PubMed · 9113562
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P J Nielsen. 1997. Multivariate versus vector analysis.. https://doi.org/10.1016/s0886-3350(97)80333-1
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PURPOSE: The aim was to compare the different techniques of cataract surgery regarding early postoperative astigmatism and visual acuity. PATIENTS AND METHODS: The data of three groups of patients (100 eyes) were analyzed retrospectively (1980-1982; 1987-1990; 1991-1993). Three different techniques of cataract surgery were used. Included in the prospective study were the data for 285 eyes, which underwent phacoemulsification, self-sealing incision and controlled induction of astigmatism. RESULTS: In the time period retrospectively investigated, we found that because of the advancements in operation methods, there was a reduction in the amount of surgically induced astigmatism. From 1980 to 1995 there was a clear increase in the number of patients with early low-grade postoperative astigmatism < 1 D (1980-1982: 6%, 1987-1990: 19%, 1991-1993: 64%, 1994-1995: 84%). There was an improvement in postoperative vision (with correction > 0.5) of 16% in 1980-1982 to 45% from 1987 to 1990, 58% from 1991 to 1993, and to 76% in 1994-1995. CONCLUSIONS: Surgical induced a stigmatism, which was considered to be a sign of unwanted increased postoperative astigmatism, was reduced from 1980 to 1993. Through controlled induction of astigmatism it was possible to compensate for preoperative astigmatism in the prospective group. Improved surgical techniques led to improvements in early postoperative visual acuity.
BACKGROUND: The refractive outcome of thermokeratoplasty for astigmatism correction depends upon the optical zone diameter (OZD) and coagulation angle (CA; distance between two coagulation spots around the flat meridian). METHODS: Astigmatism was induced in 36 spherical human eye-bank eyes (Ho:YAG laser, 15 Hz, 20 mJ/pulse, 25 pulses per coagulation spot) with different OZDs and CAs. Thirty eyes received free-hand laser application (marked positions). Six eyes were treated using a suction mask, providing a constant OZD of 8.1 mm and an angle of 22.5 degrees between the laser spots. To compare the results, silicone replicas of the eyes were made pre- and postoperatively and analyzed by video-topometery. RESULTS: With an average decrease of 4 D/mm the refractive change is inversely linear to the OZD. Changes of the CA showed significant variations between 22.5 degrees and 45 degrees, only. Mask guidance leads to the same amount of average refractive change. The deviation is +/- 3.4 D for the freehand application but only +/- 0.8 D for mask guidance. CONCLUSION: The data obtained in this in vitro study are transferred to a treatment nomogram describing the immediate postoperative refractive change, not identical with the final refraction. The results of the study are limited by the fact that astigmatism was induced in spherical corneas, rather than correcting preexisting ones.
PURPOSE: To improve the technique of deep lamellar keratoplasty. METHODS: For the recipient eye, a divide-and-conquer technique was applied to deep lamellar keratoplasty. After trephinization, the recipient cornea within the trephine was divided into four quadrants to facilitate lamellar dissection at approximately 70% depth. This procedure of division was continued until the Descemet membrane was exposed in the central area. The corneal graft was placed with an adjusted single running suture. Seventeen eyes were treated with this technique. RESULTS: In 17 eyes of 15 patients, the mean visual acuity 6 months or more after deep lamellar keratoplasty was 20/52 with eyeglass correction and 20/80 without eyeglass correction. At 6 months or more after deep lamellar keratoplasty, the mean +/- SD keratometric astigmatism in 17 eyes was 3.2 +/- 2.3 diopters. CONCLUSION: This technique facilitates deep lamellar keratoplasty and prevents high or excessive astigmatism after surgery.