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Biomedical subjects

H Moreira

Publications and source records attributed to H Moreira.

31 records · Page 2Linked to original sources
PubMed1991

Photorefractive keratectomy to create toric ablations for correction of astigmatism.

Excimer laser photorefractive keratectomy, developed to perform radially symmetric ablations to correct myopic or hyperopic refractive errors, was used to create toric ablations designed to correct cylindrical errors. An expanding slit was created, with no refractive change intended parallel to the slit opening, and central flattening was induced in the meridian in which the slit was expanded. In polymethyl methacrylate blocks, the induced cylinder (as measured with a lensometer) agreed closely (r2 = .99) with intended change, and in plastic corneas, induction of the cylinder could be demonstrated with computer-assisted topographic analysis. Adult pigmented rabbits underwent induction of toric ablations in two-diopter increments; measured keratometric change correlated with desired change (r2 = .87 at 3 weeks; r2 = .89 at 12 weeks). Toric ablations with the excimer laser appear to represent a promising strategy for the correction of cylindrical errors that do not rely on creation of deep corneal incisions, excisions, or compression sutures.

Animals↗
PubMed1991

Effect of extraocular muscle surgery on corneal topography.

A computerized videokeratoscopy system was used to evaluate changes in corneal topography after muscle surgery in 36 eyes of 18 rabbits. Topographic analysis revealed a significant flattening of the cornea in the superior and superotemporal octants after superior rectus recession (mean +/- SE, -1.78 +/- 0.16 diopters) compared with control eyes undergoing a sham procedure (-0.17 +/- 0.18 D; P less than .05). Excision of all rectus muscles caused a generalized corneal flattening (-1.42 +/- 0.13 D; P less than .001). A computerized, finite element model of the globe, including the rectus muscles, demonstrated corneal deformation as a result of extraocular muscle tension; recession of an extraocular muscle in this model caused corneal flattening in the quadrant of the recessed muscle. These data suggest that corneal topography is affected by extraocular muscle tension, corroborating clinical reports of refractive change after strabismus surgery.

Animals↗
PubMed1991

Photorefractive keratectomy for astigmatism. Initial clinical results.

Excimer laser photorefractive keratectomy, developed to perform radially symmetric ablations to correct myopic or hyperopic refractive errors, was used to perform toric ablations designed to correct cylindrical errors. An expanding slit was used to flatten the cornea in the steep meridian. Four contact lens-intolerant patients underwent this procedure for correction of astigmatism (two patients after penetrating keratoplasty, one patient after corneal ulcer, and one patient with naturally occurring high astigmatism). In each patient, surgery reduced the regular component of the astigmatism; residual irregular astigmatism limited spectacle-corrected acuity in one patient. All patients experienced a shift in spherical equivalent toward hyperopia. Toric ablations with the excimer laser appear to represent a promising strategy for the correction of compound myopic astigmatism that does not rely on creation of deep corneal incisions, excisions, or compression sutures.

Astigmatism↗
PubMed1991

Surface ultrastructure after excimer laser ablation. Expanding vs contracting apertures.

Excimer laser corneal ablation (photorefractive keratectomy) for myopia using a diaphragm delivery system was performed on eye bank and animal eyes by either progressively expanding or contracting the iris aperture. Use of an expanding aperture, in which the final ablations cover the entire treatment zone, produced a pseudomembrane over the zone that had few discontinuities. Ultrastructural examination of the corneas ablated using a progressively contracting aperture, however, revealed numerous discontinuities in the surface pseudomembrane. Use of an expanding iris aperture to perform ablations to correct myopia may be preferable as it produces a pseudomembrane with few discontinuities. Clinical studies of surface healing in humans are necessary to determine the clinical relevance of improved continuity of the surface pseudomembrane.

Animals↗
PubMed1991

Excimer laser smoothing of a reproducible model of anterior corneal surface irregularity.

A reproducible model of an irregular corneal surface was developed to test the ability of the excimer laser to treat such surfaces. Using a 193-nm argon fluoride excimer laser set at a fluence of 160 mJ/cm2, repetition rate of 10 Hz, and 185 pulses, fresh de-epithelialized pig eyes underwent phototherapeutic ablations through a piece of stainless steel wire screen that masked the cornea. This yielded an uneven corneal surface in a grid-like pattern, with the peaks 50 microns higher than the troughs. The eyes then underwent further treatment in an attempt to smooth the center of the irregularity. Hydroxypropyl-methylcellulose 0.3% protected the valleys in 12 eyes; 2 eyes were ablated without a protecting fluid. The same laser, at the above noted settings, was used, except that both 2 Hz and 10 Hz frequencies were used. Immediately after treatment, the eyes were processed for scanning electron microscopy. The eyes treated at 2 Hz showed less surface irregularity than did those treated at 10 Hz. The eyes treated without a protecting fluid, regardless of repetition rate, had the greatest irregularities. This model is simple and reproducible, and the authors' results suggest that modifying the repetition rates of the excimer laser can influence its effectiveness in smoothing irregular corneas.

Animals↗
PubMed1991

Treatment of experimental Pseudomonas keratitis with cyclo-oxygenase and lipoxygenase inhibitors.

The role of metabolites of arachidonic acid in experimental Pseudomonas keratitis was studied using inhibitors of arachidonic acid metabolism. Nordihydroguaiaretic acid 1%, which inhibits predominantly the lipoxygenase pathway, and flurbiprofen 0.03%, which inhibits predominantly the cyclo-oxygenase pathway were administered topically to rabbit eyes after intrastromal injection of Pseudomonas aeruginosa. Levels of the cyclo-oxygenase product prostaglandin E2 (PGE2) and the lipoxygenase product leukotriene B4 (LTB4) were measured, and the number of ulcers that had progressed to descemetocele formation by 24 hours was determined. Corneal ulceration was accelerated by flurbiprofen, but nordihydroguaiaretic acid limited the flurbiprofen-induced worsening. The use of flurbiprofen was associated with decreased levels of PGE2 and a relative increase in LTB4, a potent chemoattractant and activator of polymorphonuclear leukocytes. These results suggest that inhibition of the cyclo-oxygenase pathway may be contraindicated in Pseudomonas keratitis; inhibition of lipoxygenase can prevent this worsening of the keratitis.

Administration, Topical↗
PubMedDate not supplied

Retrospective comparison of simultaneous and non-simultaneous bilateral radial keratotomy.

PURPOSE: Many radial keratotomy surgeons advocate bilateral simultaneous surgery, in which there is an inherent, although rare, risk of bilateral sight-threatening complications such as microbial keratitis. This study was designed to evaluate the refractive outcomes of simultaneous and non-simultaneous radial keratotomy performed by a single surgeon. METHODS: We retrospectively compared the results of radial keratotomy performed simultaneously (both eyes operated on the same day, 20 patients) versus non-simultaneously (right and left eyes operated on different days, 71 patients) by a single surgeon. Both eyes had the same surgical procedure, including clear zone diameter and number of incisions. RESULTS: The refractive results of bilateral simultaneous and non-simultaneous surgery were largely equivalent for all parameters analyzed except one. The variability of the difference in postoperative refractive error between right and left eyes was less for those patients undergoing simultaneous surgery (p = .0008). CONCLUSION: Our data suggest that performing radial keratotomy as a bilateral simultaneous procedure increases the symmetry of the refractive effect. In view of recent reports of sight-threatening risks such as bilateral microbial keratitis following bilateral keratotomy, however, the potential risks and benefits of bilateral surgery should be carefully considered before operating on both eyes on the same day.

Adolescent↗