Aleksandar Stojanovic

Background: The primary objective of this investigation was to compare the nominal central ablation depth with the achieved central corneal stromal ablation depth after StreamLight transepithelial photorefractive keratectomy (tPRK) for myopia with WaveLight® laser by Alcon Laboratories, TX, USA. Methods: This ambispective study encompassed a retrospective analysis of 40 eyes who underwent treatment for myopia and astigmatism, followed by a prospective examination conducted 6–9 months postoperatively. Pre- and postoperative Avanti spectral-domain optical coherence tomography (SD-OCT; Optovue Inc., CA, USA) provided stromal and epithelial thickness maps. The difference between pre- and postoperative central stromal thicknesses at the corneal vertex was used to calculate the achieved stromal thickness ablation depth. This value was then compared with the corresponding central nominal depth on the laser ablation planning map. Results: A total of 40 eyes (OD/OS:18/22) of 40 patients (31.4 ± 9.2 years) were available for evaluation. The mean treated spherical equivalent was − 2.98 ± 1.46 D. The mean nominal and achieved central stromal ablation depths were 51.22 µm and 59.67 μm, respectively, showing a mean stromal excessive ablation of 16.50%. The mean pre- and postoperative central epithelial thicknesses were 53.74 μm and 59.31 μm, respectively, showing a mean postoperative thickness increase of 10.46%. This increase in the epithelial thickness rendered the mean postoperative pachymetry reduction to 54.11 μm, only 2.33% greater than the mean nominal ablation depth. Conclusions: The study revealed a central stromal ablation 16.50% greater than the nominal ablation depth. This excessive stromal removal was largely compensated for by the increase in epithelial thickness, resulting in a mean difference between the nominal ablation depth and the achieved central corneal pachymetry reduction of only 2.33%. This significant excessive central stromal ablation must be taken into consideration in the calculation of the residual stromal thickness.

Background: To evaluate repeatability and agreement in measurements of total corneal astigmatism (TCA) in keratoconic eyes, using four optical coherence tomography (OCT)‐based devices: Anterion, Casia SS‐1000, IOLMaster 700, and MS‐39.Methods: Three consecutive measurements were taken with each device in 136 eyes. TCA values were converted into components J₀ and J₄₅. The Anterion and the IOLMaster 700 also provided axial length (AL) measurements. The repeatability was calculated using pooled within‐subject standard deviation (S_w). The agreement among the four devices was assessed by pairwise comparisons and Bland–Altman plots.Results: For all devices, the repeatability of TCA measurements showed S_w ≤0.23 D for TCA magnitude, ≤0.14 D for J₀, and ≤0.12 D for J₄₅. There were statistically significant differences in TCA magnitude for each pair, except for IOLMaster 700 with MS‐39, and Anterion with MS‐39. The repeatability (S_w) of axis measurements had a statistically significant negative correlation with the TCA magnitude (p < 0.001 for all devices). Both Anterion and IOLMaster 700 had high repeatability in AL measurements (S_w: 0.007 mm for Anterion and 0.009 mm for IOLMaster 700). The difference in AL between the two was 0.015 ± 0.033 mm (p < 0.001).Conclusions: All four devices showed good repeatability in TCA measurements in keratoconic eyes, the agreement for TCA measurements between the tested devices was generally low. Anterion and IOLMaster 700 showed good repeatability and agreement in AL measurements.

Purpose: The aim of this study was to report the 12 to 96 months results of a tissue-preservation algorithm based on ray-tracing-guided transepithelial excimer laser central corneal ablation (RT t-PRK) combined with individualized pachymetry-guided accelerated crosslinking (M nomogram ACXL) in young adult patients with stable keratoconus (KC). Methods: This was a prospective interventional study including 38 eyes of 38 young adult patients (stage II KC) with a mean age of 35 years (range 26–46 years) who underwent simultaneous RT with t-PRK plus pachymetry-based ACXL in the worst eye. The treatments were performed using the iViS Suite iRES Excimer Laser (Ligi, Taranto, Italy). Ray-tracing–guided treatments were planned using the customized interactive programmed transepithelial ablation (CIPTA) 2 web software and diagnostic data were assessed by the Precisio 2 tomographer (Ligi, Taranto, Italy) and Sirius tomographer (C.S.O., Florence, Italy). The main outcome measures included uncorrected distance visual acuity, best spectacle–corrected visual acuity, Kmax, high-order aberrations, minimum corneal thickness, and posterior elevation, with a mean follow-up of 52 months (range 12–96 m). Results: The mean UDVA improved + 3.5 ±1.28 Snellen lines (SL); 38% gained ≥ 4 ±1.34 SLs, 35% ≥ 3 ±1.21 SLs, 22% ≥ 2 ±1.12 SLs, and 5% ≥ 1 ±0.75 SLs. The mean best spectacle–corrected visual acuity increased by + 4.3 ±1.3 SL. Sixty-eight percent gained ≥ 4 ±0.88 SLs and 30% ≥ 3 ±0.78 SL. No SLs were lost. Conclusions: RT t-PRK plus ACXL significantly improved the quality of vision in patients with KC, preventing overcorrection and minimizing tissue consumption.

