Renyuan Chu

Correlation Between TGF-β1 in Tears and Corneal Haze Following LASEK and Epi-LASIK

PURPOSE To compare the incidence and degree of corneal haze formation following laser subepithelial keratomileusis (LASEK) and epithelial laser in situ keratomileusis (epi-LASIK), and examine its correlation with tear film transforming growth factor-beta1 (TGF-beta1) levels. METHODS This prospective, interventional, clinical trial included 20 eyes (20 patients) randomly assigned to undergo LASEK or epi-LASIK. The level of TGF-beta1 in tear fluid was measured preoperatively and 1, 3, and 5 days postoperatively. Corneal haze was graded at 1 and 3 months after surgery, and the relationship with TGF-beta1 levels was determined. RESULTS Mean preoperative spherical equivalent refraction was -4.50 +/- 1.44 diopters (D) (range: -1.50 to -6.00 D) for LASEK eyes and -4.90 +/- 1.26 D (range: -1.75 to -6.00 D) for epi-LASIK eyes. Although mean corneal haze scores at 1 month were significantly higher in LASEK-treated eyes than in epi-LASIK treated eyes (P=.031), these scores were similar at 3 months (P=.608). Tear fluid TGF-beta1 levels were similar in LASEK and epi-LASIK eyes before surgery (P=.458) and significantly higher in the LASEK group at 1, 3, and 5 days postoperatively (P=.015, P=.023, and P=.039, respectively). A positive correlation was noted between tear TGF-beta1 levels on the first postoperative day and the degree of corneal haze at 1 month (r=0.501, P=.016). CONCLUSIONS Less corneal haze was noted after epi-LASIK than LASEK. A positive correlation between corneal haze and tear fluid TGF-beta1 levels on the first postoperative day suggest a possible mechanism for the observed difference.

Incidence of Myopia in High School Students with and without Red-Green Color Vision Deficiency

PURPOSE To investigate the influence of color vision on myopia development by testing refraction error and axial length of the eye for high school students with and without color vision deficiency (CVD). METHODS A school-based cross-sectional, cluster sample study was conducted to test the color vision and refractive error of 16,539 high school students. Students were screened for CVD using a pseudoisochromatic plate. CVD was confirmed in students failing the test using a Farnsworth-Munsell 100-Hue Test which also served to classify the subtype (protan or deutan). Three classmates of each CVD subject, matched in five myopia risk factors, were chosen to form the normal color vision (CN) control group. Ophthalmic examinations were performed to determine refractive status and axial length. RESULTS Of the students, 309 were found to have red-green CVD and 927 were selected as the CN control group. The prevalence of myopia in the CVD group (45.6%) was significantly lower than that of the CN group (65.8%; P<0.001). The CVD group was also less myopic in refraction (P<0.001) than CN, and protan subjects had shorter axial lengths than those in the control group (P=0.007). CONCLUSIONS Color vision deficiencies appear to influence the development of myopia. The observed lower incidence of myopia in people with CVD may be linked to the reduced functionality of the L/M chromatic mechanism.

One-year outcomes of Epi-LASIK for myopia

PURPOSE To evaluate the early clinical outcomes of epi-LASIK for myopia. METHODS This study comprised 302 eyes of 162 patients. Epi-LASIK was performed with an automatically rotational epikeratome (KM-5000D). Epithelial separation was achieved mechanically without the use of alcohol. After laser ablation, the epithelial sheet was repositioned and a therapeutic contact lens was applied to the cornea immediately for 3 to 5 days. Postoperative visual acuity, symptoms, epithelial sheet, contrast sensitivity, wavefront aberration, and haze formation were evaluated 3, 6, and 12 months postoperatively. RESULTS Of the 302 eyes, 72 eyes (42 patients) with a mean spherical equivalent refraction of -9.13 +/- 4.23 diopters (D) (range: -1.25 to -19.0 D) had > 1-year follow-up. One eye failed to make the epithelial sheet because of the narrow palpebral fissure. An integrated epithelial sheet with a diameter of 8 to 9 mm was made in 289 (95.7%) eyes, leaving a superior hinge of approximately 2 to 4 mm. In 1 eye, stromal tissue remained in the epithelial sheet. Free epithelial flaps were made in 12 (4%) eyes. Mild discomfort was reported by 150 patients (282 eyes, 93.4%). Twelve patients (20 eyes, 6.6%) reported moderate symptoms. At 1 day postoperatively, corneal epithelium was almost transparent or had mild focal edema in 288 (95.4%) eyes; moderate edema was reported in 14 (4.6%) eyes. At 1 year postoperatively, spherical equivalent refraction of 60 (83.3%) eyes was within +/- 1.0 D of attempted refraction. Grade 0.5 haze was found in 2 eyes; all other eyes had no haze. No eye lost any lines of best spectacle-corrected visual acuity (BSCVA), whereas 12 (16.7%) of 72 eyes gained one or two lines of BSCVA. Contrast sensitivity decreased 1 month postoperatively and was restored to preoperative levels in eyes with preoperative spherical equivalent refraction < -10.0 D. Higher order aberration increased significantly postoperatively. CONCLUSIONS Epi-LASIK is a safe and efficient method to correct myopia with the advantage that it has only mild symptoms and mild haze. A larger study with longer follow-up is needed to determine its long-term clinical outcomes.

