The safety of 250 microm residual stromal bed in preventing keratectasia after laser in situ keratomileusis (LASIK)

Tomographic Predictors of Ectasia Development After Keratorefractive Surgery

PURPOSE

The aim of this study was to identify the risk factors for postkeratorefractive surgery ectasia in unsuspicious tomographies and to report a new index coined diameter of peak locations (DPLs).

METHODS

All patients who underwent keratorefractive surgery between 2011 and 2018 at Care-Vision Laser Centers, Israel, and later developed ectasia were included. For each ectasia case, 3 matched controls were selected. Demographic and preoperative, intraoperative, and postoperative data were collected. Multivariate analysis was performed to evaluate the interdependence of the variables.

RESULTS

The retrospective study included 19 ectasia and 58 control eyes. There were no significant differences between the groups in ablation depth ( P = 0.73), preoperative spherical equivalent ( P = 0.12), percent tissue altered ( P = 0.71), residual stromal bed ( P = 0.73), and Ectasia Risk Score System ( P = 0.60). The anterior and the posterior symmetry index were significantly higher ( P < 0.001), and DPL was significantly tighter in the ectasia group ( P = 0.01). Binary multiple logistic regression found the symmetry index of the posterior cornea and DPL to be better predictors than age, percent tissue altered, Ectasia Risk Score System, residual stromal bed, and ablation depth.

CONCLUSIONS

A higher posterior symmetry index and a tighter DPL are predictors of ectasia in patients with otherwise normal tomographies. A tight DPL implies a weak area in the cornea, which is thin and slightly bulging, increasing the risk of this area becoming ectatic.

Effects of the methanol fraction of modified Seonghyangjeongki-san water extract on transient ischaemic brain injury in mice

CONTEXT

Recently in Korean medicine, the antioxidant and anti-inflammatory activities of Seonghyangjeongki-san (SHJKS) were reported. However, studies on the specific mechanisms of action of SHJKS for the treatment of ischaemic stroke are still lacking.

OBJECTIVE

This study investigates the mechanism of action of the water extract methanol fraction of modified SHJKS (SHJKSmex) on cerebral ischaemic injury.

MATERIALS AND METHODS

C57BL/6 male mice were orally administered SHJKSmex (30, 100, or 300 mg/kg) for 3 consecutive days (2 days, 1 day, and 1 h, respectively) before middle cerebral artery occlusion (MCAO). Twenty-four hours after MCAO, the infarct volumes were measured, brain edoema indices were calculated, and neurological deficit scores were determined. Inflammation-related substances in the ipsilateral hemisphere were determined by western blotting, dichlorofluorescin diacetate, thiobarbituric acid-reactive substances assay, and enzyme-linked immunosorbent assay.

RESULTS

SHJKSmex pre-treatment at 300 mg/kg decreased infarct volume by 87% and mean brain water content by 90% of the MCAO control group. Moreover, SHJKSmex effectively suppressed the expression of inducible nitric oxide synthase, reactive oxygen species, interleukin 1, and caspases-8 and -9 and increased the B-cell lymphoma 2/Bcl-2-associated X protein ratio (Bcl-2/Bax) in ischaemic mouse brain. The hippocampal pyramidal cell densities were significantly increased in the 300 mg/kg SHJKSmex-administered group compared to the MCAO control group.

DISCUSSION AND CONCLUSIONS

SHJKSmex protected the brain from ischaemic stroke in mice through its antioxidant, anti-inflammatory, and antiapoptotic activities. Our findings suggest that SHJKSmex is a promising therapeutic candidate for the development of a new formulation for ischaemia-induced brain damage.

Ectasia After Corneal Refractive Surgery: A Systematic Review

INTRODUCTION

The incidence of ectasia following refractive surgery is unclear. This review sought to determine the worldwide rates of ectasia after photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), and small incision lenticule extraction (SMILE) based on reports in the literature.

METHODS

A systematic review was conducted according to modified Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Publications were identified by a search of eight electronic databases for relevant terms between 1984 and 2021. Patient characteristics and preoperative values including manifest refractive spherical refractive equivalent (MRSE), central corneal thickness (CCT), anterior keratometry, postoperative residual stromal bed (RSB), and percent tissue altered (PTA) were summarized. In addition, annual rates of each refractive surgery were determined, and incidence of post-refractive ectasia for each type was calculated using the number of ectatic eyes identified in the literature.

