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Biomedical subjects

M C Corbett

Publications and source records attributed to M C Corbett.

34 records · Page 2Linked to original sources
PubMed1994

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↗
PubMed1994

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↗
PubMed1994

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↗
PubMed1993

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↗
PubMed1993

Subconjunctival betamethasone is of benefit after cataract surgery.

Following cataract extraction, the intraocular inflammatory response is particularly marked in some patients, who then require more intensive post-operative care. This prospective randomised double-masked controlled trial of 246 patients undergoing cataract extraction assessed the efficacy and safety of a prophylactic subconjunctival injection of betamethasone (Betnesol, Glaxo) in improving the post-operative course. Betamethasone injected subconjunctivally at the end of cataract extraction significantly reduces anterior segment inflammation (p < 0.05) on the first post-operative day. It also reduces the need for additional steroid treatment and in-patient stay (p < 0.05). The benefits are most marked in those patients prone to a greater inflammatory response: especially those with previous intraocular inflammation (p < 0.01), but also those with racial pigmentation or difficult surgery. There was no evidence of adverse effects following betamethasone; in particular there was no endophthalmitis or steroid-induced elevation of intraocular pressure. We therefore conclude that subconjunctival injection of betamethasone is a practical, safe and effective means of improving the quality and efficiency of patient care.

Aged↗
PubMed1991

Primary or secondary anterior chamber lens implantation after extracapsular cataract surgery and vitreous loss.

Whilst an anterior chamber lens implant (AC IOL) can be implanted during extracapsular cataract extraction with vitreous loss managed by anterior vitrectomy, lens implantation as a secondary procedure may avoid complications. We reviewed 47 consecutive cases of vitreous loss, 37 managed with primary and 10 with secondary AC IOLs. There was no significant difference in the level of final visual acuity but, as expected, it was reached earlier in the primary group (p less than 0.001). In the secondary group post-operative astigmatism was less marked (p less than 0.05) and the AC IOL haptic feet were correctly sited in the angle more frequently (p less than 0.05). Primary implant patients experienced more recurrent attacks of anterior uveitis (p less than 0.01) although the incidence of cystoid macular oedema and retinal detachment did not differ significantly. The results suggest that correct AC IOL positioning is more likely with a secondary procedure and that post-operative complications are fewer.

Cataract Extraction↗
PubMedDate not supplied

Ibopamine: a new preoperative mydriatic for cataract surgery.

Ibopamine is a dopaminergic mydriatic of proven use for fundoscopy. This double-blind prospective trial assessed its efficacy and safety as a preoperative mydriatic agent. 105 patients undergoing extracapsular cataract surgery were randomly allocated to receive Ibopamine 1%, Ibopamine 1% with Cyclopentolate 1%, or the control Phenylephrine 10% with Cyclopentolate 1%. Ibopamine alone achieved good mydriasis prior to anaesthesia, but this was not maintained intraoperatively. Cyclopentolate combined with Ibopamine, produced consistently greater mydriasis than when combined with Phenylephrine, but the difference became less marked as surgery continued. Analysis in relation to the stage of surgery showed that the greatest stimulus to miosis occurred during expression of the nucleus. Pulse rate and blood pressure in the 51 local anaesthetic cases showed no significant difference between the treatment groups, and there was no significant variation from baseline. The incidence of local side effects was similar in the three groups, and there were no systemic symptoms attributable to the drops. In conclusion, Ibopamine is a safe and effective mydriatic agent for cataract surgery, when used in combination with Cyclopentolate.

Aged↗
PubMedDate not supplied

Factors predisposing to postoperative intraocular inflammation.

This prospective study of 123 patients undergoing cataract extraction determined the preoperative and surgical factors predisposing to an exaggerated postoperative inflammatory response. It is important to identify the patients at increased risk of complications requiring additional prophylaxis or more intensive postoperative care, particularly when selecting patients for day case surgery. Previous intraocular inflammation or surgery was the factor most strongly associated with marked inflammation on the first postoperative day (p < 0.01, compared to uncomplicated patients). As a result, patients stayed in hospital an average of one day longer (p < 0.001) and required significantly more steroid drops (p < 0.001). Other factors of significance, but reducing importance were: difficult surgery, non-caucasian race and brown irides. Amongst uncomplicated patients, the difficulty of surgery was most significantly related to a high inflammation score (p < 0.01). Non-caucasian patients stayed in hospital significantly longer than their caucasian counterparts (p < 0.05), and required more steroid drops (p < 0.001). Of caucasian patients, those with brown irides were inpatients for significantly longer than those with blue or hazel (p < 0.05). No other factors studied significantly altered postoperative inflammation: neither the presence of diabetes, nor the technique of cataract extraction.

Aged↗
PubMedDate not supplied

A comparative study of the duration and efficacy of tetracaine 1% and bupivacaine 0.75% in controlling pain following photorefractive keratectomy (PRK).

OBJECTIVE: To evaluate if topical bupivacaine 0.75% provides better pain control after excimer laser over topical tetracaine 1% without affecting corneal wound healing, refractive outcome of visual function. DESIGN: A prospective, double-masked trial was conducted in which 38 patients were randomized to receive either tetracaine or bupivacaine every 30 minutes for 24 hours post-operatively. Pain was recorded over a four day period using a Visual Analogue Pain Scale. The rate of epithelial healing was assessed during digitized retro-illumination photography. Visual performance was recorded using best corrected Snellen acuity, objective measurements of haze, halo and glare over a six month period. RESULTS: Tetracaine afforded better pain control (p = 0.05). Full epithelial closure occurred in all patients within 72 hours and no statistically significant difference was recorded in any of the parameters measured. CONCLUSIONS: Contrary to our expectation, the longer acting anaesthetic, bupivacaine, was inferior to tetracaine. Limited and supervised use of topical anaesthetics is recommended in controlling pain following photorefractive keratectomy.

