Positive and negative impacts of flue gas desulfurization (FGD) gypsum on water quality

Flue gas desulfurization (FGD) gypsum, a by-product of carbon-based energy sources, has typically been incorporated as a component of concrete mixes and wallboard and beneficially used as an agricultural amendment to enhance terrestrial crop production and improve the quality of runoff. These various uses for the by-product aid in reducing the amount that is ultimately landfilled. Limited studies have investigated its benefits when used directly in aquatic settings, such as ponds and lakes, to increase hardness and potentially mitigate eutrophication. A 36-day field mesocosm experiment tested a larger range of FGD gypsum concentrations (500-2000 mg/L) than those previously tested in the literature to investigate its desired and potentially undesired impacts on water quality, including the algal community. High FGD gypsum concentrations, 1000 and 2000 mg/L, were found to have more undesired impacts than the 500 mg/L treatment, including an initial spike in cyanobacteria, a decrease in total zooplankton abundance, and an increase in certain trace metals in the highest treatment. Ultimately, the 500 mg/L FGD gypsum treatment was found to have fewer undesired impacts while still resulting in significant desired effects, including those on hardness and pH, as well as moderate reductions in algal abundance. This experiment provides a better understanding of the effects of FGD gypsum when directly used in an aquatic setting, determines an optimal dose for future field experiments, and helps provide the groundwork for developing an upper threshold on FGD gypsum so as to not have the negative effects outweigh the positive.

Efficient Transport Networks in a Dual Electron/Lithium-Conducting Polymeric Composite for Electrochemical Applications

In this work, an all-functional polymer material composed of the electrically conductive poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) and lithium-conducting poly(ethylene oxide) (PEO) was developed to form a dual conductor for three-dimensional electrodes in electrochemical applications. The composite exhibits enhanced ionic conductivity (∼10^-4 S cm^-1) and, counterintuitively, electronic conductivity (∼45 S cm^-1) with increasing PEO proportion, optimal at a monomer ratio of 20:1 PEO:PEDOT. Microscopy reveals a unique morphology, where PSS interacts favorably with PEO, destabilizing PEDOT to associate into highly branched, interconnected networks that allow for more efficient electronic transport despite relatively low concentrations. Thermal and X-ray techniques affirm that the PSS-PEO domain suppresses crystallinity, explaining the high ionic conductivity. Electrochemical experiments in lithium cell environments indicate stability as a function of cycling and improved overpotential due to dual transport characteristics despite known issues with both individual components.

Catalytic, Conductive Bipolar Membrane Interfaces through Layer-by-Layer Deposition for the Design of Membrane-Integrated Artificial Photosynthesis Systems

In the presence of an electric field, bipolar membranes (BPMs) are capable of initiating water disassociation (WD) within the interfacial region, which can make water splitting for renewable energy in the presence of a pH gradient possible. In addition to WD catalytic efficiency, there is also the need for electronic conductivity in this region for membrane-integrated artificial photosynthesis (AP) systems. Graphene oxide (GO) was shown to catalyze WD and to be controllably reduced, which resulted in electronic conductivity. Layer-by-layer (LbL) film deposition was employed to improve GO film uniformity in the interfacial region to enhance WD catalysis and, through the addition of a conducting polymer in the process, add electronic conductivity in a hybrid film. Three different deposition methods were tested to optimize conducting polymer synthesis with the oxidant in a metastable solution and to yield the best film properties. It was found that an approach that included substrate dipping in a solution containing the expected final monomer/oxidant ratio provided the most predictable film growth and smoothest films (by UV/Vis spectroscopy and atomic force microscopy/scanning electron microscopy, respectively), whereas dipping in excess oxidant or co-spraying the oxidant and monomer produced heterogeneous films. Optimized films were found to be electronically conductive and produced a membrane ohmic drop that was acceptable for AP applications. Films were integrated into the interfacial region of BPMs and revealed superior WD efficiency (≥1.4 V at 10 mA cm^-2 ) for thinner films (<10 bilayers≈100 nm) than for either the pure GO catalyst or conducting polymer individually, which indicated that there was a synergistic effect between these materials in the structure configured by the LbL method.

Reduced Graphene Oxide Bipolar Membranes for Integrated Solar Water Splitting in Optimal pH

The integration of light absorbers and catalysts for the water splitting process requires a membrane capable of both ion and electron management and product separation to realize efficient solar fuels systems. Bipolar membranes can maintain a pH gradient for optimal reaction conditions by the dissociation of water. Such membranes that contain graphene in the interfacial layer are fabricated by the chemical reduction of a uniformly deposited graphene oxide layer to convert sp(3) catalyst regions to sp(2) conductive regions. The resulting electrical and water dissociation properties are optimized by adjusting the exposure conditions, and treatments of less than 5 min render an interface that exceeds the conductivity requirements for integrated solar water splitting and increases the overpotential by <0.3 V. Integration with photoelectrodes is examined by characterizing the electrical interface formed between graphene and Si microwires, and we found that efficient Ohmic junctions are possible.

Use of bipolar membranes for maintaining steady-state pH gradients in membrane-supported, solar-driven water splitting

A bipolar membrane can maintain a steady-state pH difference between the sites of oxidation and reduction in membrane-supported, solar-driven water-splitting systems without changing the overall thermodynamics required to split water. A commercially available bipolar membrane that can serve this purpose has been identified, its performance has been evaluated quantitatively, and is demonstrated to meet the requirements for this application. For effective utilization in integrated solar-driven water-splitting systems, such bipolar membranes must, however, be modified to simultaneously optimize their physical properties such as optical transparency, electronic conductivity and kinetics of water dissociation.

Graphene oxide as a water dissociation catalyst in the bipolar membrane interfacial layer

Bipolar membranes are formed by the lamination of an anion- and cation-exchange layer. Upon a sufficient applied reverse bias, water molecules at the layer junction dissociate, generating OH(-) and H(+), which can be useful in electrodialysis and electrosynthesis applications. Graphene oxide has been introduced into bipolar membrane junctions (illustrated in the adjacent graphic) and is shown to be an efficient new water dissociation catalyst, lowering the overpotential by 75% compared to a control membrane. It was found that adjusting deposition conditions changes the nature of the graphene oxide films, leading to tunable membrane performance. Additionally, it is shown that their low overpotentials are stable, making for industrially viable, high-performance bipolar membranes.

Novel conducting polymer-heteropoly acid hybrid material for artificial photosynthetic membranes

Artificial photosynthetic (AP) approaches to convert and store solar energy will require membranes capable of conducting both ions and electrons while remaining relatively transparent and chemically stable. A new approach is applied herein involving previously described in situ chemical polymerization of electronically conducting poly(3,4-ethylenedioxythiophene) (PEDOT) in the presence of proton conducting heteropoly acid (HPA) phosphomolybdic acid (PMA). The electrochemical behaviour of the PEDOT/PMA hybrid material was investigated and it was found that the conducting polymer (CP) is susceptible to irreversible oxidative processes at potentials where water is oxidized. This will be problematic in AP devices should the process occur in very close proximity to a conducting polymer-based membrane. It was found that PEDOT grants the system good electrical performance in terms of conductivity and stability over a large pH window; however, the presence of PMA was not found to provide sufficient proton conductivity. This was addressed in an additional study by tuning the ionic (and in turn, electronic) conductivity in creating composites with the proton-permselective polymer Nafion. It was found that a material of this nature with near-equal conductivity for optimal chemical conversion efficiency will consist of roughly three parts Nafion and one part PEDOT/PMA.

