Mean Thinnest Corneal Thickness Research Articles

Biomechanical Analysis of Tomographically Regular Keratoconus Fellow Eyes Using Corvis ST.

Keratoconus is a bilateral, yet asymmetric disease. In rare cases, the second eye may show no signs of tomographic changes. The purpose of this study was to analyze the biomechanical characteristics in tomographically regular keratoconus fellow eyes. This retrospective, consecutive case series analyzed 916 eyes of 458 patients who presented to our keratoconus clinic between November 2020 and October 2022. Primary outcome measures included best-corrected visual acuity (BCVA), tomographic Scheimpflug analysis using Pentacam AXL (Oculus, Wetzlar, Germany), and biomechanical assessment using Corvis ST (Oculus, Wetzlar, Germany). Tomographic changes were assessed via analysis of the anterior and posterior curvature, K-max, thinnest corneal thickness (TCT), the Belin/Ambrosio Deviation Display (BAD-D), and the ABCD-Grading. Biomechanical changes were analyzed using Corvis Biomechanical Index (CBI) and Tomographic Biomechanical Index (TBI). Of 916 eyes, 34 tomographically regular fellow eyes (7.4%) were identified and included in the analysis. Overall, the mean BCVA was - 0.02 ± 0.13 logMAR. Tomographic analysis showed mean K-max of 43.87 ± 1.21 D, mean TCT of 532 ± 23 µm, and mean BAD-D of 1.02 ± 0.43. Biomechanical analysis demonstrated mean CBI of 0.28 ± 0.26 and mean TBI of 0.34 ± 0.30. While normal CBI-values were observed in 16(47%) of 34 eyes, only 13 eyes (38%) showed a regular TBI and only 7 eyes (21%) showed regular TBI and CBI. The sensitivity of CBI and TBI to detect a tomographically normal keratoconus fellow eye was 53% and 62%, respectively. A highly asymmetric corneal ectasia with regular tomographic finding in a fellow eye is rare among keratoconus patients. In such cases, a biomechanical analysis may be useful in detecting early signs of corneal ectasia. In our analysis, the TBI showed high sensitivity for detecting a biomechanical abnormality in tomographically regular fellow eyes.

Safety and efficacy of epithelial island crosslinking in keratoconus with thinnest pachymetry less than 400µ

PURPOSE:To evaluate the efficacy and safety of epithelial-island crosslinking (EI-CXL) in keratoconus with corneas thinner than 400 µm.METHODS:Twenty-six patients (30 eyes) underwent EI-CXL (preserving the epithelium over the thinnest area), using standard protocol (3 mW/cm2 for 30 min). Uncorrected and best spectacle-corrected distance visual acuity (UCDVA, BCDVA), manifest refractive spherical equivalent (SEQ), mean simulated keratometry (Kmean), maximum keratometry (Kmax), and thinnest corneal thickness (TCT) were determined preoperatively and at 1, 3, 6, and 12 months following CXL. Endothelial cell count (ECC) was determined preoperatively and at 6 months. Anterior segment optical coherence tomography (AS-OCT) was done at 1 month to determine the depth of the corneal stromal demarcation line (DL).RESULTS:After 1 year, mean UCDVA improved from 1.29 preoperatively to 1.17 (P = 0.001) and BCDVA from 0.62 to 0.57 (P = 0.011). Mean manifest SEQ decreased from -7.63 to-7.32D (P = 0.001). Mean Kmean decreased from 54.92 to 54.81D (P = 0.045), and Kmax from 67.60 to 67.42D (P = 0.072), and mean TCT changed minimally from 377.17 to 375.30 µ (P = 0.11). The mean ECC decreased from 2329 to 2268 cells/mm2 (2.6% decrease, P < 0.001). AS-OCT showed a DL in 29 out of 30 eyes at an average depth of 215.9 µ under the spared epithelium, and 299.9 µ in the de-epithelialized cornea.CONCLUSION:EI-CXL halted keratoconus progression over a 1-year period. This was associated with statistically significant endothelial loss, but less than seen with conventional epi-off CXL in thinner corneas.

