Biomedical subjects

Bruce D S Allan

Publications and source records attributed to Bruce D S Allan.

5 recordsLinked to original sources

PubMed2006

Evidence for superior efficacy and safety of LASIK over photorefractive keratectomy for correction of myopia.

PURPOSE: To examine possible differences in efficacy and safety between LASIK and photorefractive keratectomy (PRK) for correction of myopia. DESIGN: Meta-analysis/systematic review. PARTICIPANTS: Patient data from previously reported prospective randomized controlled trials (PRCTs) and a systematic review of prospective case series in the Food and Drug Administration (FDA) clinical trials database. METHODS: A comprehensive literature search was performed using the Cochrane Collaboration methodology to identify PRCTs comparing LASIK and PRK for correction of myopia. A meta-analysis was performed on the results of PRCTs. In parallel, a systematic review of prospective data from FDA case series of LASIK and PRK for correction of myopia was undertaken. MAIN OUTCOME MEASURES: Key efficacy outcomes (uncorrected visual acuity [UCVA] > or = 20/20, +/-0.50 diopters [D] of the target mean refractive spherical equivalent) and safety outcomes (loss of > or =2 lines of best spectacle-corrected visual acuity [BSCVA], final BSCVA > or = 20/40, and final BSCVA < 20/25 where preoperative BSCVA was > or =20/20). RESULTS: Seven PRCTs were identified comparing PRK (683 eyes) and LASIK (403 eyes) for correction of myopia. More LASIK patients achieved UCVA > or = 20/20 at 6 months (odds ratio, random effects model [95% confidence interval], 1.72 [1.14-2.58]; P = 0.009) and 12 months (1.78 [1.15-2.75], P = 0.01). Loss of > or =2 lines of BSCVA at 6 months was less frequent with LASIK (2.69 [1.01-7.18], P = 0.05). Data from 14 LASIK (7810 eyes) and 10 PRK (4414 eyes) FDA laser approval case series showed that more LASIK patients achieved UCVA of 20/20 or better at 12 months (1.15 [1.03-1.29], P = 0.01), significantly more LASIK patients were within +/-0.50 D of target refraction at 6 months (1.38 [1.26-1.50], P<0.00001) and 12 months (1.21 [1.08-1.36], P = 0.0009) after treatment, and loss of > or =2 lines of BSCVA at 6 months was less frequent with LASIK (2.91 [2.22-3.83], P<0.00001). CONCLUSIONS: LASIK appears to have efficacy and safety superior to those of PRK. However, the data examined are from studies conducted > or =5 years ago. It is therefore unclear how our findings relate to present-day methods and outcomes. Further trials comparing contemporary equipment and techniques are needed to reevaluate the relative merits of these procedures.

Clinical Trials as Topic↗

PubMed2005

Biometry accuracy using zero- and negative-powered intraocular lenses.

PURPOSE: To audit the accuracy of biometry using the SRK/T formula when negative- or zero-powered intraocular lenses (IOLs) are predicted and to compare the results between A-scan, B-scan, and optical methods of biometry. SETTING: Moorfields Eye Hospital, London, United Kingdom. METHODS: This retrospective analysis comprised 78 eyes of 54 patients having cataract surgery with zero- or negative-powered IOLs. Axial lengths were measured with A-scan, B-scan, applanation, or optical methods. Differences between SRK/T-predicted and actual postoperative refraction were analyzed for 75 eyes having cataract surgery. Ocular comorbidity, visual acuity, and biometry readings were also compared. RESULTS: Forty-one percent of 75 patients analyzed were within +/-1.00 diopter (D) of the predicted refraction, although there was a significant tendency toward a hyperopic overcorrection by 1.14 D (95% confidence interval, 0.89-1.39 D). This overcorrection error was consistent across all 3 biometry methods used to estimate axial length and increased with the use of stronger (more negative) IOLs. CONCLUSION: Surgeons should be aware of the tendency for negative-powered lenses to overcorrect and lead to a hyperopic outcome when using the SRK/T biometry formula in highly myopic eyes. A weaker-powered negative IOL is recommended to aim for a more myopic postoperative outcome by about 1.00 to 2.00 D.

Accommodation, Ocular↗

PubMed2005

Improved safety in contemporary LASIK.