Adult↗
PubMedDate not supplied

Do topical corticosteroids have a role following excimer laser photorefractive keratectomy?

The article reviews the evidence for and against the use of topical corticosteroids following PRK. Two significant problems after PRK are the development of corneal haze and unpredictability of the refractive outcome. These arise from changes in the anterior stroma, the deposition of new subepithelial tissue, and individual variations in the wound healing response. In rabbits, corticosteroids reduced corneal haze by limiting the synthesis of subepithelial collagen. However, in humans, controlled trials showed that corticosteroids had no lasting effect on either haze or regression, and were associated with an unacceptably high incidence of unwanted effects. The difference between species probably related to the relative absence of collagen and predominance of glycosaminoglycans during corneal wound healing in humans. Some human studies have shown rapid changes in refraction occurring within days of stopping or restarting corticosteroids. This suggests that their transient hyperopic effect is probably mediated by changes in the hydration of the tissue. Therefore, the role of corticosteroids in PRK is very limited. There is no justification for their routine use after PRK for low or moderate myopia. If corticosteroids have a role in improving haze or refractive outcome in selected patients, a means for their early identification must be found.

Administration, Topical↗
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↗
PubMedDate not supplied

Corneal optical aberrations induced by photorefractive keratectomy.

BACKGROUND: Photorefractive keratectomy causes marked alteration to anterior corneal topography, and is likely to induce major changes to the optical aberrations of the eye. METHODS: Six diopters (D) of myopia correction was attempted on one eye of 50 patients, randomly allocated to one of three different treatments: 5-mm or 6-mm single ablation zone, or a double ablation (multizone; -5.00 D correction over 4.6 mm and -1.00 D over 6 mm). Topographic data was used to estimate corneal aberration coefficients. These were compared for effect of ablation zone, before and 1 year after photorefractive keratectomy. The coefficients were used to derive modulation transfer functions for the anterior corneal surface. RESULTS: Corneal spherical aberrations and coma-like aberrations both increased significantly following photorefractive keratectomy (p < 0.001). The mean spherical aberration coefficient increased from 0.36 +/- 0.11 before, to 0.91 +/- 0.37 after treatment, while the mean coma-like aberration coefficient changed from 0.28 +/- 0.16 before, to 0.60 +/- 0.31 after treatment. Ablation zone form had a significant effect on spherical aberration (p = 0.030), but not for coma (p = 0.96). The spherical aberration coefficient increased least for the 6-mm ablation (by 0.38 +/- 0.17), compared with the 5-mm ablation (0.69 +/- 0.45) and the multizone (0.62 +/- 0.38). Corneal modulation transfer functions were reduced significantly following the photorefractive procedure. The effect was greatest for large pupil diameters and for spatial frequencies between 2 and 15 cycles per degree. CONCLUSIONS: Corneal modulation transfer function calculations suggest that a significant loss of visual performance should be anticipated following photorefractive keratectomy, the effect being greatest for large pupil diameters. Results for three ablation zones show that induced aberrations are least for the largest (6 mm) ablation zone.

Adult↗
PubMedDate not supplied

Loss and recovery of corneal sensitivity following photorefractive keratectomy for myopia.

BACKGROUND: Photorefractive keratectomy affects corneal innervation in a new, and drastic, way. This inevitably results in a significant loss of corneal sensitivity. This paper investigates the pattern of sensitivity loss and recovery following PRK for low to moderate myopia. METHODS: Patients were recruited for two separate studies. Longitudinal Study: 10 patients, treated with a -6.00 D/6 mm PRK ablation, were examined over a 1-year period. Transverse Study: A comparison was made between 35 non-contact lens wearers, 80 contact lens wearers, and 60 patients who underwent five different PRK treatments, 1 year previously. Corneal sensitivity was assessed using the Non-Contact Corneal Aesthesiometer at four corneal locations: centrally, temporally, medially, inferiorly, on all patients. RESULTS: Longitudinal Study: Corneal sensitivity was significantly reduced at week 1, with a further significant reduction at week 2. A gradual recovery in sensitivity then followed to reach preoperative levels by 1 year. Transverse Study: There was no significant difference in corneal sensitivity found as a result of different PRK ablation depths. The depth of ablation was not a factor in corneal sensitivity recovery in low to moderate myopic corrections. Corneal sensitivity in the PRK treated eyes was significantly lower than in the control groups. CONCLUSION: The immediate loss of corneal sensitivity after surgery was due to the total removal of the corneal epithelial nerve supply and a substantial portion of the underlying stromal nerves. The further decrease at week 2 was probably due to the new epithelium acting as barrier to stimulation. The gradual recovery of corneal sensitivity was most likely caused by epithelial reinnervation within the ablation zone, but this was still below normal levels at 1 year after surgery. Corneal nerve function demonstrates a biphasic pattern of loss and recovery following the excimer laser correction of low to moderate myopia.

Adult↗
PubMedDate not supplied

Discrimination between the origins and functional implications of haze and halo at night after photorefractive keratectomy.

A series of 84 eyes with up to -6.00 diopters (D) of myopia were treated by photorefractive keratectomy (PRK) using a 5.00 mm ablation zone. Three months postoperatively, 43 eyes (51%) complained of disturbed night vision, compared to 12 (14%) preoperatively. Ten (12%) had significant problems, ie, interference with driving at night. At 12 months, there were 32 patients (38%) with minor disturbances of night vision, 4 (5%) with significant problems.

Automobile Driving↗