Long-Term Safety and Efficacy of Corneal Cross-Linking in thin Corneas with Keratoconus

Objective: To evaluate the long-term safety and efficacy of corneal cross-linking in keratoconus patients with thin corneas. Methods: Forty eyes of 25 subjects having progressive keratoconus with thinnest corneal thickness (TCT) less than 400 µm were evaluated. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), corneal topography, and endothelial cell loss were assessed at baseline and followed at six-month interval till the end of 1st year of follow up and then yearly till the fifth year, de-epithelization of cornea was performed, followed by ultrasound pachymetry to measure TCT. Hypoosmolar riboflavin (0.1%) solution was applied after every 2 minutes for 25 minutes. Ultraviolet A (UVA) irradiation was performed for 30 minutes along with riboflavin for every 2 minutes. Results: Mean TCT was 381.5 ± 13.2 µm (range: 344–396 µm) without corneal epithelium. Following hypotonic riboflavin instillation, mean TCT increased by 97.8 ± 12.1 µm (range: 83–112 µm) for a mean thickness of 478.1 ± 14.9 µm (range: 409–506 µm). The average follow-up period was 61.79 ± 6.19 months (range: 42–68 months). Corrected distance visual acuity, pachymetry values and posterior elevation showed no significant difference before and after CXL at 5 years follow-up. Corneal astigmatism and maximum keratometry reading (Kmax) were significantly reduced. Mean reduction of endothelial cell count was 1.5% at the last follow-up visit. Conclusions: CXL with UVA and hypoosmolar riboflavin was effective in stabilizing keratoconus progression in patients with thin corneas however further studies are required to confirm our results.

Corneal Collagen Crosslinking Combined with Phototherapeutic Keratectomy and Photorefractive Keratectomy for Corneal Ectasia after Laser in situ Keratomileusis

Purpose: The aim of this study was to analyze the effects of corneal crosslinking (CXL) combined with phototherapeutic keratectomy (PTK) and photorefractive keratectomy (PRK) in halting the progression and improving the visual function of corneal ectasia after laser in situ keratomileusis (LASIK). Methods: PTK-PRK-CXL was performed on 14 eyes of 14 patients who developed corneal ectasia after LASIK. The visual acuity, spherical refraction and cylinder, corneal topography indices, thinnest corneal thickness (TCT), and endothelial cell count were evaluated at baseline and at 1, 3, 6, and 12 months postoperatively. Results: The mean uncorrected visual acuity improved significantly from 0.64 ± 0.36 logMAR preoperatively to 0.19 ± 0.12 logMAR at 12 months of follow-up (p < 0.001), while the mean best corrected visual acuity improved from 0.21 ± 0.14 logMAR at baseline to 0.04 ± 0.10 logMAR at 12 months postoperatively (p < 0.001). A significant decrease was observed in Kmax and Kmean values from 52.51 ± 6.74 and 43.55 ± 3.37 D at baseline to 45.72 ± 5.18 (p < 0.001) and 40.60 ± 3.05 D (p < 0.001) at the 1-year follow-up. The mean TCT decreased significantly from 419.07 ± 36.56 µm before treatment to 320.93 ± 39.78 µm at 12 months of follow-up (p < 0.001), and there was no significant endothelial cell loss (p > 0.05) beyond 6 months after treatment. Conclusion: PTK-PRK-CXL is a promising procedure to halt the progression of post-LASIK keratectasia with significant visual quality improvement.

Comparative study between oculus Wavelight Occulyzer II and Quantel Pocket II ultrasonic pachymeter in measuring central corneal thickness

Purpose The aim of this study was to compare the accuracy in measuring central corneal thickness using the oculus Wavelight Occulyzer II and Quantel Pocket II ultrasound pachymeter (UP). Patients and methods In this study, 42 eyes of 21 healthy individuals were assessed using oculus Wavelight Occulyzer II and Quantel Pocket II UP at El-Shorok Eye Hospital, Tanta, Egypt. Results In this study, the mean thinnest corneal thickness was 538.7 ± 29.35 μm with oculus Wavelight Occulyzer II and 527.6 ± 28.04 μm with Quantel Pocket II UP. Regression analysis showed that the readings of both devices are highly correlated ( r = 0.943, P = 0.001). Conclusion The readings from Wavelight Occulyzer II and UP are highly correlated. The Wavelight Occulyzer II and Quantel Pocket II UP measurements are in agreement with each other. Wavelight Occulyzer II can be used as a substitute for UP in measuring central corneal thickness.

Keratoconus management: long-term stability of topography-guided normalization combined with high-fluence CXL stabilization (the Athens Protocol).

