Minimum Corneal Thickness Research Articles

Prospective Randomized Trial of Corneal Cross-linking Riboflavin Dosing Frequencies for Treatment of Keratoconus and Corneal Ectasia

To investigate whether the riboflavin dosing frequency affects corneal cross-linking efficacy or safety, given that isotonic riboflavin solution is viscous and each installation coats the corneal surface with a film that absorbs some of the incident ultraviolet A light. Prospective, randomized, single-center equivalence trial. Patients with progressive keratoconus or ectasia after refractive surgery (n= 510). One eye per patient was prospectively randomized to 2-minute or 5-minute riboflavin dosing intervals with standard corneal cross-linking (epithelial removal and 30-minute irradiation with 3 mW/cm2 ultraviolet A light). Block randomization resulted in comparable representation of keratoconus and ectasia after refractive surgery in the 2 treatment arms. Treatment equivalence was assessed using the 2 one-sided test. Fellow eyes (n= 207) were treated with 5-minute dosing and considered in the safety analysis. The primary hypothesis was equivalent change in the topography-derived maximum keratometry value from baseline to 6 months with 2-minute vs. 5-minute dosing. A ±0.75-diopter margin of equivalence for the treatment difference between dosing regimens was considered clinically relevant. Adverse events and changes from baseline to 6 months in corrected distance visual acuity (CDVA), uncorrected distance visual acuity, and minimum corneal thickness were assessed. The mean reduction in maximum keratometry from baseline was equivalent with 2-minute and 5-minute riboflavin dosing intervals at 6 months (0.97 and 0.76 diopters, respectively; 90% confidence interval for treatment difference,-0.23 to 0.66; per-protocol population). With both dosing intervals, the mean improvement in CDVA was 0.07 logarithm of the minimum angle of resolution or 3.5 letters at 6 months. Of the 635 study and fellow eyes examined at 6 months, 134 (21%) gained and 32 (5%) lost 2 or more lines of CDVA. Three eyes (0.4%) developed sterile infiltrates, 1 (0.1%) had delayed epithelial healing with dendrites, and 3 (0.4%) had recurrent epithelial defects. Three eyes (0.4%) were re-treated. The 2 riboflavin dosing regimens produced equivalent reduction in the maximum keratometry value, with a favorable safety profile.

Topographic indices and pachymetry in healthy adolescents obtained with Sirius topographer.

To determine the normal values for the Sirius corneal topography, of some topographic indices and corneal pachymetry, in a healthy young adolescent population. A total of 176 students (mean age 12.95±0.82years) took part in this study. 352 eyes were imaged through Sirius topographer. Anterior and posterior meridians, mean pupillary power, central corneal thickness, minimum corneal thickness, and anterior and posterior asymmetry indices were analyzed. Correlations between corneal parameters and differences between anterior and posterior corneal surfaces were evaluated. Average anterior meridian was 43.37D (±1.46); average posterior meridian was 6.16D (±0.24); central corneal thickness was 550.81±29.88 micron, minimum corneal thickness was 547.36±29.93 micron; mean pupillary power was 42.95±1.46D, SIf was -0.035±0.46, and SIb was 0.012±0.091. Anterior and posterior corneal curvatures correlated negatively with MPP (r=-0.99; p=0.000 and r=-0.85 p=0.000, respectively). Anterior curvature correlated positively with posterior curvature (r=0.891; p=0.000). Positive correlations were found for SIf and SIb (r=0.58; p=0.000). Negative correlations were found for SIf and corneal pachymetry (r=-0.23; p=0.000) and for SIb and corneal pachymetry (r=-0.19; p=0.012). The difference between anterior meridian average and posterior meridian average was 1.29±0.12 and was significative (p<0.001). No differences between genders were found. These results provide normal standards for corneal values in adolescents and could represent a useful tool for future comparative studies in this age-group population.

