Stellate tarsoconjunctival lesions in ocular adenoviral infection.
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Adenoviridae Infections↗
Biomedical subjects
M C Corbett
Publications and source records attributed to M C Corbett.
Effect of collagenase inhibitors on corneal haze after PRK.
The aim of the study was to determine whether collagenase inhibitors reduce corneal haze after photorefractive keratectomy (PRK). Inhibition of the initial removal phase of healing may limit the subsequent repair and replacement phases responsible for haze and regression. Thirty rabbits received -6.00D 5 mm right PRK. They were randomized to five treatment groups: G. cysteine, G. ethylene diamine tetra-acetic acid (EDTA), G. ascorbate, Oc. tetracycline or no drops. Dichlorotriazinyl aminofluorescein (DTAF) was applied to the wound immediately after surgery in two rabbits of each group, to delineate newly-synthesized from original tissue. Corneal haze was assessed by a video-linked frame grabber with computerized grey scale analysis. Corneas were taken for histology at 1 or 3 months post-operatively. Corneal haze was not significantly different between the treatment groups and controls. The severity of the histological changes varied between individuals. Within the ablation zone the epithelium was on average 10% thicker (3--4 micro m) than outside, and in some rabbits there were irregularities of the epithelial--stromal junction. The new subepithelial tissue had a mean depth of 7.8 micro m, and the superficial stroma was disorganized to a mean depth of 49 micro m. No particular treatment demonstrated significant benefits over controls; but of the treatments used, cysteine tended to produce the best results. Eyes treated with EDTA fared worst in most respects. The collagenase inhibitors used did not improve the outcome of PRK in rabbits. It remains to be determined whether firstly, the new more potent agents would have an effect, and secondly, whether collagenase inhibitors are of benefit in humans.
Administration, Topical↗
Errors in intraocular lens power calculation after photorefractive keratectomy.
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Aged↗
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↗
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↗
Effect of beam variables on corneal sensitivity after excimer laser photorefractive keratectomy.
AIM: To investigate changes in corneal touch sensitivity following excimer laser photorefractive keratectomy (PRK) using different beam configurations. METHODS: 20 subjects were given a unilateral -3.00 D correction with either a 5 mm (26 micrograms, n = 10) or 6 mm (42 micrograms, n = 10) beam diameter. Thirty subjects underwent a unilateral -6.00 D correction with 5 mm (62 micrograms, n = 10), 6 mm (78 micrograms, n = 10), or multizone (62 micrograms, n = 10) treatments. The multizone treatment was 6 mm in diameter with the depth of the 5 mm treatment. Corneal sensitivity was measured using a slit-lamp mounted Cochet-Bonnet aesthesiometer before and at 1, 3, 6, and 12 months after PRK. Stimulus locations included points lying within the ablated zone (central) and outside (peripheral). These were compared with the equivalent locations in control (untreated) eyes. RESULTS: There was a significant reduction in corneal sensitivity within the central (ablated) zone in all treatment groups after PRK. In most groups a return to full sensitivity was achieved by 6 months with the exception of the multizone treatment group which showed significant corneal hypoaesthesia at 12 months. Peripheral corneal sensitivity was also reduced in this group up to 3 months after the procedure. A comparison between the -3.00 D and -6.00 D treatment groups showed no significant difference. However, combining data from all treatment groups, a significant correlation was found between the interocular difference in central corneal sensitivity and postoperative haze at 3 and 6 months. CONCLUSIONS: For corrections up to -6.00 D ablation depth and treatment zone diameter do not appear to be clinically important determinants of corneal hypoaesthesia. In contrast, postoperative corneal haze appears to correlate with sensitivity loss.
Adult↗
Slow and continuous maxillary expansion, molar rotation, and molar distalization.
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Child↗
Biologic and environmental risk factors for regression after photorefractive keratectomy.