Predicting blood usage in cardiac surgery--the transfusion predictor product

Blood cross-matched for patients undergoing cardiac surgery is used infrequently and represents a significant cost. We investigated the ability to predict the need for intraoperative transfusion. We hypothesized that red blood cell volume is a predictor because dilution is the primary cause for transfusion requirement intraoperatively. A total of 401 consecutive patients having cardiothoracic surgery requiring the use of cardiopulmonary bypass were retrospectively analyzed by revision of their perfusion record. This sample included 82% elective, 17% urgent, and 1% emergency procedures. The product of body surface area and preoperative hemoglobin gave us gHb/l/m2, which are the units of the Transfusion Predictor Product (TPPU). Mean patient age was 66.9 +/- 10.7 years, and 112 (28%) were women. Mean TPP was 257.2 +/- 45.5u. 52 patients (13%) received red blood cells intraoperatively. At less than TPP 211.7u, one standard deviation below the mean value, 32 patients of 69 (46%) received blood transfusion intraoperatively (p < 0.001). At a TPP greater than 211.7u, 20 patients of 322 (6%) had blood transfusion intraoperatively. Patients with a TPP > 211.7u do not require routine cross-matching of blood. Cross-matching for these patients should be individualized on the basis of predicted duration of CPB and/or other types of patient comorbidity.

Effect of larger ablation zone and transition zone on corneal optical aberrations after photorefractive keratectomy

OBJECTIVE

To evaluate the effects of photorefractive keratectomy on corneal optical aberrations using a 5.5-mm optical zone and a 7.0-mm transition zone.

METHODS

Videokeratographs of 72 eyes from 47 patients treated for low to moderate (1-9 diopters) myopia were obtained at the preoperative and 1-, 3-, 6-, 12-, and 18-month postoperative examinations. The videokeratoscopy data files were used to calculate the wavefront variance of the corneas for small (3-mm) and large (7-mm) pupils using a previously described method.

RESULTS

In general, all optical aberrations decreased postoperatively for 3-mm pupils and increased for 7-mm pupils compared with preoperative values. For 3-mm pupils, the 2 common optical aberrations (comalike [S(3)] and spherical-like [S(4)]) decreased postoperatively and never returned to preoperative values. For 7-mm pupils, however, comalike aberrations increased slightly and spherical-like aberrations increased by nearly an order of magnitude during the postoperative period. Similarly, for 3-mm pupils, the higher order S(5) and S(6) aberrations decreased throughout the postoperative period, with S(6) values showing an approximately 23-fold reduction at 12 and 18 months. For 7-mm pupils, S(5) and S(6) aberrations increased slightly, more so for S(5) (approximately 3-fold) than for S(6). Total wavefront aberrations decreased an average of 2.3 times postoperatively for 3-mm pupils, and increased significantly (P<.05) at all postoperative examinations for 7-mm pupils. Opening the pupil from 3 mm to 7 mm before surgery produced a 14-fold increase in total aberrations, whereas this same change produced an average 113-fold increase after photorefractive keratectomy.

CONCLUSIONS

Corneal optical aberrations after photorefractive keratectomy with a larger ablation zone and a transition zone are less pronounced and more physiologic than those associated with first-generation (5-mm) ablations with no transition zone.

CLINICAL RELEVANCE

Evaluating the postoperative corneal aberration structure will help us devise ways to minimize the wavefront aberrations of the eye through the creation of an ideal corneal first surface, thereby improving visual results for patients undergoing excimer laser ablations for refractive correction.

Laser in situ keratomileusis for myopia up to -11 diopters with up to -5 diopters of astigmatism with the summit autonomous LADARVision excimer laser system

OBJECTIVE

To assess the safety and effectiveness of the Summit Autonomous LADARVision active tracking narrow beam excimer laser system for laser in situ keratomileusis (LASIK) correction of myopia and astigmatism.

DESIGN

A multicenter, prospective noncomparative case series.

PARTICIPANTS

This cohort consisted of 177 eyes corrected for spherical myopia up to -11 diopters (D) and 170 eyes corrected for myopia up to -11 D spherical equivalent with astigmatism up to -5 D.

INTERVENTION

Treatments were performed at four sites in the United States using a 6-mm optic zone for spherical myopes and a 5.5-mm optic zone with a 1-mm blend for astigmats.

MAIN OUTCOME MEASURES

Visual acuity, subjective refraction, vector analysis, subject satisfaction, intraocular pressure, complications, and adverse reactions.

RESULTS

Six-month follow-up was available on 157 spherical eyes and 113 astigmatic eyes. For spherical myopes, uncorrected visual acuity (UCVA) was 20/20 or better in 60.5%, 20/25 or better in 80.3%, and 20/40 or better in 93.9%. The mean spherical equivalent was -0.29 +/- 0.45 D with 75.2% +/- 0.50 D and 94.9% +/- 1.00 D of intended. A loss of two lines of best spectacle-corrected visual acuity (BSCVA) occurred in 0.6%, and no eyes lost greater than two lines of BSCVA. For astigmatic myopes, UCVA was 20/20 or better in 52.0%, 20/25 or better in 74.5%, and 20/40 or better in 94.1%. The mean spherical equivalent was -0.23 +/- 0.49 D with 75.2% +/- 0.50 D and 95.6% +/- 1.00 D of intended. A loss of two lines of BSCVA occurred in 0.9%, and no eyes lost greater than two lines of BSCVA. Vector analysis showed that 99% of the intended cylinder was corrected on average with a mean angle of error of 4.2 degrees. Refractive stability was achieved between 1 and 3 months in 97.5% of spherical eyes and 99.4% of astigmatic eyes and confirmed between 3 and 6 months in 100% of both spherical and astigmatic eyes.

CONCLUSIONS

Eyes treated for myopia up to -11 D of spherical equivalent with or without astigmatism up to -5 D show early refractive stability, good UCVA outcomes, no significant loss of BSCVA, accurate correction of astigmatism, and slight undercorrection without a change from the photorefractive keratectomy algorithm and with a single treatment.

Contrast sensitivity evaluation after laser in situ keratomileusis

OBJECTIVE

To determine the effects of laser in situ keratomileusis (LASIK) on best-corrected visual acuity (BCVA) and contrast sensitivity.

DESIGN

Prospective, observational case series.

PARTICIPANTS

One hundred twelve eyes, in 65 patients with myopia and myopia with astigmatism, who underwent LASIK. TESTING AND MAIN OUTCOME MEASURES: Best-corrected visual acuity using the Snellen visual acuity chart and contrast sensitivity using the CSV 1000 (Vector Vision, Dayton OH) was tested before surgery and 1 week, 1 month, and 3 months after surgery in patients who underwent LASIK.

RESULTS

Contrast sensitivity was depressed for patient eyes with spherical equivalence (SE) between -1.25 diopters (D) and -13.75 D, at 12 cycles/degree for at least 3 months and at 18 cycles/degree for 1 week after LASIK. For patient eyes with SE between -1.25 D and -6.00 D, contrast sensitivity was depressed only at 12 cycles/degree for at least 3 months after LASIK. For patient eyes with SE between -6.00 D and -13.75 D, contrast sensitivity was depressed at 6, 12, and 18 cycles/degree 1 week after LASIK but returned toward preoperative levels by 1 month after surgery. Despite the slight decreases in contrast sensitivity, all scores were still within the range of normal values except for 12 cycles/degree for 3 months and 18 cycles/degree at 1 week after surgery in the high myopia group. Although highly myopic patients, compared with patients with low myopia, had slightly less BCVA before surgery, both groups maintained their preoperative BCVA at all postoperative visits.

CONCLUSIONS

Based on this study, we conclude that LASIK has little effect on BCVA and contrast sensitivity for up to 3 months after surgery.

