Evolution of excimer laser corneal surgery

Surgical outcomes of re-excimer laser phototherapeutic keratectomy (re-PTK)

To assess the surgical outcomes of re-excimer laser phototherapeutic keratectomy (re-PTK) for recurrent disease after initial PTK. Retrospective cohort study with historical comparison group. This study involved 56 patients who underwent re-PTK (mean follow-up period: 47.9 ± 36.2 months) at the Baptist Eye Institute, Kyoto, Japan. In all subjects, corrected-distance visual acuity (CDVA) before and after re-PTK was compared. Postoperative recurrence of corneal lesion with a decrease of CDVA of two lines or more was compared with postoperative best CDVA deemed as a significant relapse. The Kaplan–Meier method was used to compare the recurrence rate post-re-PTK with that after the initial PTK. The disease classification in the 78 eyes was heterozygous-type GCD (hetero-GCD, n = 47 eyes), homozygous-type GCD (homo-GCD, n = 13 eyes), band keratopathy (n = 7 eyes), lattice corneal dystrophy (n = 6 eyes), and other (n = 5 eyes). After re-PTK, homo-GCD recurred statistically significantly earlier than hetero-GCD (P = 0.0042). No significant difference was found in the recurrence rate for all diseases between post-re-PTK and post initial PTK (P > 0.05). Surgical outcomes after re-PTK were nearly equal to those after initial-PTK.

Excimer laser tissue interactions in the cornea

Excimer lasers induces significant changes to corneal structure and corneal biomechanics. The aim of this paper is to describe all laser-tissue interactions which are relevant for clinical practice, particularly, we will focus on laser ablations profiles, causes of regression and haze and prevention of those. At last the manuscript will describe the impact on corneal biomechanics of different Laser Vision Corrections techniques.

A long-term study of photorefractive keratectomy; 12-year follow-up

OBJECTIVE

To evaluate long-term refractive stability of excimer laser myopic photorefractive keratectomy (PRK).

DESIGN

A long-term (12 years) prospective follow-up study.

PARTICIPANTS

Sixty-eight patients (56.6%) of the original cohort of 120 who participated in the first United Kingdom excimer laser clinical trial underwent detailed clinical assessment at 12 years after myopic PRK.

INTERVENTION

Myopic PRK was performed using the Summit Technology UV 200 excimer laser with a 4-mm ablation zone. Patients were allocated to 1 of 6 treatment groups based on their preoperative refraction. Each group received one of the following spherical corrections: -2, -3, -4, -5, -6, or -7 diopters (D). Patients in each group received an identical treatment, and therefore, emmetropia was not the primary aim.

MAIN OUTCOME MEASURES

Refractive stability, refractive predictability, best spectacle-corrected visual acuity (BSCVA), and corneal haze.

RESULTS

The postoperative refraction remained stable at 12 years, with no significant change in mean spherical equivalent refraction between 1, 6, and 12 years. Seventy-five percent of patients who underwent a -2-D correction and 65% of patients who received a -3-D correction were within 1 D of intended correction at 12 years. Fifty-seven percent of the -4-D group and 50% of the -5-D group were within 1 D, and this was further reduced to 25% and 22% in the -6-D and -7-D groups, respectively. Four percent had residual corneal haze, and 12% had persistent nighttime halos at 12 years. Dry eyes were encountered in 3% of patients, and none of the eyes developed corneal ectasia in the long term.

CONCLUSIONS

In myopic PRK, refractive stability achieved at 1 year was maintained up to 12 years with no evidence of hyperopic shift, diurnal fluctuation, or late regression in the long term. Corneal haze decreased with time, with complete recovery of BSCVA. Night halos remained a significant problem in a subset of patients due to the small ablation zone size.

Eight-year Follow-up of Photorefractive Keratectomy for Myopia

PURPOSE

We evaluated 8-year results of excimer laser photorefractive keratectomy (PRK) for myopia in terms of stability and late complications.

METHODS

Ninety-two myopic eyes of 55 patients were treated with a single-step method using an Aesculap-Meditec MEL 60 excimer laser with a 5.0-mm ablation zone. Treated eyes were divided into three groups according to preoperative refraction: low myopes (< or = -6.00 D), medium myopes (-6.10 to -10.00 D), and high myopes (>-10.00 D).

