Undergoing Excimer Laser Photorefractive Keratectomy Research Articles

Higher incidence of steroid-induced ocular hypertension in keratoconus.

BackgroundTo compare intraocular pressure (IOP) changes following topical dexamethasone administration for 1 month in keratoconic versus normal eyes.MethodsThis is a retrospective, single-center, non-randomized case series evaluation of 350 eyes. Two groups were formed: normal/control Group A (nA =73), eyes that underwent excimer laser photorefractive keratectomy; and keratoconic (KCN) Group B (nB =277), eyes that were subjected to partial laser photorefractive keratectomy combined with collagen cross-linking (The Athens Protocol). All eyes received the same post-operative regimen of topical dexamethasone 0.1 % for at least 1 month. Goldmann applanation tonometry IOP readings and central corneal thickness (CCT) measurements were monitored. Cases with induced ocular hypertension (OHT, defined as post-operative IOP higher than 21 mmHg), were identified and correlated to refractive procedure, gender, and corneal thickness.ResultsAt 4 weeks postoperatively, OHT was noted on 27.4 % (20 /73 eyes) in Group A, and 43.7 % (121 /277 eyes) in KCN Group B, (p <0.01). Six months post-operatively (following 5-months of discontinuing topical dexamethasone treatment and commencing treatment of IOP-lowering medications), OHT rate was 1.8 % in Group A and 3.9 % in the KCN Group B.ConclusionThis study demonstrates a potentially significant pre-disposition of keratoconic eyes to the development of steroid-induced OHT.

The shape of the corneal apical zone after excimer photorefractive keratectomy.

Applying an experimental photo-keratoscope, which assesses the shape of cornea within the pupillary region, to a group of subjects who have undergone excimer laser photorefractive keratectomy over a central 4 mm chord diameter of the cornea, we report the shape of the typical cornea within the ablated zone conforms to a steepening ellipse (average shape factor, 1.25). A statistically significant difference in the mean shape factor (asphericity) between the photoablated and the normal cornea (average shape factor 0.89) was not confirmed. However, there is more variability in the shape factors found in the photorefractive keratectomy group compared with normals, within the same distance from the corneal apex. Using the criterion of overlap within two standard deviations, averaging the vertical horizontal meridians, 75% of photorefractive keratectomy eyes fall within the shape factor limits of the normal eye group. In all cases the post-ablated corneal surface was found to be regular in terms of surface quality alone. The excimer photorefractive keratectomy technique is therefore a clinically acceptable method of refractive surgery.

Intraocular Pressure Measurements Using Dynamic Contour Tonometer After Photorefractive Keratectomy

Purpose: To assess the performance of the dynamic contour tonometer (DCT) in eyes undergoing excimer laser photorefractive keratectomy (PRK). Methods: Intraocular pressure (IOP) was measured in 30 eyes after first‐time excimer laser PRK pre‐ and three months post‐operatively using Goldmann applanation tonometer (GAT), noncontact air tonometer (NCT), and the DCT. Results: There was significant correlation between central corneal thickness (CCT) and IOP measurements by GAT and NCT (CCT vs GAT: r2=0.31, p

Changes in Contrast Sensitivity Function and Ocular Higher Order Aberration by Conventional Myopic Photorefractive Keratectomy

To evaluate the relation between induced changes in ocular higher order aberrations and changes in the contrast sensitivity function in patients undergoing excimer laser photorefractive keratectomy (PRK). Myopic PRK using excimer laser was performed in 31 patients (56 eyes). The preoperative refractive error was -6.2 +/- 2.9 diopters. Before and 1 month after surgery, we measured the ocular higher order aberrations for a 4-mm pupil, and three indices of contrast sensitivity function. From the data collected, the area under the log contrast sensitivity function (AULCSF) was calculated. PRK significantly reduced AULCSF (P = 0.004), low-contrast visual acuity (P = 0.004), and letter-contrast sensitivity (P = 0.013). Coma-like (P < 0.001) and spherical-like (P < 0.001) aberrations were significantly increased by surgery. The change in AULCSF by surgery significantly correlated with the change in coma-like (r = -0.468, P < 0.001) and spherical-like (r = -0.291, P = 0.033) aberrations. The change in low-contrast visual acuity by PRK significantly correlated with the change in coma-like aberration (r = 0.599, P < 0.007), but not with change in spherical-like aberrations (r = 0.136, P = 0.326). There were significant correlations between changes in letter-contrast sensitivity and changes in coma-like (r = -0.450, P < 0.001) and spherical-like (r = -0.255, P = 0.048) aberrations. PRK significantly increases ocular higher order aberrations, which compromise contrast sensitivity function after surgery.