To investigate refractive, topometric, pachymetric, and visual rehabilitation changes induced by anterior surface normalization for keratoconus by partial topography-guided excimer laser ablation in conjunction with accelerated, high-fluence cross-linking. Two hundred thirty-one keratoconic cases subjected to the Athens Protocol procedure were studied for visual acuity, keratometry, pachymetry, and anterior surface irregularity indices up to 3 years postoperatively by Scheimpflug imaging (Oculus Optikgeräte GmbH, Wetzlar, Germany). Mean visual acuity changes at 3 years postoperatively were +0.38 ± 0.31 (range: -0.34 to +1.10) for uncorrected distance visual acuity and +0.20 ± 0.21 (range: -0.32 to +0.90) for corrected distance visual acuity. Mean K1 (flat meridian) keratometric values were 46.56 ± 3.83 diopters (D) (range: 39.75 to 58.30 D) preoperatively, 44.44 ± 3.97 D (range: 36.10 to 55.50 D) 1 month postoperatively, and 43.22 ± 3.80 D (range: 36.00 to 53.70 D) up to 3 years postoperatively. The average Index of Surface Variance was 98.48 ± 43.47 (range: 17 to 208) pre-operatively and 76.80 ± 38.41 (range: 7 to 190) up to 3 years postoperatively. The average Index of Height Decentration was 0.091 ± 0.053 μm (range: 0.006 to 0.275 μm) preoperatively and 0.057 ± 0.040 μm (range: 0.001 to 0.208 μm) up to 3 years postoperatively. Mean thinnest corneal thickness was 451.91 ± 40.02 μm (range: 297 to 547 μm) preoperatively, 353.95 ± 53.90 μm (range: 196 to 480 μm) 1 month postoperatively, and 370.52 ± 58.21 μm (range: 218 to 500 μm) up to 3 years postoperatively. The Athens Protocol to arrest keratectasia progression and improve corneal regularity demonstrates safe and effective results as a keratoconus management option. Progressive potential for long-term flattening validates using caution in the surface normalization to avoid overcorrection.

The ocular biometric and corneal topographic characteristics of high-anisometropic adults in Taiwan

Background To investigate the difference of ocular biometric and corneal topographic characteristics between the two eyes in high anisometropes with difference of 4 D or more in spherical component. Methods Fifty-one young anisometropic men were collected. Detailed ocular examinations, including cycloplegic autorefraction, best-corrected visual acuity, intraocular pressure, A-scan, and Orbscan topography were done and recorded. The comparisons between two eyes were performed and the correlations between different ocular parameters were evaluated. Results The mean axial length in the more myopic/less hyperopic eye was longer than that in the less myopic/more hyperopic eye [difference 1.8 mm, 95% confidence interval (CI) 1.6–2.0 mm, p < 0.001]. The mean thinnest corneal thickness in the more myopic/less hyperopic eye was an average of 4.0 μm thicker than that in the other eye (95% CI 1.2–6.8 μm, p = 0.007). The mean anterior chamber depth in the more myopic/less hyperopic eye was an average of 0.05 mm (95% CI 0.02–0.07 mm, p < 0.001) more than that in the other eye. The curvature and size of cornea were not significantly different. Conclusion The anterior chamber depth is deeper, axial length is longer, and thinnest corneal thickness is thicker in the more myopic/less hyperopic eye of high-anisometropic patients. Anisometropic eyes provide the chance to understand the biometric changes of eyeball with different refractive statuses in the same person. Such information is helpful for us to calculate the intraocular lenses power in cataract surgery and to do the surgical planning for corneal refractive surgery in eyes of different refractive power.

Collagen Cross-Linking in Early Keratoconus With Riboflavin in a Femtosecond Laser-Created Pocket: Initial Clinical Results

To evaluate the safety and efficacy of a novel femtosecond laser-assisted technique for intrastromal administration of riboflavin and higher fluence ultraviolet a (UVA) light in collagen cross-linking (CXL) for keratoconus. Ten eyes with early keratoconus were treated with CXL and followed for a mean of 26 months (range: 18 to 36 months). Using a femtosecond laser, a 100-microm deep, 7-mm diameter intrastromal pocket was created. Two 0.1-mL doses of 0.1% riboflavin solution were infused into the pocket and the cornea was irradiated with 7 mW/cm2 UVA light of mean 370 nm wavelength for 15 minutes. Mean uncorrected visual acuity improved from 20/40.5 to 20/32.5 best spectacle-corrected visual acuity was unchanged at 20/20, mean sphere was reduced by 0.50 diopters (D), mean cylinder was reduced by 0.90 D, and maximum mean keratometry (K) reduced from 48.7 to 47.90 D. No ectasia progression (defined as increase in K over 3-month follow-up) and no statistically significant change in endothelial cell count was noted during follow-up. The mean thinnest corneal thickness appeared to initially reduce but the mean returned to at least the preoperative level by 18 months. All patients returned to full activities within 1 day postoperative. No adverse effects were noted in any of the cases studies. This novel epithelium-sparing, rapid soak-and-treat method of intrastromal riboflavin instillation and higher fluence UVA light for CXL appears to be safe and effective. No negative biomechanical effect (ectasia/epithelial ingrowth) was noted due to the femtosecond laser-created pocket. Because minimal epithelial injury occurs using this technique, postoperative pain appears to be significantly reduced.