RESULTS

Change in myopic regression stabilized in all myopia groups within 12 months, although a small myopic shift occurred up to 8 years after PRK. Mean change in refraction between 2 and 8 years was -0.42 +/- 0.48 D for low myopes, -0.37 +/- 0.34 D for medium myopes, and -0.41 +/- 0.50 D for high myopes. The percentage of eyes within +/- 1.00 D of emmetropia 8 years after PRK was 78.3% in the low myopia group, 68.8% in the medium myopia group, and 57.1% in the high myopia group. One eye lost 2 lines of best spectacle-corrected visual acuity due to irregular astigmatism. In 13.0% of eyes, a residual trace corneal haze was observed, which had no effect on visual acuity. Apart from the loss of 2 lines of BSCVA in one eye, there were no other late complications during the study period.

CONCLUSIONS

The mean change in refraction between 2 and 8 years was less than -0.50 D, regardless of preoperative refraction, and may be attributed to natural age-related refractive change. The appearance of residual corneal haze after 8 years correlated with the amount of myopic correction. PRK was a safe and stable surgical procedure in this group of patients.

Hyperopic laser in situ keratomileusis for refractive accommodative esotropia

PURPOSE

To assess the efficacy of hyperopic laser in situ keratomileusis (LASIK) in creating orthophoria without optical correction in adult patients with refractive accommodative esotropia (RAE).

SETTING

Instituto Oftalmológico de Sabadell, Sabadell, Barcelona, Spain.

METHODS

This prospective single-center clinical trial studied 9 eyes (18 patients) with RAE having hyperopic LASIK. The mean follow-up was 20 months (range 12 to 24 months). The mean preoperative refraction was +5.01 diopters (D) and the mean deviation angle without optical correction, 36 prism diopters. The intervention was hyperopic LASIK using the Automated Corneal Shaper microkeratome (Bausch & Lomb) and the Apollo broad-beam excimer laser using a 5.5 mm optical zone and an 8.0 mm transition zone; astigmatism was treated by steepening the flattest meridian.

RESULTS

All patients achieved orthophoria or the preoperative microtropia without optical correction immediately after surgery. This was maintained throughout the follow-up. Fifty-six percent of all cases were within +/-0.5 D of emmetropia, and 89% were within +/-1.0 D. The uncorrected visual acuity improved significantly (P <.005), especially at near, and the mean best corrected visual acuity (BCVA) was maintained, although 4 eyes (22%) lost 1 line of BCVA. There were no significant complications.

CONCLUSIONS

In adult patients with RAE, treatment of the refractive error using hyperopic LASIK was safe and effective and corrected the esodeviation. Further studies in younger patients will help determine the age at which this intervention may be indicated.

Photorefractive keratectomy using a scanning-slit laser, rotary epithelial brush, and chilled balanced salt solution

PURPOSE

To evaluate photorefractive keratectomy (PRK) using a scanning-slit excimer laser combined with removal of the epithelium using a rotary epithelial brush and prebrush and postoperative cooling of the cornea with chilled balanced salt solution (BSS(R)).

SETTING

Johannesburg Laser Center, Johannesburg, South Africa.

METHODS

In a prospective study, 500 consecutive eyes with myopia ranging from 1.00 to 12.75 diopters (D) and astigmatism up to 6.50 D were treated with PRK using a Nidek EC-5000 scanning-slit excimer laser, removal of the epithelium with a rotary epithelial brush, and prebrush and postlaser cooling of the cornea with chilled BSS (4 degrees C to 6 degrees C). The mean follow-up was 9.32 months (range 1 week to 39 months). Bilateral simultaneous PRK was performed in 238 patients (95.2% of eyes).

RESULTS

After 1 week, uncorrected visual acuity was 20/20, 20/25, 20/30, 20/40, 20/60, and 20/80 in 9.80%, 38.60%, 68.20%, 89.40%, 97.80%, and 97.20% of eyes. After 6 months, in 405 eyes, it was 20/15, 20/20, 20/25, 20/30, and 20/40 in 9.38%, 69.88%, 91.11%, 94.81%, and 98.52%. After 12 months, in 222 eyes, it was 20/15, 20/20, 20/25, 20/30, and 20/40 in 6.76%, 68.92%, 83.78%, 91.89%, and 97.30%. After 18 months, in 95 eyes, it was 20/15, 20/20, 20/25, 20/30, and 20/40 in 6.32%, 69.47%, 88.42%, 91.58%, and 96.84%. Six eyes (1.20%) required retreatment.

