The effect of bacteriochlorophyll derivative WST-D and near infrared light on the molecular and fibrillar architecture of the corneal stroma.

A cross-linking technique involving application of Bacteriochlorophyll Derivative WST-11 mixed with dextran (WST-D) to the epithelium-debrided cornea and illumination with Near Infrared (NIR), has been identified as a promising therapy for stiffening pathologically weakened corneas. To investigate its effect on corneal collagen architecture, x-ray scattering and electron microscopy data were collected from paired WST-D/NIR treated and untreated rabbit corneas. The treated eye received 2.5 mg/mL WST-D and was illuminated by a NIR diode laser (755 nm, 10 mW/cm2). An increase in corneal thickness (caused by corneal oedema) occurred at 1-day post-treatment but resolved in the majority of cases within 4 days. The epithelium was fully healed after 6-8 days. X-ray scattering revealed no difference in average collagen interfibrillar spacing, fibril diameter, D-periodicity or intermolecular spacing between treated and untreated specimens. Similarly, electron microscopy images of the anterior and posterior stroma in healed WST-D/NIR corneas and untreated controls revealed no obvious differences in collagen organisation or fibril diameter. As the size and organisation of stromal collagen is closely associated with the optical properties of the cornea, the absence of any large-scale changes following treatment confirms the potential of WST-D/NIR therapy as a means of safely stiffening the cornea.

Financial modelling of femtosecond laser-assisted cataract surgery within the National Health Service using a 'hub and spoke' model for the delivery of high-volume cataract surgery.

AIMS: To develop financial models which offset additional costs associated with femtosecond laser (FL)-assisted cataract surgery (FLACS) against improvements in productivity and to determine important factors relating to its implementation into the National Health Service (NHS). METHODS: FL platforms are expensive, in initial purchase and running costs. The additional costs associated with FL technology might be offset by an increase in surgical efficiency. Using a 'hub and spoke' model to provide high-volume cataract surgery, we designed a financial model, comparing FLACS against conventional phacoemulsification surgery (CPS). The model was populated with averaged financial data from 4 NHS foundation trusts and 4 commercial organisations manufacturing FL platforms. We tested our model with sensitivity and threshold analyses to allow for variations or uncertainties. RESULTS: The averaged weekly workload for cataract surgery using our hub and spoke model required either 8 or 5.4 theatre sessions with CPS or FLACS, respectively. Despite reduced theatre utilisation, CPS (average £433/case) was still found to be 8.7% cheaper than FLACS (average £502/case). The greatest associated cost of FLACS was the patient interface (PI) (average £135/case). Sensitivity analyses demonstrated that FLACS could be less expensive than CPS, but only if increased efficiency, in terms of cataract procedures per theatre list, increased by over 100%, or if the cost of the PI was reduced by almost 70%. CONCLUSIONS: The financial viability of FLACS within the NHS is currently precluded by the cost of the PI and the lack of knowledge regarding any gains in operational efficiency.

Riboflavin for corneal cross-linking.

Corneal collagen cross-linking (CXL) with riboflavin and ultraviolet A (UVA) radiation is the first therapeutic modality that appears to arrest the progression of keratoconus and other corneal ectasias. Riboflavin is central to the process, acting as a photosensitizer for the production of oxygen singlets and riboflavin triplets. These free radicals drive the CXL process within the proteins of the corneal stroma, altering its biomechanical properties. Riboflavin also absorbs the majority of the UVA radiation, which is potentially cytotoxic and mutagenic, within the anterior stroma, preventing damage to internal ocular structures, such as the corneal endothelium, lens and retina. Clinical studies report cessation of ectatic progression in over 90% of cases and the majority document significant improvements in visual, keratometric and topographic parameters. Clinical follow-up is limited to 5-10 years, but suggests sustained stability and enhancement in corneal shape. Sight-threatening complications are rare. The optimal stromal riboflavin dosage for CXL is as yet undetermined.

A randomised, prospective study comparing selective laser trabeculoplasty with latanoprost for the control of intraocular pressure in ocular hypertension and open angle glaucoma.

