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At least 55 records · Page 3Linked to original sources
PubMedDate not supplied

Clinical importance of accurate refractor vertex distance measurements prior to refractive surgery.

PURPOSE: To determine directly measured vertex distances in a consecutive series of patients refracted at a refractor and to examine the clinical importance of such a measurements for improving refractive surgical results. METHODS: Vertex distance measurements were obtained in 189 consecutive patients by using a new device capable of taking direct and accurate measurements behind a refractor. Eyelid thickness was measured with an industrial caliper in five patients. RESULTS: The average true vertex distance was 20.4 mm with a range of 10 to 34 mm. Eyelid thickness was 3 mm in all five patients. CONCLUSIONS: Precise measurement of true refractor vertex distance is important for accuracy of refractive surgical procedures. The practice of assuming an average vertex distance of 12 to 14 mm for all refractive patients underestimates the vertex distance in many patients refracted at the refractor, resulting in overcorrecting minus and undercorrecting plus refractions.

Eyeglasses↗
PubMedDate not supplied

Current trends in cataract and refractive surgery in Japan: 1999 survey.

PURPOSE: The eighth annual survey was carried out by mail in February 2000 to investigate the current trends in cataract and refractive surgery in Japan. RESPONDENTS: Questionnaires were sent to 930 ophthalmologist members of the Japanese Society of Cataract and Refractive Surgery. Data received from 457 (49.1%) of the recipients were cross-analyzed and compared with those from the previous surveys. RESULTS: In cataract surgery, 17% of respondents were doing 51 or more cases per month, 94% preferred phacoemulsification, 58% employed the self-sealing wound closure technique, and 26% used topical anesthesia for phacoemulsification. In refractive surgery, excimer laser surgery and astigmatic keratotomy attracted notably high interest, while less attention was directed toward radial keratotomy and intrastromal corneal ring. Laser in situ keratomileusis, photorefractive keratectomy, phakic intraocular lens, intrastromal corneal ring, and radial keratotomy were judged to be useful refractive surgical procedures by 69.0%, 40.0%, 24.6%, 14.2%, and 8.0% of the respondents, respectively. CONCLUSION: There are trends toward more surgical procedures performed by a surgeon, shorter period of hospitalization, and increasing preference for small incision cataract surgery. Refractive surgery is not yet widely performed, but laser in situ keratomileusis is viewed as the most promising procedure.

Adult↗
PubMedDate not supplied

On the computer-aided and optimal design of keratorefractive surgery.

BACKGROUND: Several recent papers have discussed the use of engineering-based computer methods for the analysis of keratorefractive surgical procedures. What has been lacking is a broader view of the role of engineering analysis in keratorefractive surgery. This article demonstrates how these various analysis methods can be coupled to provide a comprehensive methodology for the design of refractive surgical procedures. METHODS: A structural model of the eye, based on a linearly elastic, transversely isotropic finite element formulation is coupled to a full-eye optical model. The optical errors due to refractive keratotomy are estimated by ray tracing through the optical model and measuring the position of the resulting focal plane relative to the retina. Computer-based optimization methods are employed to determine the surgical parameters necessary to correct myopia for a given set of surgical design goals. RESULTS: Results based on a hypothetical eye demonstrate agreement with clinical trends. Radial keratotomies are designed that eliminate refractive error while minimizing invasiveness in one case and maximizing the optical zone size in another. It is also shown that there is significant potential to customize this process on a patient-by-patient basis using clinically measured data. CONCLUSIONS: We present an overview of the research necessary to bring this approach to fruition. While only a first step, the methodology presented in this article has the potential to increase the predictability of keratorefractive surgery by substantially increasing both the quality and the quantity of the information available to the refractive surgeon preoperatively.

Biomechanical Phenomena↗
PubMedDate not supplied

Preoperative simulation of outcomes using adaptive optics.

Measurements of the wavefront of light reflected from the retina of the human eye can be used to determine optical aberrations of the human eye for large pupils. An instrument based on the Hartmann-Shack principle was developed. The wavefront is refracted by a microlens array and detected by a CCD camera. In first clinical studies human volunteer eyes and preoperative and postoperative refractive surgical patient eyes have been examined. An adaptive optical closed loop system has been devised for preoperative simulation of refractive outcomes of aberration free refractive surgical procedures.

Adaptation, Ocular↗
PubMed2000

Role of apoptosis in wound healing in the cornea.

Anterior keratocytes undergo apoptosis in response to epithelial injury. This likely represents mechanical activation of systems that vigilantly monitor the corneal epithelium for injury produced by pathogenic viruses. Keratocyte apoptosis is the first change noted after procedures in which the epithelium is injured and may be an initiator of the subsequent wound healing cascade. The working hypothesis is that inhibition of keratocyte apoptosis will limit the subsequent wound healing response. The keratocyte apoptosis response varies with the specific type of epithelial injury induced by a particular refractive surgical procedure, such as photorefractive keratectomy or laser in situ keratomileusis. Continuing efforts aim to identify pharmacological agents that effectively inhibit keratocyte apoptosis without promoting keratocyte necrosis.

Apoptosis↗
PubMedDate not supplied

Current applications of the Corneal Modeling System.

The ability of the Corneal Modeling System to incorporate curvature and thickness data into a single mathematical construct of the cornea is an important achievement. As experience with this and similar instruments is gained, a number of important issues in corneal topography can be addressed. Snellen visual acuity, refraction, and keratometric changes do not fully reveal the effects of refractive surgical procedures. Detailed analysis of corneal topography will prove necessary to understanding the quality of vision resulting from surgery, as it can explain the disparity between uncorrected visual acuity and residual refractive error after radial keratotomy. Computer-assisted topographic measurement devices will undoubtedly play a particularly important role in the design and evaluation of current and future refractive procedures. Similarly, mild topographic changes (eg, subclinical keratoconus) can be detected that are not apparent with refraction, biomicroscopy, or keratometry. The author reviews his personal experience with one instrument.

Astigmatism↗
PubMed2006

Laser eye surgery for refractive errors.

Several laser and non-laser refractive surgical procedures have been used to modify the shape of the cornea and correct myopia, hyperopia, astigmatism, and presbyopia. Introduction of the excimer laser to reshape the cornea has resulted in remarkable developments in the correction of these refractive errors. Combined with other advanced ophthalmological instruments, laser refractive eye surgery has resulted in a substantial rise in the safety, efficacy, and predictability of surgical outcomes. Despite these advances, certain limitations and complications persist. In this review, we describe the history, preoperative assessment, surgical techniques, outcomes, and complications of laser refractive surgery.

Astigmatism↗