Objective and subjective diagnostic parameters in the fellow eye of unilateral keratoconus

BackgroundKeratoconus (KC) is usually a bilateral corneal ectatic disease. For significant asymmetric presentation (so called unilateral KC), the fellow eye has the mildest and earliest form of the disease, which is typically called forme fruste keratoconus. The aim of this study was to evaluate the sensitivity and specificity of parameters derived from a Scheimpflug imaging system (Pentacam) as well as the changes in the quality of mesopic vision in the apparently normal fellow eye (forme fruste) to detect the earliest and most sensitive parameters.MethodsPatients with clinical keratoconus in one eye and forme fruste keratoconus in the fellow eye were compared to subjects with normal eyes. The patients were examined using a rotating Scheimpflug imaging system (Pentacam).The following parameters were evaluated: keratometry, minimum corneal thickness, pachymetry progression index (PPI), Ambrósio relational thickness (ART), posterior elevation, back difference elevation (BDE) and multimetric D index(D index). Receiver operating characteristic (ROC) curves were analyzed by evaluating the area under the curve (AUC) to detect the sensitivity and specificity of each parameter. Mesopic vision evaluations were performed by contrast sensitivity and glare tests for each group.ResultsA total of 48 patients with clinical keratoconus in one eye and forme fruste keratoconus in the fellow eye and 72normal subjects were evaluated. In the clinical keratoconus eyes, the mean K, back difference elevation (BDE), pachymetric progression index maximum(PPI max), and multimetric D were significantly higher compared to the normal subjects, whereas the corneal pachymetry and Ambrósio relational thickness maximum (ART max) were significantly lower. In the forme fruste eyes, the ROC analysis showed that the AUC values of the mean K, thinnest pachymetry, ARTmax, BDE, D index, and PPI max were 0.82, 0.61, 0.88, 0. 67, and 0.64, respectively. The contrast sensitivity and glare tests were significantly affected in the forme fruste cases.ConclusionIn forme fruste keratoconus eyes, the ART max is considered a highly sensitive objective parameter. Contrast sensitivity and glare is an important subjective test, which is affected in forme fruste patients.

Demarcation line depth after contact lens–assisted corneal crosslinking for progressive keratoconus: Comparison of dextran-based and hydroxypropyl methylcellulose–based riboflavin solutions

To compare the demarcation line depth after contact lens-assisted corneal crosslinking (CXL) for progressive keratoconus using dextran-based and hydroxypropyl methylcellulose (HPMC)-based riboflavin solutions. Advanced Eye Centre, Postgraduate Institute of Medical Education and Research, Chandigarh, India. Retrospective case series. Patients with preoperative epithelium-on (epi-on) minimum corneal thickness between 350μm and 450μm having contact lens-assisted CXL for progressive keratoconus were crosslinked with isoosmolar 0.1% riboflavin in 20% dextran 500 or HPMC 1.1%. The primary outcome measure was the mean demarcation line depth measured 1month postoperatively on anterior-segment optical coherence tomography. The secondary outcome measure was change in endothelial cell density (ECD) 6months from baseline. The study comprised 21 patients (21 eyes, 9 in the HPMC group and 12 in the dextran group). The mean demarcation line depth was deeper in the HPMC group (308.22μm±84.19 [SD]) than in the dextran group (235.33±64.87μm)(P<.04). This difference remained significant (P=.02) even after controllingfor the preoperative lesser epi-on minimum corneal thickness in the HPMC group (385.56±13.81μm) versus the dextran group(413.08±29.58μm)(P<.02). The ECD 6months aftercontact lens-assisted CXL was comparable to the baselinelevels in both groups (P=.19 and P=.09, respectively). During contact lens-assisted CXL, HPMC-based riboflavin seemed to be associated with a deeper demarcation line than dextran-based riboflavin, although both solutions were safe for the endothelium at 6months.

Intrasession repeatability of pachymetry measurements with RTVue XR 100 optical coherence tomography in normal cornea

