PubMed Health⌕ Search

Biomedical subjects

M W Belin

Publications and source records attributed to M W Belin.

17 recordsLinked to original sources
PubMed1996

Evaluating data acquisition and smoothing functions of currently available videokeratoscopes.

PURPOSE: To compare the accuracy of computerized videokeratography systems using identical, calibrated test objects. SETTING: Lions Eye Institute, Albany, New York. METHODS: We evaluated the accuracy and smoothing of raw data acquisition (axial solution) of seven commercially available videokeratoscopes: Alcon EyeMap, Computed Anatomy TMS, EyeSys CAS, Humphrey MasterVue, Topcon CM-1000, Optikon Keratron, and TechnoMed C-Scan. We used six calibrated test objects to simulate clinical settings: spherical, spherocylindrical, simulated myopic ablation, hyperopic ablation, and a simulated central island. RESULTS: None of the systems accurately imaged all objects. Although all systems imaged spherical objects with reasonable accuracy, errors greater than 4.0 diopters (D) frequently occurred in the central 6.0 mm optical zone (maximum error 10.0 D) Sources of error included excessive raw data smoothing, inability to read large transitions, loss of accuracy in the periphery, and poor central coverage. CONCLUSION: The clinician should be aware of the potential limitations of corneal topography when making clinical decisions.

Cornea↗
PubMed1995

PAR Corneal Topography System (PAR CTS): the clinical application of close-range photogrammetry.

The PAR Corneal Topography System (CTS) is a computer-driven corneal imaging system which uses close-range photogrammetry (rasterphotogrammetry) to measure and produce a topographic map of the corneal surface. The PAR CTS makes direct point-by-point measurements of surface elevation using a stereo-triangulation technique. The CTS uses a grid pattern composed of horizontal and vertical lines spaced about 0.2 mm (200 microns) apart. Each grid intersection comprises a surface feature which can be located in multiple images and used to generate an (x,y,z) coordinate. Unlike placido disc-based videokeratoscopes, the PAR CTS requires neither a smooth reflective surface nor precise spatial alignment for accurate imaging. In addition to surface elevation, the PAR CTS computes axial and tangential curvatures and refractive power. Difference maps are available in all curvatures, refractive power, and in absolute elevation.

Cornea↗
PubMed1993

Accuracy of the PAR corneal topography system with spatial misalignment.

The PAR Corneal Topography System is a computerized corneal imaging system which uses close-range raster photogrammetry to measure and produce a topographic map of the corneal surface. Raster photogrammetry is a standard method of extracting object information by projecting a known pattern onto an object and recording the distortion when viewed from an oblique angle. Unlike placido disc based videokeratoscopes, the PAR system requires neither a smooth reflective surface nor precise spatial alignment for accurate imaging. We studied both the accuracy of the system with purposeful misalignment (defocusing) of the test object and determined the ability to image freshly deepithelialized, keratectomized, and photoablated corneas. The PAR system was both accurate and reproducible in imaging calibrated spheres within a defined zone in space. Whole cadaver eyes were imaged both before and immediately after removal of the epithelium, lamellar keratectomy, and laser photoablation. The system demonstrated the ability to image irregular, deepithelialized, and keratectomized corneas. The ability to maintain accuracy without precise alignment and the facility to image freshly deepithelialized and keratectomized corneas may make the system suitable for intraoperative refractive monitoring.

Cornea↗
PubMed1993

Intraoperative raster photogrammetry--the PAR Corneal Topography System.

The PAR Corneal Topography System (CTS) is a computer-driven corneal imaging system that uses close-range raster photogrammetry to measure and produce a topographic map of the corneal surface. The CTS determines distortion in a projected two-dimensional grid. Unlike Placido-disc-based videokeratoscopes, the PAR CTS produces a true topographic map (elevation map) and requires neither a smooth reflective surface nor precise spatial alignment for accurate imaging. Because the system uses two noncoaxial optical paths, it can be integrated into other optical devices. A modified CTS was integrated into an experimental erbium: YAG photoablative laser. The CTS successfully imaged corneas before, after, and during laser photoablation. Its ability to image nonreflective surfaces and to be integrated into other optical systems may make it suitable for intraoperative refractive monitoring.

