Discover the most talked about and latest scientific content & concepts.

Concept: Refractive surgery


Small incision lenticule extraction or SMILE is a novel form of ‘flapless’ corneal refractive surgery that was adapted from refractive lenticule extraction (ReLEx). SMILE uses only one femtosecond laser to complete the refractive surgery, potentially reducing surgical time, side effects, and cost. If successful, SMILE could potentially replace the current, widely practiced laser in-situ keratomileusis or LASIK. The aim of this study is to evaluate whether SMILE is non-inferior to LASIK in terms of refractive outcomes at 3 months post-operatively.

Concepts: Surgery, Laser, Cornea, Ophthalmology, The Current, Refractive surgery, LASIK, Laser surgery


Combination of riboflavin/UVA cross-linking (CXL) and excimer laser ablation is a promising therapy for treating corneal ectasia. The cornea is strengthened by cross-linking, while the irregular astigmatism is reduced by laser ablation. This study aims to compare the efficacy of excimer laser ablation on porcine corneas with and without cross-linking.

Concepts: Laser, Cornea, Corneal transplantation, Refractive surgery, Contact lens, LASIK, Excimer laser, Keratoconus


OBJECTIVE: Because of the northern location of Denmark, the length of the day over the year varies from 7 to 17.5 hours. Experimental and clinical results suggest that the development of myopia may be related to ambient light exposure. The purpose of current study was to investigate whether axial eye growth, myopia progression, or corneal power change in Danish myopic children varies with the length of the day. DESIGN: Cross-sectional study. PARTICIPANTS: Two hundred thirty-five children 8 to 14 years of age found to have myopia during screening for a clinical trial ( identifier, NCT00263471; accessed December 6, 2005). All children found to have any value of spherical equivalent that was myopic (<0 diopters [D]) at the first of 2 visits were included. METHODS: Cycloplegic refraction was measured using an autorefractor, axial eye length, and corneal power using an automatic combined noncontact partial coherence interferometer and keratometer. The accumulated number of daylight hours during the measurement period was calculated for each participant using an astronomical table. MAIN OUTCOME MEASURES: Change over 6 months in axial length, refraction, and corneal power. RESULTS: Accumulated hours of daylight ranged from 1660 to 2804 hours. Significant correlations were found between hours of daylight and eye elongation (P = 0.00), myopia progression (P = 0.01), and corneal power change (P = 0.00). In children with an average of 2782±19 hours of daylight, axial eye growth was 0.12±0.09 mm, myopia progression was 0.26±0.27 D, and corneal power change was 0.05±0.10 D per 6 months, whereas in children with an average of 1681±24 hours of daylight, axial eye growth was 0.19±0.10 mm, myopia progression was 0.32±0.27 D, and corneal power change was -0.04±0.08 D per 6 months. CONCLUSIONS: Eye elongation and myopia progression seem to decrease in periods with longer days and to increase in periods with shorter days. Children should be encouraged to spend more time outside during daytime to prevent myopia. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Concepts: Cornea, Myopia, Refractive surgery, Lens, Astigmatism, Orthokeratology, Eyeglass prescription, Contact lens


To determine criteria for keratoconus or postoperative LASIK ectasia progression or improvement based on Pentacam HR (Oculus Optikgeräte GmbH) measured steepest corneal curvature.

Concepts: Cornea, Refractive surgery, Keratoconus


To discuss current applications and advantages of femtosecond laser technology over traditional manual techniques and related unique complications in corneal refractive surgical procedures, including LASIK flap creation, intracorneal ring segment implantation, astigmatic keratotomy, presbyopic treatments, and intrastromal lenticule procedures.

Concepts: Surgery, Laser, Cornea, Ophthalmology, Refractive surgery, LASIK, Hyperopia, Laser surgery


PURPOSE: To assess the repeatability and accuracy of optical biometry (Lenstar LS900 optical low-coherence reflectometry [OLCR] and IOLMaster partial coherence interferometry [PCI]) and applanation ultrasound biometry in highly myopic eyes. SETTING: Division of Preventive Ophthalmology, Zhongshan Ophthalmic Center, Guangzhou, China. DESIGN: Comparative evaluation of diagnostic technology. METHODS: Biometric measurements were taken in highly myopic subjects with a spherical equivalent (SE) of -6.00 diopters (D) or higher and an axial length (AL) longer than 25.0 mm. Measurements of AL and anterior chamber depth (ACD) obtained by OLCR were compared with those obtained by PCI and applanation A-scan ultrasound. Right eyes were analyzed. Repeatability was evaluated using the coefficient of variation (CoV) and agreement, using Bland-Altman analyses. RESULTS: The mean SE was -11.20 D ± 4.65 (SD). The CoVs for repeated AL measurements using OLCR, PCI, and applanation ultrasound were 0.06%, 0.07%, and 0.20%, respectively. The limits of agreement (LoA) for AL were 0.11 mm between OLCR and PCI, 1.01 mm between OLCR and applanation ultrasound, and 1.03 mm between PCI and ultrasound. The ACD values were 0.29 mm, 0.53 mm, and 0.51 mm, respectively. These repeatability and agreement results were comparable in eyes with extreme myopia (AL ≥27.0 mm) or posterior staphyloma. The mean radius of corneal curvature was similar between OLCR and PCI (7.66 ± 0.24 mm versus 7.64 ± 0.25 mm), with an LoA of 0.12 mm. CONCLUSION: Optical biometry provided more repeatable and precise measurements of biometric parameters, including AL and ACD, than applanation ultrasound biometry in highly myopic eyes. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Concepts: Cornea, Ophthalmology, Accuracy and precision, Myopia, Refractive surgery, Presbyopia, Eyeglass prescription, Staphyloma