PurposeTo assess intra-observer reproducibility and repeatability of corneal pachymetry measurements with RTVue XR-100 anterior segment optical coherence tomography (AS-OCT) in normal cornea. MethodsEighty-four eyes of 84 healthy volunteers were enrolled for this study. A single examiner performed 3 successive corneal pachymetry mappings with RTVue XR-100 AS -OCT in a single session. One eye was randomly selected for the analysis. Intrasession intraexaminer reproducibility and repeatability were calculated for the minimum corneal thickness (MCT), central corneal thickness (CCT, central 0–2mm), pericentral (2–5mm) and peripheral (5–6mm) annular zones of cornea, in the pachymetry mapping protocol by intraclass correlation coefficient (ICC), coefficient of variation and test retest variability. ResultsThe mean CCT was 497.08±32.83µm and MCT was 490.28±32.87µm. ICC was 0.994 for CCT and 0.983 for MCT in central 2mm zone. ICC in the pericentral 2–5mm zones and 5–6mm zone was lower than that in central 2mm zone, but were still over 0.961 in 2–5mm zone and had ICC of 0.85 in 5–6mm zone. ConclusionIn normal cornea, corneal thickness measurements produced highly repeatable pachymetry measurements at the central and paracentral zones (up to 6-mm diameter) which could be because of the high resolution and faster image acquisition with RTVue XR-100 OCT.

Alterations in corneal epithelial thickness in patients with congenital myogenic eyelid ptosis.

To evaluate whether the corneal epithelial thickness (CET) maps obtained by optical coherence tomography (OCT) of the congenital myogenic eyelid ptosis differ from controls. CET maps of 13 patients with congenital myogenic eyelid ptosis (m/f=9/4; mean age 20.5±7.5) and randomly selected one eye of 13 controls (m/f=7/6; mean age 21.5±6.5) were investigated. Three pachymetry scans of each eye were performed by OCT (RTVue-XR, Optovue Inc., USA), and the scan with the highest signal strength index was selected for the analysis. In ptosis group: Minimum corneal epithelial thickness was thinner (p=0.029), standard deviation of thickness was higher (p=0.039), the negative of min-max values were higher (p=0.007). This difference was originating from the significant thinness of the superior sectors (S, SN, ST) of the corneal epithelium than the inferior counterparts (I, IT, IN) (p=0.001, p=0.017, p=0.002), respectively. There was no difference regarding total corneal thickness measurements. The mechanic effects of ptotic eyelid to the ocular surface may reshape the corneal epithelium, which can be objectively detected by OCT.

Evaluating the safety and efficacy of photorefractive keratectomy combined with corneal collagen crosslinking for the treatment of myopia and myopic astigmatism

INTRODUCTION. The purpose of the study was to evaluate the safety and efficacy of photorefractive keratectomy (PRK) combined with corneal collagen crosslinking (CXL) in patients with potential risk of developing postoperative ectasia, who were not good candidates for LASIK. MATERIALS AND METHODS. Twenty eyes were treated with transepithelial PRK combined with CXL. Patients were evaluated preoperatively for best corrected visual acuity (BCVA), refraction, keratometry, topography, and endothelial cell count. All eyes were treated with Amaris 750s Excimer Laser and KXL system for 90 seconds at 30 mW/cm 2 . RESULTS. Mean BCVA was improved from 0.0075 ± 0.08 logMAR to 0.025 ± 0.05 logMAR postoperatively. Average keratometry reduced from 44.9 ± 1.9 D to 39.8 ± 3.9 D. Mean minimal corneal thickness reduced from 504 ± 16.7 μm to 405 ± 41 μm. None of the cases developed regression, corneal ectasia, or corneal haze. CONCLUSIONS. Photorefractive keratectomy combined with high-fluence corneal collagen crosslinking (PRK XTRA) appears to be a safe and effective treatment for patients who are not good candidates for LASIK.

Short-term Variance of Refractive Outcomes After Simultaneous LASIK and High-Fluence Cross-linking in High Myopic Correction.