CONCLUSIONS

Scanning-slit laser PRK after rotary epithelial scrubbing and prescrub and postlaser cooling allows accurate correction of myopia and astigmatism with minimal regression.

Ablation rate of PMMA and human cornea with a frequency-quintupled Nd:YAG laser (213 nm)

BACKGROUND AND OBJECTIVE

As an alternative to the standard excimer laser used for PRK, we investigated the ablation rate at 213 nm of PMMA, and human corneas under controlled hydration.

STUDY DESIGN/MATERIALS AND METHODS

The output of a frequency-quintupled Nd:YAG laser (213 nm) was transformed into a quasi-Gaussian beam. PMMA and corneal lenticules maintained under controlled hydration were ablated until perforation was detected.

RESULTS

The ablation rate of PMMA and cornea at 213 nm were similar to that at 193 nm when radiant exposure was below 200 mJ/cm2 and increased gradually between one and two times faster than that at 193 nm when radiant exposure was > 200 mJ/ cm2.

CONCLUSIONS

PMMA and cornea ablation at 213 nm are similar to that at 193 nm and are different from that at 248 nm. The difference between PMMA and cornea ablation rates should be considered when using PMMA to test ablated diopter and smoothness for photorefractive surgery.

Using a Nidek excimer laser with a rotary epithelial brush and corneal chilling: clinical results

PURPOSE

To perform a prospective study using a rotary epithelial scrubber, a prescrub, and postoperative cooling of the cornea with chilled balanced salt solution (BSS) (4 degrees C to 6 degrees C) and a Nidek EC-5000 excimer laser.

SETTING

The Johannesburg Excimer Laser Eye Centre, South Africa.

METHODS

The first 90 consecutive eyes with myopia from -1.00 to -10.50 diopters (D) and astigmatism up to 3.00 D were treated. Follow-up was from 9 to 22 months (mean 13.85 months). Bilateral photorefractive keratectomy was performed in 40 patients.

RESULTS

Bilateral vision with a bandage lens on the day after surgery was 20/30, 20/40, and 20/60 in 20%, 60%, and 100% of patients. Uniocular vision was 20/20, 20/25, 20/40, 20/60, and 20/80 in 2.2%, 4.4%, 35.5%, 71.1%, and 93.3% of eyes, respectively. Uncorrected visual acuity (UCVA) on removal of the contact lens was 20/30, 20/40(-1), and 20/60 in 15.79%, 73.48%, and 100% of eyes. After 6 months (82 eyes), UCVA was 20/20, 20/25, and 20/40 in 75.6%, 93.9%, and 100%. After 12 months (36 eyes), it was 20/20 and 20/25 in 83.3% and 100%. No eye required retreatment.

CONCLUSION

Scanning slit laser treatment after precise removal of the epithelium with a rotary scrubber, prescrub, and postlaser cooling allowed rapid, accurate correction of myopia and astigmatism.

Corneal stromal wound healing in refractive surgery: the role of myofibroblasts

While laser and incisional refractive surgery offer the promise to correct visual refractive errors permanently and predictably, variability and complications continue to hinder wide-spread acceptance. To explain variations, recent studies have focused on the role of corneal wound healing in modulating refractive outcomes. As our understanding of the corneal response to refractive surgery broadens, it has become apparent that the response of one cell, the corneal stromal keratocyte, plays a pivotal role in defining the results of refractive surgery. Studies reviewed herein demonstrate that injury-induced activation and transformation of keratocytes to myofibroblasts control the deposition and organization of extracellular matrix in corneal wounds. Myofibroblasts establish an interconnected meshwork of cells and extracellular matrix that deposits new matrix and contracts wounds using a novel and unexpected "shoe-string-like" mechanism. Transformation of keratocytes to myofibroblasts is induced in culture by transforming growth factor beta (TGFbeta) and blocked in vivo by antibodies to TGFbeta. Overall, myofibroblast appearance in corneal wounds is associated with wound contraction and regression following incisional keratotomy and the development of "haze" or increased scattered light following laser photorefractive keratectomy (PRK). By contrast, absence of myofibroblasts is associated with continued widening of wound gape and progressive corneal flattening after incisional procedures. Based on these studies, we have arrived at the inescapable conclusion that a better understanding of the cellular and molecular biology of this one cell is required if refractive surgery is ever to achieve predictable and safe refractive results.