Impact of pupil diameter on axial growth in orthokeratology.

Purpose. To compare axial elongation between myopic orthokeratology (OK) contact lens and spectacle wearers, and to investigate the impact of pupil diameter on axial growth in myopic children after OK treatment. Methods. Fifty-two Chinese children aged 9 to 14 years were enrolled in this study, 27 for the OK group and 25 for the single vision spectacle lenses (SVL) group. Subjects in each group were further divided into two subcategories according to their baseline scotopic pupil diameters. Axial length (AL) was measured at baseline and at every 6-month visit through to 24 months. Linear mixed-effect model was used to determine myopia progression (AL changes from baseline). In this model, repeated visits were taken as within-subject effect, and treatment group as well as pupil size were taken as between-subject effects. The interaction of treatment group*pupil size was analyzed. Relationships between axial growth at 24 months and baseline pupil area were analyzed in both lens groups. Results. Twenty-five subjects in the OK group and 22 subjects in the SVL group completed the 24-month study. AL increased significantly throughout the observed 24-month period (F = 32.09, p < 0.001). Pupil size significantly affected axial growth (F = 15.95, p < 0.001) and different treatment modalities (OK vs. SVL) interacted with the effect of pupil size on axial growth (F = 24.66, p < 0.001). To be more specific, axial growth was significantly slower in subjects with above average pupil sizes than those with below average pupil sizes in the OK group (F = 25.04, p < 0.001). Contrarily, pupil size did not affect axial growth in the SVL group (F = 0.46, p = 0.50). Baseline scotopic pupil area was significantly correlated to axial growth in the OK group (r2 = 0.405, p < 0.001) but not in the SVL group (r2 = 0.171, p = 0.056). Conclusions. Large pupil diameters facilitate the effect of OK to slow axial growth in myopia. We speculate that this is because of enhancement of the myopic shift in the peripheral retina.

Comparison of the change in posterior corneal elevation and corneal biomechanical parameters after small incision lenticule extraction and femtosecond laser-assisted LASIK for high myopia correction

PURPOSE To compare posterior corneal elevation (PCE) changes and corneal biomechanical changes post fematosecond laser-assisted laser in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) procedures using the Pentacam system and the Ocular Response Analyzer (ORA). DESIGN Retrospective observational case series study. METHOD 106 patients with bilateral myopia who underwent either FS-LASIK (56 patients) or SMILE (50 patients) were reviewed, only the right eye was used in the analysis. Inclusion criteria include a spherical equivalent of -6.00DS and completion of 12 months follow up. The main outcome evaluated was change in PCE at 3 months, 6 months and 12 months post-operation using the Pentacam system. Corneal biomechanical parameters were evaluated at 6 and 12 months with the ORA. RESULTS PCE change at 3 and 6 months were not significantly different between the two procedures (p=0.064, p=0.109 respectively). At 12 months, PCE change was greater in FS-LASIK than SMILE (p=0.048). One-way ANOVA showed that for either procedure, the change in PCE did not differ at 3, 6 or 12 months post operation. CH and CRF values were reduced after both procedures, with FS-LASIK demonstrating a greater reduction in CRF than SMILE at 6 and 12 months (p=0.037 and p=0.001). Both CH and CRF reduction correlated with PCE increase at 6 and 12 months. CONCLUSION FS-LASIK demonstrated a greater increase in PCE than SMILE only at 12 months, as well as a greater reduction of CRF than SMILE. There were no significant differences in PCE change over time within either group.

