1 year posterior corneal changes after Bowman Layer Transplant for keratoconus.

INTRODUCTION: To report the posterior corneal changes after Bowman Layer Transplant for keratoconus in a tertiary hospital in the UK. METHODS: 5 eyes of 5 patients receiving Bowman Layer Transplant for advanced keratoconus in Royal Gwent Hospital (Newport, UK) were included. Pre and postoperative posterior corneal astigmatism, posterior Kmean, and back surface elevation were analysed. RESULTS: No significant changes were seen in the posterior corneal astigmatism, posterior Kmean, or back surface elevation between the pre- and postoperative period. CONCLUSION: This results would support the idea that the corneal changes seen after Bowman Layer Transplant are mainly in the anterior corneal surface.

Lasting Effects: Seven Year Results of the Castrop Nomogram for Femtosecond Laser-Assisted Paired Corneal Arcuate Incisions.

PURPOSE: Long-term results of arcuate incisions are rarely reported. This is unfortunate as long-term stability of astigmatic correction is of great interest to surgeons performing astigmatic correction. This study investigates the 7 year stability of results after application of femtosecond laser-assisted arcuate incisions with the Castrop nomogram. METHODS: Prospective interventional case series at the Augen- und Laserklinik, Castrop-Rauxel, Germany. Single site, single surgeon study. Seven year results of cataract patients with low to moderate corneal astigmatism receiving femtosecond laser-assisted arcuate incisions using a TechnolasVictus SW 2.7 (Bausch & Lomb Inc, Dornach, Germany) were assessed and compared to 1 year results. Outcome evaluation was based on astigmatic vector analysis, manifest refraction, and visual acuity. RESULTS: The study analyzed 19 eyes of 19 patients 7 years after surgery. Ocular residual astigmatism changed from -0.26 to -0.39 D. Preoperative corneal astigmatism was -1.51 D. Correction Index changed from 1.0 to 1.16. The magnitude of difference vector changed from 0.26 to 0.39 D. The index of success changed from 0.20 to 0.29. Spherical equivalent remained stable. A slight tendency to change toward astigmatic overcorrection was mainly observed for patients with preoperative with the rule astigmatism, but not with patients with against the rule astigmatism. CONCLUSIONS: The Castrop nomogram showed stable results 7 years after surgery. Similar to toric IOL surgery, it is advisable to be less aggressive when correcting with the rule astigmatism, to avoid overcorrection over a long period.

Instability of Tear Film after Novel Coronavirus Disease: A Noninvasive and No Contact Method by a Scheimpflug-Placido Disc Topographer.

PURPOSE: To compare the topographical tear film break-up time (T-BUT) between individuals recovering from COVID-19 and control subjects using a noninvasive and noncontact technique with a Scheimpflug-Placido disc topographer. METHODS: One-hundred and twenty-two eyes from 61 post-COVID-19 patients and 124 eyes from 62 control subjects were included in this prospective study. All participants underwent detailed ophthalmological examination including best-corrected visual acuity, intraocular pressure measurements, slit lamp examination, and fundoscopy as well as qualitative and quantitative evaluation of the noninvasive first tear film break-up time (NIF-BUT) and noninvasive average tear film break-up time (NIAvg-BUT) with T-BUT measured with a Sirius (CSO - Costruzione Strumenti Oftalmici S. r. l., Italy) corneal topography device. RESULTS: The mean NIF-BUT in post-COVID-19 and control patients was 5.2 ± 3.4 vs. 6.5 ± 3.2 sec, respectively. The mean NIAvg-BUT in the corresponding groups was 7.5 ± 3.5 vs. 8.8 ± 3.0 sec, respectively. Both NIF-BUT and NIAvg-BUT were significantly lower in the post-COVID-19 group than in controls (p = 0.004 vs. 0.020). Topographical tear film break-up at any time during the test (17 sec) was observed qualitatively in 79 eyes (64.8%) in the post-COVID-19 group and 57 eyes (46%) in the control group (p = 0.003). Moreover, temporal quadrant involvement occurred significantly more frequently in the post-COVID-19 group (p = 0.028). CONCLUSION: Tear film stability assessment based on T-BUT showed shorter NIF-BUT and NIAvg-BUT in post-COVID-19 patients as compared to the control group. Our results suggest that post-COVID-19 patients have impaired stability of tear film, and therefore require closer monitoring regarding dry eye. In addition, tear film instability in post-COVID-19 patients can be reliably detected using a noninvasive and noncontact technique that is more comfortable for both patients and physicians.

