Biomedical subjects

Thomas W Samuelson

Publications and source records attributed to Thomas W Samuelson.

4 recordsLinked to original sources

PubMed2004

Refractive surgery in glaucoma.

PURPOSE OF REVIEW: The purpose of this review is to discuss the topics relevant to the topic of LASIK in glaucoma patients or suspects. The safety of LASIK and the implications of LASIK on glaucoma diagnostic testing are reviewed. RECENT FINDINGS: Most studies have found no change in the nerve fiber layer thickness or optic disc after LASIK. Several reports of steroid-induced glaucoma after LASIK have been published. Important new syndromes such as the interlamellar stromal cyst have been described. Most investigators, but not all, have found intraocular pressure to be lower after LASIK, most likely an artifact of measurement as a result of reduced central corneal thickness. SUMMARY: The safety of LASIK in patients with glaucoma has not been proved. However, based on the published literature, LASIK may be a viable option for some glaucoma patients. Although not an absolute contraindication, glaucoma is a relative contraindication, and careful patient education and life-long follow-up is mandatory. The clinician must be ever mindful of the important effects that LASIK may have on diagnostic testing.

Glaucoma↗

PubMed2003

Evaluation of neuroprotective qualities of brimonidine during LASIK.

PURPOSE: The effects of LASIK-induced increased intraocular pressure on the optic nerve and nerve fiber layer are poorly understood. This study evaluates the effect of LASIK on several optic nerve parameters, both structural (scanning laser polarimetry) and functional (automated perimetry). In addition, the potential neuroprotective effect of perioperative brimonidine is studied. DESIGN: Randomized self-controlled, masked trial. PARTICIPANTS: Fifty-one patients scheduled for routine, bilateral, myopic LASIK. Patients served as their own control and received brimonidine in one eye and placebo in their fellow eye. METHODS: Patients were treated with the VISX Star S3 Excimer Laser. Patients were evaluated preoperatively and at 1 day, 1 month, and 3 months after LASIK. Topical brimonidine or control vehicle was administrated three times daily for 3 days before surgery. In addition, 1 drop of the respective study drug was instilled at the end of the procedure, and the patient continued the study drug three times daily for 3 weeks after surgery in the respective (randomized) eye. MAIN OUTCOME MEASURES: Visual acuity, nerve fiber layer analysis, automated visual field, contrast sensitivity, color vision, and pupillary function. RESULTS: Brimonidine did not change the outcome of any of the parameters analyzed in this study. There was not a statistically significant change in any of the visual field parameters (mean elevation or depression, pattern standard deviation, and corrected pattern standard deviation) measured in either the placebo or brimonidine group postoperatively. However, both the placebo and brimonidine group did show a statistically significant change in many of the direct Nerve Fiber Analyzer GDx (NFA GDx) measures. The average thickness, ellipse, and superior average were generally reduced in both groups. There was, however, no statistically significant change after LASIK in either group in indirect NFA GDx parameters such as symmetry, superior ratio, inferior ratio, or superior/nasal ratio. There was no significant change in optic nerve appearance, contrast sensitivity, or color vision between treatment groups before or after LASIK. CONCLUSIONS: LASIK with or without brimonidine did not affect the structure or function of the parameters of the optic nerve studied. Direct NFA GDx measures were globally reduced after myopic LASIK; however, the ratio measures were generally unaffected. The reduction in direct, retinal nerve fiber layer measures, in the absence of change in ratio measures and other optic nerve parameters and absence of brimonidine effect, suggest an alteration in corneal birefringence after excimer laser ablation.

Administration, Topical↗

PubMed2002

Lasik enhancements: a comparison of lifting to recutting the flap.

PURPOSE: To compare the visual outcomes and incidence of complications of lifting with recutting the lamellar flap in laser in situ keratomileusis (LASIK) enhancement surgery. DESIGN: Retrospective case-control study. PARTICIPANTS: Two hundred twelve consecutive eyes undergoing a LASIK enhancement procedure at a single surgery location during a 5-year period. METHODS: Charts of participants were obtained and outcome measures obtained. MAIN OUTCOME MEASURES: Uncorrected visual acuity, best-corrected visual acuity, refractive error, complications. RESULTS: Relifting of flaps was performed in 164 of 212 eyes (77.4%), and recutting of flaps was performed in 48 of 212 eyes (22.6%). There were no significant differences in early visual outcomes between the two groups. At 1 year patients had significantly better uncorrected vision if the flap was lifted rather than recut (20/24.7 vs. 20/31.3, P < 0.008). In addition, the flap lift group had a significantly more stable refraction at 1 year than did the recut group (change in spherical equivalent: +0.05 diopters (D) vs. -0.57 D). The incidence of complications did not significantly differ between the two groups. CONCLUSIONS: LASIK enhancement surgery can be performed safely and effectively by either lifting or recutting a flap. Lifting the flap may show better long-term stability of refractive error and uncorrected acuity.

Adult↗

PubMedDate not supplied

Nomogram considerations with the Technolas 217A for treatment of myopia.

PURPOSE: To determine whether surgeon-specific nomogram adjustments are useful when using the Technolas 217A excimer laser for treating myopia and myopic astigmatism. METHODS: We conducted a prospective evaluation of 216 consecutive eyes with 6 months follow-up after treatment of myopia or myopic astigmatism with the Technolas 217A laser. Attempted vs. achieved change in refraction was analyzed with a statistical analysis software program. Factors such as age, corneal thickness (pachymetry), preoperative spherical equivalent refraction, preoperative cylinder, and optical zone were studied to evaluate their role in predicting refractive outcome at 6 months after LASIK. RESULTS: The mean value of attempted spherical equivalent refraction was -5.32 +/- 2.72 D. The mean achieved refractive correction at 6 months was -5.55 +/- 2.78 D, with a mean spherical equivalent of 0.13 +/- 0.54 D. The percent achieved effect at 1 month was 105%, and at 6 months, 103%. Preoperative spherical equivalent refraction and optical zone size were strong predictors of 6-month LASIK outcome. There was a 9% difference in the percent achieved effect between a 4 and 7-mm optical zone. There was no correlation between age, preoperative cylinder, or surgeon and 6-month outcome. CONCLUSIONS: Surgeons using the planoscan software on the Technolas 217A may experience a small initial overcorrection. There may be a benefit to reducing the treatment given with larger optical zones and smaller corrections.

Adult↗