In this brief review we will discuss the reasoning and evolution of our current use of combined very high-fluence collagen crosslinking and laser in situ keratomileusis. Several presentations and pertinent publications are reviewed, along with the key steps of the enhanced LASIK procedure. Long term outcome data support the safety and efficacy of LASIK Xtra in stabilizing myopic but also hyperopic LASIK results.In conclusion, we have compelling evidence that LASIK Xtra is a safe and effective adjunct.

Concepts: Critical thinking, Laser, The Key, Ophthalmology, Term, Refractive surgery, LASIK, Hyperopia


Comparison between treatment with wavefront optimized and custom-Q laser-assisted in situ keratomileusis (LASIK) ablations. Our study included 400 eyes of 200 patients divided into two equal groups. All patients were treated for myopia and myopic astigmatism with LASIK. The first group was treated with wavefront optimized ablation and the second group with custom-Q ablation. They were examined preoperatively and postoperatively to assess asphericity, image quality, and other classical outcome parameters. The wavefront optimized ablation group comprised 200 eyes with a mean spherical equivalent refraction (SE) of -5.2188 diopters (D) (range: -1.15 to -10.50 D); the mean Q-value changed from 0.30 preoperatively to 0.06 postoperatively. The custom-Q ablation group also comprised 200 eyes with a mean SE of -5.1575 D (range: -1.35 to -9.00 D); the mean Q-value changed from 0.32 preoperatively to 0.03 postoperatively. A statistically significant difference in postoperative change in Q-values (P = 0.02) and in postoperative visual acuity (P = 0.42) between the two groups was noted. There was no difference between the two groups regarding refractive correction. There was a marginally significant change in BSCVA (best spectacle-corrected visual acuity) between the two groups, and less impairment in the corneal asphericity in the custom-Q group.

Concepts: Ophthalmology, Refractive surgery, Lens, Presbyopia, Eyeglass prescription, Contact lens, Refractive error, Hyperopia


Purpose. To investigate the effects of 30 nights of overnight orthokeratology (OOK) on corneal epithelial permeability (Pdc) and corneal biomechanical properties. Methods. BE Retainer (Precision Technology Services) and Paragon CRT (Paragon Vision Sciences, Inc.) lenses were used. Visits were scheduled approximately 4 hours after awakening at baseline and after 1, 5, 10, 14, and 30 days of treatment. Pdc was measured at baseline and at Day 30, while corneal biomechanical properties and visual acuities (VA) were measured at all visits. Results. Thirty-nine neophytes and soft contact lens wearers completed the study. There was no difference in Pdc between baseline (ln(Pdc) [95% confidence interval (CI)] = -2.65 [-2.80, -2.50]) and Day 30 (ln(Pdc)[CI] = -2.68 [-2.85, -2.50]) (p=0.88). Corneal Hysteresis (CH) and Corneal Resistance Factor (CRF) reduced significantly from baseline (CH [CI] = 10.89 [10.59, 11.19] mm Hg and CRF [CI] = 10.35 [9.99, 10.72] mm Hg) to Day 30 (CH [CI] = 10.59 [10.31, 10.87] mm Hg and CRF [CI] = 9.58 [9.26, 9.89] mm Hg) (p=0.001 for CH and p<0.001 for CRF). Post-treatment VA did not reach baseline targets, and the difference was worse with low-contrast letters. Asians (n=18) had significantly worse VA than non-Asians (n=21) under most conditions through Day 5, and the difference extended through Day 14 with low-contrast letters under mesopic conditions. The percentage of participants who achieved 20/20 uncorrected was 17% Asians and 40% non-Asians after Day 1 and reached 69% Asians and 83% non-Asians at Day 30. Conclusions. 30 nights of OOK did not alter Pdc when measured 4 hours after awakening. OOK caused CH and CRF to decrease, but the changes were not clinically significant compared to diseased and post-surgical cases. Asians, who had lower baseline CH in this study, responded slower to OOK based on early uncorrected VA and over-refraction measurements.

Concepts: Measurement, Epithelium, Cornea, Myopia, Refractive surgery, Orthokeratology, Contact lens, Paragon Vision Sciences


To establish a corneal correction equation for the Shammas post-hyperopic laser in situ keratomileusis (LASIK) (Shammas-PHL) formula and to evaluate its accuracy in cases with and without available pre-LASIK data.

Concepts: Laser, Eye, Cornea, Refractive surgery, Lens, LASIK, Intraocular lens, Dioptre