8 results on '"Chan, Tommy"'
Search Results
2. Changes in Corneal Volume at Different Areas and Its Correlation with Corneal Biomechanics after SMILE and FS-LASIK Surgery.
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Wei, Pinghui, Cheng, George PM, Zhang, Jiamei, Ng, Alex LK, Chan, Tommy CY, Jhanji, Vishal, and Wang, Yan
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CORNEA surgery ,CORNEA physiology ,BIOMECHANICS ,CORNEAL topography ,OPHTHALMIC surgery ,POSTOPERATIVE period ,LASIK ,REPEATED measures design ,RETROSPECTIVE studies ,DATA analysis software ,DESCRIPTIVE statistics ,ONE-way analysis of variance - Abstract
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 mm
3 ,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. [ABSTRACT FROM AUTHOR]- Published
- 2020
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3. Effect of corneal curvature on optical zone decentration and its impact on astigmatism and higher-order aberrations in SMILE and LASIK.
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Chan, Tommy C. Y., Wan, Kelvin H., Kang, David S. Y., Tso, Tiffany H. K., Cheng, George P. M., and Wang, Yan
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LASIK , *CURVATURE , *EYE laser surgery , *ASTIGMATISM , *ZONING - Abstract
Purpose: To determine the association between anterior corneal curvature and optical zone centration as well as its impact on aberration profiles in small-incision lenticule extraction (SMILE) and laser in situ keratomileusis (LASIK).Methods: Seventy-eight eyes of 78 patients treated with SMILE (45 eyes) and LASIK (33 eyes) were included. The centration of the optical zone was evaluated on the instantaneous curvature difference map between the preoperative and 3-month postoperative scans using a superimposed set of concentric circles. The correlation between optical zone decentration and anterior keratometry values was evaluated. The effect of optical zone decentration on vector components of astigmatic correction and induction of higher-order aberrations (HOA) was assessed.Results: The mean decentration distance was 0.21 ± 0.11 mm for SMILE and 0.20 ± 0.09 mm for LASIK (p = 0.808). There was a significant correlation between anterior keratometric astigmatism and decentration distance (r = 0.653, p < 0.001) for SMILE but not for LASIK (r = − 0.264, p = 0.138). Astigmatic correction was performed in 67 eyes. Optical zone decentration and the vector components of astigmatic correction were not correlated (p ≥ 0.420). Significant correlation was demonstrated between the decentration distance and the induced total coma (SMILE: r = 0.384, p = 0.009; LASIK: r = 0.553, p = 0.001) as well as the induced total HOA (SMILE: r = 0.498, p = 0.001; LASIK: r = 0.555, p = 0.001).Conclusion: Anterior cornea astigmatism affected the treatment centration in SMILE but not LASIK. Subclinical decentration was associated with the induction of total coma and total HOA, but it did not affect the lower-order astigmatic correction. [ABSTRACT FROM AUTHOR]
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- 2019
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4. Refractive regression after laser in situ keratomileusis.
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Yan, Mabel K, Chang, John SM, and Chan, Tommy CY
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VISION disorders ,LASIK ,OPHTHALMIC surgery ,QUALITY of life ,MYOPIA - Abstract
Uncorrected refractive errors are a leading cause of visual impairment across the world. In today's society, laser in situ keratomileusis (LASIK) has become the most commonly performed surgical procedure to correct refractive errors. However, regression of the initially achieved refractive correction has been a widely observed phenomenon following LASIK since its inception more than two decades ago. Despite technological advances in laser refractive surgery and various proposed management strategies, post‐LASIK regression is still frequently observed and has significant implications for the long‐term visual performance and quality of life of patients. This review explores the mechanism of refractive regression after both myopic and hyperopic LASIK, predisposing risk factors and its clinical course. In addition, current preventative strategies and therapies are also reviewed. [ABSTRACT FROM AUTHOR]
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- 2018
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5. Vector analysis of high (≥3 diopters) astigmatism correction using small-incision lenticule extraction and laser in situ keratomileusis.
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Chan, Tommy C.y., Wang, Yan, Ng, Alex L.k., Zhang, Jiamei, Yu, Marco C.y., Jhanji, Vishal, and Cheng, George P.m.
