterior-posterior correlations of corneal astigmatism (R: 0.65 to 0.75), eccentricity (R: 0.27 to 0.38) and asphericity (R: 0.29 to 0.41) were all positive, with slightly different correlation coefficients between the myopic groups. The anterior-posterior correlations of mean corneal curvature were strongly negative with similar correlation coefficients in all quantile groups of six corneal and anterior chamber parameters (R: -0.84 to -0.91), except Sim Km (R: -0.36 to -0.64). The anterior-posterior correlations of corneal astigmatism were all positive with slightly different correlation coefficients between the quantile groups of SimKm (R: 0.66 to 0.74). The anterior-posterior correlations of corneal eccentricity (R: 0.30 to 0.44) and asphericity (R: 0.33 to 0.45) were positive and slightly different between the quantile groups of SimKm, pachy apex and corneal volume. In conclusion, anterior-posterior correlations of corneal curvature, astigmatism, eccentricity and asphericity can be affected by the severity of myopia and some other corneal parameters.

Tomography-based definition of keratoconus for Down syndrome patients

Background To assess the diagnostic ability of Pentacam HR (Oculus Optikgeräte, GmbH, Wetzlar, Germany) tomographic indices in discriminating keratoconus (KC) and KC suspect (KCS) in 10- to 30-year-old patients with Down syndrome (DS). Methods In this study, DS patients were enrolled through special needs schools, the National Down Syndrome Society, and relevant non-profit organizations. Diagnoses were made independently by two experienced specialists. Forty Pentacam indices related to corneal thickness, volume, density, keratometry, power, shape, aberration, and elevation were extracted. For each index, the accuracy for KC and KCS diagnosis was evaluated using discriminant analysis and the area under receiver operating characteristic curve (AUROC). From each enrolled case, data from only one eye was entered in the analyses. Results Analyses were performed on data from 25 KC, 46 KCS, and 154 non-ectatic DS eyes. The best discriminants for KC were anterior higher order aberrations (HOA) (cutoff > 0.643, AUROC = 0.879), posterior vertical coma (cutoff > 0.0702 μm, AUROC = 0.875), anterior vertical coma (cutoff > 0.4124 μm, AUROC = 0.868), and total HOA (cutoff > 0.608, AUROC = 0.867). The difference between AUROCs were not statistically significant (all P > 0.05). For KCS, the best discriminants were minimum corneal thickness (cutoff ≤ 480.0 μm, AUROC = 0.775), corneal volume (cutoff ≤ 55.3 μm, AUROC = 0.727) and Belin Ambrosio display-total deviation (BAD-D) (cutoff > 2.23, AUROC = 0.718) with no significant difference between AUROCs (all P > 0.05). Conclusions In this sample of DS patients, best KC discriminators were HOA and coma which showed good diagnostic ability. For KCS, best predictors were minimum corneal thickness, corneal volume, and BAD-D with relatively good diagnostic ability. Defining a new set of KC diagnostic criteria for DS patients is suggested.

Influence of corneal guttae and nuclear cataract on contrast sensitivity

AIMSTo evaluate the contrast sensitivity in patients with nuclear cataract and corneal guttae compared to patients with nuclear cataract without guttae.METHODSIn this retrospective, single-centre case series, 50 eyes of 50 patients fulfilling the inclusion criteria were enrolled. Patients with corneal guttae and nuclear cataract (n=25, study group) underwent triple Descemet membrane endothelial keratoplasty (DMEK). Patients with nuclear cataract and healthy corneas underwent cataract surgery (n=25, control group). Inclusion criteria were preoperative best-corrected visual acuity ≥20/40, no corneal oedema and similar lens opacity (nuclear opalescence 2.0–2.9). Outcome measures included MARS letter and OPTEC 6500P contrast sensitivity test, corneal volume, central corneal thickness and anterior and posterior corneal densitometry.RESULTSPreoperative MARS letter and OPTEC 6500P contrast sensitivity was significantly worse in the study group (MARS: p<0.001; OPTEC 6500P: p<0.007 at low spatial frequencies in daylight with and without glare and nightlight without glare). After surgery, there was no significant difference in MARS letter contrast sensitivity between groups (p=0.225). OPTEC 6500P contrast sensitivity remained significantly lower in the study group in daylight and nightlight with and without glare at most spatial frequencies (p<0.01) postoperatively. Preoperative and postoperative corneal volume, central corneal thickness and anterior corneal densitometry were equal in both groups (p>0.05). Posterior densitometry was significantly higher in the study group than in the control group preoperatively (p<0.001) but turned into equal values postoperatively (p=0.07).CONCLUSIONSCorneal guttae cause an additional significant decrease in contrast sensitivity in eyes with nuclear cataract. This is in favour of performing a triple DMEK even in eyes with a visual acuity of ≥20/40.