Machine learning algorithm improves accuracy of ortho-K lens fitting in vision shaping treatment.

PURPOSE: To construct a machine learning (ML)-based model for estimating the alignment curve (AC) curvature in orthokeratology lens fitting for vision shaping treatment (VST), which can minimize the number of lens trials, improving efficiency while maintaining accuracy, with regards to its improvement over a previous calculation method. METHODS: Data were retrospectively collected from the clinical case files of 1271 myopic subjects (1271 right eyes). The AC curvatures calculated with a previously published algorithm were used as the target data sets. Four kinds of machine learning algorithms were implemented in the experimental analyses to predict the targeted AC curvatures: robust linear regression models, support vector machine (SVM) regression models with linear kernel functions, bagging decision trees, and Gaussian processes. The previously published calculation method and the novel machine learning method were then compared to assess the final parameters of ordered lenses. RESULTS: The linear SVM and Gaussian process machine learning models achieved the best performance. The input variables included sex, age, horizontal visible iris diameter (HVID), spherical refraction (SER), cylindrical refraction, eccentricity value (e value), flat K (K1) and steep K (K2) readings, anterior chamber depth (ACD), and axial length (AL). The R-squared values for the output AC1K1, AC1K2 and AC2K1 values were 0.91, 0.84, and 0.73, respectively. The previous calculation method and machine learning methods displayed excellent consistency, and the proposed methods performed best based on flat K reading and e values. CONCLUSIONS: The ML model can provide practitioners with an efficient method for estimating the AC curvatures of VST lenses and reducing the probability of cross-infection originating from trial lenses, which is especially useful during pandemics, such as that for COVID-19.

Impact of COVID-19 on keratoconus patients waiting for corneal cross linking.

PURPOSE: Royal College of Ophthalmologist recent guidance recommended delaying cross-linking services during the COVID-19 pandemic. This study investigates the effects of such delays in the delivery of cross-linking services in patients with keratoconus progression. METHODS: Retrospective observational study of 46 patients with keratoconus progression, whose cross-linking was delayed due to the COVID-19 pandemic. Demographic and clinical details were obtained from assessments on the day of listing, and subsequent review on the day of the procedure. Topographic indices included keratometry of the posterior and anterior corneal surface, maximum keratometry (Kmax), thinnest corneal thickness, ABCD progression and progression based on standard criteria recommendations (1.5 D Kmax & 20 microns thinning). RESULTS: A total of 46 eyes were analysed with an average time between being listed for CXL and having the procedure done was 182 ± 65 days. The delay due to COVID-19 was of 3 months. In this time period they had a significant worsening of all keratometric indices and lost almost one line of visual acuity (0.19 ± 0.19 to 0.26 ± 0.18 LogMAR, p: 0.03). Thirty two eyes (70%) demonstrated progression in accordance with the ABCD progression criteria, while 18 eyes (39%) showed either an increase in Kmax of more than 1.5D or a thinning in corneal thickness of at least 20 µm. CONCLUSIONS: The treatment delay for the keratoconus patients caused further progression and vision worsening. We recommend that corneal collagen crosslinking needs to be considered as a high priority intervention.

Comparison of Higher-Order Aberrations After Single-Step Transepithelial and Conventional Alcohol-Assisted Photorefractive Keratectomy

Objectives: To compare the asphericity and higher-order aberration (HOA) outcomes of single-step transepithelial photorefractive keratectomy (tPRK) and conventional alcohol-assisted PRK (aaPRK) in patients with myopia and myopic astigmatism. Materials and Methods: Of the 108 eyes of 54 patients enrolled in the study, tPRK was performed on 54 (50%) eyes and aaPRK was performed on 54 (50%) eyes. The following parameters were compared: corrected distance visual acuity (CDVA), spherical equivalent (SE), flat and steep keratometry, intraocular pressure, central corneal thickness, asphericity, and HOAs including horizontal and vertical coma, horizontal and vertical trefoil, spherical aberration, second-order vertical coma, and aberration coefficient. Results: The demographic and baseline characteristics were similar between the two groups (p>0.05, for all). The aberration coefficient value was significantly lower in patients treated with aaPRK compared to patients treated with tPRK at postoperative 3 months, 6 months, and 1 year (p=0.022, p=0.019, and p=0.017, respectively). Differences in the other variables were statistically insignificant (p>0.05 for all). Conclusion: Both tPRK and aaPRK procedures obtain similar postoperative CDVA, SE, asphericity, and HOA outcomes, except the aberration coefficient value.