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Biomedical subjects

K L Cohen

Publications and source records attributed to K L Cohen.

At least 19 recordsLinked to original sources
PubMed1995

Assessment of radial aspheres by the Arc-step algorithm as implemented by the Keratron keratoscope.

PURPOSE: To assess the accuracy with which the Keratron (Optikon 2000, Rome, Italy) measured rotationally symmetric, radially aspheric test surfaces according to an arc-step profile reconstruction algorithm and to discriminate between error caused by the algorithm and error from other sources. METHODS: Height, local power, and axial power calculated from radius of curvature centered on the instrument's axis were reported by the Keratron for four surfaces that had radial profiles similar to normal corneas. The Keratron profile reconstruction algorithm was simulated by using ray tracing. Keratron measurements were compared with the surfaces' formulas and the ray-traced simulations. RESULTS: The heights reported by the Keratron were within 0.25 microns from the four surfaces at less than 3 mm from the keratoscope axis and generally within 1 micron of the height calculated from the surfaces' formulas. The Keratron's axial powers were within +/- 0.1 diopter of the simulation of the axial solution between 1 and 4 mm of the axis but were greater central to 1 mm and peripheral to 4 mm. The Keratron's local powers were within -0.25 diopters at less than 4 mm from the axis and peripherally were between +1.75 diopters and -0.75 diopter of power calculated from the surface's instantaneous radii of curvature. Height error because of the arc-step algorithm was less than -0.2 micron. CONCLUSIONS: The Keratron's arc-step profile reconstruction algorithm contributed to its ability to measure height more accurately than keratoscopes that use spherically biased algorithms and provided measurement of local power.

Algorithms↗
PubMed1995

Assessment of the power and height of radial aspheres reported by a computer-assisted keratoscope.

PURPOSE: The two purposes of this study were (a) to assess the accuracy with which a keratoscope, the Topographic Modeling System (TMS-1), calculated the heights and powers of rotationally symmetric, radially aspheric test surfaces and (b) to determine whether the TMS-1 used an axial solution for radius of curvature to determine the power of a sphere that would produce the same semichord as would the test surface on a keratograph. METHODS: The TMS-1 heights and powers were studied for four test surfaces that had radial profiles similar to those of normal corneas. The powers of the surfaces were calculated from the local radius of curvature derived from the surfaces' manufacturing formulas. The heights and powers that would result from an axial solution were calculated in a TMS-1 simulator. TMS-1 data were compared with data from the surfaces' formulas and with data from the simulation. RESULTS: The TMS-1 data were almost identical to the heights and powers calculated from the simulated axial solution. The TMS-1 data were similar to the heights and powers calculated from the mathematical formulas from the apex to 2 mm from the apex but differed by up to 85 microns of height and 10 diopters of power in the periphery. CONCLUSIONS: The TMS-1 appeared to use the axial solution that does not calculate power from local radius of curvature. Clinicians should use caution when inferring corneal shape from power maps based on an axial solution, especially outside the central 2-mm radius of a normal cornea, because such power does not depict corneal curvature.

Cornea↗
PubMed1995

Sulfur hexafluoride gas in the repair of Descemet's membrane detachment.

We report a case of successful attachment of a detached Descemet's membrane using an intracameral injection of sulfur hexafluoride (SF6). Three months after cataract surgery, a 77-year-old woman was seen for almost total detachment of Descemet's membrane. Surgical repair with a through-and-through mattress suture was unsuccessful. One month later, Descemet's membrane was apposed by injecting 0.25 ml of 100% SF6 into the anterior chamber. Six months later the central corneal thickness measured 0.48 mm, and Descemet's membrane was attached. We believe this to be the first reported case of successful attachment of Descemet's membrane using an intracameral injection of 100% SF6.

Aged↗
PubMed1992

A new, band-shaped and whorled microcystic dystrophy of the corneal epithelium.