Photorefractive Keratectomy For Hyperopia and Aphakia with a Scanning Spot Excimer Laser

OBJECTIVE

To study the safety, efficacy, predictability, and stability of photorefractive keratectomy (PRK) for hyperopia and aphakia.

METHODS

Fifteen eyes of 15 patients (mean age, 33 +/- 5.95 yrs) were enrolled in the study and divided into three groups. The first group was comprised of six eyes that had hyperopia ranging from +1.75 to +4.75 D; the second group had seven hyperopic eyes ranging from +5.00 to +9.75 D; the third group included two eyes of two aphakic patients. All eyes had PRK with a 193 nm argon fluoride excimer laser (Chiron-Technolas, Keracor 116) with a 10 Hz repetition rate and a fluence of 120 mJ/cm2. The total follow-up time in all eyes was 12 months.

RESULTS

In the lower hyperopia group, 0% eyes were within +/- 0.50 D and 66% (N = 4) of eyes were within +/- 1.00 D of emmetropia with the other two eyes between +1.00 and +2.00 D at 1 year after PRK. In the higher hyperopia group, all eyes had at least +3.00 D of hyperopia at 1 year. In the aphakic group, both eyes achieved less than 50% of the target correction of +10.00 D at 1 year. Final uncorrected visual acuity ranged from 20/20 to 20/30 in the lower hyperopia group, 20/30 to 20/50 in the higher hyperopia group, and count fingers in the aphakic group.

CONCLUSIONS

PRK is a relatively safe, stable, and effective procedure with reasonably good predictability for eyes with less than +5.00 D of baseline hyperopia, and poor predictability for eyes with more than +5.00 D of baseline hyperopia. PRK is ineffective in the correction of aphakia.

Correction of Hyperopia Induced by Photorefractive Keratectomy Using Non-contact Ho:YAG Laser Thermal Keratoplasty

PURPOSE

To evaluate the safety and effectiveness of non-contact holmium:YAG laser thermal keratoplasty in correcting hyperopia induced by photorefractive keratectomy (PRK).

METHODS

Non-contact holmium:YAG laser thermal keratoplasty was applied to 14 eyes with significant hyperopia induced by PRK. The mean spherical equivalent refraction before holmium:YAG laser thermal keratoplasty was +4.20 +/- 1.80 diopters (D) (range, +1.75 to +6.25 D). The results were evaluated 12 months after holmium:YAG laser thermal keratoplasty.

RESULTS

No sight-threatening complications occurred. Recovery of spectacle-corrected visual acuity took from 2 to 6 weeks. The immediate significant myopic shift that developed in all eyes gradually receded over 6 to 8 weeks. All eyes were relatively stable after 9 months. At 12 months, there was no statistically significant difference (p < .005) between the mean preoperative spectacle-corrected visual acuity (0.71 +/- 0.12) and the mean postoperative uncorrected visual acuity (0.65 +/- 0.28). At 12 months there was a mean increase of 4.60 +/- 1.20 D in central keratometric power. Total regression did not occur in any eye.

CONCLUSIONS

Non-contact holmium:YAG laser thermal keratoplasty offers a safe and effective alternative to correct PRK-induced hyperopia.

Photorefractive Keratectomy for Compound Myopic Astigmatism With an Eye Cup Erodible Mask Delivery System

BACKGROUND

The erodible mask is a new energy delivery system for the 193-nm argon fluoride excimer laser. It consists of a polymethyl-methacrylate button, whose profile is transferred by photoablation onto the corneal surface. We present the 6- and 12-month results of this technique in the correction of compound myopic astigmatism.