Efficacy of abciximab readministration in coronary intervention

Abciximab, an Fab monoclonal antibody fragment that blocks the platelet glycoprotein IIb/IIIa receptor, is increasingly used as an adjunct to coronary intervention. Little is known, however, about the efficacy and safety of readministration of abciximab. This study examined and characterized outcomes of patients receiving abciximab for a second time. From April 1995 to June 1997, 164 consecutive patients were readministered abciximab at our 3 institutions. We retrospectively examined and analyzed in-hospital outcomes in this cohort. The median time to readministration was 95 days. The angiographic success rate of percutaneous intervention was 99.5%. Rates and 95% confidence intervals of in-hospital events were death 2% (0.7% to 6.1%), myocardial infarction 3% (1% to 7%), coronary bypass surgery 0% (0% to 2.2%), and intracranial hemorrhage 2% (0.4% to 5.3%). Severe thrombocytopenia was observed in 4% of patients (1.4% to 7.8%) after readministration. Allergic or anaphylactic reactions were not observed. Major bleeding was associated with excessive concomitant antithrombotic therapy. Patients undergoing readministration of abciximab within 2 weeks of first administration experienced a higher incidence of severe thrombocytopenia (12% vs. 2%, p = 0.046). Thus, abciximab remains clinically efficacious when readministered as an adjunct to percutaneous coronary intervention. However, concomitant heparin administration must be carefully monitored and warfarin therapy should be avoided. Vigilant surveillance for thrombocytopenia should be employed. Reduced dosing may be necessary when abciximab is readministered within days of the initial administration.

Comparison of ketorolac tromethamine, diclofenac sodium, and moist drops for ocular pain after radial keratotomy

PURPOSE

To compare the 2 most popular commercially available topical nonsteroidal anti-inflammatory drugs (NSAIDs) in the treatment of ocular pain following radial keratotomy (RK).

SETTING

Multicenter clinical trial.

METHODS

Ninety-seven RK patients were randomly assigned to 1 of 3 treatment groups: ketorolac tromethamine, diclofenac sodium, and moist drops as a control. The patients used 1 drop of the masked medication and 1 drop of ofloxacin 3 times a day for 3 days prior to surgery. They received 1 drop of the masked medication 1 hour before surgery, immediately after surgery, and 4 times a day thereafter. Patients were given a written questionnaire preoperatively and were also instructed to call a central computerized telephone system to answer prerecorded questions about ocular comfort. The calls were placed 30 minutes and 1, 2, 3, 4, 5, 6, 24, and 48 hours after surgery.

RESULTS

Two hundred ten statistical values were calculated to compare symptoms in the unoperated eye at baseline with symptoms in the operated eyes at each of 9 postoperative time points. Only 7 of the 210 values (3.3%) were significantly different among patient groups (operated versus unoperated eyes) by psychometric testing.

CONCLUSIONS

Both ketorolac tromethamine and diclofenac sodium were more effective in reducing post-RK discomfort than the control (moist artificial tears). Given the large number of tests and the small number that tested as significant, the significant differences (7 of 210 measurements) observed among the 3 treatment groups probably occurred by chance, although the improved foreign-body sensation, functionality, and compliance scores in the ketorolac group during the first 4 hours might be clinically important.

Photorefractive keratectomy for low-to-moderate myopia and astigmatism with a small-beam, tracker-directed excimer laser

OBJECTIVE

To assess the safety and effectiveness of the Autonomous Technologies Corporation LADARVision excimer laser system for photorefractive keratectomy correction of myopia and astigmatism.

DESIGN

A multicenter, prospective, noncomparative case series.

PARTICIPANTS

The cohort consisted of 467 eyes corrected for spherical myopia and 211 eyes corrected for myopia with astigmatism.

INTERVENTION

Treatments were performed at six sites in the United States using a 6-mm ablation zone for spherical myopes and a 5.5-mm zone with a 1.0-mm blend for astigmats.

MAIN OUTCOME MEASURES

Visual acuity, subjective refraction, corneal haze, intraocular pressure, complications, adverse reactions, patient satisfaction, and corneal endothelial changes.

RESULTS

Twelve-month follow-up was available on 414 spherical eyes and 175 astigmatic eyes. The results for spherical eyes with correction between -1 and -5.99 diopters (D) were: uncorrected visual acuity (UCVA) of 20/40 or better achieved by 98.1%, 20/20 or better by 72%, 1.8% lost 2 lines and 0.3% lost greater than 2 lines of best spectacle-corrected visual acuity (BSCVA); 76.4% were within 0.50 D of the target correction and 94.4% were within 1.00 D. The results for myopia with astigmatism with spherical equivalent correction between -1 and -5.99 D were: UCVA of 20/40 or better in 97.4%, 20/20 or better in 61.7%, 2.5% lost 2 lines and no eyes lost greater than 2 lines BSCVA; 73.9% were within 0.50 D of the target correction and 95% were within 1.00 D. For spherical myopes combined with myopic astigmats corrected for 6 to 10 D, results were: UCVA of 20/40 or better in 93.4%, 20/20 or better in 61.2%, 2.3% lost 2 lines and no eyes lost greater than 2 lines of BSCVA; 67.2% were within 0.50 D of the desired correction and 87.8% were within 1.00 D. Refractive stability was achieved between 3 and 6 months for the spherical and astigmatic groups. No eyes had corneal haze graded as moderate or greater, and there was no significant decrease in endothelial cell density.

CONCLUSIONS

Patients treated for 1 to 10 D of spherical equivalent myopia, with or without astigmatism, showed early refractive stability, excellent UCVA, no significant loss of BSCVA, no loss of endothelial cell density, and very low levels of corneal haze to 12 months after surgery.

Diurnal fluctuations in corneal topography 10 years after radial keratotomy in the Prospective Evaluation of Radial Keratotomy Study

PURPOSE

To correlate clinically observed fluctuations in manifest refraction, visual acuity, keratometry, and intraocular pressure (IOP) with changes in the anterior corneal surface as measured by videokeratography in patients 10 years after radial keratotomy (RK).

SETTING

Four clinical centers in the United States that participated in the Prospective Evaluation of Radial Keratotomy (PERK) study.

METHODS

Thirty-two eyes of 20 PERK patients who noted diurnal fluctuations in vision had clinical examination and videokeratography (TMS-1, Computed Anatomy Inc.) in the morning and evening of the same day a mean of 10.3 years (range 7.8 to 11.7 years) after RK. The videokeratographs were analyzed in terms of various indexes generated by custom-designed software. Morning-to-evening changes in the means of the various clinical and videokeratographic values were assessed using pairwise methods.

RESULTS

The mean increase in myopia was 0.36 diopters (D) +/- 0.58 (SD) from morning to evening (P < .01). Analysis of the videokeratographs showed a corresponding increase in average corneal power (ACP), reflecting a steepening of 0.52 +/- 0.45 D (P < .001). The change in ACP was correlated with a change in the manifest spherical equivalent refraction (R = 0.39, P = .03) and a change in best spectacle-corrected visual acuity (R = 0.38, P = .03) over the same period. Similarly, simulated keratometry (SimK) readings correlated with the change in the manifest spherical equivalent refraction (R = 0.38, P = .03 for SimK1; R = 0.37, P = .35 for SimK2; R = 0.4, P = .02 for average SimK), although the standard clinical keratometric data did not (P = .26 for K1, P = .11 for K2, and P = .09 for the mean K). The elevation depression magnitude, a measure of the low-frequency irregularities of the cornea, showed a decrease of 0.32 +/- 1.59, which also correlated with the change in the manifest spherical equivalent refraction (R = 0.37, P = .04). Intraocular pressure tended to decrease from morning to evening (mean change of -0.97 +/- 3.29 mm Hg), but the difference was not significant. Variations in IOP in individual patients, however, were correlated with changes in the manifest spherical equivalent refraction (R = 0.37, P = .04).

