Posterior scleral reinforcement combined with patching therapy for pre-school children with unilateral high myopia.

PURPOSE: Our purpose was to investigate the effect of posterior scleral reinforcement (PSR) combined with patching therapy for pre-school children with unilateral high myopia. METHODS: A total of 32 pre-school children with unilateral high myopia were recruited. They were randomly divided into the PSR and control group, each of which had 16 patients. The patients in the PSR group underwent the simplified PSR surgery followed by rigid gas permeable contact lens wear and traditional patching therapy, while the patients in the control group were only prescribed contact lens wear and patching. Patients were reviewed and the axial length, refraction, best-corrected visual acuity, and stereoscopic vision were respectively examined postoperatively at yearly intervals for three years. RESULTS: The best-corrected visual acuity was significantly higher in the PSR group than that in the control group at any study visit. A statistically significant difference in axial length was found between the PSR group (27.38 ± 1.30 mm) and the control group (28.29 ± 0.74 mm) at the postoperative three-year (p = 0.03) time point. There was a statistical difference in refractive error between the PSR group (-13.13 ± 2.55 D) and the control group (-15.42 ± 1.83 D) at 3-year follow-up. No significant difference was found between the two groups with respect to the stereoscopic vision by the end of follow-up at 3 years (p =0.103). CONCLUSIONS: PSR combined with the patching therapy has the potential to arrest the progression of high myopia and to help the treatment for amblyopia.

Refractive change in the adult rabbit eye after corneal relaxation with the femtosecond laser.

BACKGROUND: A new procedure to correct myopia that does not disturb the cornea in the optical zone and avoids injuring the corneal epithelium could be a key advance in corneal refractive surgery. The aim of this study is to observe the refractive change in the adult rabbits undergoing femtosecond laser-assisted multilayer intrastromal ablation in the mid-periphery of the cornea without injury of epithelium. METHOD: The right eyes of 8 New Zealand White adult 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 µm and ending at 90 µm from the surface, with each successive layer placed 45 µm 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, limiting ablation to the mid-periphery of the cornea. The laser settings were as follows: spot/line separation, 10 µm; diameter, 8.0 mm; energy for ablating the stroma, 1.3 µJ. An authorefractor was used to assess the manifest refraction. RESULTS: Mean spherical equivalent (SE) (mean ± SD, SD: standard deviation) was significantly increased at postoperative week 1 (1.67 ± 0.26 D, p < 0.0001), month 1 (1.65 ± 0.23 D, p < 0.0001), and month 3 (1.60 ± 0.22 D, p < 0.0001) compared to baseline (0.68 ± 0.27 D). Mean spherical equivalent showed no significant change between postoperative week 1 and month 3 (p = 0.1168). CONCLUSION: Femtosecond laser-assisted multilayer corneal intrastromal ablation in the mid-periphery may cause a consequent hyperopic shift with no refractive regression.

Inhibition of corneal fibrosis by Smad7 in rats after photorefractive keratectomy.

BACKGROUND: Haze or corneal subepithelial fibrosis is one of the common complications after refractive surgery procedures, such as photorefractive keratectomy (PRK), laser epithelial keratomileusis, and epipolis laser in situ keratomileusis, which would result in refractive regression, decreased visual quality, and corneal opacification. Haze directly resulted from corneal fibrosis mediated by transforming growth factor ß (TGFß). Smad7, an inhibitory Smad, can inhibit TGFß signal transduction. Recently, the effects of Smad7 on the inhibition of fibrosis in several organs have been studied, while little is known about the effects on cornea after PRK. This study was aimed to determine the effects of lentiviral-mediated Smad7 gene expression on corneal fibrosis in rats after PRK. METHODS: Four different experimental groups were established using right eyes of Sprague-Dawley rats. Thirty-two eyes underwent de-epithelialization only and served as a sham operation group (group 1). Ninety-six eyes underwent PRK operation and were further divided into group 2 (the PRK group) without lentivector administration, group 3 (the Lv-blank group) with control lentiviral vector without Smad7 administration, and group 4 (the Lv-Smad7 group) with Smad7 expressing lentiviral vector Smad7 administration. At 1 day, 1 week, 1 month, and 3 months after PRK, the transfection efficiency was determined by measuring the fluorescence signal as well as Smad7 protein and mRNA levels. Corneas were further processed for immunoblotting to assess the phosphorylation of Smad2 as a downstream event of TGFß/Smad signaling. The expression of fibrotic markers, such as α-smooth muscle actin (α-SMA), Type III collagen (collagen III), and cell cycle-related marker Ki67, was measured by quantitative real-time reverse transcription polymerase chain reaction (RT-PCR). RESULTS: Lentivirus-mediated exogenous Smad7 gene expression in rat corneal tissue resulted in reduced activation of TGFß/Smad signaling caused by downregulation of phosphorylation of Smad2. Smad7 also downregulated the expression of TGFß2. Markers of cell proliferation and fibrosis, including Ki67, α-SMA, and collagen III, were inhibited by Smad7 up to 3 months after PRK operation. CONCLUSION: Smad7 gene transfer inhibits fibrogenic responses of cornea in rats after PRK.