RESULTS

In total, 57 eyes (70 eyes including those with preoperative risk factors for ectasia) were identified to have post-PRK ectasia, while 1453 eyes (1681 eyes including risk factors) had post-LASIK ectasia, and 11 eyes (19 eyes including risk factors) had post-SMILE ectasia. Cases of refractive surgery performed annually were estimated as 283,920 for PRK, 1,608,880 for LASIK, and 96,750 for SMILE. Reported post-refractive ectasia in eyes without preoperative identifiable risk factors occurred with the following incidences: 20 per 100,000 eyes in PRK, 90 per 100,000 eyes in LASIK, and 11 per 100,000 eyes in SMILE. The rate of ectasia in LASIK was found to be 4.5 times higher than that of PRK.

CONCLUSION

Post-refractive ectasia occurs at lower rates in eyes undergoing PRK than LASIK. Although SMILE appears to have the lowest rate of ectasia, the number of cases already reported since its recent approval suggests that post-SMILE ectasia may become a concern. Considering that keratoconus is a spectrum of disease, pre-existing keratoconus may play a larger role in postoperative ectasia than previously accounted for in the literature.

Safety and Efficacy of Myopic LASIK performed on Thin Corneas

Purpose:

The aim was to report on the visual outcomes and safety of myopic LASIK performed in patients with corneas of central thickness below average(<540μm) and normal topography.

Methods:

This is a retrospective cohort study conducted at a private practice setting on Mexican Hispanic patients who underwent myopic LASIK between January 2014 and January 2015. An analysis of records of patients >18 years-old with previous normal topography, stable refraction, corrected visual acuity ≥ 20/20 (Snellen), Central Corneal Thickness (CCT) < 540μm and at least 12 months follow up after surgery was conducted. The main outcome measures were standard visual outcomes (efficacy, safety, refractive stability) and Percent Tissue Altered (PTA) analysis was conducted.

Results:

A total of 51 patients (102 eyes) were included; 56% (n=57) were female. The mean age was 26.52 ± 8.06 (range 18-55 years) with a mean follow up of 13.9 ± 1.2 months. Preoperative CCT was 515.44 ± 17.87μm (range 452- 540μm), with a mean refractive spherical equivalent (SEQ): -4.08 ± 2.17 D (range -0.75 to -9.75 D), and mean refractive cylinder: -1.44 ± 1.29 D (range 0.00 to -6.00 D). Mean predictability of postoperative SEQ was -0.20 ± 0.40 D (range -1.25 to +1.25). Postoperative SEQ was ±0.50 D in 71%, ±1.00 D in 93% of the eyes. Postoperative uncorrected distance visual acuity was ≥20/20 in 78% and ≥20/25 in 95%. One line of CDVA was lost in 3% of the eyes, no eyes lost ≥2 lines. No ectasia cases were observed during follow-up.

Conclusion:

LASIK surgery in Mexican Hispanic patients with thinner than “normal” corneas (<540 μm) is safe, efficient and predictable at 1 year follow up for myopic refractive corrections with no evidence of postoperative keratectasia.

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.

Pentacam HR Indices Variation in Normal Corneas with Different Corneal Thickness

Purpose

To evaluate the effect of variable corneal thickness on Pentacam HR diagnostic indices in normal corneas.

Methods

Retrospective study was conducted at Al Watany Eye Hospital, Cairo, Egypt. Consecutive 160 eyes of young myopic subjects without KC were evaluated using Pentacam HR (WaveLight Allegro Oculyzer II, Erlangen, Germany). The elevation- and thickness-based indices were recorded. Enrolled corneas were categorized into three groups according to TCT quartiles; group 1 (39 eyes) included corneas with TCT <523 µm, group 2 (81 eyes) with TCT between 523 and 564 µm, while group 3 (40 eyes) enrolled TCT >564 µm. The possible effect of pachymetry on Pentacam HR indices was assessed using partial correlation tests.

Results

In normal corneas, back elevation from best fit sphere (BE from BFS) and that from best fit toric ellipsoid (BFTE) were the elevation indices that showed statistically significant differences among groups (P=0.013 and 0.019, respectively). Regarding pachymetric indices, maximum pachymetry progression index (PPI max) showed statistical significance (P=0.001). Partial correlations, after excluding age and refractive error effects, showed that TCT was correlated with BE from BFS, BE from BFTE, and PPI max (P=0.001, 0.001,0.002, respectively).