Purpose: To determine the effect of femtosecond laser cutting parameters on small-incision lenticule extraction (SMILE) results by evaluating cap thickness, interface light scattering, and visual and refractive outcomes. Setting: SynsLaser Clinic, Oslo, Norway. Design: Retrospective. Methods: 58 right eyes treated with SMILE using a programmed cap thickness of 130 μm were divided into 2 groups according to laser settings: Group 1: 165 nJ pulse energy and 4.5 μm spot separation (n = 36); Group 2: 125 nJ pulse energy and 4.2 μm spot separation (n = 22). The cap thickness was measured within the central 5 mm of the horizontal meridian using spectral-domain optical coherence tomography. Postoperative interface light scattering was graded based on the percentage area showing light scattering: 0: no scattering; 1: ≤25%; 2: 26% to 50%; 3: 51% to 75%; and 4: >75%. Results: At 3 months postoperatively, cap thickness was 138.9 ± 6.2 μm in Group 1 and 149.4 ± 3.5 μm in Group 2 (P < .001). Interface scattering was 0.9 ± 1.0 in Group 1 and 0.3 ± 0.9 in Group 2 (P < .05), with no scattering in 33.3% and 86.4% of the eyes, respectively. The postoperative spherical equivalent refraction was −0.03 ± 0.44 diopters (D) in Group 1 and −0.04 ± 0.31 D in Group 2. In Group 1, 83.3% of the eyes were within ± 0.5 D of the desired outcome, and 69.4% achieved an uncorrected distance visual acuity of 20/20 or better. In Group 2, these values were 95.5% and 86.4%, respectively. Conclusions: Lower pulse energy with tighter spots seems to reduce interface light scattering and improve refractive outcomes while also significantly increasing cap thickness.

PURPOSE: To evaluate the outcomes of transepithelial, topography-guided, epithelial mapping–assisted ablation in the treatment of regression after myopic refractive surgery. METHODS: A retrospective consecutive case series of 70 eyes of 52 patients with regression after previous corneal refractive surgery for treatment of myopic and compound myopic astigmatism underwent re-treatment using transepithelial topography-guided and epithelial mapping–assisted custom ablation with a wide and smooth transition zone design. The ablation profile was based on data from corneal topography, whereas the epithelial ablation depth was decided by corneal epithelial mapping obtained by optical coherence tomography. RESULTS: The mean follow-up time after re-treatment was 13.6 ± 9.4 months (range: 6 to 51 months). At the patients' last follow-up visit, 98.5% and 76.5% had uncorrected distance visual acuity of 20/40 and 20/20 or better. Safety and efficacy indexes were 1.05 and 0.92, respectively. The mean spherical equivalent was reduced from −1.10 ± 0.65 to −0.16 ± 0.34 diopters. Both total root mean square, odd-order, and even-order higher order aberrations improved significantly ( P = .021, .040, and .030, respectively), whereas corneal asphericity remained unchanged ( P = .662). Epithelial thickness profile showed significant smoothing between the central 2-mm and 2- to 5-mm paracentral areas. CONCLUSIONS: Transepithelial topography-guided and epithelial mapping–assisted custom re-treatment with a wide and smooth transition zone design is safe and effective for addressing myopic regression in patients who have previously undergone myopic refractive surgery. [ J Refract Surg. 2019;35(8):525–533.]