Changes in Corneal Volume at Different Areas and Its Correlation with Corneal Biomechanics after SMILE and FS-LASIK Surgery

Purpose. To investigate the variations of corneal volume (CV) after small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) and analyze the influences of biomechanical properties on the changes of refraction and CV. Methods. Ninety-seven eyes of 97 patients undergoing SMILE and FS-LASIK were included in this retrospective study. CV was measured with Scheimpflug-based corneal topography at preoperatively and at day 1, week 1, and months 1 and 3 postoperatively. CV measured within 5 mm diameter was defined as central region volume (CV5) and between 5 mm and 10 mm diameter was defined as peripheral region volume (CV5-10). An Ocular Response Analyzer (ORA) was used to assess corneal biomechanical properties including corneal hysteresis (CH) and corneal resistant factor (CRF). The reduction of study parameters (△) were calculated by subtracting the preoperative value at various time points from the postoperative values. Results. CV had significant reduction after the SMILE and FS-LASIK procedure (P<0.05). CV5 increased significantly from postoperative day 1 to month 3 (P<0.001) in SMILE, while both CV5 and CV5-10 increased significantly in FS-LASIK (P<0.001). The increase in CV5 after SMILE was 0.11 ± 0.16 mm3，which was significantly different from FS-LASIK (0.20 ± 0.13 mm3, P=0.004). In the SMILE group, △CV5 correlated with △CRF (r = 0.498, P<0.001) and △CH (r = 0.374, P=0.007). In the FS-LASIK group, △CV5 and △CRF had a significant correlation (r = 0.363, P=0.012), but not with △CH. Conclusions. Dynamic changes in corneal volume were found after SMILE and FS-LASIK surgery. The central region significantly increased after SMILE, while both central and peripheral regions increased following FS-LASIK in the early postoperative period. SMILE was associated with less change in biomechanical properties per unit of reduction in CV compared with FS-LASIK.

Posterior corneal features in patients with Down syndrome and their relation with keratoconus

AimsTo characterise posterior corneal surface features in patients with Down syndrome (DS) and to compare them with healthy and mild keratoconus corneas.MethodsThis restrospective, comparative, non-randomised, clinical study included 123 eyes, divided into three groups (37 eyes of patients with DS, 46 with mild keratoconus and 40 controls), and took place at Vissum Alicante. Only patients with no previous ocular surgery, no corneal scars and no active ocular disease other than keratoconus were included. The Sirius System topographer (CSO, Firenze, Italy) was used in order to analyse posterior corneal surface keratometry, shape and keratoconus screening indices, posterior corneal aberrations, corneal volume and pachymetry.ResultsPatients with DS, when compared with healthy controls, have a steeper (mean keratometry 7 mm (KM): −6.30±0.44 vs −6.15±0.22; p<0.05) and more irregular (root mean square per unit of area: 4.5 mm 0.22±0.22 vs 0.09±0.03, p<0.001; posterior vertex of the ectatic area: 33.22±44.29 vs 10.63±2.88, p<0.001) posterior corneal surface, with higher aberrations (high-order aberrations (HOAs): 1.07±1.43 vs 0.15±0.06, p<0.001; coma-like: 0.88±1.09 vs 0.13±0.07, p<0.001) and thinnest pachymetry (497.68±26.88 vs 538.95±31.67, p<0.001). At the same time, no statistically significant difference was found between patients with DS and patients with mild keratoconus (p>0.05) in KM (−6.38±0.34), HOA (0.56±0.36), coma-like (0.51±0.34) and pachymetry (500.56±36.83).ConclusionsPosterior corneal surface of patients with DS is steeper, more irregular and shows more higher order aberrations, as well as reduced volume and thinner pachymetry than patients with healthy corneas. Additionally, posterior corneal surface in patients with DS shows similar characteristics to those found in mild keratoconus.