Expression of Smad7 inhibits fibrogenic responses of keratocytes to transforming growth factor ß2.

BACKGROUND: Transforming growth factor ß (TGFß) is one of the most important growth factors in the development of fibrosis and scarring on cornea. Smad7, an inhibitory Smad, can inhibit TGFß signal transduction. In recent years, effects of lentiviral-mediated Smad7 on inhibition of fibrosis on some organs have been studied, while little is known about the effects on cornea. This study aimed to determine the effects of lentiviral-mediated Smad7 gene expression on keratocyte proliferation and fibrosis induced by TGF ß2 in vitro. METHODS: Keratocytes were cultured from corneal tissue isolated from Sprague-Dawley (SD) rats and transfected with Smad7 expressing lentiviral vector (Lv-Smad7) or non-functioning control vector (Lv-blank). Following the exposure to TGFß2, keratocytes were processed for immunoblotting to assess the phosphorylation of Smad2 as down-stream event of TGFß/Smad signaling. Expression of fibrotic markers α-smooth muscle actin (α-SMA), type III collagen (collagen III) were measured by Western blotting and quantitative real time polymerase chain reaction (PCR). Overall cell proliferation was determined by 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and the expression of cell cycle-related marker Ki67 at both mRNA and protein levels. RESULTS: The Smad7 gene transfer suppressed TGFß/Smad signaling in keratocytes by down-regulating phosphorylation of Smad2. Markers of cell proliferation and fibrosis including Ki67, α-SMA, collagen III were inhibited by introduction of Smad 7 into TGFß exposed keratocytes. Consequently, the rate of cell proliferation was attenuated. CONCLUSION: Smad7 gene transfer inhibited fibrogenic responses of keratocytes to TGFß2.

[Long-term studies on clinical therapeutic efficiency of posterior scleral reinforcement surgery].

OBJECTIVE: To assess the safety and efficiency of posterior scleral reinforcement surgery by analyzing data collected for more than ten years after the surgery. METHODS: Sixteen patients (32 eyes) with high myopia who underwent scleral reinforcement were followed up for more than ten years (10 to 13 years). RESULTS: Best corrected visual acuity was stable (t = 0.26, P > 0.05). The average axial elongation was 0.056 mm per year postoperation after surgery. The ratio of choroidal neovascularization in the operation group was 3.1% (1/32). CONCLUSIONS: Posterior scleral reinforcement is a safe and effective. This procedure can prevent the development of choroidal neovascularization in high myopia. A control study with a larger group of cases as well as related basic is still required.

Influence of internal optical astigmatism on the correction of myopic astigmatism by LASIK.

