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Biomedical subjects

S G Farah

Publications and source records attributed to S G Farah.

5 recordsLinked to original sources
PubMed2001

Posterior corneal surface changes after refractive surgery.

OBJECTIVE: To determine the frequency of changes in posterior corneal surface after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). DESIGN: Nonrandomized, comparative trial. PARTICIPANTS: Ninety-five eyes (71 patients) that underwent PRK (n = 45) or LASIK (n = 50). CONTROLS: Twenty nonsurgery eyes were used to validate the method of analysis of the posterior corneal curvature (PCC). Seventy nonsurgery eyes were used for comparisons. METHODS: Float, apex-fixed best fit corneal curvature (ABC), and posterior elevation difference were evaluated in 20 elevation topography maps at 6 zone diameters (3-7 and 10 mm) and at two time points. Corneal elevation maps before and after PRK or LASIK were analyzed by the ABC and float methods and compared with a nonsurgery group. MAIN OUTCOME MEASURES: Posterior corneal curvature change (mm) was classified as flattening, steepening, or no change. RESULTS: Flattening of more than 0.12 mm was found in 22.2% of eyes (n = 10) in the PRK group, a change of +/-0.12 mm was found in 53.3% of eyes (n = 24), and steepening of more than 0.12 mm was found in 24.4% of eyes (n = 11) using the float method and in 28.9% of eyes (n = 13), 35.6% of eyes (n = 16), and 35.6% eyes (n = 16), respectively, using the ABC method. In the LASIK group, the float method registered flattening in 20% of eyes (n = 10), no change in 52% of eyes (n = 26), and steepening in 28% of eyes (n = 14), whereas the ABC method registered flattening in 30% of eyes (n = 15), no change in 40% of eyes (n = 20), and steepening in 30% of eyes (n = 15). The nonsurgery group showed a similar change in PCC at two different time points similar to that of the PRK and the LASIK groups. CONCLUSIONS: The differences observed in the PCC after PRK or LASIK were not statistically significantly different from those observed over time in the nonsurgery control group.

Adult↗
PubMed2000

Outcome of corneal and laser astigmatic axis alignment in photoastigmatic refractive keratectomy.

PURPOSE: To compare the refractive results of laser astigmatic treatment in eyes in which the astigmatic axes of the eye and laser are aligned by limbal marking at the 6 o'clock position and in eyes that are not marked. SETTING: University Hospital and Clinics, Madison, Wisconsin, USA. METHODS: This retrospective study comprised 143 eyes that had photoastigmatic refractive keratectomy with the VISX Star excimer laser. The eyes were divided into marked (G1) and unmarked (G2) groups. Based on the preoperative astigmatism, each group was subdivided into low astigmatism (</=1.00 diopter [D]) and high astigmatism (>/=1.25 D). Early postoperative manifest refractions (1.0 to 2.5 months) were analyzed. The Alpins vector analysis method was used to calculate the target induced astigmatism, surgically induced astigmatism, difference vector (DV), magnitude of error (ME), angle of error (AE), and index of success (IS). RESULTS: There was no significant difference between the groups in DV, ME, and IS. When the subgroups were analyzed, the DV and ME were comparable; the IS in the G1 high astigmatism subgroup was significantly better than that in the G2 high astigmatism subgroup (0.22 +/- 0.08 and 0.29 +/- 0.04, respectively; P <.0001). There was comparable scatter of AE values; 30% and 36% in G1 and G2, respectively, had an AE of 0. Similar scatter was observed in the subgroups. Of the eyes that had an AE of 0, 90% and 43% in the high astigmatism subgroups of G1 and G2, respectively (P <.05), had full correction of astigmatism. CONCLUSION: Limbal marking and subsequent eye and laser astigmatic axis alignment improved the refractive outcome of laser astigmatic treatment of >/=1.25 D. A preliminary report of an ongoing prospective randomized study of eyes that had laser in situ keratomileusis is included.

Adult↗
PubMed1998

Laser in situ keratomileusis: literature review of a developing technique.

We reviewed papers published in peer-reviewed journals describing techniques and results of laser in situ keratomileusis (LASIK) and summarized the instruments used, nomograms, preoperative and postoperative refractions, predictability, outcome, safety, and complications. We performed a similar review of abstracts published in the abstract books of the 1996 meeting of the International Society of Refractive Surgery, the 1997 meeting of the Association for Research in Vision and Ophthalmology, and the 1997 meeting of the American Society of Cataract and Refractive Surgery. The number of LASIK and photorefractive keratectomy (PRK) patients described in the abstracts were sorted by city. Mean weighted latitudes were calculated and compared for each procedure. The mean preoperative refraction in the papers was -12.59 diopters (D), which was statistically higher than that in the abstracts, -8.71 D (P < .001), and the mean postoperative refraction, -1.10 and + 0.93 D, respectively. The mean percentage of cases within +/- 1.00 D was 67.0% in the papers and 82.5% in the abstracts. Uncorrected visual acuity (UCVA) of 20/40 or better was achieved in 49.2% of eyes in the papers and 83.2% of those in the abstracts; a UCVA of 20/20 or better was achieved in 22.0 and 56.6%, respectively. The portion of eyes that lost two or more lines of best corrected visual was 8.0% in the papers and 0.9% in the abstracts. Complications in the papers included irregular flap (4.0%), incomplete cut (2.5%), free cap (4.9%), perforated lenticule (2.6%), short flap (3.0%), sliding flap (1.4%), interface debris (6.8%), central island (5.3%), decentration (4.7%), epithelial ingrowth (4.3%), induced astigmatism (5.1%), wrinkles (5.9%), haze (8.7%), night vision problems (14.0%), and reoperation (8.2%), Mean latitude for LASIK cases (27.00 degrees +/- 13.73 [SD] was significantly lower than that for PRK cases (42.85 +/- 11.7 degrees). Visual outcomes of LASIK surgery show significant improvements when recent abstracts are compared with published papers. This may reflect continued improvement in the surgical techniques, surgeons' skills, and visual outcomes.

Adolescent↗