Two-Year Results of Photorefractive Keratectomy With Scanning Spot Ablation for Myopia of Less Than -6.0 Diopters

To investigate the efficacy, predictability, stability, and safety of photorefractive keratectomy (PRK) with scanning spot ablation for the treatment of myopia of less than -6.0 D. Twenty eyes of 20 patients (11 men, 9 women) were enrolled into the study. The mean age was 26.2 +/- 5.4 years. Mean spherical equivalent myopia was -3.53 +/- 1.13 D, ranging from -2.25 to -6.00 D. Patients underwent excimer laser PRK for the treatment of myopia. Follow-up time was at least 24 months in all patients. Mean spherical equivalent refraction was +0.84 +/- 0.99 D at 1 month, +0.19 +/- 0.54 at 3 months, -0.01 +/- 0.53 at 12 months, and -0.13 +/- 0.50 at 24 months. There was a mean regression of 0.65 D between 1 and 3 months. At 24 months, 16 (80%) of the eyes remained within +0.50 D of emmetropia and 18 (90%) of the eyes remained within +/- 1.0 D of emmetropia. Nineteen (95%) of the eyes had uncorrected visual acuity of 20/40 or better. The mean corneal haze score was maximum at 3 months (0.88 +/- 0.22). There was no clinically significant corneal haze (greater than 2+). One eye (5%) lost 2 or more lines of best-corrected visual acuity. Excimer laser PRK with the scanning spot ablation technique is effective, predictable, stable, and safe for the treatment of myopia of less than -6.0 D.

Regression of myopia induced by pregnancy after photorefractive keratectomy.

We evaluated refractive corneal changes that occurred in women who become pregnant after undergoing excimer laser photorefractive keratectomy (PRK) for the treatment of myopia. Refractive results of 18 eyes of nine women who underwent PRK and became pregnant during the follow-up period were reviewed. All eyes were followed for a least 12 months after PRK. Subjective refraction, slit-lamp microscopy, and intraocular pressure were measured at each follow-up examination. Twelve of 18 eyes (66%) had myopic regression during the follow-up period. The regression was associated with 1+ to 2+ corneal haze in 10 of these 12 eyes (83.3%). The three women (6 eyes) who had stable refractions after PRK became pregnant at least 5 months postoperatively. The corneal haze and the associated myopic regression improved in 50% of the eyes after delivery. Pregnancy seems to induce effects on corneal wound healing following PRK.

Increased release of tumour necrosis factor-α in human tear fluid after excimer laser induced corneal wound

AIMSTo measure the pre- and postoperative tear fluid tumour necrosis factor-α (TNF-α) concentration and release in patients undergoing excimer laser photorefractive keratectomy (PRK).METHODSTear fluid samples from 18 PRK patients were...

Platelet-derived growth factor-BB (PDGF-BB) in tear fluid: a potential modulator of corneal wound healing following photorefractive keratectomy

PURPOSE. To measure the pre- and postoperative tear fluid platelet-derived growth factor-BB (PDGF-BB) concentrations of patients undergoing excimer laser photorefractive keratectomy (PRK). METHODS. Tear fluid samples from PRK patients were collected with scaled microcapillary tubes preoperatively (Day 0, N = 23), on the second (Day 2, N = 24) and on the seventh (Day 7, N = 14) postoperative days. The PDGF-BB concentration was measured using a sandwich enzyme immunoassay, and the PDGF-BB release was calculated by multiplying the concentration by the tear fluid flow in the collection capillary. RESULTS. The mean tear fluid flow in the capillary was 17.4 µl/min (range 1.4–55.0) on Day 0, 62.6 µl/min (4.3–125.0, p = 0.0000) on Day 2, and 15.5 µl/min (1.2–50.0, NS) on Day 7. Seventeen percent (4/23) of the Day 0 samples contained detectable concentrations of PDGF-BB (range 95–1330 ng/l). On Day 2 all (24/24) tear samples showed significantly increased concentrations (mean 507 ng/l, range 45–2280 ng, p = 0.0001) and releases (mean 27.6 pg/min, range 1.0–98.0; p = 0.0000). On Day 7 PDGF-BB was still measurable in 9/14 samples (mean concentration 194 ng/l, range < 5–925 ng/l, and mean release 1.9 pg/min, range 0.04–6.8 pg/min). CONCLUSIONS. PDGF-BB is an inducible component of tear fluid. In spite of hypersecretion caused by the corneal wound, PDGF-BB concentrations raised significantly during the initial wound healing. Increased PDGF-BB release during the two postoperative days following PRK suggests a role in corneal wound healing.