Animals↗
PubMed1990

Update on topical cyclosporin A. Background, immunology, and pharmacology.

Systemic cyclosporin A (CsA) is currently being used for immunosuppression in solid organ transplantation. Its unique mechanism of action and low myelotoxicity have vastly improved the prognosis for patient survival. A reversible and irreversible nephrotoxicity has complicated its use. CsA works via the inhibition of both lymphokine release and subsequent activation of cytotoxic T cells. The corneal allograft model presents several unique features that make it amenable to local immunosuppressant therapy. Following topical application, CsA corneal levels have been obtained above the experimentally determined levels necessary for local immunosuppression. CsA represents one of a new class of specific, potent immunomodulators, which may improve the prognosis for patients at high risk for allograft rejection.

Administration, Topical↗
PubMed1989

Topical cyclosporine in high-risk corneal transplants.

Cyclosporine (cyclosporin A, CsA) is a selective T-cell immunosuppressant that works primarily through inhibition of both antigen presentation and lymphokine production. It has dramatically improved the prognosis for solid organ transplantation. Significant nephrotoxicity has been associated with its systemic use. Topical CsA 2% was used in 11 high-risk corneal transplant patients (8 men; 3 women; average age, 44 years). Ten (91%) of 11 corneas remained clear at an average follow-up of 16 months (range, 6-24 months). All patients had transient epithelial keratitis. Systemic whole blood levels of CsA measured by high-performance liquid chromatography (HPLC) ranged from 14 to 64 ng/ml. All previous reports on the use of topical CsA in high-risk corneal transplant patients have not detected systemic CsA levels.

Administration, Topical↗
PubMed1989

Unilateral graft rejection after bilateral antigenically identical corneal transplantation.

A unique case of unilateral graft rejection after bilateral antigenically identical corneal transplantation is described. The local risk factors (corneal vascularity and elevated intraocular pressure) were present to a greater extent in the nonrejected eye. The influence of other factors on the corneal microenvironment and their relationship to graft/host interactions is discussed.

Age Factors↗
PubMed1988

Keratoconus. Evaluation of recent trends in the surgical and nonsurgical correction of keratoconus.

Recent focus on the optical correction for "contact lens failure" keratoconus patients has been in the use of epikeratoplasty as an alternative to penetrating keratoplasty. In a 2-year retrospective review of keratoconus patients, 33 were referred as "contact lens failures" and as such might be considered candidates for surgical intervention. Of these, 29 patients (average keratometry, 50.4; range, 43-73) were successfully refitted with contact lenses. All patients obtained wearing times of 12 hours and achieved a visual acuity of 20/40 or better, with 85% realizing 20/30 or better. The data suggest that with concerted effort most keratoconus patients may be successfully refitted despite initial contact lens failure.

Adolescent↗
PubMed1988

Corneal ulcers in house staff: are risk factors identifiable?

Thirty-six incoming house officers and 20 incoming third-year medical students had conjunctival cultures taken before and after hospital exposure. The groups were divided evenly between contact-lens and noncontact-lens wearers. A decrease in incidence of positive conjunctival cultures was observed after hospital exposure. Within this group, a lower incidence of positive cultures was observed in contact-lens wearers compared with noncontact-lens wearers. The clinical records of corneal ulcer patients during a three-year period from October 1982 through October 1985 were also reviewed. Significant associated risk factors were identified, the largest of which was contact-lens wear.

Adolescent↗
PubMed1984

Orbital dacryops.

Two patients presented with an enlarging orbital mass that proved to be simple dacryops, a condition in which a cyst arises in the palpebral lobe of the lacrimal gland. The cyst in one patient was lined by one to two layers of relatively flat epithelial cells favoring a lacrimal gland ductal origin. In the second patient, the cyst was lined by a nonkeratinized stratified squamous epithelium with numerous goblet cells consistent with a conjunctival origin.

Adult↗
PubMed1981

Secondary syphilitic uveitis.

