Theo Seiler

Myopic Photorefractive Keratectomy with the Excimer Laser: One-year Follow-up

To evaluate the efficacy, predictability, and stability of myopic photorefractive keratectomy (PRK), the authors completed a 1-year follow-up study on a consecutive series of 26 sighted eyes undergoing this procedure. The results of this follow-up are presented. In addition, side effects and complications in another 255 sighted eyes with a follow-up of 3 months to 1 year are reported to judge the safety of the procedure. Twenty-four of 26 eyes (92%) were within +/- 1.0 diopter (D) of the intended final refraction (baseline, -1.4 to -9.25 D). Fifty-eight percent of the eyes were stable within +/- 0.25 D between 6 and 12 months. One year after surgery, none of the patients lost or gained more than one line of best corrected (spectacle) visual acuity. Uncorrected visual acuity improved to 20/40 or better in 96% of the eyes and to 20/20 or better in 48% of the eyes (not including the eyes that were intentionally undercorrected). However, visual acuity with glare decreased from 20/27 preoperatively to 20/31 after 1 year. Scarring occurred in 2.8% of the treated corneas. Risk factors for scarring include noncompliance with postoperative steroid medication, high myopic corrections, and high steroid responders (3.1%). Collagen vascular and other autoimmune diseases are a contraindication for PRK.

Complications of Myopic Photorefractive Keratectomy with the Excimer Laser

BACKGROUNDnAlthough many thousands of myopic eyes have been operated on by excimer laser photorefractive keratectomy (PRK), the safety of this procedure is still a concern.nnnMETHODSnThe results and complications of PRK have been studied for up to 2 years in a prospective trial including 193 eyes in 146 patients. In addition, specific complications of PRK are described that occurred in patients outside the prospective study.nnnRESULTSnTwo eyes (1.2%) lost two lines of best-spectacle-corrected visual acuity 1 year after surgery, but at 2 years one of these eyes had regained baseline visual acuity. At 1 year, 12 eyes (7.1%) had lost more than two lines of visual acuity under glare conditions. Significant complications such as manifest scarring, overcorrection, undercorrection, and continued regression are dependent on attempted refraction. Eccentric ablations with resultant induced astigmatism are rare and the incidence is dependent on the experience of the surgeon. Progressive hyperopia did not occur.nnnCONCLUSIONnExcept in corrections greater than 6 diopters, complications after PRK are rare. Assuming an appropriate patient selection, PRK may be considered a relatively safe procedure compared with other refractive procedures.

Effective spherical aberration of the cornea as a quantitative descriptor in corneal topography

ABSTRACT Following excimer laser photorefractive keratectomy and other refractive surgical procedures, complaints of halos, glare, and monocular diplopia are common. These procedures increase the asphericity of the cornea, which may cause the optical distortions. We used ray tracing techniques to estimate the longitudinal monochromatic aberration of the cornea from the measured corneal topography (effective spherical aberration) in 15 normal eyes with varying degrees of astigmatism and in ten eyes after photorefractive keratectomy. Best spherical corrected visual acuity in the astigmatic eyes was highly correlated with effective spherical aberration (r = ‐0.9527, P < .001). In the eyes that had photorefractive keratectomy, the effective spherical aberration was highly correlated with measured glare visual acuity (r = 0.875, P < .002). These results suggest that effective spherical aberration is a valuable topographic measure that provides information about the optical performance of aspheric corneas.

Application of the holmium:YAG laser for refractive surgery III

We report on two clinical trials, one involving 10 patients in the United States and the other in Berlin, Germany with 15 patients, all treated for hyperopia with a new laser surgical procedure known as laser thermokeratoplasty (LTK). The procedure involves making a circular array of corneal coagulations using an Ho:YAG laser, fiber-optic handpiece, and contact focusing tip. The extent of steepening of central corneal curvature is controlled by the diameter of the treatment zone. The LTK procedure induces an immediate and significant reduction in hyperopic refractive error. Although the clinical investigations are at an early stage, results of the clinical trials indicate that the LTK procedure may prove to be a reliable means of effecting a permanent change in refraction in patients suffering from hyperopic refractive disorders.