Release of TGF-ß1 and VEGF in tears following photorefractive keratectomy

PURPOSE. To study the presence and release of tear fluid transforming growth factor-ß1 (TGF-ß1) and vasoendothelial growth factor (VEGF) of 19 patients undergoing excimer laser photorefractive keratectomy. METHODS. Tear fluid samples were collected with scaled micro-capillary tubes preoperatively (Day 0) and on the first or second (Day 1–2) and seventh (Day 7) postoperative days. Since postoperative tear fluid flow was significantly higher, we calculated the release of both growth factors by multiplying the concentration by the tear fluid flow in the capillary. RESULTS. The median tear fluid flow in the capillary was 8.1 µl/ min (range 0.7–20.8) on Day 0, 46.3 µl/min (3.1–135.1) on Day 1–2, and 10.2 µl/min (1.8–65) on Day 7. The median TGF-ß1 concentration and release values were: Day 0: 4.5 ng/ml (0–23) and 24 pg/min (0–257), Day 1–2: 9 ng/ml (0–32) and 446 pg/min (0–4602; p = 0.0014), and Day 7: 6.5 ng/ml (0–44) and 53 pg/min (0–470), respectively. The median VEGF concentrations and releases were: Day 0: 19 ng/ml (14–23) and 128 pg/min (11–458), Day 1–2: 15 ng/ml (11–20) and 695 pg/ min (14–2567; p = 0.0007), and Day 7: 17.5 ng/ml (15–22) and 167 pg/min (27–1235), respectively. CONCLUSIONS. TGF-ß1 and VEGF are components of normal tear fluid. The significantly increased release of both growth factors after excimer laser photorefractive keratectomy may influence the corneal wound healing process.

Psychological aspects of excimer laser surgery for myopia: reasons for seeking treatment and patient satisfaction.

To determine the reasons patients seek excimer laser treatment for myopia and to measure levels of patient satisfaction with each phase of this relatively new treatment. A unique 38 item visual analogue questionnaire was developed and applied to 100 consecutive patients (n = 100) who had undergone excimer laser photorefractive keratectomy for myopia or myopic astigmatism at a single centre. All subjects underwent extensive ophthalmic assessment and patient education before treatment. A 90% response rate was achieved (n = 90). Improved unaided vision (85.6%), freedom from spectacles (83.3%), and difficulties with contact lens wear (72.7%) were the most common reasons for seeking treatment. The majority of patients felt that the quality of their life had improved (85.5%) and 82% felt that the quality of their unaided vision was as good as they had anticipated. overall, 95.5% of patients were pleased that they had undergone this procedure. The vast majority (98.9%) of patients felt that they fully understood the operation pretreatment but almost one quarter (23.9%) found the actual operation distressing. Only 15.7% found postoperative pain did not respond adequately to prescribed analgesia. This study demonstrates a very high level of patient satisfaction after excimer laser treatment for myopia and myopic astigmatism. It suggests that most patients seek treatment to enjoy better vision free from optical aids and that a high level of patient education preoperatively may establish realistic expectations and satisfaction with overall outcome.

Clinical analysis of steep central islands after excimer laser photorefractive keratectomy.