METHODS

We performed the mask procedure on 21 eyes of 16 subjects (mean age, 30.7 years; range, 24 to 46) to correct combined myopia and astigmatism. Attempted myopic correction ranged between -1.50 diopters (D) and -10.00 D (mean, -7.07 D). Attempted astigmatic correction ranged between -1.50 D and -4.00 D (mean, -2.46 D).

RESULTS

Mean procedure error was: sphere +0.74 D (range, -3.00/+5.00), cylinder -1.41 D (range, -3.50/0.00) at 1 month after surgery; sphere +0.18 D (range, -2.50/+ 3.50), cylinder -1.56 D (range, -4.00/0.00) at 6 months; and sphere -1.30 D (range, -3.00/0.00), cylinder was -1.25 D (range, -2.00/-0.50) at 12 months (10 eyes). During follow up, haze values were never higher than 1, except for one case of haze 2 that regressed to 0 during follow up. Postoperative uncorrected visual acuity improved in all eyes where emmetropia was envisaged; none of the eyes lost spectacle-corrected visual acuity lines 6 or 12 months after surgery.

CONCLUSIONS

The erodible mask proved effective and fairly predictable mainly in the correction of the spherical component of refractive error, while the correction of astigmatism revealed greater unpredictability, with a constant trend to undercorrection.

Efficacy and safety of excimer laser photorefractive keratectomy and radial keratotomy for bilateral myopia

PURPOSE

To compare the safety and efficacy of radial keratotomy (RK) and photorefractive keratectomy (PRK) to correct myopia.

METHODS

In this randomized, prospective, parallel-group study, 33 patients with bilateral myopia of 1.00 to 5.00 diopters (D) had PRK in one eye and RK in the other. The order of surgeries and treatment assignments were randomized, and the bilateral surgeries were within 1 week for each patient. Data were collected using standardized procedures. Clinical measurements and satisfaction surveys were taken in masked fashion.

RESULTS

Eyes that had PRK had statistically significantly more residual myopia than RK-treated eyes at 3, 6, and 12 months postoperatively. This result was attributed to the use of an older excimer laser PRK algorithm that was used at the initiation of the study. No eye that had PRK was overcorrected by 0.50 D or more at 1 year postoperatively, while seven eyes that had RK were overcorrected by at least 0.50 D and six were overcorrected by 1.00 D. Eyes that had PRK had a statistically significant mean shift in the myopic direction between 6 and 12 months postoperatively; two RK eyes had hyperopic shifts of 1.00 D. Three RK eyes and two PRK eyes failed to achieve an uncorrected visual acuity of 20/40 or better by 12 months postoperatively. No eye lost any best corrected visual acuity.

CONCLUSION

The two procedures were comparably safe and effective in treating mild to moderate myopia under this protocol. Eyes that had PRK were somewhat more myopic at 1 year after surgery, attributable to the older PRK ablation algorithm. Adoption of newer (current) laser algorithms has improved the predictability of PRK. There was also evidence of reduced variability of outcome in the PRK group. The PRK eyes did not exhibit hyperopic shifts during the 1 year follow-up.

Surface microarchitectural design in biomedical applications: preparation of microporous polymer surfaces by an excimer laser ablation technique

In this report we demonstrate a microprocessing method to prepare microporous polymer films by an excimer laser ablation technique, which may enable the fabrication of functional biomedical devices such as advanced artificial organs. The irradiation of a KrF excimer laser pulses (wave-length 248 nm; fluence 1 J/cm2 pulse) onto several polymer films was achieved by passing a laser pulse through an optical microscope, resulting in the formation of an etched pit on the irradiated surface due to ablative photodecomposition. The number of pulses and the micropositioning of the irradiation were precisely controlled by a computer-aided control unit. Minimal ablation was observed for polyethylene with very small absorption coefficient (alpha) at 248 nm. For polymers which absorbed the laser photons, the etch depth increased linearly with number of pulses. The etch depth per pulse decreased with an increase in alpha values. An excellent structural quality, with micron-order precision of an etched pit, was found for those polymers with larger alpha values, such as polyimide, segmented polyurethane, and polycarbonate.