To analyze the visual and refractive outcomes of LASIK with and without simultaneous cross-linking for correction of myopia. Patients who received femtosecond laser-assisted LASIK with and without adjunctive cross-linking according to patient's preference were examined longitudinally for 6 months. Patients with myopic manifest refraction spherical equivalent of 5.00 diopters (D) or greater and estimated residual stromal thickness of greater than 250 µm were included. Overall, 120 eyes of 60 patients were included (60 eyes of 30 patients for LASIK with cross-linking; 60 eyes of 30 patients with LASIK only). No significant difference was observed in age, preoperative corrected distance visual acuity, manifest refraction spherical equivalent, manifest sphere and cylinder, minimal corneal thickness, and residual stromal bed thickness between both groups (P ≥ .245). The uncorrected distance visual acuity and efficacy index were significantly worse on day 1 in eyes receiving adjunctive cross-linking (P = .0001). At 6 months, 86.7% and 95% of the eyes achieved uncorrected distance visual acuity of 20/25 or better in LASIK with cross-linking and LASIK only, respectively. The variance of postoperative spherical equivalent and sphere was significantly higher in eyes undergoing LASIK with cross-linking from 1 week up to 6 months compared to LASIK only (P ≤ .002). None of the patients required re-treatment up to 6 months postoperatively. Adjunctive cross-linking during LASIK was associated with worse visual outcomes during the first postoperative week. The variance of spherical equivalent was also high in these patients over a 6-month follow-up. [J Refract Surg. 2016;32(10):664-670.].

Role of the Endothelial Layer in the Deswelling Process of Organ-Cultured Human Corneas Before Transplantation.

Before corneal transplant surgery, a deswelling process of organ-cultured corneas is required. This study compares the deswelling kinetics of corneas with an intact endothelial cell layer and disrupted or removed endothelium by measuring central corneal thickness (CCT) over time using anterior segment spectral domain optical coherence tomography. Ten donor pairs were cultured in organ culture. The right and left corneas were alternately assigned to one of 2 deswelling groups. Deswelling in the first group [endothelial group (EG)] was induced using a medium with dextran 5%. Corneas of the second group [nonendothelial group (NEG)] were deprived of their endothelial cell layer by trypsinization and were then placed in the same deswelling medium. CCT (mean ± SD) was measured by anterior segment spectral domain optical coherence tomography before deswelling (0 hours) and after 1, 2, 3, 6, 12, 24, 48, 72, and 144 hours. Deswelling kinetics was analyzed through the nonlinear platform in SAS/JMP11 Pro. Before deswelling, CCT was 1071.0 μm (±129.6 μm) and 1133.8 μm (±124.3 μm) in the EG and NEG, respectively. Minimum corneal thickness was obtained after 24 hours in the EG (531.9 ± 47.5 μm) and 6 hours in the NEG (645 ± 81.2 μm). CCT was significantly (P < 0.01) higher in the NEG than EG after more than 6 hours. Corneal dehydration after organ culture seems to be a multifactorial process, which not only depends on osmotic effects of the deswelling compound but also requires the presence of an intact endothelial cell layer.

Quantitative Evaluation of the Natural Progression of Keratoconus Using Three-Dimensional Optical Coherence Tomography

We quantified the chronologic progression of keratoconus using anterior segment optical coherence tomography (AS-OCT). A total of 217 eyes from 113 patients with keratoconus, keratoconus suspect, or forme fruste keratoconus were evaluated by corneal tomography using swept-source OCT. Age-dependent changes in the radius of the posterior best-fit sphere (Rpost), minimum corneal thickness (Tmin), and distance from the thinnest point to the corneal vertex (Dmin) were examined over follow-up periods of up to 5.79 years and were analyzed using generalized estimating equation (GEE) nonlinear regression model. Annual changes in Rpost (mean, -0.017 mm) and Tmin (-2.69 μm) were significantly higher in younger patients (P < 0.01, GEE nonlinear regression) and in patients with higher maximal K value (Kmax; P < 0.01, GEE nonlinear regression), whereas no changes were observed in Dmin. Even in patients 30 years or older, 14% of eyes revealed remarkable progression in Rpost. In eyes with acute hydrops, annual changes in Rpost (-0.22 mm) and Tmin (-33.8 μm) before acute corneal hydrops were more than 10 times faster than those in other eyes (P < 0.001, GEE nonlinear regression). Chronologic measurements of corneal tomography in keratoconus demonstrated that the progression of steepening at posterior corneal surface was found not only in patients under 30 years but also in older patients, particularly in advanced keratoconus. The rate of progression can be measured by mapping of corneal curvature and thickness using OCT, and the risk of progression was greater in younger patients with steeper Kmax.

Wave Front-Guided Photorefractive Keratectomy Using a High-Resolution Aberrometer After Corneal Collagen Cross-Linking in Keratoconus.