AIM: To compare 90 degrees , 180 degrees , and 360 degrees selective laser trabeculoplasty (SLT, 532 nm Nd:YAG laser) with latanoprost 0.005% for the control of intraocular pressure (IOP) in ocular hypertension (OHT) and open angle glaucoma (OAG). METHODS: A prospective, randomised clinical trial in the Department of Ophthalmology, St Thomas's Hospital, London, and Clayton Eye Centre, Wakefield, West Yorkshire. 167 patients (167 eyes) with either OHT or OAG were randomised to receive 90 degrees , 180 degrees , and 360 degrees SLT or latanoprost 0.005% at night and were evaluated at 1 hour, 1 day, 1 week and 1, 3, 6, and 12 months. RESULTS: The mean follow up was 10.3 months (range 1--12 months). Early, transient, complications such as postoperative ocular pain, uveitis, and 1 hour IOP spike occurred in a number of eyes after SLT, with pain being reported more frequently after 360 degrees than 90 degrees treatments (p>0.001). Success rates defined in terms of both a 20% or more and a 30% or more IOP reduction from baseline measurements with no additional antiglaucomatous interventions were better with latanoprost than 90 degrees (p<0.001) and 180 degrees SLT (p<0.02) treatments. Differences in success rates between latanoprost and 360 degrees SLT did not reach statistical significance (p<0.5). Success rates were greater with 180 degrees and 360 degrees compared to 90 degrees SLT (p<0.05). With 360 degrees SLT, 82% of eyes achieved a >20% IOP reduction and 59% a >30% reduction from baseline. Although success rates were better with 360 degrees than 180 degrees SLT treatments, differences did not reach statistical significance. There were no differences with regard to age, sex, race, pretreatment IOP, OHT versus OAG, laser power settings, and total laser energy delivered between eyes which responded, in terms of a >20% and a >30% IOP reduction, and those that did not respond with 180 degrees and 360 degrees SLT treatments. CONCLUSIONS: Success rates were higher with latanoprost 0.005% at night than with 90 degrees and 180 degrees SLT treatments. 90 degrees SLT is generally not effective. 360 degrees SLT appears to be an effective treatment with approximately 60% of eyes achieving an IOP reduction of 30% or more. Transient anterior uveitis with associated ocular discomfort is not unusual in the first few days after SLT. Late complications causing ocular morbidity after SLT were not encountered.

A randomised, prospective study comparing trabeculectomy with viscocanalostomy with adjunctive antimetabolite usage for the management of open angle glaucoma uncontrolled by medical therapy.

AIMS: To compare trabeculectomy with viscocanalostomy augmented with adjunctive antimetabolite use for the control of intraocular pressure (IOP) in open angle glaucoma (OAG). METHODS: 45 patients (50 eyes) with uncontrolled OAG were randomised to either trabeculectomy (25 eyes) or a viscocanalostomy technique (25 eyes). Preoperatively, all eyes were graded in terms of risk factors for drainage failure and were given intraoperative antimetabolites (5-fluorouracil 25 mg/ml (5-FU), mitomycin C (MMC) 0.2 mg/ml and 0.4 mg/ml) according to a standard protocol. RESULTS: There were no significant differences between the groups in age, sex, type of OAG, preoperative medications, risk factors for drainage failure, and preoperative IOP. Mean follow up was 20 months (range 3-24 months). It was 12 months or longer in all eyes, except two lost to follow up at 3 months. At 12 months, complete success (IOP<21 mm Hg without antiglaucoma medications) was seen in 91% of eyes undergoing trabeculectomy, but in only 60% of eyes undergoing viscocanalostomy (p<0.02). Similarly, at the last follow up visit (mean 20 months) complete success was seen in 68% of eyes undergoing trabeculectomy and 34% with viscocanalostomy (p<0.05). In terms of qualified success (IOP<21 mm Hg with or without glaucoma medications) and mean IOP measurements postoperatively there were no difference between the groups, although the mean number of antiglaucomatous medications required postoperatively was less with trabeculectomy (0.39) than viscocanalostomy (1.04) (p<0.05). Needling procedures were more commonly required after trabeculectomy (p<0.02). YAG goniotomy was required in three eyes (13%) after viscocanalostomy. Early transient complications such as anterior chamber shallowing and encysted blebs were more common in the trabeculectomy group (p<0.05). Late postoperative cataract formation was similar between the two groups. CONCLUSION: In terms of complete success and number of antiglaucomatous medications required postoperatively, IOP control appears to be better with trabeculectomy. Viscocanalostomy is associated with fewer early transient postoperative complications.