Correcting simple myopic astigmatism with the excimer laser

For one year we followed 46 eyes that had photoastigmatic refractive keratectomy with an excimer laser to correct simple myopic astigmatism. Mean preoperative cylinder was -2.50 +/- 0.70 diopters (D); mean preoperative best corrected visual acuity was 20/25 +/- 1 Snellen line. Mean postoperative refraction one year after surgery was -0.5 +/- 0.2, and mean uncorrected visual acuity was 20/25 +/- 1 Snellen line. In all eyes, the final axis of the residual cylinder was +/- 5 degrees around the preoperative axis. Uncorrected visual acuity equaled best preoperative acuity in 24 eyes. Eight eyes gained one line of best corrected visual acuity, six gained more than one line, and eight lost one line. No patient lost more than one line of uncorrected visual acuity. No significant complications such as haze, halos, eccentric ablation, or hypercorrection were observed.

An Empirical Model of Hyperopic Shift With Corticosteroid Modulation and Refractive Power Prediction After Photorefractive Keratectomy

Data from a selected sample of 158 patients who received excimer laser photorefractive keratectomy (PRK) in our center and obtained a desirable refractive outcome at 6-months were analyzed retrospectively to establish an empirical model of refractive power after PRK. This model, generated by a computer-assisted regression program, is presented as a multivariate non-linear quadratic equation. Since the coefficients of each variable (attempted correction and postoperative days) are statistically significant, the estimated influence of the variables on the postoperative refraction from this regression model is reliable and consistent. Therefore, this model has been used to direct the use of corticosteroids for modulating post-PRK refraction. The predictability of this model has also been corroborated by separate data from 1-year follow up of PRK recipients. The recipients whose refraction at 6 months agree with the calculation from this model have obtained an excellent outcome; while those whose refractive outcome deviates from this model have gotten undesirable results.

Multizone Photorefractive Keratectomy for Myopia of 9 to 14 Diopters

We performed photorefractive keratectomy (PRK) using new multizone software of the Summit Omnimed excimer laser (Summit Technology, Inc., Waltham, Mass.) on thirteen highly myopic eyes. Average preoperative myopia was -10.94 diopters (D) (range -8.60 D to -13.50 D). Mean postoperative spherical equivalent refraction was -0.15 D (range +1.50 D to -4.00 D), at 3 months postoperatively. Uncorrected visual acuity of all the eyes improved markedly. There was no serious complication except one eye that lost two lines of spectacle corrected visual acuity possibly due to decentration. Though we need longer follow-up data and a larger sample size, the new multizone software seems to be effective for correcting high myopia.

Photorefractive keratectomy for the correction of myopia and astigmatism

Photorefractive keratectomy corrects myopia with or without astigmatism by decreasing the refractive power of the central cornea. The Colliac matrix formula determines the anterior corneal radius of curvature expected to achieve emmetropia. We used the formula as an algorithm for the computer-controlled delivery of the laser beam. The formula was evaluated by using theoretical and clinical cases. We examined the relationship between the correction induced by photorefractive keratectomy, the diameter of ablation zone, and the thickness of the ablated corneal lenticule on the optical axis. Comparison between attempted and achieved keratometric readings showed the accuracy of the formula to be in the order of +/- 0.75 diopter.

Excimer laser correction of myopic astigmatism

The excimer laser allows the controlled ablation of corneal tissue to correct refractive error. By using a combination of spherical and slit apertures, it is possible to correct both myopia and astigmatism. We report the results of 139 consecutive eyes that had photoastigmatic refractive keratectomy (PARK) for myopic astigmatism (myopia < or = -15.00 diopters [D] with astigmatism < or = -6.00 D) and compare these results with 107 consecutive and concurrent eyes that received photorefractive keratectomy (PRK) for myopia (< or = -15.00 D). The same excimer laser was used by 27 different surgeons. All patients were followed for at least three months. In the PARK group, 68% were within +/- 1.00 D at six months and 77% were within +/- 2.00 D. In the PARK group, these figures were 87% and 97%, respectively. Uncorrected visual acuity of 20/40 or better was achieved in 72% of PARK and 90% of PRK patients at six months. Minor adverse reactions occurred in 6% of PARK and 11% of PRK patients. No significant surgeon effect was seen. Photoastigmatic refractive keratectomy provides a realistic approach to the surgical correction of myopic astigmatism and is comparable to PRK in safety and efficacy.