PURPOSE: To investigate the influence of the origin of astigmatism on the correction of myopic astigmatism by LASIK. METHODS: A retrospective study was conducted of the records of 192 patients (192 eyes) undergoing LASIK for correction of myopia and myopic astigmatism from January to September 2010. Ocular residual astigmatism (ORA) and lenticular astigmatism (LA) were determined by vector analysis using objective refraction and Pentacam (Oculus Optikgeräte GmbH) imaging of both corneal surfaces. Patients were divided into two groups according to ORA (high ORA group: ORA/preoperative refractive astigmatism >1; normal ORA group: ORA/preoperative refractive astigmatism ≤ 1) and LA (high LA group: LA/preoperative refractive astigmatism >1; normal LA group: LA/preoperative refractive astigmatism ≤ 1). Procedural efficacy was compared between those eyes with and without a significant amount of internal optical astigmatism using index of success. RESULTS: Mean preoperative vectors for the astigmatism of the anterior cornea, posterior cornea, and lens were -1.33 × 3.0°, -0.33 × 95.3°, and -0.27 × 103.3°, respectively. Mean indices of success in the high and low ORA groups were 1.75 and 0.59, respectively (t=7.81, P<.001). Mean indices of success in the high and low LA groups were 2.07 and 0.70, respectively (t=12.36, P<.001). The higher indices of success in the high ORA and high LA groups suggest a lower efficacy of LASIK in treating astigmatism primarily located intraocularly. CONCLUSIONS: Myopic LASIK is less effective in correcting astigmatism when astigmatism is mainly located at the internal optics. Topography and refractive value should be incorporated in the treatment of patients when a significant amount of internal optical astigmatism is detected preoperatively.

Effects of femtosecond laser-assisted multilayer intrastromal ablation in the midperipheral cornea.

We describe the femtosecond laser-assisted midperipheral multilayer intrastromal ablation technique, which combines the benefit of radial keratotomy, ie, not disturbing the optical zone, with currently available technology to correct myopia. The technique was performed in 2 patients, both of whom experienced a decrease in mean corneal power. In 1 patient, the manifest refraction improved, with a 1-line increase in uncorrected visual acuity 1 day postoperatively. The multilayer intrastromal ablation technique, which flattens the cornea and decreases corneal power, can be used to correct moderate myopia without injuring the corneal epithelium.

[Analysis of flap thickness by anterior segment optical coherence tomography in different flap preparation styles of excimer laser surgery].

OBJECTIVE: To assess and compare the accuracy and regularity and short-term change of corneal flap in different flap preparation styles. METHODS: Eighty eyes of 40 cases were treated with laser-assisted subepithelial keratectomy. One hundred and fifty-five eyes of 78 cases were treated with laser in situ keratomileusis with 90 microm microkeratome flap preparation and eighty-two eyes of 42 cases were treated with laser in situ keratomileusis with 100 microm femtosecond laser flap preparation. Anterior segment optical coherence tomography was used to assess the thickness of epithelial or stromal flaps created with M2 microkeratome or VisuMax femtosecond laser by the same investigator 1 hour, 1 day, 1 week, 1 month and 3 months postoperatively, respectively. The thickness of twenty-five measuring points across each flap in LASIK, which were 1.5 mm, 2.5 mm and 3.5 mm away from vertex of cornea on the horizontal, vertical, 45 degrees and 135 degrees meridian respectively and the vertex of cornea itself, was evaluated. The results were analyzed with t-test or ANOVA by SPSS software. RESULTS: The thickness of epithelial flaps was (57.91 + or - 6.76), (54.94 + or - 4.65), (54.96 + or - 2.70), (55.26 + or - 4.27) and (53.86 + or - 5.56) microm at 1 hour, 1 day, 1 week, 1 month and 3 months respectively, with statistical significant difference between 1 hour and the other time points (F = 20.25, P < 0.05). The average thickness of stromal flaps on the vertex of cornea in microkeratome group was (129.16 + or - 12.10) microm, while (112.69 + or - 5.12) microm in the femtosecond laser group, which means the accuracy of flap preparation with femtosecond laser is better than with microkeratome. The absolute difference between actual and average thickness was (13.16 + or - 4.78) and (5.26 + or - 1.21) microm in the microkeratome group and femtosecond laser group, which means the reproducibility of flap preparation with femtosecond laser is better than with microkeratome as well. Flap morphology showed the feature of thin central area and thick peripheral area in microkeratome flap and uniformity in femtosecond laser flap, which illustrated the better regularity of femtosecond laser flap preparation. CONCLUSIONS: Anterior segment optical coherence tomography is a safe, quick and reliable facility to examine and assess flap morphology. Our results showed the accuracy and regularity of femtosecond laser flap preparation outweighed microkeratome flap preparation.