To examine topographic irregularities known as steep central islands that may occur after excimer laser refractive surgery and affect visual acuity. We reviewed the computed corneal topographic maps of 35 eyes that had undergone excimer laser photorefractive keratectomy with an excimer laser for compound myopic astigmatism or anisometropic myopia. Steep central islands were defined as areas of steepening of at least 3 diopters and 1.5 mm in diameter. A classification system was developed based on the presence of steep central islands during the postoperative period as follows: class 0, absent; class 1, present at 1 week; class 2, present at 1 month; class 3, present at 3 months. Steep central islands were seen in 25 eyes (71%) at 1 week, 18 eyes (51%) at 1 month, seven eyes (20%) at 3 months, and four eyes (11%) at 6 months. After surgery without nitrogen gas blowing, 16 of 25 patients had class 2 or 3 steep central islands compared with two of 10 eyes when gas blowing was used. Loss of best spectacle-corrected visual acuity of 2 Snellen lines or more was seen in eight of 18 eyes with class 2 or 3 steep central islands at 1 month and three of 18 eyes at 3 months. A similar loss occurred in one of 17 eyes with class 0 or 1 steep central islands at 1 month and none of 17 eyes at 3 months. In all eyes with only class 2 steep central islands, loss of at least 1 Snellen line of best spectacle-corrected visual acuity at 1 month was associated with visual restoration at 3 months when the island was no longer present. Loss of best spectacle-correlated visual acuity is associated with steep central island formation, and may prolong visual rehabilitation after excimer laser photorefractive keratectomy.

Assessment of subjective pain following photorefractive keratectomy. Melbourne Excimer Laser Group.

Although researchers have reported that postoperative pain in patients undergoing excimer laser photorefractive keratectomy (PRK) surgery is common in the first 24 hours after excimer surgery, factors associated with increased postoperative pain have not been reported. The purpose of this study was to prospectively document self-reported pain following excimer laser surgery and explore associated factors. Consecutive patients undergoing excimer laser photorefractive keratectomy (PRK) surgery to correct myopia and/or myopic astigmatism were asked to prospectively grade, on a four-point scale, the amount of pain they were experiencing immediately after treatment and again 2, 4, 8, 24, and 48 hours after surgery. They were also asked to record the type and dose of all medication taken during that time period. Pain questionnaires were returned by 62 patients (72%), ranging in age from 20 to 54 years. The mean self-reported pain overall peaked 24 hours after treatment. Amount of myopia and prior excimer experience were not related to use of analgesia or self-reported pain (both p > 0.10). Patients who had three additional topical drops of indomethacin postoperatively reported significantly less pain 24 hours after treatment (t = 5.95, p = 0.0001). These results have implications for the education of patients about the likely course of healing after PRK. A course of five drops of topical indomethacin should be evaluated with a randomized clinical trial to assess efficacy in inhibiting ocular pain after PRK.

Corneal Topography of Phase III Excimer Laser Photorefractive Keratectomy: Optical Zone Centration Analysis

To determine the amount of optical zone decentration in patients who have undergone excimer laser photorefractive keratectomy (PRK) and assess associations of both decentration and optical zone size with clinical outcomes. Optical zone centration in 185 patients after PRK was analyzed using computer-assisted videokeratography. A comparison of decentration among the five study centers was performed. Associations of clinical outcomes with procedure decentration and optical zone size were assessed. Decentration from the pupil center ranged from 0.00 to 1.44 mm (mean, 0.46 mm): 21.8% were decentered 0.25 mm or less, 42.5% > 0.25 mm and < or = 0.50 mm, and 97.1% < or = 1.00 mm. In both eyes, the average decentration from the pupil center was located inferonasally. Decentrations among the five study centers were significantly different. Decentration was associated with attempted refractive correction, change in keratometric cylinder, and patient satisfaction. There was a trend toward worse postoperative uncorrected visual acuity with greater decentration but no association with best-corrected vision, predictability, or refractive astigmatism. No significant relation was found between decentration and glare/halo ranking; however, three of six patients with 1.00 mm or greater of decentration demonstrated a high glare/halo grade. Although optical zone size was not associated with glare or halo, subjective patient satisfaction was greater with a 5.0-mm optical zone than with a 4.5-mm optical zone. Centration is an important surgeon-controlled variable in excimer laser PRK. Decentration of excimer laser refractive procedures was found to be nonrandom and may be influenced by preoperative pupil management. Moreover, the amount of decentration may influence clinical outcomes. Improved techniques and centering procedures on nonmiotic pupils may improve future results.