Five family members and three unrelated patients (four women, four men, 23 to 71 years old) had a dystrophy of the corneal epithelium. Direct slit-lamp examination showed bilateral or unilateral, gray, band-shaped, and feathery opacities that sometimes appeared in whorled patterns. Retroillumination showed intraepithelial, densely crowded, clear microcysts. Light and electron microscopy disclosed diffuse vacuolization of the cytoplasm of epithelial cells in the affected area. Visual acuity was so reduced in three patients that abrasion of the corneal epithelium was performed. The corneal abnormalities recurred within months, with the same reduction in visual acuity as before. The corneal opacities were progressive in two patients but diminished noticeably in another after he began using a hard contact lens. We found no other ophthalmic irregularities or associated systemic abnormalities and no indication of drug-induced keratopathy.

Adult↗
PubMed1990

Lack of effect of clonidine and pentoxifylline in short-term therapy of diabetic peripheral neuropathy.

The goal of this study was to confirm or rule out anecdotal reports of beneficial effects of clonidine and pentoxifylline in the treatment of painful diabetic peripheral neuropathy. Clonidine was administered to 16 subjects at two dosage levels (0.1 and 0.2 mg/day) and was compared to placebo in a crossover design, with each phase lasting 4 wk. Either pentoxifylline (400 mg 3 times/day) or placebo was given to 21 subjects in a 12-wk trial. Discomfort was characterized and rated with a subjective pain score (range 0-20). There was a significant decrease in pain score from baseline with both active drugs (P less than 0.05), but this was no better than the response to placebo (P less than 0.30 for clonidine and P less than 0.95 for pentoxifylline). This study does not demonstrate a short-term benefit of either clonidine or pentoxifylline in the treatment of peripheral neuropathy.

Clonidine↗
PubMed1990

Cat endothelial morphology after corneal transplant.

The cat has been suggested as a superior model to evaluate penetrating keratoplasty and corneal endothelial damage and repair. Morphologic change is felt to be a sensitive indicator of endothelial stress response. We documented corneal thickness and endothelial morphometric parameters of eight cats before and after homograft penetrating keratoplasty using an Eisner contact glass. One-hundred-cell samples from preoperative and 6.18 +/- 0.57 weeks and 9.25 +/- 0.84 months (means +/- standard errors of the means) postoperative photomicrographs were computer analyzed. Cell density (cells/mm2), coefficient of variation of cell area, percent hexagonal cells, and mean figure coefficient were measured. Values are given as means +/- standard errors of the means. Preoperative coefficient of variation for area, 19.1 +/- 0.4, was significantly greater (22.0 +/- 1.0) six weeks after surgery. At nine months, cell density (1487 +/- 114) and percent hexagonal cells (59.6 +/- 2.1) were significantly less than six week values (cell density = 2053 +/- 201, percent hexagonal cells = 68.1 +/- 1.5) and preoperative values (cell density = 2395 +/- 94, percent hexagonal cells = 69.3 +/- 1.1). Thus there is evidence of polymegethism six weeks after surgery and persistent decreased cell density and pleomorphism nine months after surgery.

Analysis of Variance↗
PubMed1989

Intraocular lens explantation with and without penetrating keratoplasty.

We reviewed the records of 33 consecutive patients who had undergone intraocular lens (IOL) explantations for IOL-related complications. Results from 19 eyes that underwent penetrating keratoplasty at the time of explantation (pk eyes) were compared with the results from 14 eyes that underwent only IOL explantation (npk eyes). Uveitis was the most common indication for explantation in the npk eyes; frank bullous keratopathy was the most common in the pk eyes. Fifteen of the IOLs explanted from the pk eyes were anterior chamber IOLs, 13 of which were the semiflexible, closed-loop type. Ten of the npk eyes had anterior chamber IOLs explanted, six of which also were the semiflexible, closed-loop type. Visual acuities in the pk group were significantly worse than they were in the npk group, both before and after explantation. Based on this review, we conclude that if anterior chamber and iris-supported IOL complications occur and medical therapy fails, IOL explantation prior to the need for penetrating keratoplasty may improve visual acuity.

Aged↗
PubMed1989

Postoperative zygomycetes endophthalmitis.