[The expression of Ki-67, TGF-beta(2) and alpha-SMA after the femtosecond laser-assisted intrastromal scanning in rabbit cornea].

OBJECTIVE: To study how the cornea would express Ki-67, TGF-beta(2) and alpha-SMA and how the cornea would heal when it is scanned intrastromally. METHODS: Twenty New Zealand white rabbits were randomly numbered and used for the experiments. The 60 kHz Intralase femtosecond laser delivery system was used to scan 35 rabbit corneas (of these corneas, 5 right corneas were from 5 rabbits). The unoperated 5 left eyes were used as control. The laser settings were: spot/line separation, 10 microm; diameter, 8.5 mm; energy for scanning the stroma, 1.3 microJ; scanning depth, 135 microm, no edge cuts were performed. Slit lamp was used to observe the cornea at 0.5 h, 1 h, 2 h, and 3 months after surgery. On day 1, 3, 7, 30, 90 after surgery, 6 and 1 scanned corneas at each time point were taken for Western blot and immunocytochemical detection respectively to detect the expression of TNF-alpha, Ki-67, TGF-beta(2) and alpha-SMA. RESULTS: Microbubbles were found in corneal stroma after surgery. The number of microbubbles tended to decrease significantly with time. At 2 h, the cornea turned to be transparent again. During 3-month follow-up, the cornea was always transparent and no haze appeared. Western blot analysis and immunocytochemical detection demonstrated that the expression of Ki-67 began to increase at day 1(0.0670 + or - 0.0008) and reached the peak at day 3 after surgery (0.6923 + or - 0.005). While there were significant difference with the control group at day 90 after surgery (t = 24.12, 57.22, 43.26, 39.78, 18.35;P < 0.05), a gradual decrease in expression of ki-67 could be detected from day 3 to 90. There were no significant change in the expression of TGF-beta(2) (t = 0.933, 0.856, 0.934, 0.970, 1.132) and alpha-SMA (t = 1.126, 1.235, 0.993, 1.175, 1.211) at all time points after surgery (P > 0.05). CONCLUSIONS: After intrastromal scanning, the expression of Ki-67 increases and the keratocyte is activated and proliferated. However, due to no epithelium injured and TGF-beta(2) confined to the epithelium, the activated and proliferated keratocytes could not be transformed into myofibroblasts.

[The effects on corneal wound healing of LASIK with ultra-thin corneal flaps and LASEK in rabbits].

OBJECTIVE: To evaluate the corneal wound-healing response of LASIK with ultra-thin corneal flaps and LASEK in rabbits. METHODS: It was an experimental study. Thirty-two adult New Zealand rabbits were divided into 2 groups with 16 each. Two surgical procedures, LASIK with ultra-thin corneal flaps and LASEK were performed on the right eye of each group, with the left eye as control. A myopic ablation of 10 diopters was performed in each group. Corneal wound-healing and histopathological changes of the ablation zone were studied through slit lamp, light microscope and transmission electronic microscope. The expression levels of collagen I , collagen III, fibronectin (FN) and transforming growth factor beta-1 (TGF-beta1) were investigated by immunohistochemistry and RT-PCR assays. RESULTS: In the group of LASIK with ultra-thin corneal flaps, the corneas were clear without haze followed by slight wound healing and fast recovery. While in the group of LASEK, corneal wound healing was obviously delayed. There was haze in grade 1 (62.5%) and grade 2 (37.5%) in 1 month, with grade 0.5 (43.75%) and grade 1 (56.25%) in 3 months. 1 month and 3 months after surgery, proteins and mRNA of collagen III, FN and TGF-beta1 were expressed in the anterior corneal stromal layer in each group. But the expression was much higher in the group of LASEK (t = 18.47, 11.98, P < 0.05). The protein and mRNA expression of collagen I had no difference between the two groups (t = 0.72, 0.36, 0.47, 2.38, P > 0. 05). The mRNA expression of collagen I, collagen III, FN and TGF-beta1 had no statistical difference between the groups of control and LASIK with ultra-thin flap in 3 months (t = 2.42, 1.54, -0.83, P > 0.05). CONCLUSION: According to the animal experiments, it was suggested that the corneal wound-healing response of LASIK with ultra-thin corneal flaps was much better than that of LASEK.