To evaluate the clinical outcomes of wave front-guided (WFG) photorefractive keratectomy (PRK) using a high-definition aberrometer in corneas with keratoconus at least 1 year after corneal collagen cross-linking (CXL). Prospective uncontrolled interventional case series study including a total of 34 consecutive eyes of 25 patients with keratoconus previously treated with CXL. All cases underwent WFG PRK using the VISX STAR S4 IR excimer laser and the iDesign system. All eyes had keratoconus grade I or II according to the Amsler-Krumeich classification. Visual, refractive, and ocular aberrometric outcomes were evaluated during a 12-month follow-up. Astigmatic changes were analyzed with the Alpins vector method. A significant improvement was observed in the uncorrected and corrected distance visual acuities (P < 0.001). The mean efficacy and safety indices at 12 months postoperatively were 1.58 ± 1.11 and 1.96 ± 1.52, respectively. Manifest sphere and cylinder were reduced significantly (P < 0.001), with 76.5% of the eyes having a spherical equivalent within ±1.00 D at 12 months postoperatively. The mean difference vector and magnitude of error were 1.06 ± 0.92 and 0.43 ± 0.86 D, respectively. Some corneal irregularity indices were reduced significantly with surgery (P ≤ 0.005) as well as the level of ocular higher order aberrations, primary coma, and trefoil (P < 0.001). Sequential WFG PRK using the iDesign system and the STAR S4 IR excimer laser after CXL is an effective option to correct the spherocylindrical error and to minimize the level of higher order aberrations in mild and moderate keratoconus if the maximum intended ablation depth does not exceed 15% of the minimal corneal thickness.

In Vivo Confocal Microscopy After Contact Lens-Assisted Corneal Collagen Cross-linking for Thin Keratoconic Corneas.

To study in vivo confocal microscopy (IVCM) after contact lens-assisted corneal collagen cross-linking (CACXL) in keratoconic eyes with thin corneas. This prospective interventional case series included patients with progressive keratoconus with minimum corneal thickness less than 400 µm after removing epithelium. CACXL was done once functional corneal thickness was confirmed to be 400 µm or greater after applying a riboflavin-soaked, ultraviolet barrier-free contact lens. Postoperative IVCM at 1, 3, and 6 months was performed. Ten eyes underwent CACXL. Mean preoperative minimum corneal thickness after epithelial removal was 376 µm (range: 364 to 397 µm). IVCM at 1 month showed CACXL-induced apoptosis evenly distributed at 350 ± 30 µm measured from epithelial surface. The demarcation line between edematous stroma and deep stroma beyond 350 µm that appeared unaltered was appreciable at 1 and 3 months but not at 6 months. Corneal reinnervation was visible at 3 months and was fully restored by 6 months. Regular endothelial mosaic was seen at all times. At 6 months, keratocyte repopulation of anterior stroma, disappearance of edema, and deposition of denser extracellular matrix surrounding activated keratocytes was seen with hyperreflective microbands still detectable. Average endothelial count was 2,135 ± 56 cells/mm(2) preoperatively versus 2,190 ± 41 cells/mm(2) at 6 months postoperatively. CACXL increases functional corneal thickness during ultraviolet light application, thus over-coming conventional pachymetric limitations of CXL. Cytotoxic effects of CACXL are similar to IVCM changes seen in conventional CXL and were concentrated in anterior and intermediate stroma up to 300 ± 30 µm without epithelium. Anterior segment optical coherence tomography should be performed after contact lens application and before ultraviolet light treatment to confirm an increase in functional thickness greater than 400 µm. For thinner corneas, combination treatments should be evaluated. [J Refract Surg. 2016;32(5):326-331.].

Forward light scatter and visual acuity before and after intrastromal corneal ring segment implantation at different stages of keratoconus.