Femtosecond Laser-Assisted Corneal Small Incision Allogenic Intrastromal Lenticule Implantation in Monkeys: A Pilot Study.

PURPOSE Lenticule implantation can be used to correct vision problems. However, it is significantly restrained by the sources of autologous lenticules. The aim of the present study was to investigate the feasibility and effects of femtosecond laser-assisted corneal small incision allogenic intrastromal lenticule implantation (AILI) in monkeys. METHODS Six healthy adult monkeys were included in this study. Femtosecond lenticule extraction (-4.0 diopter [D] correction, 5.0-mm optical zone) was performed in one eye of two monkeys and both eyes of one monkey. Each extracted refractive lenticule was allogenically transplanted into a femtosecond laser-created corneal stromal pocket in one eye of the other two monkeys and one monkeys both eyes. Pre- and postoperative (1 or 3 days, 1 month, and 6 months) slit lamp microscopy, corneal topography, anterior segment optical coherence tomography, and in vivo confocal microscopy were performed. RESULTS Corneal edema occurred in the early postoperative days with a large number of hyperreflective particles around the borders. Corneal tissue edema gradually decreased. Nerve fiber regeneration could be detected in the lenticule layer at 6 months. Overall, 3.27 ± 1.2 D corneal power was increased at 6 months, accounting for 82% of the intended correction. At the same time point, corneal stroma was 69 ± 11 μm thicker than preoperative ones and was roughly equal to the maximum thickness of implanted lenticules. No significant complications were observed. CONCLUSIONS The AILI technique seems to be feasible and safe for increasing corneal stromal thickness and changing corneal refractive power, which may provide a useful method for treatment of keratoectasia, presbyopia, and hyperopia.

Morphologic and Histopathologic Changes in the Rabbit Cornea Produced by Femtosecond Laser–Assisted Multilayer Intrastromal Ablation

PURPOSE To observe morphologic and histopathologic changes in the midperiphery of the rabbit cornea produced by femtosecond laser-assisted multilayer intrastromal ablation, determine whether this method may be used to correct myopia, and study how the cornea heals when the epithelium is not injured. METHODS The right eyes of 10 New Zealand White rabbits were used for the experiments. A 60-kHz femtosecond laser delivery system was used, and three lamellar layers of laser pulses were focused starting at a corneal depth of 180 microm and ending at 90 microm from the surface, with each successive layer placed 45 microm anterior to the previous layer. In the interface of the applanation contact lens cone, a 6-mm diameter aluminum circle was placed at the center to block the laser, and ablation was limited to the midperiphery of the cornea. The laser settings were spot/line separation, 10 microm; diameter, 8.5 mm; energy for ablating the stroma, 1.3 microJ. Topography examination was used to document changes in corneal power. Light microscopy, transmission electron microscopy (TEM), and confocal microscopy in vivo were applied to observe changes in the cornea. RESULTS There was significant change in mean corneal power between baseline and postoperative month 3 (n = 8; P = 0.0001), with a decrease from 46.82 D to 44.42 D. There was no haze formation or refractive regression throughout the follow-up. There were no corneal structural abnormalities under light microscopy. Activated keratocytes and necrotic debris were visible under confocal microscopy. Fibroblasts were observed, and no myofibroblasts appeared under TEM. CONCLUSIONS Multilayer intrastromal ablation by the femtosecond laser with intact epithelium in the midperiphery of the corneal stroma can flatten the cornea without causing haze formation or refractive regression. This procedure allows the cornea to heal differently than when traditional corneal refractive surgery is performed and the epithelium is damaged.

Accuracy of WASCA aberrometer refraction compared to manifest refraction in Chinese adult myopes.