[Clinical study of diffuse lamellar keratitis after laser in situ keratomileusis].

OBJECTIVE: To investigate a new clinical grading scale of diffuse lamellar keratitis (DLK) following laser in situ keratomileusis (LASIK) and to observe the clinic outcomes of eyes treated with corresponding classified therapy. METHODS: It was a prospective case-control study. Eyes that developed DLK after LASIK were diagnosed by a new criterion of clinical grading scale based on both severity and scope of inflammatory cells infiltrations in the corneal interface. Dose and frequency of topical or systemic corticosteroid were determined by the classified profiles according to each grade. Clinical symptoms, corneal inflammatory cells infiltrations, visual acuity, refractive error and intraocular pressure (IOP) were evaluated on 1, 3, 5, 7, 10 days and 1 month after diagnosis as well as at the time of diagnosis. RESULTS: Among the 35 eyes of 29 patients that developed DLK, mild inflammatory cells infiltrations were mostly seen. Thirty eyes had degree I DLK and 3 had degree II DLK. One eye had degree III DLK and one had degree IV DLK. Inflammatory cells infiltrations in 20 eyes invaded peripheral zone (zone 1) and those in 11 eyes invaded mid-peripheral zone (zone 2). Inflammatory cells infiltrates in 4 eyes invaded central zone (zone 3). Nineteen eyes had degree I zone 1 DLK. Thirty three eyes were diagnosed between the 1st day and the 3rd day after surgery. Uncorrected visual acuity (UCVA) was worse than preoperative best spectacle corrected visual acuity (BSCVA). Inflammatory cells infiltrations retreated within 6.06 2.04 days after classified corticosteroid therapy. One month after the treatment, UCVA had improved to the level of preoperative BSCVA. BSCVA in 30 eyes were equal to or better than those before surgery. Spherical equivalent of the refractive error was (-0.21 +/- 1.16) D. There was no statistic difference in the retreat time of inflammatory cells infiltrations, recovery of visual acuity and refractive error among the different grades of DLK or among the DLK treated with different therapy profiles. No eye suffered from high intraocular pressure during the treatments. CONCLUSIONS: Clinical grading scale and corresponding classified therapy were proved to be effective in the treatment for DLK.

Sonic hedgehog expression and its role in form-deprivation myopia in mice.

PURPOSE: To investigate whether sonic hedgehog (Shh) plays a role in postnatal eye development and the development of experimentally induced myopia. METHODS: Expression of Shh, Patched-1 (Ptc-1), and Gli3 was evaluated in the eyes of 13- to 14-day-old C57B/L6 mice with form-deprivation myopia (FDM) (n = 100) and controls (n = 100) using real-time PCR and Western blot analysis. In a second experiment, 336 mice were divided into two groups: the first wore a unilateral translucent diffuser to induce myopia and the second served as a control. Both groups received four intravitreal injections of either Shh-N (Sonic hedgehog amino-terminal peptide) or cyclopamine (a specific inhibitor of the Shh pathway) every other day. Retinoscopic refraction and axial length measurements were performed on the 11th day of form deprivation. Sections of the eyes were observed using a light microscope. RESULTS: Inducing myopia caused a significant increase in expression of Shh mRNA (7 days: t = 6.09, p = 0.004; 14 days: t = 3.48, p = 0.025) and protein (7 days: t = 4.06, p = 0.015; 14 days: t = 4.25, p = 0.013). Expression of both Gli3 mRNA (t = 7.61, p = 0.002) and protein (t = 2.89, p = 0.045) increased after 7 days of occlusion. Administration of Shh-N stimulated the development of myopia and axial growth in both occluded (refraction: F = 7.49, p = 0.001; axial length: F = 9.89, p < 0.001) and non-occluded eyes (refraction: F = 14.20, p < 0.001; axial length: F = 20.37, p < 0.001). Cyclopamine reduced myopic refractive error and axial elongation in occluded eyes (refraction: F = 27.91, p < 0.001; axial length: F = 15.18, p < 0.001). It also influenced non-occluded eyes, reducing axial growth and shifting the refraction toward hyperopia (refraction: F = 14.81, p < 0.001; axial length: F = 3.99, p = 0.024). No difference in retinal thickness was found between experimental and control eyes. CONCLUSIONS: The Shh signaling pathway may influence both form-deprivation myopia and the postnatal growth of eyes with normal visual input.