Ultrasound biomicroscopic assessment of the cornea following excimer laser photokeratectomy

Excimer laser photokeratectomy is used as a refractive tool and in the treatment of superficial corneal disease. Ultrasound biomicroscopy is a new method of ultrasound imaging developed in our laboratories that allows subsurface imaging of ocular structures at microscopic resolution. We used this imaging method to examine 12 patients following excimer laser keratoablation. Following treatment, the normal appearance of a highly reflective Bowman's membrane below the epithelial echo was absent in the treatment zone. Corneal thinning was also noted. Postoperative scarring in the treatment area could be imaged as highly reflective regions in the superficial stroma. In therapeutic cases, corneal opacities could be imaged pretreatment and their depth assessed. The degree of opacity removal could be analyzed post-treatment. Ultrasound biomicroscopy helped assess corneal changes secondary to excimer laser photokeratectomy.

ArF-excimer laser-induced secondary radiation in photoablation of biological tissue

Secondary radiation, emitted during and after the irradiation of corneal, dermal, and dental tissue by an ArF-excimer laser (193 nm), was qualitatively and quantitatively characterized. Emission of secondary radiation was found in the range of 200-800 nm. The intensity of secondary radiation in the range of 200-315 nm (UVC and UVB) is approximately 20% of the total intensity at high laser fluences (> 2 J/cm2), and approximately 50% at moderate laser fluences (< 500 mJ/cm2); 10 muJ/cm2 in the UVC and UVB were measured at the sample surface, at fluences (< 1J/cm2) which are of relevance for clinical procedures on soft tissues. In dental tissue processing, very high fluences (> 5 J/cm2) are required. As a consequence, laser-induced plasma formation can be observed. Secondary radiation can be used as a visible guide for selective removal of carious altered tissue. The data we have found might be of assistance in estimating potential hazards for future mutagenic studies in the field.

Keratophakia and keratomileusis: safety and effectiveness. American Academy of Ophthalmology

The purpose of the Committee on Ophthalmic Procedures Assessment is to evaluate on a scientific basis new and existing ophthalmic tests, devices, and procedures for their safety, efficacy, clinical effectiveness and appropriate uses. Evaluations include examination of available literature, epidemiological analyses when appropriate, and compilation of opinions from recognized experts and other interested parties. After appropriate review by all contributors, including legal counsel, assessments are submitted to the Academy's Board of Directors for consideration as official Academy policy.

Expression of tenascin and fibronectin in the rabbit cornea after excimer laser surgery

In order to investigate the effects of excimer laser surgery on corneal wound healing, 25 rabbits underwent anterior keratectomy at a depth of 100 or 300 microns with a Meditec MEL 50 excimer laser. After various intervals the animals were killed and the cornea excised and investigated immunohistochemically for the expression of extracellular matrix (ECM) proteins, fibronectin and tenascin. Fibronectin was shown to occur earlier than tenascin, and the two also had different distribution patterns. Wound depth showed no clear effect on the localization and time of ECM protein expression. This study indicates that corneal wounds caused by excimer laser radiation and those caused by mechanical surgery differ as to healing mechanisms.

Central photorefractive keratectomy for myopia. Partially sighted and normally sighted eyes

Ten partially sighted and 19 normally sighted eyes underwent excimer laser photorefractive keratectomy for the correction of myopia. Nine of the partially sighted and 17 of the normally sighted eyes had 12 months of follow-up. Epithelial healing was complete in all eyes by day 6. None of the eyes had recurrent erosions, infections, or other medical complications. An increase in corneal haze after surgery was followed by a slow trend toward clearing. Average uncorrected visual acuity in the 7 normally sighted eyes with attempted corrections of 5 diopters (D) or less was 20/40 from month 2 on; the eyes with greater than 5 D attempted corrections had an average of 20/80--at month 2, which declined to 20/200--by month 6. Best spectacle-corrected visual acuity was within +/- 1 Snellen line of preoperative values in 14 of the normally sighted eyes, improved 2 or more lines in 2 eyes, and worsened two or more lines in two eyes. Hard contact lens overcorrection restored all of the two-line loss in 1 eye and 1 line of the 3-line loss in the other. Refraction and keratometry indicated corneal flattening without induced astigmatism.