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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.