CONCLUSIONS

Diurnal fluctuations in corneal topographic indexes can be used to evaluate the diurnal fluctuations in refraction and visual acuity after RK. The study findings provide statistical support for the idea that IOP contributes to the diurnal fluctuation in visual acuity after RK.

Corneal topography of small-beam tracking excimer laser photorefractive keratectomy

PURPOSE

To evaluate the topographic characteristic of photorefractive keratectomy (PRK) for low myopia performed with a small-beam (0.9 mm) tracking excimer laser.

SETTING

Department of Ophthalmology, LSU Eye Center, Louisiana State University Medical Center School of Medicine in New Orleans, and the Refractive Surgery Center of the South at the Eye, Ear, Nose, & Throat Hospital, New Orleans, Louisiana, USA.

METHODS

Sixty-seven eyes of 47 patients had PRK with a small-beam tracking laser. Of these, 49 eyes had data permitting evaluation of ablation centration; usable data for topographic analysis were available for 59 eyes preoperatively, 54 eyes at 1 month, 42 eyes at 3 months, and 25 eyes at 6 months, permitting measurement of various topographic parameters, including the cylinder (CYL), average corneal power (ACP), surface regularity index (SRI), surface asymmetry index (SAI), corneal eccentricity index (CEI), and coefficient of variation of corneal power (CVP).

RESULTS

Preoperatively, all eyes were topographically normal. Postoperatively, no eye exhibited a "central island" by even the least-restrictive definition, and all eyes had best spectacle-corrected visual acuities (BSCVAs) of 20/20 or better at all follow-ups. Mean decentration of the ablations from the pupil centers was 0.42 mm +/- 0.28 (SD) (n = 49). There was no correlation between measured decentration and BSCVA (P = .46). The central cornea was flattened (decreased ACP; P < .001) and made oblate (decreased CEI; P < .001) as expected. There was no increase in SRI or SAI (irregular astigmatism) at 6 months compared with preoperative values (P = .91); however, CYL and CVP (varifocality) increased slightly (P = .04 and .02, respectively).

CONCLUSION

The absence of significant regular or irregular astigmatism 6 months after PRK with the small-beam laser is an improvement over published results achieved with wide-beam lasers and is consistent with the excellent visual acuity results in this cohort.

Photorefractive keratectomy with a small spot laser and tracker

BACKGROUND

The Autonomous Technologies LADARVision excimer laser system utilizes an eye tracking mechanism and a small spot for photorefractive keratectomy.

METHODS

One hundred and two eyes of 102 patients were treated for -1.50 to -6.25 D of spherical myopia at the spectacle plane using a 6-mm diameter ablation zone. One year follow-up was available for 93 eyes (91%).

RESULTS

Uncorrected visual acuity for eyes treated for distance vision was 20/40 or better in 99% (n = 90), and 20/20 or better in 70% (n = 64) of eyes at 12 months. Spectacle-corrected visual acuity was 20/25 or better in all 92 eyes reported; no eye lost more than 2 lines of spectacle-corrected visual acuity, and only 1 eye (1.0%) experienced a loss of 2 lines (20/12.5 to 20/20) at 1 year. The refractive result was within +/- 0.50 D of the desired correction in 75% (n = 70), and within +/- 1.00 D in 93% (n = 86) of eyes at 12 months. Refractive stability was achieved between 3 and 6 months. Corneal haze was graded as trace or less in 100% of the 93 eyes. No significant reductions were noted in contrast sensitivity or endothelial cell density.

CONCLUSIONS

Patients treated with the Autonomous Technologies LADARVision excimer laser system for -1.50 to -6.25 D of spherical myopia with 1 year follow-up had uncorrected visual acuity of 20/20 or better in 70%, no significant loss of spectacle-corrected visual acuity, no reduction of endothelial cell density or contrast sensitivity, and low levels of corneal haze.

Comparison of the effectiveness of 4 anti-inflammatory drops in relieving photophobia after pupil dilation

PURPOSE

To compare the relative effectiveness of diclofenac, flurbiprofen, ketorolac, and prednisolone acetate in relieving photophobia after pupil dilation for fundus examination.

SETTING

Eye, Ear, Nose, and Throat Hospital, New Orleans, Louisiana, USA.

METHODS

This prospective, blind, placebo-controlled study comprised 105 patients randomly assigned to 1 of 10 treatment groups. Five minutes after instillation of dilating drops, each patient received drops of different test medications in the right and left eyes. Light sensitivity and pupil measurement tests were performed over 2 hours after the pharmacological mydriasis. After photostimulation, patients were asked to rate their photosensitivity on numerical and analog scales and to indicate a filter value required to alleviate right-induced discomfort. Test results were analyzed to detect differences among the pain levels associated with each treatment.

RESULTS

There were no significant differences between the placebo and any active treatment drug at any time during the study.

CONCLUSION

These findings suggest that mediators other than prostaglandins may have a role in photosensitivity or that increased postmydriatic photosensitivity is a result of higher light levels entering the eye through the dilated pupil.

Corneal hydration and central islands after excimer laser photorefractive keratectomy

PURPOSE

To determine whether uneven corneal surface hydration during excimer laser photorefractive keratectomy (PRK) is related to postoperative occurrence of central islands.

SETTING

LSU Eye Center, New Orleans, Louisiana, USA.

METHODS

A retrospective study reviewed intraoperative videotapes and postoperative videokeratography of 49 eyes of 49 patients who had excimer laser PRK for myopia. The uniformity of corneal hydration within the photoablation zone, particularly the frosty appearance of the ablated zone, was characterized. The presence or absence of a topographic central island (steepening of at least 3.0 diopters and 1.5 mm in diameter) was determined from the 1 month postoperative videokeratographs.

RESULTS

Twelve eyes (24.5%) developed central islands postoperatively. A statistically significant association was observed between the uneven surface hydration (central accumulation of fluid) within the ablation zone intraoperatively and the formation of central islands postoperatively (P < .001, Kruskal-Wallis test; Kendall tau rank correlation = 0.534; P < .001).

CONCLUSION

Nonuniform fluid distribution during photoablation was a risk factor for central island formation after PRK. Intraoperatively, the presence of excess fluid in the central cornea appeared as a shiny area. This mirror-like surface layer may reduce the rate of central ablation by reflecting and absorbing a significant amount of the incident excimer laser light.

In vivo confocal microscopy of Fuchs' endothelial dystrophy

PURPOSE

The purpose of this study is to analyze in vivo confocal microscopic findings of corneas with Fuchs' endothelial dystrophy.

METHODS

Central corneas of 17 eyes of 11 patients aged 41-86 years were examined using in vivo scanning slit confocal microscopy after being diagnosed with Fuchs' endothelial dystrophy. The cellular structure of the corneas was analyzed morphologically and quantitatively and compared to control results from 22 healthy corneas.

RESULTS

Bullae were detected in the basal epithelial layer of one eye. Eight of 17 eyes (47%) exhibited an abnormal Bowman's layer: diffuse bright reflection and absence of nerves. Eleven eyes (65%) exhibited abnormal anterior stroma: lacunae and diffuse increased light reflection due to edema. In 12 eyes (71%), lacunae or dark bands 5-20 microm wide against increased background reflection were noted in the posterior stroma. Descemet's membrane was thickened in all eyes. Dark bands were detected in six eyes (35%). Guttae (137-1,231/mm2) 20-40 microm in diameter were found in every endothelial cell layer. The mean endothelial cell count was 1,202 +/- 850 (cells/mm2 +/- SD; range, 0-2,735). There was a positive correlation between endothelial cell counts obtained by specular microscopy and those obtained by confocal microscopy (r = 0.95).