Conclusions

Some Pentacam HR indices varied with different corneal thickness in normal corneas. This necessitates inclusion of pachymetric subgroups in the normative database. The use of the more robust indices (average pachymetry progression index and front elevations) is recommended in relatively thin or thick corneas.

Effects of Mydrin eye-drops on central corneal thickness values in adult patients with myopia

OBJECTIVE

This study aimed to evaluate the effect of Mydrin eye-drops on central corneal thickness values and investigate the duration of the effect.

METHODS

In this prospective randomised self-controlled study, we enrolled 60 myopic patients (120 eyes) undergoing corneal laser refractive surgery. The central corneal thickness was measured before and one and four hours after administration of Mydrin eye-drops (major components are tropicamide and phenylephrine hydrochloride) using the Orbscan II anterior segment analysis system and a SP-2000P non-contact specular microscope, respectively.

RESULTS

Using the Orbscan II system, the baseline central corneal thickness (545 ± 27 µm) was significantly lower than that at one hour after Mydrin eye-drop application (559 ± 31 µm; p < 0.001); it was comparable to that at four hours post-Mydrin eye-drop administration (544 ± 26 µm; p < 0.74). Measured by non-contact specular microscopy, the baseline central corneal thickness (508 ± 26 µm) was significantly lower than that at one hour after Mydrin eye-drop application (521 ± 29 µm; p < 0.001); it was comparable to that at four hours after Mydrin eye-drop administration (506 ± 24 µm; p = 0.62). A significant difference was observed in the central corneal thickness at one and four hours after Mydrin eye-drop application by both methods (p < 0.001). Bland-Altman plots showed agreement between the measurements by the two methods at different times.

CONCLUSION

Central corneal thickness increases one hour after topical application of Mydrin eye-drops and is normalised at four hours following the administration of the drops. For patients scheduled to undergo excimer laser corneal refractive surgery, the central corneal thickness should be measured before or four hours after administration of Mydrin eye-drops.

A review of collagen cross-linking in cornea and sclera

Riboflavin/UVA cross-linking is a technique introduced in the past decades for the treatment of keratoconus, keratectasia, and infectious keratitis. Its efficacy and safety have been investigated with clinical and laboratory studies since its first clinical application by Wollensak for the treatment of keratoconus. Although its complications are encountered during clinical practice, such as infection inducing risk, minimal invasion merits a further investigation on its future application in clinical practice. Recently, collagen cross-linking in sclera shows a promising prospect. In present study, we summarized the representative studies describing the clinical and laboratory application of collagen cross-linking published in past decades and provided our opinion on the positive and negative results of cross-linking in the treatment of ophthalmic disorders.

Risk Factors in Post-LASIK Corneal Ectasia

Purpose. To evaluate the risk factors for post-laser in situ keratomileusis (LASIK) ectasia. Materials and Methods. Medical records of 42 eyes of 28 (10 women, 18 men) patients who developed corneal ectasia after LASIK were retrospectively reviewed. Topographical features and surgical parameters of those patients were evaluated. Results. The mean age of patients was 34.73 ± 6.50 (23–48) years and the mean interval from LASIK to the diagnosis of post-LASIK ectasia was 36.0 ± 16.92 (12–60) months. The following factors were determined as a risk factors: deep ablation (>75 μm) in 10 eyes, FFK (forme fruste keratoconus) in 6 eyes, steep cornea (>47 D) in 3 eyes, pellucid marginal degeneration (PMD) in 2 eyes, thin cornea (<500 μm) in 2 eyes, thin and steep cornea in 2 eyes, thin cornea and deep ablation in 5 eyes, FFK and steep cornea in 2 eyes, and FFK, steep cornea, and deep ablation in 1 eye. However no risk factor has been determined in 9 eyes (21.4%). Conclusion. The findings of our study showed that most of the patients who developed post-LASIK ectasia have a risk factor for post-LASIK ectasia. However, the most common risk factor was deep ablation.

