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Biomedical subjects

M G Doane

Publications and source records attributed to M G Doane.

At least 19 recordsLinked to original sources
PubMed2001

Keratoprosthesis: preoperative prognostic categories.

PURPOSE: Recent advances aimed at preventing and treating complications after keratoprosthesis surgery have improved prognosis, but it has been suspected that various preoperative diagnoses may carry substantially different postoperative outcomes. This article attempts to clarify the ranking of prognostic categories for patients undergoing keratoprosthesis surgery. METHODS: A retrospective review of the outcome in a recent series of 63 patient eyes operated at the Massachusetts Eye and Ear Infirmary between 1990 and 1997 and followed up for a minimum of 21 months. Anatomic retention of the device and the loss of vision caused by complications were recorded. The patients were divided into four categories according to preoperative cause. RESULTS: Anatomically, one keratoprosthesis extruded spontaneously. Another 10 were permanently removed because of complications. Of the 63 eyes, 10 never achieved a visual acuity of at least 20/200 vision because of preexisting retinal or optic nerve damage. The remaining 53 had a visual acuity of 20/200 to 20/20 as follows: Stevens-Johnson syndrome (n = 7), after 2 years: 33%, after 5 years: 0%; chemical burn (n = 17), after 2 years: 64%, after 5 years: 25%; ocular cicatricial pemphigoid (n = 20), after 2 years: 72%, after 5 years: 43%; graft failure in noncicatrizing conditions (dystrophies, degenerations, or bacterial or viral infections) when a repeat graft was expected to have a poor prognosis (n = 19), after 2 years: 83%, after 5 years: 68%. The difference in outcome between the Stevens-Johnson syndrome outcome group and the graft failure group or the ocular cicatricial pemphigoid group was statistically significant. In the group of 53 eyes, visual acuity was restored to 20/200 to 20/20 for a cumulative total of 138 years. CONCLUSION: Outcome of the keratoprosthesis surgery varied markedly with preoperative diagnosis. Most favorable was graft failures in non-cicatrizing conditions, whereas Stevens-Johnson syndrome was the worst. Ocular cicatricial pemphigoid and chemical burns occupied a middle ground. The difference between the groups seemed to correlate with the degree of past preoperative inflammation.

Adult↗
PubMed2000

Androgen influence on the meibomian gland.

PURPOSE: The hypothesis in the study was that androgens control meibomian gland function, regulate the quality and/or quantity of lipids produced by this tissue, and promote the formation of the tear film's lipid layer. To test this hypothesis, a study was conducted to determine whether androgen receptor protein exists in the epithelial cell nuclei of rat meibomian glands and, in addition, whether androgen deficiency and/or treatment influences the gross morphology, neutral lipid content, and fatty acid profile of the rabbit meibomian gland, as well as the appearance of the tear film lipid layer. METHODS: Rat lids were obtained and processed for immunohistochemistry. Meibomian glands from intact, androgen- and/or placebo-treated rabbits were analyzed by histology, and glandular lipids were evaluated by gas chromatography, high-performance liquid chromatography (HPLC), and mass spectrometry. The rabbit tear film lipid layer was assessed by interferometry. RESULTS: In the current study androgen receptor protein existed within acinar epithelial cell nuclei of rat meibomian glands; androgen deficiency was associated with alterations in the lipid content of the rabbit meibomian gland; 19-nortestosterone treatment modulated the fatty acid profile in the total and neutral lipid fractions of the rabbit meibomian gland; and androgens did not appear to influence the gross morphology of meibomian tissue or to exert a demonstrable effect on the rabbit tear film lipid layer. CONCLUSIONS: The findings show that the meibomian gland is an androgen target organ and that androgens influence the lipid profile within this tissue. However, the extent to which androgens regulate the production of these lipids and whether this action may impact tear film stability remain to be determined.

Androgens↗
PubMed1996

Fabrication of a keratoprosthesis.