A randomised, prospective study comparing trabeculectomy augmented with antimetabolites with a viscocanalostomy technique for the management of open angle glaucoma uncontrolled by medical therapy.

AIMS: To compare trabeculectomy with viscocanalostomy for the control of intraocular pressure (IOP) in open angle glaucoma (OAG) uncontrolled by medical therapy. METHODS: 48 patients (50 eyes) with uncontrolled OAG were randomised to either trabeculectomy (25 eyes) or a viscocanalostomy technique (25 eyes). Preoperatively, eyes were graded in terms of risk factors for drainage failure. Those undergoing trabeculectomy were given intraoperative antimetabolites (5-fluorouracil 25 mg/ml (5-FU), mitomycin C (MMC) 0.2 mg/ml and 0.4 mg/ml) according to a standard protocol. Antimetabolites were not used intraoperatively in eyes undergoing viscocanalostomy, but they were randomised to the use of viscoelastic (Healonid GV) for intraoperative intracanalicular injection. RESULTS: There were no significant differences between the groups in age, sex, type of OAG, preoperative medications, risk factors for drainage failure, and preoperative IOP. Mean follow up was 19 months (range 6-24 months). It was 12 months or longer in all eyes, except one lost to follow up at 6 months. At 12 months, complete success (IOP <21 mm Hg without antiglaucoma medications) was seen in all eyes undergoing trabeculectomy (100%), but in only 64% of eyes undergoing viscocanalostomy (p<0.001). The mean IOP was lower at 12 months (p<0.001) with trabeculectomy and the number of eyes with IOPs of 15 mm Hg or less was greater (p<0.05). The mean IOP at 12 months was lower in eyes that had undergone viscocanalostomy using intraoperative intracanalicular Healonid GV injection compared to those where only balanced saline solution had been used (p<0.01). However, in terms of complete success there was no difference between the viscocanalostomy groups (p<0.1). With the exception of measurements at 1 week, visual recovery (logMAR acuity) was similar and laser flare and cell values showed little differences between the groups. Corneal topography and keratometry at 12 months were little different from preoperative values. Postoperative interventions (subconjunctival 5-FU and needling procedures) were similar between the groups. Transient complications such as early bleb leak and hyphaema were more common in the trabeculectomy group (p<0.05). Postoperative cataract formation was more common after trabeculectomy (p<0.05). CONCLUSIONS: IOP control appears to be better with trabeculectomy. Viscocanalostomy is associated with fewer postoperative complications, although significant complications permanently impairing vision did not occur with either technique.

Anterior corneal optical aberrations induced by photorefractive keratectomy for hyperopia.

PURPOSE: Photorefractive keratectomy (PRK) for hyperopia requires both a steepening of the central cornea and a flattening of the mid-periphery to achieve its effect and is likely to affect the optical aberrations of the eye. METHODS: Nine patients underwent PRK to correct between +2.00 and +4.00 D of hyperopia (first eye treated for each patient) using the Summit Technology Apex Plus excimer laser. Anterior corneal aberrations for pupil diameters of 3, 5.5 and 7 mm were estimated from corneal topography data (TMS-1), assuming a uni-index, single surface cornea. Refractive error was assessed using retinoscopy and standard subjective tests. RESULTS: Apart from the intended change in refraction (mean spherical equivalent manifest refraction, +4.60 +/- 1.60 D before surgery and +0.70 +/- 1.60 D at 1 year after surgery), the most significant change was in spherical aberration. Anterior corneal spherical aberration was positive (+1.60 +/- 0.60 D for a 5.5-mm pupil) before surgery and became negative after surgery (-1.80 +/- 1.20 D at 1 year). The change in spherical aberration was related to the achieved change in refractive error. CONCLUSIONS: The large change (approximately 3.00 D) in spherical aberration (from positive to negative aberration) has implications for the optical performance of the whole eye, where the effects of lenticular aberration must also be considered.