Fungal endophthalmitis is an uncommon complication of intraocular surgery. We report, to our knowledge, the first case of a postoperative Zygomycetes endophthalmitis that occurred after uncomplicated phacoemulsification and the insertion of a posterior chamber intraocular lens. Diagnosis, in the presence of negative aqueous and vitreous cultures, was confirmed by immunofluorescence staining of an anterior chamber inflammatory mass. Successful treatment of the eye with 20 micrograms of intraocular amphotericin B (Fungizone) may have been made possible in part by the fact that the posterior capsule remained intact, keeping the eye bicompartmental.

Amphotericin B↗
PubMed1988

Pneumocystis carinii thyroiditis.

A 38-year-old black man with a history of acquired immunodeficiency syndrome associated with intravenous drug abuse presented with two weeks of left-sided neck swelling. Results of thyroid function tests were within normal limits. Thyroid scan demonstrated nonvisualization of the left lobe. Fine-needle aspiration of the thyroid revealed the presence of Pneumocystis carinii organisms in the thyroid tissue. Although chest radiography and computerized tomography of the chest detected several nodules and cavitary lesions, the results of bronchoalveolar lavage and transbronchial biopsy were negative for P. carinii. The patient showed a response to treatment with trimethoprim/sulfamethoxazole. Thyroidal involvement with P. carinii has previously been documented only in the setting of overwhelming, fatal pulmonary infection. The current case expands the clinical spectrum of extrapulmonary pneumocystosis and documents its successful treatment.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Efficacy and safety of nonsteroidal anti-inflammatory drugs in the therapy of diabetic neuropathy.

A study comparing ibuprofen (600 mg four times a day) vs sulindac (200 mg twice a day), and a placebo in the treatment of painful diabetic peripheral neuropathy was conducted in 18 male outpatients. Discomfort was characterized and rated with a subjective neuropathy score. The response to both ibuprofen and sulindac was better than it was to placebo in the entire group. There were no changes in glucose control or renal function. Further studies are necessary to evaluate the significance of aldose reductase-inhibitor properties of nonsteroidal anti-inflammatory drugs and to select the "best" one of these drugs for the treatment of diabetic neuropathy.

Aldehyde Reductase↗
PubMed1986

Effect of trephine tilt on corneal button dimensions.

Wound disparity, mismatch between the size and shape of the donor corneal button and its wound, probably determines the direction and amount of postkeratoplasty astigmatism. Tilting a hand-held trephine is thought to contribute to an oval wound and to wound disparity. We examined the contribution of trephine tilt to wound size and shape. Eyebank eyes were hand trephined at 0, 5, 10, 15, 20, and 25 degrees of tilt. The button endothelial edges were analyzed by the photogrammetric index method. All index values were significantly different from those for a theoretically circular or symmetric button. Although the most oval buttons were at 20 and 25 degrees, buttons were similarly oval and asymmetric for trephine tilt from 0 to 15 degrees. Neither ovality nor asymmetry correlated with angle of tilt. Even when no attempt is made to tilt a hand-held trephine, oval and irregularly shaped wounds may result.

Corneal Transplantation↗
PubMed1985

Orbital cellulitis secondary to dacryocystitis following blepharoplasty.

The authors report what they believe to be the first case of a blepharoplasty procedure complicated by an acute postoperative dacryocystitis that precipitated orbital cellulitis. The patient had a preoperatively compromised nasolacrimal drainage system. Because acute dacryocystitis and resulting orbital cellulitis are potential postoperative complications of a blepharoplasty, blepharoplasty candidates should undergo preoperative evaluation of their nasolacrimal drainage systems.

Cellulitis↗
PubMed1984

Haemophilus influenzae corneal ulcer in a therapeutic contact lens wearer.

Haemophilus influenzae is an unusual corneal pathogen and an unusual cause of corneal ulcers in Western society. In previous reports corneal complications from H. influenzae have been secondary to a conjunctivitis. The first case of a primary H. influenzae corneal ulcer as a complication of therapeutic contact lens wear is presented. Since other uncommon bacteria have been reported as causes of contact lens related corneal ulcers, the bacteriology of contact lens related corneal ulcers is reviewed. Ophthalmologists need to be aware that H. influenzae infections in adults are becoming more frequent.

Aged↗