For patients with opaque corneas that have a poor prognosis when using regular corneal transplants, a clear plastic "window" in the form of a keratoprosthesis may offer the only hope of usable vision. Various forms of such devices have been used for many years with varying degrees of success. The design, fabrication, and optical testing of two variations of a polymethylmethacrylate (PMMA) keratoprosthesis are described. Type 1 consists of a twin-plate collarbutton-style design that is used in eyes that have sufficient tear fluid production to maintain wetting of the anterior surface of the eye. Type 2 is of a similar design, with an added anterior cylinder that protrudes through a permanently closed eyelid, and is used in end-stage dry eyes.

Cornea↗
PubMed1994

Some factors influencing outcome after keratoprosthesis surgery.

Eleven patients with severe corneal disease have been operated with a collar-button-shaped keratoprosthesis and have been followed for 9-36 months. Two of the devices have been removed, but the remainder are securely in place. Six of the patients have benefitted substantially in terms of improved vision. The complications have been reviewed, and some factors for success have been identified. Thus, to keep the keratoprosthesis temporarily buried beneath tissue (conjunctiva or skin), application of collagenase-suppressing medication and reduction of evaporative damage to the wound around the device seem particularly important.

Biocompatible Materials↗
PubMed1992

Short-term, low-contrast visual acuity reduction associated with in vivo contact lens drying.

Hydrogel contact lens surfaces partially desiccate during extended interblink intervals, producing a microscopically rough and irregular surface that scatters light. Such light scattering could reduce retinal image contrast, elevating thresholds for target perception. To test this idea, we measured low (7%)-contrast visual acuity of subjects who wore: (1) hydrogel contact lenses, (2) rigid gas permeable (RGP) lenses, and (3) no contact lenses when the subjects blinked normally and when they suppressed blinking. Acuity thresholds were determined using computer-generated acuity stimuli and a staircase psychophysical procedure. Cessation of blinking resulted in small reductions in low-contrast acuity for subjects wearing RGP lenses (mean loss: 0.1 line) or no lenses (mean loss: 0.3 lines). Subjects wearing hydrogel lenses, however, generally exhibited substantial reduction of acuity (mean loss: 4.1 lines) when blinking was suppressed.

Adult↗
PubMed1990

Anterior segment fluorescein videoangiography with a scanning angiographic microscope.

The scanning laser ophthalmoscope can be modified to operate as a scanning laser biomicroscope for use in anterior segment fluorescein angiography. The substantial depth of focus, large field of view, co-axial illumination, low light levels, real-time television operation, and videorecording with immediate recall provide advantages not available with conventional photographic methods. Video techniques give a resolution slightly inferior to photography, but this is unlikely to be significant in clinical practice. A technique of traversing the entire anterior episcleral vasculature has been developed to give a comprehensive and reproducible angiographic record. Previous fluorescein studies suggesting the primary importance of retrograde (centrifugal) flow in the perforating anterior ciliary arteries were not supported; methodologic explanations are advanced. Several principles are proposed to improve techniques of anterior segment angiography.

Adult↗
PubMed1989

An instrument for in vivo tear film interferometry.

An instrument has been designed and constructed that facilitates the measurement of in vivo tear film topology, thickness, and wetting, using the principles of thin film interferometry. The use of this tear film interferometer (TFI) allows objective evaluation of the breakup characteristics of the tear film on contact lens surfaces and provides a means for examining the dynamic changes in thickness, thickness distribution, and wetting properties during sequential interblink periods. The effects of contact lens material, wetting solutions, and cleaning regimens can be compared objectively. The instrument is easy to use, no additives to the natural tear fluid are required.

Contact Lenses↗
PubMed1984

High-speed photographic evaluation of intraocular lens movements.

Iridodonesis and pseudophakodonesis were examined in detail with a high-speed camera capable of picture rates up to 500/sec. Tilting, or "wobble," of iris-supported intraocular lenses was extreme, with a tilt of nearly 24 degrees with respect to the visual axis of the globe being documented, even with a moderate speed of globe rotation. Oscillations of the lens continued for several cycles after the globe stopped its rotation. Such lenses can, in some instances, tilt sufficiently to contact the endothelial surface of the cornea. In the case of some anterior chamber intraocular lenses, the iridodonesis is sufficient to cause constant rubbing of the iris on the posterior surface of the lens and its haptics , suggesting that vault, finish, haptic configuration, and placement of the lens may be critical factors in anterior chamber intraocular lens design.