Application of the holmium:YAG laser for refractive surgery: an update of clinical progress

We describe the results of a 30 patient Phase I clinical trial using the Laser Thermokeratoplasty (LTK) treatment for correction of hyperopic astigmatism. We report the results for 29 patients who have reached 2 months post-operative. The average pre-op cylinder was reduced from -3.06 Diopters (D) to -1.21 D. Average spherical equivalent (SE) refractive error was reduced from +2.28 to +1.34 D. Six patients have reached 4 months post-op; the average cylinder of these patients has been reduced from -1.92 to -0.79 D while the average SE has been reduced from +1.29 to +0.31 D. Although patients had varying degrees of astigmatism pre-op, all treatments were performed with identical parameters (intended to correct a small amount of astigmatism) to enable us to determine the effect of the procedure without the influence of other factors such as varying zone diameter or laser fluence. The predictability and stability of the LTK procedure are supported by a recent study of 20 patients treated in Germany by Seiler for low to moderate degrees (2 - 4 D) of hyperopia. After 6 months post-op, 16 of 20 patients are within +/- 1 D of the attempted correction. Longer-term follow-up will be necessary to determine the ultimate refractive stability of the LTK procedure.

Photorefractive keratectomy at 193 nm using an erodible mask

Clinical experience with more than ten thousand sighted eyes has demonstrated great promise for correcting myopia with photorefractive keratectomy (PRK). Previously reported techniques have incorporated computer-controlled irises, diaphragms, and apertures to regulate the desired distribution of 193 nm radiation onto the eye. This paper reports on an entirely new approach for performing PRK which utilizes an erodible mask to control the shape transfer process. Compared to the more traditional techniques, the erodible mask offers promise of correcting a broad range of refractive errors. In this paper the erodible mask and associated hardware are described in detail. We describe the shape transfer experiments used to predict the functional relationship between the desired refractive correction and the mask shape. We report on early clinical results from five patients with myopic astigmatism. We conclude that the early shape transfer experiments overestimated the spherical component of the correction by 1.25 diopters and underestimated the cylindrical component by approximately 0.85 diopters. The data suggest there may be biological effects which evoke different healing responses when myopic PRK corrections are performed with and without astigmatism. Clinical trials are proceeding with the mask shapes adjusted for these observations.

Photorefractive keratectomy (PRK) at 193 nm using an erodible mask: new developments and clinical progress

This paper reports on our progress using an erodible mask to perform photorefractive keratectomy (PRK) for the correction of myopic astigmatism. We describe modifications to the mask, the mask eye cup and the surgical microscope aimed at simplifying the procedure and improving the ergonomics of the hardware. We report the clinical results of the post-op exam for 20 patients who have undergone PRK for myopic astigmatism under a Phase IIA study. The results compare favorably with an earlier Phase IIA study for performing PRK with a computer-controlled iris. Most important, the clinical data show the absence of any significant corneal haze and no significant decrease in spectacle corrected visual acuity. Although more long term follow-up is needed, the preliminary results support the safety and effectiveness of using an erodible mask to perform PRK for myopic astigmatism.

Wirkung von Laserstrahlung auf Gewebe

In den vorangegangenen Kapiteln wurden physikalische und apparative Grundlagen der Lasertechnik fur deren Einsatz in der Medizin beschrieben. Der nun folgende Abschnitt thematisiert biologische und medizinische Wirkungen von Laserstrahlung auf Gewebe. Die Kenntnis der Mechanismen und Effekte einer Bestrahlung mit Lasern ist von fundamentaler Bedeutung fur verschiedene medizinische Disziplinen.

Eigenschaften verschiedener Lasertypen

In diesem Kapitel werden die wichtigsten Lasertypen, die in der Medizin Verwendung finden, mit ihren physikalischen Eigenschaften wie Wellenlange, Pulsform, Leistung und ihrem technischen Aufbau vorgestellt /2.1 – 2.10/. Je nach Art des optischen Mediums unterscheidet man Gas-, Festkorper-, Farbstoff- und Halbleiterlaser. Das Spektrum kommerziell vertriebener medizinischer Laser umfast den Wellenlangen-Bereich zwischen etwa 200 nm und 10 μm, es erstreckt sich vom Ultravioletten, Sichtbaren bis ins Infrarote. Tabelle 2.1 stellt die im Handel am starksten vertretenen Laser zusammen; die Mehrzahl von ihnen wird auch in der Biologie und Medizin zumindest in experimentellen Studien eingesetzt. Im klinischen Betrieb haben sich insbesondere folgende Typen durchgesetzt: CO2- Nd: YAG-, Ar-, He-Ne-, Metalldampf-, Farbstofflaser und die Laserdiode. Weitere Lasermodelle werden intensiv erprobt und in ihrer medizinischen Wirkung erforscht, z.B. Excimer-, Er:YAG-, CO-Laser u. a..

Lasergeräte für medizinische Anwendungen

In den Kapiteln 1 und 2 wurden die optischen Grundlagen und der prinzipielle Aufbau von Lasern beschrieben. Im folgenden soll speziell auf die Konstruktionsprinzipien und die Eigenschaften von Lasern fur verschiedene Bereiche der Medizin eingegangen werden. Ohne Zweifel ist der wichtigste Einsatzbereich die Ophthalmologie.