A patient with secondary syphilis had positive serum and cerebrospinal fluid findings. Fluorescent-antibody darkfield testing demonstrated spirochetes (Treponema pallidum) in the aqueous. There were clinical signs of secondary syphilis, including palmar skin lesions and frontal balding, and bilateral nasal altitudinal visual field loss. The discrete, waxy, yellow-white retinal lesions became increasingly pigmented and later migrated anteriorly into the vitreous chamber. The patient was treated with large amounts of penicillin (total dosage, 440 million units) and probenecid. Visual acuity improved to R.E. : 6/9 (20/30) and L.E.: 6/12 (20/40) and the inflammatory reaction disappeared. A second aqueous tap eight weeks after therapy ended showed no spirochetes by fluorescent-antibody testing.

Aqueous Humor↗
PubMedDate not supplied

Keratoconus and related noninflammatory corneal thinning disorders.

Keratoconus and other noninflammatory corneal thinning disorders (keratoglobus, pellucid marginal degeneration and posterior keratoconus) are characterized by progressive corneal thinning, protrusion and scarring; the result is distorted and decreased vision. The etiology and pathogenesis of these disorders are unknown but may be associated with a variety of factors, including contact lens wear, eye rubbing, Down's syndrome, atopic disease, connective tissue disease, tapetoretinal degeneration and inheritance. Recent advances in techniques for biochemical and pathological investigation are now allowing further exploration in these areas. Early diagnosis is aided by the finding of irregular corneal astigmatism with inferior corneal steepening. Treatment ranges from simple spectacle correction to keratoplasty. In this review, the past and present literature on corneal thinning disorders is reviewed and practical approaches to diagnosis and management are outlined.

Collagen↗
PubMedDate not supplied

The PAR Technology Corneal Topography System.

BACKGROUND: Computer-assisted videokeratography has emerged as a useful clinical and research tool. All of the currently available commercial units utilize a modified placido disk image and require a smooth reflective surface. The PAR Technology Corneal Topography System (PAR CTS) is a prototype of a new computer-assisted corneal imaging device. The system produces a true topographic map (elevation map) by analyzing a projected grid on the corneal surface, as opposed to a placido disk reflection, and utilizes the technique of raster photogrammetry to define elevation points on the corneal surface. Because the system defines elevation points, not curvature, mathematical modeling is easily accomplished. Current software displays include a true topographic map, a spherical subtraction map in both relative and absolute scales, and a meridian analysis that is adapted to display refractive photoablative surgery. METHODS: We evaluated the accuracy of this device by analyzing three calibrated test spheres (55.76, 42.21, and 33.55 diopters). The test spheres were steel balls coated with a thin white silicone polyester coating that was necessary for grid projection. The test spheres were measured by a Taylor-Hobson contact profilometer possessing submicron accuracy. To determine the reproducibility of the system, three investigators measured three noncalibrated balls (20 mm, 18 mm, and 12 mm). The optical system was purposely decentered and refocused after each reading. RESULTS: Utilizing the CTS custom optics, system accuracy at the 8-millimeter test area was 0.03 (SD 0.03), 0.00, (SD 0.02), and 0.07 (SD 0.01) D respectively. Smaller diameter test areas resulted in a predicted loss of accuracy. Maximum intraobserver variability was 0.09, 0.06, and 0.11 D respectively, and maximum interobserver variability measured 0.18, 0.12, and 0.16 D. CONCLUSIONS: These data demonstrate that the PAR CTS is both highly accurate and reproducible in determining topography of spheres that approximate the curvature of the human cornea.

Algorithms↗
PubMedDate not supplied

Contact lenses in the visual correction of keratoconus.

A two and one-half year (April 1985-October 1987) retrospective review of all newly referred keratoconus patients was performed to determine the treatment regimen of previously diagnosed "contact lens failures." The records of 48 patients (average age 32 +/- 9.0 years; 24 males, 24 females) were reviewed. Thirty-nine patients had been diagnosed as "contact lens failures" and referred for surgical intervention. Of these 39 patients, seven eyes were excluded from evaluation (four with prior grafts, two cases of unilateral keratoconus, and one with a dense central scar). Of the remaining 71 eyes, 57 (80%) (average keratometry 50.7 +/- 5.1 D, range 43-73) were successfully refit with contact lenses. All obtained a daily wearing time of 12 hours or more and a visual acuity of 20/40 or better--with 87% realizing 20/30 or better. The data suggest that the vast majority of keratoconus patients previously thought to be contact lens intolerant can be successfully refit and achieve excellent visual acuity and prolonged wearing times.

Astigmatism↗