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.

[Enhance research on refractive surgery].

Refractive surgery has become one of the hotspots of ophthalmology in our country. After analyzing refractive surgery related papers, the author put forward the idea that enhancement shall be done through strengthen innovation consciousness, deepen and refining the target of academic papers, uniform of operation program and material collection, strengthen the combination of basic research and clinical research and strengthen study on binocular vision in research of refractive surgery.

[The effect of the flap thickness on forward shift of posterior corneal surface in excimer laser surgery correcting high myopia].

OBJECTIVE: To investigate the influence of flap thickness of laser in situ keratomileusis (LASIK) and subepithelial keratomileusis on the forward shift of the posterior corneal surface in high myopia METHODS: It was a case-control study. In this study, 151 right high myopic eyes of patients [spherical equivalent range - 6.00 to - 10.00 diopter, 46 subepithelial keratomileusis eyes (epithelial sheet group), 64 LASIK eyes with 110 microm flap thickness (thin flap group) and 41 LASIK eyes with 130 microm flap thickness (normal flap group)] were evaluated preoperatively and postoperatively with the Pentacam to determine the shape change in the posterior corneal surface. Changes in posterior shape were calculated by comparing refraction and elevation of posterior corneal surface in the part corresponding to the pupil center preoperatively and postoperatively. RESULTS: The mean estimated residual bed thickness (RBT) of epithelial sheet eyes, thin flap eyes and normal flap eyes was (362 +/- 23), (320 +/- 25) and (300 +/- 21) microm, respectively. The RBT difference between epithelial sheet group and thin or normal flap group was statically significant (F = 85.685, P <0.001) and the difference between 2 LASIK groups was also significant (P < 0.05). There was no significant difference between three groups in ablation depth (P > 0.05). The mean posterior corneal refraction and elevation change of epithelial sheet eyes, thin flap eyes and normal flap eyes in the pupil center was (-0.12 +/- 0.14)D and (0.9 +/-1.8) microm, ( -0.20 +/- 0.22)D and (1.3 +/- 1.6) microm, (-0.21 +/- 0.18)D and (1.5 +/- 1.5) microm, respectively. A significant correlation between posterior elevation and refraction change was present in all 3 groups. The amount of posterior corneal elevation change correlated significantly with the ablation depth in thin flap group and normal flap group (r = 0.265, 0.311; P <0.05). CONCLUSION: In treating high myopia, both subepithelial ablation and LASIK surgery induce tiny forward shift of posterior corneal surface when the RBT was thick enough. Deeper ablation or thicker corneal flap may increase the trend of forward shift of posterior corneal surface.

Effect of flap thickness on higher order wavefront aberrations induced by LASIK: a bilateral study.