To assess forward light scatter (stray light) before and after intrastromal corneal ring segment (ICRS) implantation at different stages of keratoconus and to examine correlation between postoperative stray light and visual acuity (VA). In 27 eyes of 27 subjects with keratoconus, stray light was determined using the compensation comparison technique before and 6months after ICRS implantation. Monocular corrected distance VA (CDVA) was measured using a high-contrast logMAR letter chart. Corneal higher-order aberrations (HOAs), contrast sensitivity (CS) and minimum corneal thickness (CT) were also measured. Mean CDVA was 0.42±0.28 preoperatively and 0.24±0.15 logMAR postoperatively (p<0.01). Mean corneal coma-like aberration decreased postoperatively (RMS 0.55±1.18μm, p<0.01). Minimum CT increased 25.31±18.59μm (p<0.01). Mean preoperative and postoperative stray light were 1.36±0.31 and 1.48±0.32 log units, respectively (p<0.01). Mean changes produced in stray light (worsening) were 0.03±0.21 (p>0.05) for stage I, 0.13±0.14 (p=0.013) for stage II and 0.18±0.21 (p=0.023) for stage III. Significant positive correlation (r=0.47, p=0.01) was detected between postoperative stray light and postoperative CDVA such that as stray light increased, CDVA worsened (higher logMAR values). Postoperative stray light was neither associated with HOAs, CS nor minimum CT. Stray light values in these patients with keratoconus were higher than normal preoperatively. In eyes with stage II and III keratoconus, stray light increased 6months after ICRS placement. Higher postoperative stray light was correlated with a worse visual acuity outcome.

Outcomes of femtosecond laser-assisted mushroom-configuration keratoplasty in advanced keratoconus

To evaluate the long-term outcomes after femtosecond laser (FSL)-assisted mushroom-configuration keratoplasty in advanced keratoconus. Thirteen eyes with Amsler-Krumeich stage IV keratoconus underwent FSL-assisted mushroom-configuration penetrating keratoplasty (PKP) and deep anterior lamellar keratoplasty (DALK) at a tertiary referral centre. Preoperative risk factors included low orneal thickness, high keratometry measurements, previous hydrops, and central stromal scarring. Main outcome measures were visual acuity and refractive outcome. The median follow-up was 33 months (range: 4-43). Preoperatively, the mean corrected distance visual acuity (CDVA) was 1.22±0.47 LogMAR (range: 0.5-1.9 LogMAR), mean minimum corneal thickness was 282±100.8 μm (range: 147-478 μm), and mean average keratometric (K) value was 63.4±7.63 dioptre (D; range: 57.0-75.7 D). Four patients underwent PKP and nine underwent DALK (two converted to PKP). Five patients subsequently underwent a modified arcuate mushroom interface dissection (AMID) procedure for astigmatic correction. At the final follow-up, the mean CDVA was 0.05±0.13 LogMAR (range: -0.10 to 0.20 LogMAR), mean spherical equivalent was -3.21±3.21D, mean cylindrical refractive error was 3.23±2.20 D, and mean average K was 43.1±1.53 D. Complications included early graft dehiscence, corneal vascularisation, stromal rejection, and sclerokeratitis. Sutures were completely removed at the mean 18.4 months for PKP and 9.1 months for DALK postoperatively. FSL-assisted mushroom-configuration keratoplasty is feasible and safe in patients with stage IV keratoconus. AMID could further enhance the refractive outcome safely.

Assessment of Corneal Epithelial Thickness in Asymmetric Keratoconic Eyes and Normal Eyes Using Fourier Domain Optical Coherence Tomography.

Purpose. To compare the characteristics of asymmetric keratoconic eyes and normal eyes by Fourier domain optical coherence tomography (OCT) corneal mapping. Methods. Retrospective corneal and epithelial thickness OCT data for 74 patients were compared in three groups of eyes: keratoconic (n = 22) and normal fellow eyes (n = 22) in patients with asymmetric keratoconus and normal eyes (n = 104) in healthy subjects. Areas under the curve (AUC) of receiver operator characteristic (ROC) curves for each variable were compared across groups to indicate their discrimination capacity. Results. Three variables were found to differ significantly between fellow eyes and normal eyes (all p < 0.05): minimum corneal thickness, thinnest corneal point, and central corneal thickness. These variables combined showed a high discrimination power to differentiate fellow eyes from normal eyes indicated by an AUC of 0.840 (95% CI: 0.762–0.918). Conclusions. Our findings indicate that topographically normal fellow eyes in patients with very asymmetric keratoconus differ from the eyes of healthy individuals in terms of their corneal epithelial and pachymetry maps. This type of information could be useful for an early diagnosis of keratoconus in topographically normal eyes.