BACKGROUND/PURPOSE: After photorefractive keratectomy (PRK), the final refraction in the majority of patients is near the intended refraction. However, a significant proportion of patients show regression, which is commonly associated with corneal haze. This study aims to determine whether biologic and environmental factors influence the outcome of PRK. METHODS: One hundred patients prospectively underwent -3.00- or -6.00-diopter corrections. Three months after surgery, 100% of patients answered a questionnaire that recorded their biologic characteristics, medical and ocular history, and postoperative exposure to physical and chemical insults. Multivariable analysis identified those factors associated with regression. RESULTS: Multivariable analysis showed that the risk of regression was increased significantly in patients who underwent higher dioptric or smaller diameter treatments (P = 0.045) and in those who had had regression after treatment of the first eye (P = 0.019). There was no difference between the sexes, but regression was 13.5 times more likely in females who were taking oral contraceptives. Regression was increased in those exposed to solar radiation (odds ratio, 7.6; 95% confidence interval, 1.82-32.22) and sun beds (odds ratio, 2.4; 95% confidence interval, 0.64-9.39), and was significantly greater in patients with ocular-surface disorders (on univariable analysis only; P = 0.034). Regression was not associated with previous contact lens wear, swimming, cigarette smoking, or minor ocular trauma. CONCLUSION: The questionnaire identified biologic and environmental risk factors for regression. The biologic risk factors may be used preoperatively to counsel patients and, where necessary, advise them against surgery. The environmental risk factors are largely avoidable by modification of patient behavior.
Adult↗
An in vivo investigation of the structures responsible for corneal haze after photorefractive keratectomy and their effect on visual function.
PURPOSE: To make serial measurements of corneal haze and microscopic anatomy after photorefractive keratectomy (PRK) and compare the results with visual function measured at the same time points in the same single group of human subjects. METHODS: Ten patients underwent -6.00-diopter, 6-mm PRK. The patients were reviewed frequently for 12 months. Corneal haze was measured objectively in two ways: (1) an opacification index was determined from the variance in digitized retroillumination images; and (2) light reflected and scattered back from the cornea was assessed by gray-scale analysis of video slit images. In vivo confocal microscopy recorded the anatomic changes occurring in the cornea, and computer analysis of the images quantified the keratocytes and subepithelial deposit. Visual performance was assessed by Snellen visual acuity, contrast sensitivity, and glare-induced visual dysfunction. RESULTS: In the first week, epithelial irregularity resulted in a transient reduction in all aspects of visual function. In the first month, keratocyte disturbances reduced contrast sensitivity at high frequencies and produced glare. Over the next couple of months, the subepithelial deposit resulted in a more prolonged loss of contrast sensitivity at low frequencies and glare-induced visual dysfunction due to the scattering of light. In several patients, these visual defects persisted after 1 year. CONCLUSIONS: Epithelial and keratocyte disturbances only transiently affect visual function. The subepithelial deposit is more persistent and can have a lasting effect on visual performance. Therefore, attempts to improve the visual outcome of PRK must be aimed at controlling the synthesis of subepithelial material.
Adult↗
Effect of ablation profile on wound healing and visual performance 1 year after excimer laser photorefractive keratectomy.
BACKGROUND: Early photorefractive keratectomy ablations were of limited diameter and depth to maintain the integrity of the globe and to minimise postoperative haze. This study evaluated the effects of deeper, larger diameter wounds on refractive stability and corneal haze, and investigated the effects of ablation profile on wound healing and visual performance. METHODS: One hundred patients undergoing -3.00D and -6.00D corrections were randomised to receive 5 mm, 6 mm, or multizone treatments. The multizone treatment was 6 mm in diameter, but only the depth of the 5 mm treatment. Outcome was measured by Snellen visual acuity, residual refractive error, objective techniques for haze and halos, pupil diameter, subjective night vision, and requirement for retreatment. RESULTS: Overall, the results of 6 mm treatments were superior to those of 5 mm and multizone treatments: they had a smaller hyperopic shift (p < 0.01), a more predictable (p < 0.001) and stable refractive outcome, less haze (p < 0.05), smaller halos (p < 0.05), fewer subjective night vision problems, and fewer patients required retreatment. CONCLUSIONS: Analysis of these data and a literature review of corneal wound healing demonstrated that the improved outcome associated with the 6 mm beam did not relate to the depth of ablation. The factor with greatest apparent influence on the development of haze and regression was the slope of the wound surface over the entire area of the ablation. Tapering the wound edge provided no additional benefit, and contributed to night vision problems. It is, therefore, recommended that small diameter or multizone treatments should not be used in low and moderate myopia.