PURPOSE To investigate the accuracy of the Carl Zeiss Meditec Wavefront Supported Custom Ablation (WASCA) aberrometer in refraction testing for Chinese myopic adults. METHODS Manifest refraction and WASCA were performed on 360 eyes of 360 consecutive Chinese myopic adults without cycloplegia. Both vector analysis and conventional notation were applied for comparing results, and differences between WASCA and manifest refraction for each component were calculated for accuracy evaluation. Correlation coefficients, regression equations, and mean errors of each component between the two methods were also tested. RESULTS Pearson correlation coefficient for M, J(0), J(45), sphere, and cylinder was 0.9680, 0.9320, 0.8655, 0.9668, and 0.8761, respectively. Mean error for the components above was -0.39+/-0.71 diopters (D), -0.02+/-0.16 D, 0.01+/-0.12 D, -0.42+/-0.70 D, and 0.06+/-0.30 D, respectively. In patients whose manifest vector M was < or =-6.00 D, mean errors of sphere and vector M were larger than the remainder of the study group. Ninety percent cylinder errors were within +/-0.50 D. Mean error of axis was 7.4 degrees, with 50% of eyes within 5 degrees. In cases with < or =-0.75 D astigmatism, mean error of axis was 9.8 degrees, which was larger than the remainder of the study group by 4.9 degrees. CONCLUSIONS For Chinese myopic adults, the concordance between WASCA and manifest refraction is, on average, high. However, for eyes with low to moderate spherocylindrical refraction, WASCA is less accurate in predicting sphere and vector M. It is also less effective for the measurement of axis in patients with astigmatism <0.75 D.

Outcomes of Epi-LASIK for the Correction of High Myopia and Myopic Astigmatism after More than 1 Year

Purpose: To present the clinical results of epi-LASIK in a high myopia and myopic astigmatic population followed for more than 1 year. Methods: This retrospective study comprised 67 eyes of 52 patients who underwent epi-LASIK for the correction of high myopia and myopic astigmatism. Epi-LASIK was performed with an automatically rotational epikeratome (KM-5000D, Wuxi Kangming Medical Device Corp., Wuxi, China) and the MEL80 (Carl Zeiss Meditec, Jena, Germany) excimer laser. The postoperative symptom, epithelial flap, vision, refraction and haze formation were investigated. The astigmatic change was calculated by the Alpins vector analysis method. Results: The follow-up period was 13.27 months. Mean preoperative spherical equivalent (SE) refraction and cylinder were –13.39 diopters (D) and –2.02 D. An integrated epithelial sheet with a diameter of about 8–9 mm was made in 65 (97.01%) eyes leaving a superior hinge of approximately 2–4 mm. The mean epithelial healing time was 5.55 days. More than 1 year after the treatment, no eye lost more than 1 line of best spectacle-corrected visual acuity. The mean SE and cylinder were –2.25 and –0.79 D. The mean astigmatism correction index was 1.06. The index of success of 0.51 reflected a 49% success in achieving cylinder correction. The change induced by the laser ablation at the intended axis of cylinder reduction was 93%. At the same interval, 7.46% of eyes had trace haze and others were clear. Haze did not affect the visual acuity in any eye. Conclusions: Epi-LASIK appeared to be effective and safe in the treatment of high myopia and myopic astigmatism with the advantages of having lower postoperative pain and satisfactory refractive and visual outcome postoperatively.

Determination of the nerve growth factor level in the central cornea after LASIK and Epi-LASIK treatment in a rabbit model system.

Purpose: Corneal refractive surgery results in nerve damage. Nerve regeneration is a complex process that involves nerve growth factor (NGF). Here, a comparative study was conducted to determine the NGF level in the central cornea after laser in situ keratomileusis (LASIK) and epipolis laser in situ keratomileusis (epi-LASIK) treatment. Method: Twenty-four New Zealand white rabbits underwent randomly assigned epi-LASIK treatment on 1 eye and LASIK treatment on the other eye. Experimental animals were sacrificed 1 day, 3 days, 7 days, and 1 month after treatment, and the NGF level was determined by immunohistochemistry and Western blot analyses. Statistical analyses were performed using a Student t test (P < 0.05). Results: Immunohistochemical staining demonstrated a weak NGF signal in the cornea of control and LASIK-treated rabbit eyes. After epi-LASIK treatment, the level of NGF increased significantly in the epithelial layer at the 1- and 3-day time point, and returned to control levels 7 days after treatment. Western blot analyses showed that the NGF level was significantly lower after LASIK treatment as compared to epi-LASIK treatment, 1 day and 3 days after treatment (t = −6.50, −5.85; P = 0.023, 0.028), with no significant difference between the two groups at the 7-day and 1-month time points (P > 0.05). Conclusion: This study demonstrates for the first time that the NGF level in the central corneal epithelial layer of rabbit eyes is significantly increased early after epi-LASIK treatment in contrast to LASIK treatment, and decreased to control levels 1 week after treatment.