Stereopsis and Accommodation Following Photorefractive Keratectomy (PRK) for Myopia

Objective: To study the effect of excimer laser photorefractive keratectomy (PRK) for myopia on accommodation and stereopsis. Study Design: Myopes treated with Summit Technology UV 200 excimer laser PRK were followed prospectively for a mean period of 13 months (range, 9–16 months). Setting: The Laser Unit of the Mater Private Hospital, Dublin, Republic of Ireland. Patients: Twenty-one patients with a mean age of 25.95 years (range, 20–33 years) and a mean refractive error of −3.80 D (range, −1.50–6.00 D) underwent excimer laser PRK for myopia. Mean prelaser amplitude of accommodation (AA) was 10.0 D (range, 8–13). Mean prelaser near stereopsis was 52 second of are (range, 40–140) and mean distant stereopsis was 143 second of arc (range, 30–240). Main Outcome Measures: AA, near and distant stereopsis, accommodative convergence/accommodation (AC/A) ratio and ocular alignment were assessed preoperatively and at 3 and 12 months postoperatively. Nine of the 21 patients underwent PRK in their 2nd eye and had these measurements carried out 3 months following the 2nd treatment. Subjective complaints of asthenopic or presbyopic symptoms were recorded. Results: No patients complained of asthenopic or presbyopic symptoms. Only 3 patients (14.28%) had asymptomatic persistent reduction of AA of ≥ 2 D (mean, 3 D). Near stereopsis was reduced by a mean of 88 seconds of arc in 11 patients (52.3%) at the 3 months visit (range, 10–360). Four of those affected (36.3%) regained their preoperative near stereopsis spontaneously by the end of the study follow-up period and 4 others (36.3%) 3 months following treatment of the 2nd eye. Distant stereopsis was reduced by a mean of 103 seconds of arc (range, 60–180) in 8 patients (38%). Only those who underwent PRK in the 2nd eye (3 patients) recovered their preoperative distant stereopsis. No change in AC/A ratio or ocular alignment was noted in any case. Significantly greater numbers of patients recovered distant stereopsis following treatment of the 2nd eye than recovered it spontaneously ( P = 0.01, tailed value). There was no such significant difference for near stereopsis. Conclusions: Binocular function is disturbed in half those undergoing PRK for myopia for their 1st eye. Despite this, no patients complained of asthenopia or reduced binocular function. Treatment of the fellow eye restored near and distant stereopsis in all cases studied.

Effect of photorefractive keratectomy on visual functioning and quality of life.

The authors present the results of the psychosocial outcomes of 45 patients undergoing excimer laser photorefractive keratectomy (PRK). The patients were evaluated by means of self-report questionnaires preoperatively and 6 months after surgery to determine the effect of uncorrected vision change on the patients quality of life. The measurements include the following variables: clinical end points (spherical equivalent refraction); visual function (night driving, day driving, near vision, far vision, glare disability); functional status (physical, social, and role functioning, mental status); general well-being (health perceptions, personal well-being, overall quality of life); and satisfaction with surgery (expectations, satisfaction with medical staff, postoperative pain, satisfaction with treatment outcomes). Preliminary results indicate that changes of uncorrected vision after PRK are reflected by improvement in each of the quality-of-life functions.

Correction of Myopia and Astigmatism Using an Ablatable Mask

Most excimer laser refractive procedures use a computer driven mechanical diaphragm to shape the laser beam. Studies are currently underway using an ablatable polymethylmethacrylate (PMMA) mask to transfer a new spherical or toric curve to the cornea for the correction of myopia and astigmatism; it may leave a smoother corneal surface than diaphragm procedures. As part of a Phase IIb FDA clinical study, 25 eyes of 25 patients underwent excimer laser photorefractive keratectomy using a hand held ablatable mask. Fifteen eyes had attempted spherical corrections of up to 6.00 diopters (D) and 10 had toric corrections of up to 6.00 D of sphere and 2.75 D of astigmatism. Seventy-four percent of all eyes achieved uncorrected visual acuity of 20/40 or better--86% in the spherical group and 63% in the astigmatism group. Sixty-nine percent of eyes were within +/- 1 D of the attempted correction. In eyes treated for astigmatism, mean astigmatism decreased from 1.48 D preoperatively to 0.86 D postoperatively. Approximately one half of the eyes treated for astigmatism had a decrease in cylinder of more than 0.5 D. One eye lost 2 Snellen lines of best spherical corrected visual acuity. Video keratography showed toric ablations to result in an elliptical optical zone. Analysis of centration of the procedure showed 66% of ablations centered within 1.0 mm of the center of the pupil aperture. The ablatable mask represents a promising modality for the treatment of eyes with both myopia and myopic astigmatism.