Adult↗
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↗
A prospective, randomized, double-masked trial to evaluate the role of topical anesthetics in controlling pain after photorefractive keratectomy.
PURPOSE: To investigate the role of 1% tetracaine in controlling pain after photo-refractive keratectomy (PRK) and determining its effect, if any, on epithelial healing, refractive outcome, and visual performance. METHODS: In this study, 44 patients were randomized to receive either Gutt. 1% tetracaine or placebo after undergoing PRK. Drops were instilled at 30-minute intervals during waking hours for 24 hours postoperatively. In addition, all patients received two coproxamol (paracetamol + dextropropoxyphene) tablets every 6 hours for 2 days. Visual Analogue Pain Charts were used to record pain levels for 4 days after surgery. Serial digitized retro-illumination photography was used to assess rates of epithelial healing, and surface epithelial quality was monitored using topography. At fixed intervals over a 6-month period visual performance was assessed by measuring refractive outcome, best-corrected visual acuity, objective haze, halo, and glare. RESULTS: Patients in the tetracaine group had significantly less pain (P < 0.0001). Both groups demonstrated full epithelial closure within 72 hours. Similar numbers of patients in both groups at 1 week showed topographic irregularity that completely resolved by 1 month. No statistically significant difference was seen in any of the parameters monitoring visual performance. CONCLUSIONS: Tetracaine in conjunction with coproxamol is effective in reducing pain after PRK without adversely affecting corneal wound healing or visual performance.
Acetaminophen↗
The assessment of clinical investigations: the Greenwich Grading System and its application to electrodiagnostic testing in ophthalmology.
The aim of the study was to describe the Greenwich Grading System, a simple method developed for assessing the value of a clinical investigation, and to investigate its application to electrodiagnostic testing (EDT) in ophthalmology patients. This was done by means of a retrospective case analysis carried out on 95 unselected, consecutive patients referred from a district ophthalmology department for electrophysiological investigation at a regional neurosciences centre. The classification was developed to quantify the effect of EDT on the diagnosis, investigation and treatment in each case. From this, an overall value of EDT in management could be assessed for different groups of patients. It was found that the classification was easy to apply and analyse. EDT was valuable in 80% of patients referred, and was classified as essential or important in 53 (56%) patients. In no patient did EDT adversely affect the clinical outcome. The diagnosis was changed in 7 (7%) patients, and made in 5 (5%). Diagnostic certainty was increased in a further 62 (65%) patients. Other investigations were avoided by performing electrophysiology in 28 (29%) cases. Treatment was initiated in 6 (6%) cases and altered in 8 (8%). It is concluded that the Greenwich Grading System, as applied to EDT in ophthalmology, demonstrated the value of electrophysiological investigation in ophthalmology patients and identified the patient groups which benefit most from testing.
Electrodiagnosis↗
The effects of topical corticosteroids and plasmin inhibitors on refractive outcome, haze, and visual performance after photorefractive keratectomy. A prospective, randomized, observer-masked study.
BACKGROUND: This study of 86 patients with 12 months of follow-up was designed to determine whether topical corticosteroids or plasmin inhibitors have an effect on the outcome of photorefractive keratectomy. METHODS: Patients were allocated randomly to either steroid (0.1% fluorometholone for 6 months), plasmin-inhibitor (aprotinin 40 IU/ml for 3 weeks), or control (no treatment) groups and underwent either -3.00- or -6.00-diopter (D) corrections. RESULTS: With -3.00-D corrections, the mean refractive change was significantly greater at 3 and 6 months (P < 0.05) in the steroid group compared with the control group. When steroids were discontinued, the difference became insignificant within 3 months. Similarly, with -6.00-D procedures the mean refractive change was greater at 6 weeks and 3 and 6 months (P < 0.01), but the refractive change again became insignificant 3 months after stopping steroid treatment. Four patients treated with steroids had a hyperopic shift greater than +2.00 D of that intended at 12 months. Similar overcorrections were not noted in the other treatment groups. There were no differences in refractive outcome between the aprotinin and control groups at any stage. With -6.00-D procedures, objective measurements of haze were significantly greater in the aprotinin group compared with the control group at 9 and 12 months (P < 0.05). With this exception, there were no differences in haze, forward or backward scatter of light, best-corrected visual acuity, or halo measurements between the groups. CONCLUSIONS: Corticosteroids can maintain a hyperopic shift during their administration, but this effect is reversed on cessation of treatment. Objective tests have shown that steroids have no effect on corneal haze or visual performance after PRK. There is no justification for routinely submitting all patients to long-term steroid regimens and their associated side effects. Treatment with aprotinin produced no beneficial effect on refractive outcome, and haze was greater in the -6.00-D procedures. The concept of modulating the plasminogen activator/plasmin system to regulate wound healing after PRK is discussed.
