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Biomedical subjects

M G Kerr Muir

Publications and source records attributed to M G Kerr Muir.

At least 19 recordsLinked to original sources
PubMed1998

Keratocyte density and size in conscious humans by digital image analysis of confocal images.

PURPOSE: Confocal microscopy can give images of high magnification and resolution in undisturbed living tissue. It provides new information about the cellular structure of the cornea. Our aim was to measure the density, size and distribution of keratocytes. METHODS: Healthy cornea in four subjects was examined using tandem scanning confocal microscopy. Methods for digital analysis of images were developed. RESULTS: Keratocyte density in confocal cross-sections was greatest immediately under Bowman's membrane (maximum 800 cells/mm2) and decreased sharply towards posterior cornea (minimum 65 cells/mm2). Cross-sectional cell size ranged from 78 to 211 microns2, but did not correlate with depth in the tissue. CONCLUSIONS: Results are consistent with those of earlier work using histological and biochemical techniques in isolated tissue. The methods we have developed enable studies of ongoing processes in conscious humans and can be used to examine diseased tissue as well as the response to injury.

Adult↗
PubMed1997

Confocal microscopy using oblique sections for measurement of corneal epithelial thickness in conscious humans.

PURPOSE: Thickness measurements by confocal microscopy in conscious human subjects may be liable to error as a result of instability of the eye or instrument. Our aim was to evaluate a technique which was expected to be less sensitive to such problems. METHOD: Thickness of corneal epithelium was determined from oblique confocal sections through cornea. A contact lens of known thickness worn by subjects was used to calibrate images. RESULTS: There were two layers in images which could have corresponded to the stromal/epithelial interface. The mean result in each subject ranged from 38 to 53 microm using the more superficial layer and 46 to 60 microm using the deeper one. The smaller values gave the distance between the epithelial surface and the sub-epithelial nerve plexus and thus seemed to correspond to epithelial thickness. CONCLUSIONS: Measurements of epithelial thickness by our new method are comparable with results of earlier studies.

Adult↗
PubMed1995

The effects of ablation diameter on the outcome of excimer laser photorefractive keratectomy. A prospective, randomized, double-blind study.

OBJECTIVE: To determine the effects of the ablation diameter on the outcome of excimer laser photorefractive keratectomy. DESIGN: Eighty patients were randomized to either a 5.00-mm or a 6.00-mm treatment group and within these groups underwent either a -3.00-diopter (D) or a -6.00-D correction based on their preoperative refraction. A Summit Omnimed excimer laser was used throughout the study. RESULTS: In eyes treated with a 6.00-mm-diameter ablation, the initial hyperopic shift was reduced, with significant differences at 1 week with -3.00-D corrections and at 1 and 4 weeks with -6.00-D corrections (P < .01). At 6 months, the refractive changes were greater and closer to that intended with 6.00-mm-diameter ablations. The predictability of photorefractive keratectomy was significantly improved with 6.00-mm zones, with a reduction in variance of the refractive changes at all stages postoperatively (P < .05 to P < .001). With -3.00-D corrections, objective measurements showed significantly less anterior stromal haze in eyes treated with 6.00-mm zones at 6 months (P < .05). With -6.00-D corrections, haze was significantly reduced at 1, 3, and 6 months in the eyes treated with 6.00-mm zones (P < .05). Five eyes treated with 5.00-mm zones experienced severe regression of the correction, with marked corneal haze and a reduction of 3 or more lines of best corrected Snellen visual acuity at 6 months. No eyes treated with 6.00-mm zones were similarly affected. Computerized measurements of "night" halo were significantly lower in the 6.00-mm treatment groups at 1 week and at 1 and 6 months in the eyes with -3.00-D corrections and at 1 week and at 1 month in the eyes with -6.00-D corrections (P < .05). At 6 months, seven patients treated with 5.00-mm zones complained of severe disturbances of night vision. No eyes in the 6.00-mm group were similarly affected. CONCLUSIONS: Treatment with 6.00-mm ablation diameters precipitated less initial overcorrection, greatly improved the predictability of photorefractive keratectomy, and was associated with a reduction in complications impairing postoperative visual performance.

Adult↗
PubMed1993

Treatment of band keratopathy by excimer laser phototherapeutic keratectomy: surgical techniques and long term follow up.

A series of 122 eyes with band keratopathy was treated by excimer laser phototherapeutic keratectomy (PTK), with a mean follow up of over 12.3 months (range 3 to 60 months). A single photoablation zone was used to remove the opacity over the visual axis in smooth surfaced band deposition. In eyes with reduced vision, an improvement was reported in 88% and in a series of 66 eyes mean Snellen visual acuity increased significantly (p < 0.05, t = 2.27). A reduction in glare was reported in 88% and in a series of 17 patients, visual contrast sensitivity (p < 0.01) and measurements of disability glare (p < 0.01) improved postoperatively. The mean hyperopic shift in 32 eyes at 6 months was 1.4 D (range 0-4.25 D). Multiple overlapping ablation zones, with mechanical debulking of large calcium plaques, were used to smooth the irregular corneal surface in eyes with rough bands. Ocular discomfort was improved in 95%. Band keratopathy recurred in nine eyes (8%) within 2 to 30 months (mean 12 months) of surgery, with silicone oil responsible in five eyes. Reablation was necessary in three eyes and performed successfully in all cases. Excimer laser PTK is a safe and effective outpatient treatment for band keratopathy.