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VECTOR analysis , *LASIK , *ASTIGMATISM , *VISUAL acuity , *T-test (Statistics) , *EYE diseases , *THERAPEUTICS - Abstract
Purpose To compare the astigmatic correction in high myopic astigmatism between small-incision lenticule extraction and laser in situ keratomileusis (LASIK) using vector analysis. Setting Hong Kong Laser Eye Center, Hong Kong. Design Retrospective case series. Methods Patients who had correction of myopic astigmatism of 3.0 diopters (D) or more and had either small-incision lenticule extraction or femtosecond laser–assisted LASIK were included. Only the left eye was included for analysis. Visual and refractive results were presented and compared between groups. Results The study comprised 105 patients (40 eyes in the small-incision lenticule extraction group and 65 eyes in the femtosecond laser–assisted LASIK group.) The mean preoperative manifest cylinder was −3.42 D ± 0.55 (SD) in the small-incision lenticule extraction group and −3.47 ± 0.49 D in the LASIK group ( P = .655). At 3 months, there was no significant between-group difference in uncorrected distance visual acuity ( P = .915) and manifest spherical equivalent ( P = .145). Ninety percent and 95.4% of eyes were within ± 0.5 D of the attempted cylindrical correction for the small-incision lenticule extraction and LASIK group, respectively ( P = .423). Vector analysis showed comparable target-induced astigmatism ( P = .709), surgically induced astigmatism vector ( P = .449), difference vector ( P = .335), and magnitude of error ( P = .413) between groups. The absolute angle of error was 1.88 ± 2.25 degrees in the small-incision lenticule extraction group and 1.37 ± 1.58 degrees in the LASIK group ( P = .217). Conclusion Small-incision lenticule extraction offered astigmatic correction comparable to LASIK in eyes with high myopic astigmatism. [ABSTRACT FROM AUTHOR]
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- 2018
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6. Combined application of prophylactic corneal cross-linking and laser in-situ keratomileusis - a review of literature.
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Chan, Tommy C. Y., Ng, Alex L. K., Chan, Karen K. W., Cheng, George P. M., Wong, Ian Y. H., and Jhanji, Vishal
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REFRACTIVE lamellar keratoplasty , *OPHTHALMIC surgery , *CORNEA , *EXCIMER lasers , *VITAMIN B2 - Abstract
Laser in-situ keratomileusis ( LASIK) is safe and effective laser refractive procedures in treating refractive errors. However, regression of treatment and iatrogenic keratectasia remain to be a major concern, especially in treating thin cornea with high ametropia. Collagen cross-linking ( CXL) is an effective method in stopping keratoconus progression through increasing the biomechanical strength of the cornea. Adjuvant cross-linking to refractive procedures can theoretically help prevent regression and reduce the risk of keratectasia development by increasing the mechanical stability of cornea. During the procedure, riboflavin is directly applied to the corneal stroma, thereby reducing the need of de-epithelialization as in the conventional protocol for keratoconus. Currently, there is still no consensus regarding the indication of CXL during refractive procedure, nor any standardized treatment protocol. This article aims to summarize the current evidence regarding the use of adjuvant CXL in LASIK. [ABSTRACT FROM AUTHOR]
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- 2017
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7. Impact of ocular residual astigmatism on predictability of myopic astigmatism correction after small-incision lenticule extraction.
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Chan, Tommy C.Y., Wan, Kelvin H., Zhang, Lin, and Wang, Yan
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LASIK , *ASTIGMATISM , *CRYSTALLINE lens - Published
- 2019
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8. Longitudinal Comparison of Outcomes After Sub-Bowman Keratomileusis and Laser in Situ Keratomileusis: Randomized, Double-Masked Study.
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RACHEL CHUNG YIN WONG, MARCO YU, CHAN, TOMMY C. Y., CHONG, KELVIN K. L., and JHANJI, VISHAL
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REFRACTIVE lamellar keratoplasty , *LASIK , *CLINICAL trials , *MYOPIA , *POSTOPERATIVE care , *FOLLOW-up studies (Medicine) , *CONTROL groups , *HEALTH outcome assessment , *PATIENTS - Abstract
PURPOSE: To compare the outcomes of sub-Bowman keratomileusis (100-mm flap) and laser in situ keratomileusis (LASIK) (120-mm flap) using 150-kHz femtosecond laser. DESIGN: Randomized, double-masked, contralateral clinical trial. METHODS: One hundred patients (200 eyes) with myopia or myopic astigmatism were included. Postoperative examinations were performed at week 1 and months 1, 3, 6, and 12. Main outcome measures included postoperative uncorrected (UCVA) and best-corrected distance visual acuity (BCVA); manifest refraction spherical equivalent; efficacy and safety indices; corneal thickness; and complications. RESULTS: The mean age of patients was 33.9 ± 7.9 years. Overall, the preoperative UCVA, BCVA, and manifest refraction spherical equivalent were 1.349 ± 0.332, -0.022 ± 0.033, and -5.81 ± 1.61 diopters, respectively. No significant difference was observed in preoperative (P ≥ .226) or intraoperative parameters (P ≥ .452) between both groups, except residual stromal thickness (P<.001). The UCVA, manifest refraction spherical equivalent, and central corneal thickness stabilized by 1 week, while the thinnest corneal thickness stabilized by 3 months postoperatively. There was no significant difference between both groups for any parameter during all follow-up visits (P ≥ .132) except the 3-month safety index, which was better in the sub-Bowman keratomileusis group (P = .007). Soft opaque bubble layer was noted intraoperatively in 12 cases (7, 100-mmgroup; 5, 120-mmgroup; P=.577). No postoperative complications were observed. CONCLUSIONS: Our study did not find any differences in the visual and refractive outcomes between femtosecond-assisted sub-Bowman keratomileusis and LASIK. Both surgeries resulted in quick visual recovery as early as 1 week postoperatively. [ABSTRACT FROM AUTHOR]
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- 2015
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