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.

Hyperopic photorefractive keratectomy with the erodible mask and axicon system: two year follow-up.

PURPOSE: To evaluate efficacy and long-term stability of hyperopic photorefractive keratectomy (H-PRK) using the erodible mask and Axicon system. SETTING: Department of Ophthalmology, St. Thomas' Hospital, London, England. METHODS: Forty-three patients (43 eyes), with a mean preoperative refraction (spherical equivalent) of +4.54 diopters (D) (range +1.75 to +7.50 D), were treated using an Apex Plus(R) excimer laser (Summit Technology). This uses an erodible mask to ablate a 6. 50 mm diameter hyperopic correction and an Axicon to fashion a 1.50 mm blend zone around the correction. The overall ablation diameter was 9.50 mm. Follow-up was 2 years. RESULTS: At 2 years, the mean manifest refraction was +0.16 D (range +4.125 to -4.000 D), with the induced correction appearing stable after 9 months. Based on the Munnerlyn algorithm, predictability was acceptable for corrections up to +4.50 D, with 68% of eyes within +/-1.00 D of the predicted correction. It was poorer for +6.00 D corrections, with 33% of eyes within +/-1.00 D of that expected. Patient satisfaction was high. Forty eyes (93%) had an improvement in uncorrected near visual acuity and 37 (86%), an improvement in uncorrected distance acuity. A peripheral ring of haze, 6.5 mm in diameter, appeared in all eyes 1 month postoperatively. Its intensity was maximal at 3 to 9 months and then diminished over time. There were no significant differences in measurements of the central corneal transparency at 12 and 24 months and those preoperatively. Measurements of flicker contrast sensitivity, forward light scatter (glare), and scotopic halos showed no significant differences between preoperative values and those measured after 6 months. CONCLUSIONS: Achieved H-PRK corrections with the erodible mask and Axicon system agreed closely with the Munnerlyn algorithm, with refractive stability after 9 months. Predictability was acceptable for corrections up to +4.50 D. Axial corneal transparency was not compromised and visual performance, in terms of best spectacle-corrected visual acuity, forward light scatter, and night halos, was not impaired.

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.

The status of hyperopic laser-assisted in situ keratomileusis.

The development of excimer laser technology, coupled with advances in lamellar corneal surgery, has heralded a new era in the treatment of refractive errors. This paper discusses the current status of hyperopic laser-assisted in situ keratomileusis. This surgical modality is at a relatively early stage of investigation but appears to offer promise for the surgical correction of hyperopia. This paper considers the evolution of the technique, analyzes the current literature, and discusses the current indications, limitations, and possible future developments.

Photorefractive keratectomy. A 6-year follow-up study.

OBJECTIVE: This study aimed to assess the long-term stability and efficacy of excimer laser photorefractive keratectomy. DESIGN: Patients who participated in the first United Kingdom photorefractive keratectomy clinical trial were asked to attend a 6-year follow-up assessment. PARTICIPANTS: Eighty-three patients (68%) of the original cohort of 120 participants were observed for 6 years. A Summit Technology UV200 excimer laser with a 4-mm ablation zone had been used with patients allocated to one of six groups according to their preoperative refraction. Each group received one of the following spherical corrections: -2, -3, -4, -5, -6, or -7 diopters (D). Within each group, all patients received an identical treatment, and thus emmetropia was not the goal in all patients. INTERVENTION: The induced refractive change, objective corneal haze, glare, and halo measurements, together with possible late-phase complications, were analyzed. MAIN OUTCOME MEASURES: All groups achieved a refractive undercorrection, and the magnitude of the undercorrection was related to the size of the attempted correction. The induced refraction stabilized by 6 to 12 months and has been maintained up to the 6-year follow-up stage. RESULTS: Ninety-one percent of patients who underwent a -2.00-D correction and 76% of patients who received a -3.00-D correction were within +/- 1 D of the intended refraction at 6 years. Fifty-seven percent of the -4.00-D group and 50% of those in the -5.00-D group were within +/- 1 D, and this was reduced further to 43% in the -6.00-D group and 19% in the -7.00-D group. Six patients (7%) had evidence of residual corneal haze, which was visually significant in two patients (3%). Ten patients (12%) had significant night halos due to the small 4-mm ablation zone that was used in this early treatment trial. CONCLUSIONS: There was no further regression of the refraction after 1 year, and, more important, there was no sign of hyperopic shift or diurnal fluctuation in the patients' refraction. In addition, corneal haze appeared to reduce further with time, with no intraocular or retinal side effects being noted. Night halos remain a significant reported problem in a small number of patients who were treated with the 4-mm ablation zone.