CONCLUSION

In vivo confocal microscopic findings of Fuchs' endothelial dystrophy are described for the first time in a series of cases. Pathological changes in Fuchs' dystrophy were detected in all corneal layers, more frequently in the posterior layers. Endothelial cell counts obtained with confocal microscopy were statistically similar to those obtained with standard specular microscopy.

Normal human corneal cell populations evaluated by in vivo scanning slit confocal microscopy

PURPOSE

To analyze cellular populations in healthy human corneas.

METHODS

The study group consisted of 58 eyes of 45 patients with normal corneas. The age distribution was 45 +/- 17 years (mean +/- SD; range, 20-84). Scanning slit confocal microscopy of the central corneas was performed. The images were analyzed visually for cell morphology, and the densities and areas of cells were measured.

RESULTS

No statistically significant differences were measured in cell densities or cell areas of any corneal layer between female and male patients (p = 0.22-0.50) nor between right and left eyes (p = 0.16-0.45). The area of superficial epithelial cells was 913 +/- 326 microm2 (mean +/- SD; range, 518-2,112), and the superficial epithelial cell density was 1,213 +/- 370 cells/mm2 (mean +/- SD; range, 473-1,929). The area of basal epithelial cells was 177 +/- 19 microm2 (mean +/- SD; range, 138-242), and the basal epithelial cell density was 5,699 +/- 604 cells/mm2 (mean +/- SD; range, 4,135-7,267). The average apparent keratocyte density was 1,058 +/- 217 cells/mm2 (mean +/- SD; range, 604-1,599) in the anterior stroma, and 771 +/- 135 cells/mm2 (mean +/- SD; range, 493-1,145) in the posterior stroma. The difference in apparent keratocyte densities between the anterior and posterior stroma was statistically significant (p < 0.001). The average endothelial cell area was 334 +/- 51 microm2 (range, 273-553), and the cell density was 3,055 +/- 386 cells/mm2 (mean +/- SD; range, 1,809-3,668). The endothelial cell density had a negative, statistically significant correlation with age (r = -0.68, p < 0.001). The densities of the other corneal cell layers did not have a statistically significant correlation with age.

CONCLUSION

In vivo scanning slit confocal microscopy is a useful tool for studying corneal cell populations. Central corneal cell densities were found to decrease significantly with age only in the endothelium. For the first time in human corneas using in vivo confocal microscopy, this study statistically confirms a higher apparent number of keratocytes in the anterior stroma than in the posterior stroma.

Topographic assessment of irregular astigmatism after photorefractive keratectomy

OBJECTIVE

To correlate new quantitative topographic indexes of corneal irregular astigmatism to best spectacle-corrected visual acuity (BSCVA) following excimer laser photorefractive keratectomy (PRK).

SETTING

Department of Ophthalmology, LSU Eye Center, and Refractive Surgery Center of the South, Ear, Nose & Throat Hospital, New Orleans, Louisiana; Manhattan Eye, Ear and Throat Hospital, New York, New York, USA.

METHODS

Videokeratography data (TMS-1) were obtained preoperatively and 1, 3, 6, 12, 18, and 24 months postoperatively from 100 eyes having PRK for low to mild myopia. Algorithms measured fine local irregularity with the surface regularity index (SRIp), varifocality with the coefficient of variation of corneal power (CVPp), and central islands with the elevation/depression magnitude (EDM).

RESULTS

The SRIp and CVPp increased after surgery and remained significantly higher than the preoperative levels throughout the 24 month follow-up (P < .05). The increase in EDM was significant from 1 to 6 months (P < .05) but not thereafter. Multiple regression analysis revealed that variables having a statistically significant relationship with postoperative BSCVA were CVPp and EDM at 1 month, CVPp at 3 months, and CVPp, haze, and age at 6 months. No statistically significant correlation between any measures of irregular astigmatism and BSCVA was found after 1 year of follow-up.

CONCLUSION

The quantitative measures used in this study are sensitive methods by which irregular astigmatism after keratorefractive procedures can be classified, evaluated, and compared.

Effect of pupillary dilation on corneal optical aberrations after photorefractive keratectomy

BACKGROUND

Complaints of glare, halos, and disturbances of night vision after photorefractive keratectomy (PRK) probably result from changes in the corneal aberration structure induced by the laser ablation procedure. The purpose of this article is to characterize changes in the corneal aberration structure after PRK and to demonstrate the effect of pupil dilation on these changes.

METHODS

Videokeratographs obtained preoperatively (n = 112) and at 1 (n = 94), 3 (n = 103), 6 (n = 91), 12 (n = 60), 18 (n = 53), and 24 (n = 44) months postoperatively from 112 eyes of 89 patients who had undergone PRK for myopia were analyzed. The data were used to calculate the wavefront variance of the cornea for both small (3-mm) and large (7-mm) pupils.

RESULTS

For both the 3- and 7-mm pupil, coma-like aberrations increased significantly from preoperative values to 1-month postoperative values (P < .05 and P < .001, respectively); for 7-mm pupils, the postoperative values never returned to preoperative values (P < .001, 24 months). For the 3-mm pupil, spherical-like aberrations decreased significantly 1 month after surgery (P < .001), and never returned to preoperative values. For the 7-mm pupil, spherical-like aberrations increased significantly 1 month after surgery (P < .001) and did not return to preoperative values. Opening the pupil from 3 to 7 mm increased spherical-like aberrations only 7-fold before PRK. After PRK, however, pupillary dilation caused a 300-fold increase in this type of aberration. For both pupil sizes at all times after PRK, the magnitude of the surgically induced aberration correlated with the amount of the attempted correction (P < .001, r2 = 0.6 at 1 month for a 7-mm pupil).

CONCLUSIONS

Photorefractive keratectomy increases the wavefront variance of the cornea; PRK changes the relative contribution of coma-like and spherical-like aberrations; after PRK, the diameter of the entrance pupil greatly affects the amount and character of the aberrations; and the magnitude of the aberration increases with the attempted correction.

CLINICAL RELEVANCE

Quantitative characterization of irregular astigmatism with the measurement of aberration structures following corneal surgery and the correlation of these data with visual performance in clinical trials provide the basis for understanding patient complaints and for improving surgical approaches. Our analysis shows that, whereas induced aberrations are minimal for simulated day-time vision (3-mm pupil), the increase in aberrations measured for simulated night vision (7-mm pupil) supports the use of large treatment zones to reduce visual disturbances such as glare and halos.

Disparity between keratometry-style readings and corneal power within the pupil after refractive surgery for myopia

PURPOSE

Because keratometry readings may no accurately reflect the refractive changes after keratorefractive surgery for myopia, better methods for the assessment of corneal curvature in the postsurgical cornea are needed.

METHODS

We developed a procedure to calculate the average central power (ACP) of the cornea within the entrance pupil from videokeratography. Videokeratograph-derived keratometry-style readings (average K; K) and calculated ACPs, as well as the differences between the two values, were compared in four groups: normal corneas (n = 30), corneas with regular astigmatism (n = 30); post-radial keratotomy corneas (RK, n = 85), and post-excimer laser photorefractive keratectomy corneas (PRK, n = 63). Intraocular lens (IOL) powers calculated by using K or ACP in the Sanders-Retzlaff-Kraff formula were compared.

RESULTS

In the groups with normal corneas or regular astigmatism, none of the eyes showed a difference between K and ACP > 0.25 D. However, six (7%) of the RK eyes and 16 (25%) of the PRK eyes had differences > 0.55 D; in these eyes, the disparity between IOL powers calculated by using K and IOL powers calculated by using ACP was > 0.5 D.