Adult↗
PubMed1992

Glaucoma and the iridocorneal endothelial syndrome.

The records of 66 patients with the iridocorneal endothelial (ICE) syndrome were retrospectively reviewed. Glaucoma occurred in 33 (50%) of the patients with ICE syndrome and was most common in the variants in which abnormal cells involve the entire posterior corneal surface (disseminated ICE and total ICE). Of 25 patients with glaucoma, the diagnosis of ICE syndrome was overlooked initially in 17 (68%). Medical glaucoma treatment was generally ineffective. Of 22 patients (88%) who underwent surgery (typically trabeculectomy), 10 (45%) required more than one procedure. The success rates of first operations at 1 and 5 years were 60% and 21%, and those of second and third operations at 1 year were 20% and 17%. During the course of their management, 11 patients (44%) developed visual field loss. The diagnosis of ICE syndrome should be considered in younger patients with unilateral glaucoma and confirmed by specular microscopy. Management of glaucoma due to ICE syndrome is surgical, and means of improving its long-term success need to be addressed.

Adult↗
PubMed1992

Excimer laser photorefractive keratectomy. 18-month follow-up.

PURPOSE: This study, comprising 120 patients (follow-up, 12 to 22 months; mean, 18 months), was designed to evaluate the efficacy and safety of excimer laser photo-refractive keratectomy. METHODS: Ablation zone diameter (4 mm), ablation rate (0.22 microns/pulse), fluence (180 mJ/cm2), and frequency (10 Hz) were kept constant, and all patients used a standard topical corticosteroid regimen. RESULTS: Overcorrection was followed by regression to a stable refraction by 4 months. At 1 year, 95% and 70%, respectively, of patients undergoing - 2.00 diopters (D) and -3.00 D corrections and 40% and 20% of those undergoing -6.00 D and -7.00 D corrections were within +/- 1.00 D of intended refraction. Anterior stromal "haze," maximal at 6 months and diminishing thereafter, was detected in 110 patients (92%). However, best-corrected Snellen visual acuity was reduced in only 22 (18%). Good correlation existed between haze and regression (r = 0.68). Night "halos," due to the relatively small 4-mm diameter ablation zone, were reported by 94 patients (78%) in the early postoperative period, and, at 1 year, 12 (10%) declined treatment of the other eye because of persistence of this problem. CONCLUSION: Marked individual variation was found after photorefractive keratectomy. However, in low myopia, predictability is "fair," and the procedure is safe. The authors conclude that excimer laser photorefractive keratectomy holds considerable promise for refractive surgery in the future.

Adult↗
PubMed1988

Neodymium: YAG laser iridotomies--short-term comparison with capsulotomies and long-term follow-up.

This study addresses three aspects of anterior segment Nd:YAG laser treatment--acute endothelial damage, as assessed by endothelial specular photomicrography (ESP), acute and long-term intraocular pressure (IOP) changes, and long-term iridotomy patency. The acute ESP and IOP changes in 26 eyes (21 patients) after Nd:YAG laser iridotomies were compared to 39 eyes (37 patients) after Nd:YAG laser capsulotomy. Similar endothelial damage occurred in both groups, although less damage was noted in the group of 9 eyes in which capsulotomies were undertaken in the presence of an intraocular lens. In a parallel study 53 eyes (44 patients) were followed for a mean of 83 weeks (19 months) from the time of Nd:YAG iridotomy. There were no late closures and no late rises in IOP. The level of acute IOP rise after treatment did not predict long-term IOP. We conclude that Nd:YAG iridotomy is an effective procedure in the long-term, and that both iridotomy and capsulotomy are accompanied by noteworthy acute endothelial changes and intraocular pressure rises.

Cornea↗
PubMed1987

Air, methylcellulose, sodium hyaluronate and the corneal endothelium. Endothelial protective agents.

In a randomised trial the endothelial protective agent used during extracapsular cataract extraction and intraocular lens insertion was air in 19 eyes (group 1), methylcellulose in 25 eyes (group 2) and sodium hyaluronate in 22 (group 3). The cell population densities of each eye were estimated immediately before and three months after the operations to determine the degree of cell loss. Eyes showing mechanical (touch) damage on the second postoperative day were eliminated. The numbers of eyes in each group which showed a statistically significant cell loss were compared, and the mean cell losses in each group were tested for significant differences. It appears that air actually damages the endothelium while methylcellulose and Na-hyaluronate are not harmful, and afford a high, essentially equal degree of endothelial protection.

Adult↗
PubMed1987

Postoperative grey-white lines of the posterior cornea and endothelial cell damage.