Comparison of very-high-frequency ultrasound and spectral-domain optical coherence tomography corneal and epithelial thickness maps

To compare corneal thickness and epithelial thickness measurements in maps obtained using the RTVue spectral domain optical coherence tomography (SD-OCT) system and the Artemis 2 immersion arc-scanning very-high-frequency ultrasound (VHF-US) system. Department of Ophthalmology, Columbia University Medical Center, New York, New York, USA. Comparative study. Eyes of normal volunteers were scanned with the SD-OCT system followed by the VHF-US system and then again by the SD-OCT system. On each map, the minimum corneal thickness and mean values of corneal thickness and epithelial thickness in the 3.0 mm radius zone and in 0.5 mm wide concentric annuli of up to a 3.0 mm radius around the corneal vertex were determined. Both eyes of 12 normal volunteers were scanned. The corneal thickness values from both devices were highly correlated (R > 0.96); in the 3.0 mm radius zone, they were not statistically significantly different. There was no statistically significant change in epithelial thickness or corneal thickness in SD-OCT measurements taken before versus after immersion US. Although highly correlated (R > 0.76), the SD-OCT epithelial thickness values were systematically thinner (1.7 ± 2.1 μm) than the VHF-US measurements in the 3.0 mm radius zone (P < .01). The corneal thickness measurements in the 3.0 mm radius zone in normal eyes were equivalent between the 2 systems. Although correlated, the VHF-US epithelial thickness measurements were systemically thicker than the SD-OCT values. Drs. Silverman and Reinstein have a commercial interest in Arcscan, Inc. Dr. Reinstein is a consultant to Carl Zeiss Meditec. None of the other authors has a financial or proprietary interest in any material or method presented.

Evaluation of Corneal Thickness and Volume Parameters of Subclinical Keratoconus Using a Pentacam Scheimflug System

ABSTRACT Purpose: To evaluate the efficacy of corneal thickness and volume parameters measured with the Pentacam Scheimflug system in discriminating subclinical keratoconus corneas and normal corneas. Methods: This study included 19 patients (19 eyes) with subclinical keratoconus and 29 patients (29 eyes) with myopic astigmatism as the control group. Corneas were evaluated using a Pentacam Scheimflug system (2002 model, Oculus, Berkshire, UK). We evaluated corneal thickness and volume parameters, including central corneal thickness (CCT), minimum corneal thickness (MCT), depressed corneal thickness (DCT), maximum progression index (MaxPI), average progression index (AvPI), minimum progression index (MinPI), and corneal volume values for the 3.0 mm (CV3), 5.0 mm (CV5), and 7.0 mm (CV7) central circles. Receiver operating characteristic (ROC) curves were used to compare the sensitivity and the specificity of the parameters. Partial least squares (PLS) analysis was used to construct models with corneal thickness and volume parameters for early diagnosis. Results: There were significant differences in all parameters (p < 0.001), except CV3 and CV5, between subclinical keratoconus and normal corneas. The diagnostic accuracy for all parameters was high, with an area-under-the-curve (AUC) of approximately 1. The optimal cutoff values for DCT, MinPI, AvPI, and MaxPI were 5.5, 0.95, 1.05, and 1.45 for subclinical keratoconus, respectively. The PLS model for subclinical keratoconus fit well to the CCT, MCT, MaxPI, AvPI, MinPI, CV3, and CV7 data. Conclusion: Thickness and volume parameters measured by the Pentacam Scheimflug system effectively discriminate subclinical keratoconus corneas from normal corneas.

Corneal collagen cross-linking (CXL) in thin corneas.