The aim of the study is to raise the awareness of the influence of coma-like higher-order aberrations (HOAs) on power and orientation of refractive astigmatism (RA) and to explore how to account for that influence in the planning of topography-guided refractive surgery in eyes with coma-like-aberrations-dominant corneal optics. Eleven eyes with coma-like-aberrations-dominant corneal optics and with low lenticular astigmatism (LA) were selected for astigmatism analysis and for treatment simulations with topography-guided custom ablation. Vector analysis was used to evaluate the contribution of coma-like corneal HOAs to RA. Two different strategies were used for simulated treatments aiming to regularize irregular corneal optics: With both strategies correction of anterior corneal surface irregularities (corneal HOAs) were intended. Correction of total corneal astigmatism (TCA) and RA was intended as well with strategies 1 and 2, respectively. Axis of discrepant astigmatism (RA minus TCA minus LA) correlated strongly with axis of coma. Vertical coma influenced RA by canceling the effect of the with-the-rule astigmatism and increasing the effect of the against-the-rule astigmatism. After simulated correction of anterior corneal HOAs along with TCA and RA (strategies 1 and 2), only a small amount of anterior corneal astigmatism (ACA) and no TCA remained after strategy 1, while considerable amount of ACA and TCA remained after strategy 2. Coma-like corneal aberrations seem to contribute a considerable astigmatic component to RA in eyes with coma-like-aberrations dominant corneal optics. If topography-guided ablation is programmed to correct the corneal HOAs and RA, the astigmatic component caused by the coma-like corneal HOAs will be treated twice and will result in induced astigmatism. Disregarding RA and treating TCA along with the corneal HOAs is recommended instead.

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.

To identify corneal epithelial- and stromal-thickness distribution patterns in keratoconus using spectral-domain optical coherence tomography (SD-OCT). We analyzed SD-OCT findings in 20 confirmed cases of keratoconus (group 1) and in 20 healthy subjects with corneal astigmatism ≥2 D (group 2). Epithelial and stromal thicknesses were measured at 11 strategic locations along the steepest and flattest meridians, previously located by corneal topography. Vertical mirrored symmetry superimposition was used in the statistical analysis. The mean maximum keratometry measurements in groups 1 and 2 were 47.9±2.9 D (range, 41.8–52.8) and 45.6±1.1 D (range, 42.3–47.5), respectively, with mean corneal cylinders of 3.3±2.2 D (range, 0.5–9.5) and 3.6±1.2 D (range, 2.0–6.4), respectively. The mean epithelial thickness along the steepest meridian in group 1 was the lowest (37.4±4.4 µm) at 1.2 mm inferotemporally and the highest (59.3±4.4 µm) at 1.4 mm supranasally from the corneal vertex. There was only a small deviation in thickness along the steepest meridian in group 2, as well as along the flattest meridians in both groups. The stromal thickness distribution in the two groups was similar to the epithelial, while the stromal thickness was generally lower in group 1 than in group 2. SD-OCT provides details about the distribution of corneal epithelial and stromal thicknesses. The epithelium and stroma in keratoconic eyes were thinner inferotemporally and thicker supranasally compared with control eyes. The distribution pattern was more distinct in epithelium than in stroma. This finding may help improve the early diagnosis of keratoconus. ClinicalTrials.gov NCT02023619

To evaluate one-step topography-guided transepithelial ablation in the treatment of low to moderate myopic astigmatism using a 1KHz excimer laser. Retrospective study of 117 consecutive eyes available for evaluation 12 months after surgery. Pre- and post-operative visual and refractive data as well as post-operative pain and haze were analyzed. A novel technique integrating custom refractive- and epithelial- ablation in a single uninterrupted procedure was used. The mean pre-operative spherical equivalent (SE) and the mean cylinder were: –3.22 diopters (D) ±1.54 (SD) (range –0.63 to –7.25 D) and –0.77 D ±0.65 (range 0 to –4.50 D), respectively. At 12 months after surgery: no eyes lost ≥2 lines of corrected distant visual acuity (CDVA). Safety and efficacy indexes were 1.27 and 1.09, respectively. Uncorrected distant visual acuity (UDVA) was ≥20/20 in 96.6% of the eyes. Manifest refraction spherical equivalent was within ±0.5 D of the desired refraction in 93.2% of the eyes. Average root mean square (RMS) wavefront error measured at central 6 mm, increased from 0.38 pre-operatively to 0.47 µm post-operatively. Refractive stability was achieved and sustained 1 month after surgery. No visually significant haze was registered during the observation period. Post-operative pain was reported in 4.5% of patients. One-step transepithelial topography-guided treatment for low to moderate myopia and astigmatism performed with a 1 KHz laser, provided safe, effective, predictable and stable results with low pain and no visually significant haze.