Excimer laser photorefractive keratectomy for the correction of hyperopia using an erodible mask and axicon system.

PURPOSE: The purpose of the study is to evaluate photorefractive keratectomy for the correction of hyperopia using the erodible mask and Axicon system. METHODS: Forty-three patients (43 eyes) with a mean refraction (spherical equivalent) of +4.54 diopter (D) (range, +1.75 to +7.50 D) were treated using a Summit Technology "Apex Plus" excimer laser. This system uses an erodible mask to create a 6.50-mm diameter hyperopic correction over the axial cornea. An Axicon then is used to fashion a 1.50-mm "blend zone" around the correction. On the basis of preoperative refractions, patients were assigned to 3 groups: 2 groups of 14 patients underwent either "+2.00 D" or "+3.00 D" corrections and 15 patients had "+4.00 D" corrections. RESULTS: All patients had a reduction in their hyperopia with an overcorrection, especially in the first month after surgery and some stability in the refractive change at 3 to 6 months. The mean manifest refraction (n = 43) at 6 months was -0.17 D (range, +4.50 D to -3.125 D). Patient satisfaction was high. At 6 months, all eyes had an improvement in unaided near visual acuity. Unaided distance acuity was improved in 37 eyes (86%). A ring of haze 6.5 mm in diameter appeared in all eyes 1 month after surgery. Night halo measurements at 6 months showed no differences from preoperative levels. Flicker contrast sensitivity and forward light scatter (glare) measurements showed no differences after surgery. CONCLUSIONS: In this short-term study, photorefractive keratectomy for hyperopia using the erodible mask and Axicon system appeared to be a promising procedure. Visual performance, in terms of flicker contrast sensitivity, forward light scatter, and night halos, was not compromised. There was an overcorrection based on the manufacturer's algorithms. Manipulation of the treatment algorithms should improve future predictability.

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.

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.

Indocyanine green angiography of the peripapillary region in glaucomatous eyes by confocal scanning laser ophthalmoscopy.

PURPOSE: To investigate the peripapillary region in glaucomatous eyes by indocyanine green angiography. METHODS: Indocyanine green angiography of the optic disk and peripapillary region was evaluated by modified confocal scanning laser ophthalmoscopy in 22 eyes of 22 patients with glaucoma and in 10 normal eyes of 10 control patients with unilateral choroidal melanoma. The occurrence and extent of indocyanine green angiographic anomalies were correlated with optic disk morphology and the severity of glaucoma. RESULTS: In the 32 eyes of 32 patients, two types of peripapillary defects were identified in the late-phase angiograms. The first was hypofluorescent areas in the peripapillary region and was more common in eyes with glaucoma (P < .02); their occurrence and extent correlated with age (P < .01). In nine of the 17 eyes, alpha (peripheral) zone peripapillary atrophy corresponded with the areas of peripapillary indocyanine green hypofluorescene. The second defect, hypofluorescent halos adjacent to and extending around the full circumference of the optic disk margins, did not correlate with any of the study factors. CONCLUSIONS: Indocyanine green angiography showed areas of hypofluorescene in the peripapillary region in late-phase angiograms in 68% of glaucomatous eyes compared with 20% of control eyes. These hypofluorescent areas might be either of result of blockage of background fluorescence by pigment or caused by an absence of vascular tissue (choriocapillaris).

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.

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.

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.