Corneal collagen cross-linking (CXL) is a therapeutic procedure aiming at increasing the corneal stiffness in the keratoconus eyes by induction of cross-links within the extracellular matrix. It is achieved by ultraviolet-A (370 nm) irradiation of the cornea after saturation with the photosensitizer riboflavin. In the conventional CXL protocol, a minimum de-epithelialized corneal thickness of 400 μm is recommended to avoid potential irradiation damage to the corneal endothelium. In advanced keratoconus, however, stromal thickness is often lower than 400 μm, which limits the application of CXL in that category. Efforts have been undertaken to modify the conventional CXL procedure to be applicable in thin corneas. The current review discusses different techniques employed to achieve this end and their results. The overall safety and efficacy of the modified CXL protocols are good, as most of them managed to halt the progression of keratectasia without postoperative complications. However, the evidence of safety and efficacy in the use of modified CXL protocols is still limited to few studies with few patients involved. Controlled studies with long-term follow-up are required to confirm the safety and efficacy of the modified protocols.

Single session, intrauser repeatability of anterior chamber biometric and corneal pachy-volumetric parameters using a new Scheimpflug + Placido device

PurposeTo analyze single session, intrauser reliability of a Scheimpflug device for anterior chamber (AC) and corneal parameters. MethodsIn this observational study, 100 normal candidates underwent Scheimpflug analysis with Sirius 3D Rotating Scheimpflug Camera and Topography System (Costruzione Strumenti Oftalmici, Italy). Two scans in dark room conditions were performed by the same experienced user. The candidates were asked to keep both eyes closed for 5min before the scans. Exclusion criteria were previous ocular surgery, corneal scarring and anterior segment/posterior segment anomalies. Only the right eyes were used for the analysis. Both corneal (central, minimum, and apical thickness, volume, horizontal visible iris diameter, and apical curvature) and anterior chamber (volume, depth, angle, horizontal diameter) measurements were evaluated. ResultsThere was no difference in the means of repeated measurements (p>0.05, ANOVA). Intraclass correlations between the measures were high and ranged from 0.995–0.997 for corneal to 0.964–0.997 for anterior chamber (AC) parameters. The precision of repeatability measures (1.96×Sw) was approximately 5μ for the central and minimum corneal thickness, 8μ for the apical corneal thickness, 0.06mm for AC (anterior chamber) depth and less than 2° for the AC angle. ConclusionsSirius Scheimpflug system has high repeatability for both corneal and AC parameters in normal eyes.

Accelerated Corneal Collagen Cross-Linking in Thin Keratoconic Corneas

To report the outcomes of accelerated corneal collagen cross-linking in patients with thin corneas (minimum corneal thickness < 400 µm). Thirty-four eyes of 34 patients with a minimum corneal thickness less than 400 µm were included. All patients underwent accelerated corneal collagen cross-linking (irradiance power of 30 mW/cm² at 3 minutes with a total surface dose of 5.4 J/cm²). Uncorrected (UDVA) and corrected distance visual acuity (CDVA), manifest refraction (diopters [D]), and topography were evaluated at baseline and at the 1-, 6-, and 12-month follow-up visit. Endothelial cell density (cells/mm²) was calculated preoperatively and postoperatively at 12 months. The corneal stromal demarcation line was measured using anterior segment optical coherence tomography at 1 month postoperatively. The mean age of all patients (14 women and 20 men) was 23.08 ± 3.90 years (range: 16 to 29 years). UDVA and CDVA increased but not significantly. UDVA improved from 0.67 ± 0.32 (20/93 ± 20/41 Snellen) to 0.56 ± 0.28 logMAR (20/72 ± 20/38 Snellen) (P = .033) and CDVA improved from 0.49 ± 0.19 (20/61 ± 20/30 Snellen) to 0.42 ± 0.19 logMAR (20/52 ± 20/30 Snellen) (P = .009) at the last follow-up visit. The mean spherical and cylindrical refractions did not significantly change (P = .100 and 0.139, respectively). At the last follow-up visit, the flat keratometry decreased from 47.40 ± 2.52 to 46.95 ± 2.48 D, steep keratometry decreased from 51.04 ± 3.71 to 50.62 ± 3.57 D, and apex keratometry decreased from 57.58 ± 4.49 to 56.26 ± 4.47 D (P = .001, = .0019, = .001, respectively) from baseline. The mean endothelial cell density changed from 2,726.02 ± 230.21 to 2,714.58 ± 218.26 cells/mm² at 12 months postoperatively (P =.086). The results of this study revealed that accelerated corneal collagen cross-linking stabilized the progression of keratoconus without a significant endothelial cell density loss during the 12 months of follow-up.