CONCLUSION

These results suggest that basing the calculation of IOL powers on keratometry readings in patients who have undergone RK. PRK, or possibly other refractive procedures may result in a residual refractive error in some eyes. In particular, patients undergoing surgery involving a small optical zone or large attempted correction or both, as well as those with low postoperative keratometry readings, may be at risk for this problem if IOL placement becomes necessary in later years.

Near vision contrast sensitivity after photorefractive keratectomy

BACKGROUND

To evaluate near vision contrast sensitivity as a measure of visual performance after photorefractive keratectomy (PRK).

SETTING

LSU Eye Center, New Orleans, Louisiana.

METHODS

Using Holladay Contrast Acuity Test cards, near (reading) vision for five levels of contrast sensitivity was evaluated in a cross section of 53 eyes of 31 patients 25 to 732 days after PRK. Twenty-four normal eyes of 22 myopic patients served as controls.

RESULTS

Near contrast sensitivity decreased at all tested contrast levels for approximately 7 months after PRK and then returned to baseline. This phenomenon paralleled the fluctuation in best corrected distance Snellen acuity.

CONCLUSIONS

These preliminary results indicate that Snellen visual acuity and near contrast sensitivity returned to baseline within 1 year after PRK.

Diclofenac Sodium Attenuates Neural Activity after Photorefractive Keratectomy in Rabbits

BACKGROUND

Photorefractive keratectomy for treating myopia has been associated with severe postoperative pain. The purpose of the present study was to investigate, in a rabbit model, the early effects of laser ablation on the physiology of the sensory nerves of the cornea.

METHODS

Neurophysiologic monitoring of the corneal nerves was carried out 4 to 6 hours after 5-mm diameter, circular PRK ablations with a central depth of 85 microns. The effect of topical 0.1%, 0.25%, and 0.5% diclofenac sodium on the physiologic response to chemical and mechanical stimulation was evaluated. Corneas were prepared for anatomic studies of corneal innervation.

RESULTS

Heightened neural activity was observed in the corneal nerves after ablation, and exaggerated responses to sensory stimulation with hypertonic sodium chloride solutions were recorded. Diclofenac sodium at 0.1% decreased the response to 0.5 M NaCl and 0.7 M NaCl to 67 +/- 9% and 68 +/- 7% (mean +/- standard error) of the control response. Mechanically sensitive nerves were more resistant to diclofenac; 0.1% diclofenac had no effect, but 0.25% diclofenac reduced the response significantly (P < 0.05). Anatomic observations showed that the ablation extended through the neural plexus. By 72 hours, long neurites tipped with growth cones had advanced into the injured region, indicating the initiation of neural regeneration.

CONCLUSIONS

Diclofenac sodium was effective in attenuating neural activity in the cornea after excimer laser ablation. The action of this agent was shown to be different from that of a topical anesthetic, which rapidly and totally inhibited the response to all forms of stimulation.

Comparison of Corneal Epithelial Wound Healing After Photorefractive and Lamellar Keratectomy

BACKGROUND

The rate of corneal epithelial wound healing may be determined, in part, by the characteristics of the stromal surface. The excimer laser has the ability to produce a highly uniform ablated surface, which may facilitate reepithelialization after photorefractive keratectomy (PRK).

METHODS

The rate of corneal epithelial wound healing after excimer laser PRK was compared with the rate of reepithelialization after manual lamellar keratectomy. Ten rabbits received a 4-mm diameter ablation in one eye (fluence = 160 mJ/cm2) and a shallow, 5-mm diameter, manual lamellar keratectomy in the contralateral eye. At 0, 4, 8, 12, 24, 36, 48, 60, and 72 hours after wounding, sodium fluorescein was instilled, and photographs were taken, converted to video images, and digitized. Wound area was calculated for each time point and converted to wound radius; the slopes of the wound radius, plotted over time, were compared to determine rates of healing. Scanning electron microscopy was performed immediately after wounding to examine surface regularity.

RESULTS

By 24 hours after wounding, corneas that had undergone PRK demonstrated a significantly faster rate of epithelial wound healing compared with eyes that underwent lamellar keratectomy (33.4 +/- 1.9 microns/hr vs 27.8 +/- 1.4 microns/hr, respectively, for 12 to 72 hours) (p < 0.0001). Scanning electron microscopy showed greater stromal surface irregularity in the corneas that had undergone lamellar keratectomy, compared with the laser-ablated corneas.

CONCLUSIONS

This study demonstrates that the rate of epithelial wound healing is significantly faster after excimer laser PRK than after lamellar keratectomy in the rabbit. Variations in surface regularity and wound edge profile may contribute to differences in wound healing.

Tracker-Assisted Photorefractive Keratectomy for Myopia of -1 to -6 Diopters

BACKGROUND

The Autonomous Technologies T-PRK (Tracker-assisted Photorefractive Keratectomy) excimer laser system uses a small beam scanner that allows flexibility in the ablation pattern that is applied to the cornea and incorporates a sophisticated LADARVision eye tracker that is capable of following saccadic movements. This paper describes the first clinical results on sighted eyes for the correction of low myopia.

METHODS

Forty-two normal sighted eyes of 42 patients were treated for spherical myopia between -1.00 diopters (D) and -6.00 D with 6 mm ablations. Visual acuity, refractive error, contrast sensitivity (with and without glare), corneal haze, endothelial cell density, and patient satisfaction were measured.

RESULTS

Mean manifest refraction was -0.39 D +/- 0.68 D at 1 month with regression to -0.94 D at 3 months and -1.05 D at 6 months. At 6 months, 5 (20%) eyes were +/- 0.50 D and 14 (56%) eyes were +/- 1.00 D. Consistent with this undercorrection and regression, uncorrected visual acuity (UCVA) of 20/20 and 20/40 or better was achieved by 10 (40%) and 34 (85%) eyes at 3 months and 16 (40%) and 17 (68%) eyes at 6 months. None of the eyes lost 2 or more lines of spectacle corrected visual acuity. Corneal haze was graded as 1/2 trace or less in 89% to 100% of eyes at all intervals. There was no loss of endothelial cells (mean +/- SD cell density centrally: preop 3115 +/- 322 and 6 months 3220 +/- 333) and contrast sensitivity recovered to baseline levels at 3 months.

CONCLUSIONS

The Autonomous Technologies T-PRK excimer laser system is safe and effective for the reduction or correction of myopia from -1.00 D or -6.00 D. The refractive results may be improved by adjusting the calibration to reduce the undercorrection and by instituting use of topical corticosteroids on an individual basis for those who regress.

Hydrogel intracorneal lenses in aphakic eyes

BACKGROUND

The theoretical benefits of synthetic keratophakia over conventional corneal lamellar procedures are the elimination of donor concerns and superior refractive predictability. Additionally, synthetic material can be inspected for optical quality and power, and it can be sterilized. Furthermore, visual recovery should be more rapid since epithelium is not removed from the central part of the cornea and the need for keratocyte repopulation is eliminated.

OBJECTIVE

To present results on patients who received an intracorneal implant (Kerato-Gel, Allergan Medical Optics, Irvine, Calif) that was made from lidofilcon A, a glucose-permeable hydrogel with an equilibrium water content of 68%.

METHODS

The intracorneal implants were implanted in 35 adult patients for correction of aphakia. Inclusion criteria excluded patients with aphakia who were candidates for intraocular lenses.