Cataract Extraction↗
PubMed1984

Turnover and drainage of tears.

The method by which the tear fluid exits from the region of the palpebral fissure has been actively contested for several centuries. By combining the observations of two independent investigators who reported their work nearly 70 years ago with current studies using contemporary techniques of high-speed photography, a compatible explanation of the tear drainage process can be presented.

Blinking↗
PubMed1981

Blinking and the mechanics of the lacrimal drainage system.

High-speed photography, using picture rates up to 500/sec, has confirmed many key aspects of the tear drainage process reported over the years by various investigators. The punctal openings are seen to elevate themselves from the lid margin at the start of the closing phase of the blink, allowing their forceful meeting and occlusion by the time the closing lid is halfway down. Completion of lid closure then compresses the canaliculi and lacrimal sac, forcing contained fluid through the drainage system. The elastic expansion of the channels during the opening phase of the blink forms a suction, holding the lid margins at the punctal region together as the lids open. During the latter part of this opening, the punctal areas are seen to "pop' apart suddenly as the vacuum is broken, and tear fluid from the marginal tear strips is drawn into the puncta in the first few seconds following the blink.

Biomechanical Phenomena↗
PubMed1980

Interactions of eyelids and tears in corneal wetting and the dynamics of the normal human eyeblink.

We used a high-speed camera system to study in detail the eyelid motion dynamics of the human eyeblink. Films were made from a hidden location through a one-way mirror. In this manner, normal, unforced blinks were recorded. The descent of the upper eyelid reached its maximum speed at about the time that it crossed the visual axis, generally in the range of 17 to 20 cm/sec, but occasionally reaching a speed of over 40 cm/sec. The motion of the lower eyelid was mostly horizontal, in a nasally directed movement, with a total displacement in the range of 20 to 5 min. A distinction must be made between normal, unforced blinks, and voluntary, forced eyelid motion. In a normal blink, no appreciable upward rotation of the globe is observed. A forced blink or a restraint of motion of the upper eyelid results in a significant demonstration of Bell's movement. The globe moves posteriorly up to 1 to 6 mm as the upper eyelid descends, probably caused by eyelid pressure during the closing phase of the blink.

Adult↗
PubMed1978

Penetration routes of topically applied eye medications.

Tritium-labeled hydrocortisone acetate and pilcarpine hydrochloride solutions were topically applied to the eyes of rabbits. In one group of animals, the drugs were excluded from contact with the cornea by a cylindrical well glued to the eye surface. In another group, the drug solutions were allowed contact with the entire anterior surface of the eye. Total application time in all cases was five minutes, then the eyes were flushed with saline. Samples of aqueous humor, stroma, and iris-ciliary body were taken after five, 20, 35, 65, and 125 minutes and counted in a liquid scintillation counter. With hydrocortisone, up to 70 times more drug reached the stroma when the cornea was exposed; 40 times more reached the iris. Peak stromal levels occurred by 20 minutes, dropping to one third of peak value by two hours. With pilocarpine, about five times more drug reached the iris-ciliary body when corneal access was allowed; the level peaked in about five minutes. These results illustrate the important role of tear film distribution and blinking in delivering remotely applied drugs over the cornea with subsequent entry to interior sites.

Administration, Topical↗
PubMed1975

Clinical experience with a mobile ocular perfusion pump.

The continuous delivery in fluids to the ocular surfaces of 12 patients, for a collective total of 1,500 days, was achieved by means of a mobile perfusion pump. One patient used this device intermittently for a total of 21/2 years. Severe dry-eye symptoms were ameliorated in each patient by the constant perfusion. In various situations, the following perfusion fluids have been tried: commercial balanced salt solution, commercial artificial tear solutions, acetylcysteine, and autologous and homologous serum and plasma. In spite of disadvantages related to its size and weight, the pump seems to be of considerable value, especially following severe chemical burns and after keratoplasty or reconstruction of the lids and fornices in the severely dry eye.

Adult↗