PURPOSE: To examine the risk of serious visual loss in contemporary LASIK. DESIGN: Retrospective, noncomparative, consecutive case series combined with a structured literature review and comparison with historical controls. PARTICIPANTS: One thousand consecutive cases of LASIK performed from January 2000 to January 2004 by 1 surgeon. One thousand nine hundred eighty-two cases with 6-month review data in postmillennial Food and Drug Administration (FDA) trials of LASIK for myopia and astigmatism and 5203 patients with 6 month review data in similar premillennial FDA trials. METHODS: LASIK was performed with the Hansatome microkeratome and a VISX Star (S2, S3, or S4) laser. There were 899 myopic treatments (spherical equivalent < or =-10.5 diopters [D]; average -4.2 D; standard deviations [SD] D = 1.9 D; astigmatism < or =4.75 D), 87 hyperopic treatments (spherical equivalent < or =+4.25 D; average +2.4 D; SD = 0.9 D; astigmatism < or =3.5 D), and 14 treatments for mixed astigmatism (< or =4.5 D). Outcome data were obtained from a review of case notes and compared with historical data from FDA trials. MAIN OUTCOME MEASURES: Best-spectacle corrected visual acuity (BSCVA) preoperatively and at final review was compared in our case series with reference to the United Kingdom driving standard (BSCVA> or =20/30). Subsidiary outcome measures included duration of follow-up, intraoperative, and postoperative complication rates. Six-month postoperative data on standard safety criteria (numbers of patients losing > or =2 lines BSCVA, BSCVA <20/40, and final BSCVA <20/25 for patients with preoperative BSCVA > or =20/20) were examined in FDA trials. RESULTS: In our clinical series, no case with a preoperative BSCVA of 20/20 or better had a final BSCVA of <20/30 at final review (97.5% confidence interval [CI], 0%-0.37%); 4 eyes had a BSCVA <20/25 (0.41%; 95%CI, 0.11%-1.02%). The median interval between surgery and final review was 2 months (range, 1-45 months). In FDA studies recruiting pre-2000, 1.4% of patients lost > or =2 lines of BSCVA versus 0.6% in postmillennial studies (P = 0.005); 0.45% of patients in premillennial studies lost BSCVA to <20/40 compared with no patients in postmillennial studies (P = 0.001); and 1.68% of patients in premillennial studies with a preoperative BSCVA > or =20/20 had a postoperative BSCVA <20/25 compared with 0.16% in postmillennial studies (P< or =0.001). CONCLUSIONS: Compared with premillennial results, the risk of visual loss is significantly reduced in contemporary LASIK.

Adult↗

PubMed2005

Interaction with collagen IV protects lens epithelial cells from Fas-dependent apoptosis by stimulating the production of soluble survival factors.

PURPOSE: To investigate the sensitivity of lens epithelial cells (LECs) to Fas-dependent apoptosis and to determine the role of interaction with the extracellular matrix (ECM) in the regulation of Fas-dependent apoptosis. METHODS: Sensitivity to Fas-mediated apoptosis of primary human LECs and HLE-B3 LECs cultured on different substrates was determined by Hoechst staining after incubation with Fas-stimulating or control IgM. Fas expression was determined by Western blot analysis. Effects of varied cell density and conditioned media from HLE-B3 cells cultured on different substrates on the Fas sensitivity of HLE-B3 cells cultured on tissue culture (TC) plastic were determined. RESULTS: Primary LECs cultured as free-floating anterior capsulotomy specimens were resistant to Fas-dependent apoptosis. The LE cell line, HLE-B3, was sensitive to Fas-dependent apoptosis when cultured on TC plastic but not on lens capsule. Culture on collagen IV, but not on laminin, rendered HLE-B3 cells resistant to Fas-dependent apoptosis, although Fas was still expressed. Primary LECs cultured on TC plastic after migration from lens capsule explants were resistant to Fas-dependent apoptosis if the lens capsule and attached cells were still present, but not if the lens capsule had been removed. Conditioned medium from LECs cultured on collagen IV, but not TC plastic, protected cells cultured on TC plastic from Fas-dependent apoptosis. The protective effect of culture on collagen IV diminished with decreasing cell density. CONCLUSIONS: LECs are protected from Fas-dependent apoptosis by interaction with collagen IV. Soluble factors released by the LECs cultured on collagen IV protect LECs from Fas-dependent apoptosis.

Apoptosis↗

PubMed2002

Fixed dilated pupil (Urrets-Zavalia syndrome) after air/gas injection after deep lamellar keratoplasty for keratoconus.

PURPOSE: To describe three cases of fixed dilated pupil and presumed iris ischemia (Urrets-Zavalia syndrome) after anterior chamber air/gas injection after deep lamellar keratoplasty for keratoconus. METHODS: Interventional case series. Three eyes of three patients with keratoconus underwent deep lamellar keratoplasty and intraoperative or postoperative injection of air/gas in the anterior chamber to appose the host-donor lamellar graft interface. RESULTS: Urrets-Zavalia syndrome was diagnosed on clinical grounds in three cases and was associated with the Descemet membrane microperforation intraoperatively and introduction of air/gas into the anterior chamber intraoperatively or postoperatively. CONCLUSION: A fixed dilated pupil is an uncommon complication of penetrating keratoplasty for keratoconus that can also develop after deep lamellar keratoplasty. Leaving an air or gas bubble in the anterior chamber of a phakic eye after deep lamellar keratoplasty is a risk factor and should therefore be avoided.

Adult↗