Femtosecond Laser-assisted Lamellar Keratoplasty

To evaluate the outcomes and safety of lamellar keratoplasty (LK) assisted by a femtosecond laser. Twenty-one eyes of 21 patients affected by different corneal pathologies (5 posttraumatic corneal scar, 3 postkeratitis corneal leucoma, and 13 keratoconus) underwent LK procedures by using a femtosecond laser. The mean thinnest corneal thickness, evaluated with ultrasound corneal pachymetry and with confocal microscopy, was 434.19 +/- 62.60 (SD) microm (range, 333-548 microm). Mean preoperative uncorrected visual acuity was 0.09 +/- 0.28 SD and mean preoperative best spectacle-corrected visual acuity was 0.28 +/- 0.15 SD. A femtosecond laser was used to perform corneal cuts on both donor and recipient corneas. The donor corneal lamella diameters were 0.20-mm larger and thicker than the recipient to restore a physiologic corneal thickness and shape: mean donor diameter was 8.34 +/- 0.28 mm (range, 8.2-8.7 mm) and mean thickness was 352 +/- 40.27 microm (range, 220-400 microm). Mean follow-up was 20.86 +/- 5.76 months (range, 12-30 months). Early postoperative evaluation showed a clear graft in all cases. A normal corneal pattern topography and a physiologic thickness (mean corneal pachymetry, 542.48 +/- 33.20 microm) and transparency were restored. Twelve months after surgery, the mean postoperative uncorrected visual acuity was 0.45 +/- 0.34 SD, and the mean best spectacle-corrected visual acuity was 0.63 +/- 0.16 SD. Although the numbers in our study are small, our early results indicate that femtosecond laser-assisted lamellar keratoplasty shows promise as a safe and effective surgical choice in the treatment of various corneal pathologies.

Evaluation of Central and Peripheral Corneal Thickness with Ultrasound Biomicroscopy in Normal and Keratoconic Eyes

Our study was designed to calculate central and peripheral corneal thickness in patients affected with early stages of keratoconus and in normal subjects using ultrasound biomicroscopy (UBM). To obtain an objective and reliable assessment of the corneal thinning in affected eyes, we developed a keratoconus index (KI) by means of the UBM measurements. By means of the commercial version of the ultrasound biomicroscope (system model 840; Zeiss-Humphrey Instruments, San Leandro, CA, USA) using a 50-MHz probe, we studied 30 normal and affected eyes. In keratoconic eyes, we measured the thinnest corneal thickness (TCT) at the apex of the conus and at four peripheral sites at a distance of 2.5 mm from the central site (peripheral corneal thickness: PCT). The same procedure was performed in the normal eyes. To obtain an objective and reliable assessment of the corneal thinning, we calculated the ratio between the mean PCT and the mean TCT (Keratoconus Index: KI = PCT/TCT), in keratoconic eyes. In normal eyes, the KI was calculated on the basis of the ratio between the mean PCT and the mean central corneal thickness (CCT). In keratoconic eyes, the mean corneal thickness at the thinnest part of the conus was significantly different from the CCT in normal patients (Student's t test, p < 0.001). The peripheral measurements were not significantly different from keratoconic and normal eyes. The mean KI was 1.482 (SD, 0.095) in the keratoconic eyes, whereas it was 1.189 (SD, 0.086) in the normal subjects. The statistical analysis of the KI calculated on the basis of the UBM measurements showed that the KI values are significantly different from healthy subjects and from keratoconic patients (Student's t test, p < 0.001). UBM can be considered a useful tool in the study of keratoconus. We believe that calculation of the KI by means of UBM gives the possibility of obtaining an objective assessment of corneal thinning. Therefore this parameter can be useful in the staging and in the follow-up of these patients.