[Comparison of Lasik with femtosecond laser versus Lasik with mechanical microkeratome: predictability of flap depth, corneal biomechanical effects and optical aberrations]

OBJECTIVES

To compare the predictability of flap thickness, high-order optic aberrations (HOAs), and biomechanical properties of cornea between patients treated by Lasik with mechanical microkeratome versus patients treated by FemtoLasik.

SETTING

Department of ophthalmology, Pellegrin University Hospital, Bordeaux, France.

PATIENTS AND METHODS

We conducted a retrospective study on 53 myopic patients who underwent Lasik with either mechanical microkeratome (MK group) or femtosecond laser (FS group). Refraction, central corneal thickness, high-order optic aberrations (HOAs), corneal hysteresis (CH), and corneal resistance factor (CRF), were analysed pre- and postoperatively in both groups. The central corneal thickness was measured with OCT-Visante(®) (Carl-Zeiss, Meditec), biomechanical parameters with ORA(®) (Reichert), and optical aberrations with the Wave Scan(®) (AMO) aberrometer.

RESULTS

We included 44 eyes of 22 patients in the MK group and 62 eyes of 31 patients in the FS group. Preoperatively, the mean best-corrected visual acuity was 0.95 in both groups. In the MK group, the flap was significantly thicker than expected (162/130 μm), but in the FS group, there was no significant difference (117/120 μm). The biomechanical properties of the cornea were lower in both groups independently of the flap cutting technique. The HOAs increased after Lasik and were not influenced by the flap cutting technique.

CONCLUSION

Neither mechanical microkeratome, nor femtosecond laser for flap creation, increases HOAs and the biomechanical changes of the cornea, according to ORA(®), significantly after Lasik.

Reasons for not performing LASIK in refractive surgery candidates in Yemen

PURPOSE

To determine and analyze the reasons that laser in situ keratomileusis (LASIK) was not performed in patients who requested refractive surgical correction of their refractive errors.

METHODS

A retrospective observational study was performed in Yemen Magrabi Hospital between June 2005 and October 2006; the case records of 1596 new consecutive patients who presented for refractive surgery at our refractive surgery unit were reviewed. Data on the ocular status, refractive problems, and investigations performed were analyzed. The reasons for not performing LASIK in the cases that were rejected were recorded and analyzed.

RESULTS

A total of 1191 patients (74.6%) were advised to have LASIK of the 1596 patients examined. LASIK was not advised in 405 patients (25.4%). The most common reasons for rejecting LASIK were suboptimal central corneal thickness (25.9%), high myopia >-11.00 D (17.0%), keratoconus (15.5%), cataract (11.4%), and suspicious corneal topography (forme fruste keratoconus) (9.4%).

CONCLUSIONS

Patients who request refractive surgery have a variety of problems and attention must be given to these patients. Suboptimal corneal thickness, high amount of refractive error, and keratoconus were found to be the leading causes of not performing LASIK in Yemeni patients.

Age and refraction in 46,000 patients as a potential predictor of refractive stability after refractive surgery

PURPOSE

To analyze the process of emmetropization and determine the potential for progression of refractive error following refractive surgery.

METHODS

The prevalence of refractive error was retrospectively examined in 46,384 consecutive patients (77,124 eyes) at an outpatient clinic in Amman, Jordan. Biometry was also obtained in 4240 eyes. Correlation of axial length and corneal power as a function of age was determined based on these data.

RESULTS

Patients were distributed into four distinct groups: emmetropia, hyperopia, low to moderate myopia, and high (> 6.00 diopters [D]) myopia. The prevalence of myopia was found to be 23.8%. High myopia occurred in 3.8% of patients, and 17.5% of patients were hyperopic. Patients with < 1.00 D of myopia at age 10 and < 3.00 D of myopia at the time of refractive surgery had a stable refraction at age 18. In patients with high myopia, 7.4% demonstrated a progression of corneal power and axial length that does not stabilize until age 30. Finally, the refractive error of hyperopic patients tended to progress from age 30 to age 50.

CONCLUSIONS

Myopes with < 1.00 D of myopia at age 10 and < 3.00 D of myopia at the time of refractive surgery are unlikely to progress. High myopes and hyperopes have potential to progress. Patients in which the axial length of the eye exceeds 26 mm in conjunction with higher corneal powers are likely in a state of decomposition and are at risk of marked progression of refractive error following refractive surgery. The likelihood of progression should be determined prior to surgery and explained to the patient.