RESULTS

A total of 19 patients were followed up through 2 years postoperatively. For 16 patients with 2-year postoperative refractive data, the average spherical equivalent was -0.63 +/- 2.07 diopters (D). At 2 years, 88% of patients were within +/- 3.00 D of plano and 50% were within +/- 1.00 D. the mean change in Snellen's line for corrected visual acuity was -3.25 lines at 2 years for all patients and -2.0 lines for a subgroup of five patients who were free of vision-limiting preoperative disease.

CONCLUSIONS

Results suggest that this intracorneal implant is well tolerated by the cornea and can provide predictable refractive results in patients with high-risk aphakia. Limitations of the procedure are uneven microkeratome resections, loss of best-corrected visual acuity, and irregular astigmatism in some patients. Although these data show good evidence of biocompatibility of the implant material, technical surgical progress is needed to advance this procedure into clinical therapeutic practice.

In vivo confocal microscopy of corneal wound healing after excimer laser photorefractive keratectomy

We used real-time scanning confocal microscopy to evaluate early changes in corneal wound healing after excimer laser photorefractive keratectomy (PRK). Adult New Zealand White rabbits were given photorefractive keratectomy treatments appropriate for 5.00 to 8.00 D of myopia (44.5 to 71.0 micros depth, with a 5-mm diameter treatment zone). Daily confocal microscopic examinations showed acute loss of keratocytes in the anterior corneal stroma by 5 hours; losses were maximal between 24 and 48 hours for 5.00 D and 6.00 D ablations and between 72 and 96 hours for 7.00 D and 8.00 D ablations. The oval nuclei of normal keratocytes gave way to spindle-shaped fibroblasts accompanied by an accumulation of fibrillary extracellular matrix. Fibroblasts density increased toward the end of the week. Deeper ablations resulted in a longer period of keratocyte depletion and delayed onset of fibroblast activity. No epithelial, deep stromal, or endothelial abnormalities were detected, nor was stromal inflammation found. Light microscopy 1 week after PRK revealed superficial fibroplasia, which correlated with the en face images obtained with real-time in vivo confocal microscopy. The confocal microscope has a number of advantages as a clinical tool for investigation of laser-induced changes in corneal keratocytes and the stromal matrix, which may play a role in determining visual outcome after PRK.

Excimer laser photorefractive keratectomy after radial keratotomy

BACKGROUND

Correction of residual myopia after radial keratotomy may be attempted with repeated keratotomy surgery, but predictability can be less than satisfactory. Excimer laser photorefractive keratectomy (PRK) provides an alternative approach to improving the refractive result in these patients.

METHODS

Twenty-five eyes of 20 patients at five clinical locations underwent PRK for residual myopia after radial keratotomy. The number of incisions ranged from 4 to more than 16. Clear zones ranged from 3 mm to 4 mm. Best corrected visual acuity was 20/20 or better in 16 of the 25 eyes, with a range from 20/12 to 20/80. Uncorrected visual acuity was 20/200 or worse in 15 of the 25 eyes, with a range from 20/25 to finger counting. The interval between radial keratotomy and PRK averaged 33.5 months, with a range from 5 to 96 months. Nineteen eyes had 6 months or more of follow up; 15 had 12 months or more.

RESULTS

Corneal haze was maximal 1 month after surgery (mean +/- SE, 0.65 +/- 0.09), and declined to 0.35 +/- 0.16 at 12 months. Twelve months after PRK, mean keratometric readings were 40.19 +/- 0.81 diopters (D) and mean spherical equivalent refraction was -1.42 +/- 0.47 D. Nine (60%) of the 15 eyes with 12 months follow up were within 1 D of emmetropia and 12 (80%) were within 2 D. Eight (53%) of the 15 eyes had uncorrected visual acuities of 20/40 or better. Spectacle-corrected visual acuity in the eyes with 12 months follow up improved in 4, did not change in 4, and worsened in 6.

CONCLUSIONS

The results of PRK are less predictable in eyes that have previously undergone radial keratotomy, and these eyes respond with more haze after PRK than normal eyes.

Clinical analysis of excimer laser photorefractive keratectomy using a multiple zone technique for severe myopia

PURPOSE

In an investigational procedure, excimer laser photorefractive keratectomy for severe myopia was performed at three clinical trial centers to determine the effectiveness of the multiple zone technique.

METHODS

A VisX Model Twenty/Twenty excimer laser (VisX, Santa Clara, California) was used to perform photorefractive keratectomy on 14 severely myopic eyes (-10.37 to -24.5 diopters) of 12 patients by using a multiple zone technique. Postoperative follow-up ranged from six months to two years; retreatments were performed on four patients, with a follow-up of at least nine months.

RESULTS

At six months postoperatively, before retreatment, three of the 14 eyes were within 2 diopters and seven of the 14 eyes were within 4 diopters of attempted correction. Regression of effect to more severe myopia was worse in five eyes treated with nitrogen gas blowing. Retreatments also demonstrated considerable myopic regression. Three patients had loss of two or more lines of best-corrected visual acuity, and these patients also had moderate or severe levels of haze.

CONCLUSION

Excimer laser photorefractive keratectomy for severe myopia using a multiple zone technique is associated with considerable regression, haze, and loss of best-corrected visual actuity, especially when performed in association with nitrogen gas blowing.

A corneal lens/shield system to promote postoperative corneal epithelial healing

We used a disposable bandage soft contact lens piggybacked onto a medicated, 12-hour corneal collagen shield to promote postoperative corneal epithelial healing and to provide sustained delivery of high levels of medications after corneal surgery in patients known to have poor corneal epithelial wound healing characteristics. Our experience with three patients indicates that the collagen shield dissolves completely by the first postoperative day and that the bandage lens remains in place with good mobility until it is removed when epithelialization is complete. This system eliminates the need for painful manipulation and placement of a bandage soft contact lens in an edematous, inflamed eye during the immediate postoperative period.

Quantitative histological studies of primate corneas after excimer laser photorefractive keratectomy

OBJECTIVE

To evaluate histological changes in the primate cornea after excimer laser photorefractive keratectomy (PRK) and to correlate them with clinical observations.

METHODS

Sixteen African green monkey (Cercopithecus aethiops sabaeus) corneas were examined by light and transmission electron microscopy 6 weeks to 18 months after 1.5- or 3-diopter PRK.

RESULTS

All specimens had a smooth stromal surface surrounded by a smooth, centrally tapered Bowman's layer. Epithelial thickness appeared to peak 12 months after PRK. The trend was for the epithelium to be thickest in the central-treated area; this phenomenon was more obvious in the 3-diopter-treated corneas. The numbers of activated keratocytes beneath the treated zone peaked at 4 months and decreased thereafter, while the numbers in the untreated areas decreased in the first 2 months after surgery, increased by 4 months, and did not change thereafter. Regenerated basal lamina averaged 86% intact over ablated areas; thickness was normal and no duplications were seen. Overall, the density of hemidesmosomes was significantly less in ablated areas compared with unablated areas.

CONCLUSIONS

These findings support the relationship between clinical observations of corneal haze after PRK, reestablishment of the epithelial cell layer, and the potential for stromal remodeling by active fibroblastic keratocytes beneath the ablation zone. Overall, quantification of several morphological parameters indicated that the values for the treated zone tended, with time, to approach those of the untreated cornea after PRK.

Pupillary block during cataract surgery

Sudden phakic pupillary block occurred immediately upon cortical cleaving hydrodissection during cataract surgery in two patients. We believe this unique complication is related to the recent introduction of viscoelastics with properties that enhance the maintenance of the anterior chamber during capsulorhexis. We postulate that the cause of the block was a combination of O-ring capsulocortical and iridocapsular seals that tamponade hydrodissection fluid posteriorly. Additional precipitating factors were diabetes, poorly dilating pupils, and increased vitreous pressure, which may have contributed to the sudden and irreversible nature of this block. If this complication is not recognized, an aqueous misdirection syndrome may ensue, requiring pars plana vitrectomy. Immediate mechanical breakage of the pupillary and capsular block, resulting in an immediate decrease in intraocular pressure from greater than 70 mm Hg, may cause severe retinal vascular damage. These cases stress the importance of mechanical pupil dilation to prevent this serious complication of cataract surgery.