Adult↗
Disturbances in night vision after excimer laser photorefractive keratectomy.
Eighty-four patients with up to -6.00 dioptres of myopia underwent photorefractive keratectomy (PRK), using 5.00 mm ablation zones. Three months post-operatively 38 (45%) complained of disturbances in night vision, compared with 21 (25%) pre-operatively. In the majority, these disturbances were regarded as negligible. However, 9 (11%) reported significant problems, defined as an inability to drive safely at night with the treated eye. At 12 months, 32 patients (38%) complained of impaired night vision, 4 (5%) of whom had significant problems. A series of measurements were performed to investigate the origins of these disturbances, especially in patients reporting significant problems. Visual impairment from forward scattered light was investigated using a computerised technique. Back scattered light was measured with a charge coupled device-camera system and a computer program was used to assess the degree of halation around a bright light source on a high-resolution monitor. Pupillary diameters were measured by infrared television pupillometry. At 6 months, those reporting a starburst effect around lights at night had small hyperopic shifts, minimal halos and high forward and back light scatter measurements. Patients who reported halo phenomena had large hyperopic shifts, little light scatter and large pupillary diameters. Of the 4 patients who reported significant disturbances at 12 months, all had persistent halo problems. Those with starburst effects in the early post-operative period noticed an improvement with time as their corneal haze gradually improved. Perturbations of night vision after PRK manifest as starbursts and halos around lights.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Intraocular adrenaline maintains mydriasis during cataract surgery.
Cataract surgery is performed more easily if mydriasis can be maintained until the intraocular lens has been inserted. Intraocular irrigation with adrenaline is thought to be of benefit in this respect, and is used by some surgeons but not others. This prospective double blind controlled trial assessed the efficacy and safety of using perioperative adrenaline during extracapsular cataract surgery, as an adjunct to preoperative topical mydriatics. Seventy patients were randomised to receive intraocular irrigation fluid with or without 1:1,000,000 adrenaline. The adrenaline entering the eye through the anterior capsulotomy needle helped to resist the miosis induced by expression of the nucleus (7.1 versus 6.5 mm). The mydriasis maintained during irrigation aspiration was significantly greater in the group receiving adrenaline (6.6 versus 6.0 mm, p < 0.02). Their pupil diameters were also significantly larger at 20 minutes (p < 0.001) and 30 minutes (p < 0.01) into surgery. Pupillary constriction to a diameter of less than 5 mm occurred more frequently in the group not receiving adrenaline. Pulse rate and blood pressure in the 27 patients who had local anaesthesia showed no significant difference between the treatment groups (p > 0.05), and there was no significant variation from baseline (p > 0.05). Intraocular irrigation with adrenaline 1:1,000,000 is a safe and effective means of maintaining mydriasis during cataract surgery.
Administration, Topical↗
Keratometry using the Goldmann tonometer.
Keratometry using the Goldmann tonometer is a reliable and readily available guide to corneal astigmatism following cataract surgery. In regular corneal astigmatism the Goldmann tonometer rings are distorted into skewed ellipses. The axis of the cylinder can be measured by rotating the tonometer head until an undistorted ellipse is obtained. The power is then assessed by comparison with standard ellipses. The difference in the intracular pressure readings (mmHg) in the two principal meridians was also a good guide to the presence of astigmatism. Goldmann keratometry was performed by a single masked observer in 71 patients 8 weeks after routine extracapsular cataract surgery. This was compared with Javal-Schiotz Keratometry performed by an independent observer. In 83% of patients the axis was measured to within 20 degrees. The 95% confidence interval for the power was +/- 2.90 DC; and 87% of patients would have sutures removed appropriately.
Astigmatism↗