PURPOSE: To investigate the effect of flap thickness on wavefront aberrations induced by LASIK. METHODS: LASIK was performed on 56 eyes of 28 patients with refraction errors that were well matched between the right and left eyes. For each patient, a planned 160-microm flap was created for one randomly selected eye using the Moria M2 microkeratome (130-microm head; thick flap group), and a 110-microm flap was created for the contralateral eye with the same microkeratome (90-microm head; thin flap group). Flap thickness was measured using ultrasonic pachymetry. Wavefront aberrations were measured in the anterior cornea using the Orbscan II (Bausch & Lomb) and in the whole eye using the Wavefront Supported Custom Ablation (WASCA) aberrometer (Carl Zeiss Meditec) preoperatively and at 1 month and 1 year postoperatively. RESULTS: Mean flap thickness was 155 +/- 13 microm in the thick flap group and 112 +/- 11 microm in the thin flap group. Mean root-mean-square of higher order wavefront aberrations were changed for the different test times in the cornea (F = 29.9, P < .0001) and the whole eye (F = 48.0, P < .0001). There was no significant difference between the two flap groups for the cornea (F = 0.76) or for the whole eye (F = 0.07). Similar results were observed for higher order Zernike aberrations such as spherical aberration and comas. CONCLUSIONS: The results suggest higher order wavefront aberrations induced by LASIK are independent of flap thickness. Complications in visual outcome for patients with different flap thickness should be attributed to factors other than aberrations.

[The experience of initiating the projects in ophthalmologic research].

The choice of subjects plays a significant role in scientific research. About how to make a good choice, author's brief experience is to keep one theme, two essentials, three thinking and four methods. One theme refers to innovation. The headspring of innovation is associative thinking, which bases on extensive knowledge and excellent summing-up. Two essentials refer to the essential of being steadfast and earnest and the essential of "nail" which stands for persistence. Three thinking refer to associative thinking, logical thinking and converse thinking. Four methods refer to method of reading, method of practice, method of consultation and method of inversion.

[Influence of diameter of optical zone ablation on LASIK-induced higher order optical aberrations in myopia].

OBJECTIVE: To analyze the effects of optical zone ablation diameter on LASIK-induced higher order optical aberrations in myopia. METHODS: Four hundred and sixty-one eyes of 236 patients treated with LASIK for myopia were divided into high, moderate and low myopia group according to preoperative spherical equivalent diopter. In each group, eyes were divided into four subgroups according to optic zone ablation diameter. Before and after surgery 6 months, monochromatic wavefront aberrations of each eye were objectively measured using WASCA Analyzer Aberrometer. F test and q test were used to analyze the difference of total high order, horizontal coma, vertical coma, and spherical aberrations among four subgroups in each group at 4, 5, and 6 mm pupil size. RESULTS: Before surgery no significant difference of higher order aberrations among four subgroups was found. After surgery, there was significant difference of total high order, and spherical aberrations among four subgroups. Total high order, and spherical aberrations in larger optical zone ablation diameter subgroup were significantly lower than that in smaller one. The difference was significant at 4, 5, and 6 mm pupil size in high myopia group, and 6 mm pupil size in low myopia group. At 6 mm pupil size, the difference was significant between each subgroup in high myopia group and subgroup I and subgroup IV in low myopia group. There was no significant difference of horizontal coma, and vertical coma aberrations among four subgroups. CONCLUSIONS: Optical zone ablation diameter has influence on LASIK-induced higher order optical aberrations. Larger optical zone can decrease total higher order and spherical aberrations after LASIK. The effects are more significant in high myopia group than in low myopia group.

[Clinical analysis of measuring corneal thickness with non-contact method].

OBJECTIVE: To compare accuracy of the Pentacam with A-ultrasonoscope in the measurement of central corneal thickness. METHODS: According to the degree of myopia, 107 myopic patients (211 eyes) were divided into four groups. The central corneal thickness was measured with the Pentacam system and A-ultrasonoscope. The results were compared statistically and the differences between these two methods were analyzed. RESULTS: Mean values of central corneal thickness measured by the Pentacam system and A-ultrasonoscope was (535.58 +/- 36.34) microm and (536.73 +/- 37.18) microm, respectively. There was no difference in the results obtained by these two methods in each myopia group (P > 0.05). The 95% limits of agreement were (-1.88, -0.42). CONCLUSIONS: The data shows that the results obtained by Pentacam system do not have significant difference as compared with that from the A-ultrasonoscope. The Pentacam system can provide precise results and has the advantage of simplicity and non-contact. Therefore, it would be a promising instrument for the evaluation of central corneal thickness before the cornea refractive surgery.