Effects of scleral reinforcement on the elongation of growing cat eyes

OBJECTIVE

We investigated the effect of scleral reinforcement on ocular elongation in the rapidly growing eyes of juvenile cats.

METHODS

Bands made from donor sclera or expanded polytetrafluoroethylene were used to reinforce one eye of each animal; contralateral eyes underwent sham surgery.

RESULTS

During 5 months of follow-up, normal intraocular pressures implied normal functioning of angle structures. A-scan on the central axis showed no difference in globe lengths. Direct physical measurements of the posterior aspect of the globe at enucleation revealed significant decreases in off-center lengthening where reinforcement was present compared with unreinforced areas in the same eyes and in the contralateral unbanded eyes. Venous beading in fundus photographs of three eyes suggested impairment of venous outflow.

CONCLUSIONS

Scleral reinforcement appears to control expansion of the growing cat eye to a limited extent, but the effects on vision and retinal perfusion require further investigation.

Topical bupivacaine and proparacaine: a comparison of toxicity, onset of action, and duration of action

Bupivacaine is a local ocular anesthetic with a long duration of action when administered by retrobulbar injection. To determine the potential for the use of bupivacaine as a topical ocular anesthetic, the onset and duration of action and toxicity of various concentrations of bupivacaine were studied after instillation in rabbit eyes. The onset and duration of action were not significantly different from that of topical 0.5% proparacaine. Increasing the pH of the bupivacaine solution from 5.7 to 6.5 nearly doubled the duration of action, but the increase was not sufficient to be clinically important. Slit lamp biomicroscopic examination and scanning electron microscopy showed that bupivacaine was less toxic to the corneal epithelium than 0.5% proparacaine. Healing after keratectomy was significantly more rapid in eyes treated with 0.75% bupivacaine, compared with eyes treated with 0.5% proparacaine. These results suggest that bupivacaine may be less toxic to the corneal epithelium than proparacaine and could be clinically useful for topical ocular anesthesia, particularly if pharmacologic modifications can increase the duration of anesthesia provided by this drug.

Assessment of the long-term corneal response to hydrogel intrastromal lenses implanted in monkey eyes for up to five years

The biocompatibility of hydrogel intracorneal lenses (ICLs) implanted in monkey eyes was evaluated for periods ranging up to five years. Seventy-three plus or minus powered ICLs made of Lidofilcon A (68% water) or Lidofilcon B (79% water) were implanted following lamellar dissection with a microkeratome. Ten sham surgical procedures were performed without ICL implantation as controls. Eyes were followed for up to five years by slitlamp biomicroscopy and specular microscopy. Light and transmission electron microscopic evaluations of enucleated eyes were performed at various intervals. Minimal tissue reaction was noted; both hydrogel materials appeared to be equally well tolerated. Failures usually occurred as a result of microkeratome problems encountered during surgery. Histopathological changes to the cornea included epithelial thinning anterior to the thickest portion of the ICL, fibroblastic activity along the ICL-stromal interface, and deposition of an amorphous extracellular material adjacent to the ICL. These observations did not appear to be clinically significant as the eyes were quiet by slitlamp examination. Removal of three ICLs eight to ten months prior to enucleation restored the normal histological characteristics of the cornea. The endothelial cell density of ICL-implanted eyes decreased by 4.3% (n = 17) six months after surgery but remained stable thereafter. The variation in endothelial cell area and percentage of hexagonal cells did not change over 50 months. The results appear to demonstrate that high water content synthetic ICLs can be well tolerated in the monkey cornea for up to five years.

Contralateral occipital depression related to obstetric forceps injury to the eye

Obstetric forceps pressure strong enough to leave a periorbital depression and corneal injury would probably be severe enough to leave an occipital depression from the opposite forceps blade. The presence of a depression at the correct occipital position would support the diagnosis of forceps injury when the birth history is unknown and the cornea has decompensated enough to make observation of the Descemet's membrane scrolls difficult. We studied six patients with known or suspected obstetric forceps injury to the cornea. Complete ocular examinations included examination for periorbital forceps depressions and posterior skull depressions 180 degrees from the affected cornea (which correlates with the opposite blade of the forceps). All of the patients with Descemet's scrolls had posterior skull depressions. This method of palpation for a contralateral skull depression may assist in the diagnosis of forceps-induced corneal decompensation.

Changes in corneal topography after excimer laser photorefractive keratectomy for myopia

Computer-assisted analysis of corneal topography was performed in 17 normally sighted human eyes during the first year after excimer laser photorefractive keratectomy (PRK) for myopia. Laser ablation of the central cornea produced an optical zone with a smooth power transition to the peripheral cornea. Decentration of the ablation was noted in some eyes (less than 0.5 mm in 3 eyes, 0.5 to 1.0 mm in 10 eyes, 1 to 1.5 mm in 3 eyes, and 2.1 mm in 1 eye), suggesting that careful alignment of the laser beam is critical. Improved methods to align the ablation within the center of the entrance pupil are needed. In 12 of 17 eyes, the topographic pattern appeared to stabilize between 3 and 7 months after PRK. In the remaining five eyes, central ablation power changed by more than 0.5 diopters (D) between the 6- and 12-month examinations. Regression was more common and more pronounced in eyes with intended corrections more than 5 D, whereas the majority of eyes with intended corrections of 5 D or less showed good correspondence between the final change in central ablation power and the attempted correction. Two eyes had a loss of at least two lines of best spectacle-corrected visual acuity that was attributable to irregular astigmatism, decentration of the ablation, and/or corneal opacification.

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.

Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study five years after surgery. The Perk Study Group

In the Prospective Evaluation of Radial Keratotomy (PERK) Study, 793 eyes of 435 patients with 2 to 8 diopters (D) of myopia received a standardized surgery consisting of 8 incisions with a diamond-bladed knife set at 100% of the thinnest paracentral ultrasonic corneal thickness measurement and a diameter of the clear zone of 3.0 to 4.5 mm; 97 eyes (12%) received an additional 8 incisions. There were 757 eyes (95%) followed for 3 to 6.3 years. After surgery, uncorrected visual acuity was 20/40 or better in 88% of eyes. The refractive error was within 1 D of emmetropia for 64% of eyes; 19% were myopic and 17% were hyperopic by more than 1 D. Between 6 months and 5 years after surgery, 22% of the eyes had a refractive change of 1 D or more in the hyperopic direction. For 25 eyes (3%) there was a loss of 2 or more lines of best spectacle-corrected visual acuity.

Immunogenicity of epikeratophakia tissue lenses containing living donor keratocytes

The purpose of this study was to compare the survival of epikeratophakia tissue lenses prepared with cryolathing and lyophilization (frozen lenses) and without (fresh lenses) in donor-sensitized recipients with vascularized corneas. Fresh lenses placed in vascularized corneas of immune recipients were subjected to immune attack. Frozen lenses placed in vascularized corneas of immunized recipients did not elicit an immune reaction. Neither fresh nor frozen lenses elicited immune reactions in nonvascularized corneas of immune recipients or in nonvascularized, nonimmune recipients. These results indicate that although the fresh lenses are more antigenic than the lenses in which the cells have been killed by freezing and lyophilization, the fresh lenses prepared using the BKS-1000 technique containing living stromal keratocytes are not likely to stimulate allograft immune reactions in unsensitized patients with avascular graft sites.