'Snailtracks' (grey-white streaks and patches on the posterior corneal surface which occur postoperatively) have recently been implicated as possible markers of corneal endothelial cell damage. We have examined this phenomenon in vivo with the slit-lamp and specular microscope. We recognised three types of linear form and, in contradiction of other observers, found that each was always coincident with a wrinkle in Descemet's membrane. Moreover, we were able to demonstrate only minimal endothelial cell damage in only a few of the tracks.

Cataract Extraction↗
PubMed1987

Corneal thickness, astigmatism, and atopy.

Keratometry and regional pachometry were performed on atopic patients with no history or signs of atopic keratoconjunctivitis. In a series of 80 eyes there was a skewed distribution towards thinner corneas (p less than 0.01) and a preponderance of against-the-rule astigmatism. The maternal age at birth of this group of patients was higher than that in the general population. These findings are discussed in the context of the known association of atopy with keratoconus.

Adult↗
PubMed1986

Corneal endothelial changes following short pulsed laser iridotomy and surgical iridectomy.

Pre- and post-operative endothelial specular photo-microscopy was performed on 46 eyes of 29 patients who had been randomly assigned to iridotomy with the Nd:YAG or the dye laser, or to surgical peripheral iridectomy for the relief of pupil block glaucoma. Localised damage to the endothelium was observed in two eyes following Nd:YAG laser iridotomy and in one eye following dye laser iridotomy. No endothelial changes were recognised after surgical peripheral iridectomy. Central corneal endothelial cell densities remained unchanged following all procedures.

Aged↗
PubMed1985

Damage to the corneal endothelium during Nd/YAG photodisruption.

Damage to the human corneal endothelium, as seen by specular microscopy, associated with short pulsed neodymium: yttrium-aluminium-garnet (Nd/YAG) laser iridotomy and capsulotomy, is described. A specular and scanning electron microscopical study of fresh in vitro rabbit eyes submitted to Nd/YAG iridotomy was performed to investigate the nature of the endothelial damage. The majority of lesions showed irreversible changes ranging from individual cell destruction to disruption of large areas of the endothelium, while cells adjacent to these lesions had changes of an apparently reversible nature. It was possible to correlate accurately these scanning electron microscopic changes with the appearances seen with the clinical specular microscope. The extent of such damage appears to be related to the quantity of power delivered, its delivery mode, the number of laser bursts, and the target tissue/endothelium distance. The possible causes for such damage are discussed.

Animals↗
PubMed1985

Damage to the corneal endothelium by Q-switched Nd:YAG laser posterior capsulotomy.

Clinical specular microscopy of the corneal endothelium of eyes immediately before and after Nd:YAG laser posterior capsulotomy revealed apparent endothelial damage. Comparative specular and scanning electron microscopical studies in rabbits showed extensive cell destruction, and clinical observations indicated 'healing' of the lesions by extensions from neighbouring cells. Possible causes of the damage are discussed.

Animals↗
PubMed1983

Ocular hypertension and posture.

Thirty-seven patients with ocular hypertension (OH) and 29 age matched controls were studied. Intraocular pressure (IOP) measurements were made in the sitting position and, immediately after changing posture, in the lying position. Sixty-three (85%) of the OH eyes and all the control eyes showed either stable IOP readings on changing posture of small elevations up to 3 mmHg. Eleven (15%) of the OH eyes showed larger elevations of IOP, between 5 and 9 mmHg when the patients changed to the lying position. We suggest that an IOP measurement in the lying position should be included in the routine evaluation of the patient with ocular hypertension.

Female↗
PubMedDate not supplied

Effects of ablation diameter, depth, and edge contour on the outcome of photorefractive keratectomy.

PURPOSE: To investigate the effects of the ablation diameter, depth, and edge contour on the outcome of excimer laser photorefractive keratectomy (PRK). METHODS: A prospective study was conducted in which 60 patients (60 eyes) were randomly allocated to 5.00-mm, 6.00-mm, or 5.00 to 6.00-mm multizone treatment groups. All eyes underwent a -6.00 diopter (D) correction using a Summit Omnimed excimer laser. RESULTS: In eyes treated with 6.00-mm diameter zones, the initial hyperopic shift was reduced, with significant differences at 1 and 4 weeks (p < 0.01). At 6 and 12 months, the refractive changes were closer to the intended correction with 6.00-mm diameters. The predictability of PRK was improved with 6.00-mm zones, with a significant reduction in variance of the refractive changes, at all stages postoperatively (p < 0.05 to p < 0.001). Objective measurements of haze were significantly less at 1, 3, and 6 months with 6.00-mm ablations (p < 0.05). There were no differences between the 5.00-mm and the 5.00- to 6.00-mm multizone groups. Computerized measurements of "night" halo were significantly smaller in the 6.00-mm treatment group at 1 week and 1 month (p < 0.05). At 12 months, two patients treated with 5.00-mm zones and three with the 5.00- to 6.00-mm multizone complained of severe night vision disturbances. No 6.00-mm eyes were similarly affected. CONCLUSIONS: Treatment with a 6.00-mm spherical ablation diameter produced less initial overcorrection, improved predictability, and was associated with a reduction in postoperative halos and night vision disturbances. Creating a superficial blend zone with a 5.00- to 6.00-mm multizone treatment had no beneficial effect on the outcome.

Adult↗