Short-Term Corneal Endothelial Changes after Photorefractive Keratectomy

Clinical results show that photorefractive keratectomy (PRK) offers good predictability, efficacy, and safety. However, its potential risks on the human corneal endothelium are poorly known. We report the results of a prospective study conducted to evaluate the corneal endothelium changes after photorefractive keratectomy. Preoperative and serial postoperative specular microscopy was performed in 14 eyes undergoing excimer laser photorefractive keratectomy. The endothelium was analyzed for a variety of parameters, including cell density, coefficient of variation in cell size, and hexagonality. The follow-up was 6 months. The mean cell density was unchanged from 2463 cells/mm2 to 2498 cells/mm2 at 6 months after photorefractive keratectomy. The coefficient of variation of cell size (polymegathism) changed from 0.303 to 0.280 at 1 month, to 0.293 at 3 months, and to 0.290 at 6 months after surgery. The changes in this parameter were statistically significant when comparing pre- versus 1 month postoperative values. The hexagonality was unchanged from 72.08% at baseline to 73.35% at 6 months. No endothelial abnormalities were found after photorefractive keratectomy. Our results suggest a cell migration from the peripheral to central cornea after photorefractive keratectomy in contact lens wearing patients prior to photorefractive keratectomy.

Excimer laser photorefractive keratectomy: 12 months' follow‐up

To report the results of 12 months' follow-up of patients with myopia treated with excimer laser photorefractive keratectomy. A prospective study of patients undergoing excimer laser photorefractive keratectomy for myopia was commenced in September 1991. The study included 50 eyes (38 patients) with preoperative myopia of -1.50 to -6.00 dioptres and a maximum astigmatism of 0.75 dioptres. Forty-six (92%) of the 50 eyes had an uncorrected acuity of 6/6 or better at 12 months, and 49 eyes (98%) had 6/12 or better. No patients had lost their best corrected acuity at 12 months. Forty-five eyes (90%) were within 0.50 dioptres of emmetropia and 47 eyes (94%) were within 1.00 dioptre of emmetropia. Excimer laser photorefractive keratectomy is a safe and predictable procedure for low to moderate myopia. It will increasingly be offered to patients as an alternative to the use of spectacles and contact lenses.

Effect of Centering Excimer Laser PRK on Refractive Results: A Corneal Topography Study

Computer-assisted analysis of corneal topography, using an EyeSys Corneal Analysis System instrument, was performed on 20 normally sighted human eyes that underwent excimer laser photorefractive keratectomy (PRK) to correct high myopia from 6.00 to 17.00 D (mean 10.90 +/- .SD 2.90 D). Ablations utilized one or two zones, at a single time, with an ExciMed UV200 193-nanometer excimer laser (Summit Technology, Inc, Waltham, Mass). Mean follow up was 28.9 weeks (+/- 13). Decentered treatment caused an average error of 1.06 D in the attempted refractive result.

A morphological study of rabbit corneas after laser keratectomy.

We have examined the morphology of the collagen and proteoglycans in rabbit corneas that have undergone excimer laser photorefractive keratectomy using a clinical, 193 nm excimer laser. The photoablation was carried out to a stromal depth of 100 microns and a diameter of 6 mm. All ablated corneas developed a haze that was most intense between week 4 and week 8 and which showed no improvement after week 16. The corneas were stained with the cationic dye cuprolinic blue to visualise proteoglycans and were then processed for transmission electron microscopy. The ultrastructural location of proteoglycans (keratan sulphate and dermatan sulphate) was observed in the corneal wounds at different time intervals. Corneas that had undergone steroid treatment post-operatively were also examined. In the healing tissue proteoglycan filaments of abnormal size were observed, which became most prominent after 2 weeks. As healing progressed these abnormal filaments decreased but after 45 weeks some were still present, indicating that the proteoglycan content had not returned to normal.