The clinical course of acquired complete heart block in children with acute myocarditis

A case of biopsy-proven myocarditis in a 7-year-old complicated by advanced atrioventricular (AV) block prompted a review of the medical literature to determine the prognosis for recovery of AV conduction or need for pacemaker implantation. A total of 40 patients younger than 20 years of age were identified, with return of AV conduction within 7 days in 27 patients (67%), permanent pacing in 11 patients (28%) with persistent AV block, and death in 2 patients (5%).

Pheochromocytoma multisystem crisis in a patient with multiple endocrine neoplasia type IIB and pyelonephritis

A patient with pyelonephritis developed multiorgan failure resulting in death. Clinical findings were consistent with multiple endocrine neoplasia type II, with bilateral pheochromocytomas identified by computed tomography scan. We hypothesize that either the infection or the administration of radiocontrast media led to a massive release of catecholamines from the pheochromocytomas. As a result, tissue perfusion was severely compromised, and multiorgan failure developed. This exceedingly rare complication of pheochromocytoma has been termed pheochromocytoma multisystem crisis.

A comparative assessment of endothelium from pseudophakic and phakic donor corneas stored in organ culture

AIMS

To evaluate the endothelial quality of corneas obtained from pseudophakic donors and to compare the data with matched phakic controls.

METHODS

Corneas from eyes with posterior chamber intraocular lenses (PCIOLs) and corneas from phakic eyes (controls) were stored for 1-2 weeks in organ culture and then examined after staining with Alizarin red S. The corneas were divided into two groups according to the duration of storage. Endothelial cell density, the percentage of hexagonal cells, and the coefficient of variation (CV) were determined.

RESULTS

There was no statistically significant difference between the 14 PCIOL corneas and the 13 controls stored in organ culture for 7 days for any of the three parameters studied. The mean cell density was 2155 (SD 529) cells/mm(2) in the PCIOL corneas and 2118 (453) cells/mm(2) in the controls (p=0.85). The mean percentage of hexagonal cells was 52% (8%) and 58% (7%), respectively (p=0.06). The mean CV was 0.32 (0.18) in the pseudophakic corneas and 0.39 (0.18) in the controls (p=0.33). Moreover, there was no significant difference between the PCIOL corneas and the controls stored for up to 2 weeks.

CONCLUSIONS

The corneal endothelium from eyes with PCIOLs appears to be similar to that of phakic eyes after 1-2 weeks in organ culture. This finding suggests that corneas from pseudophakic eyes should not routinely be disqualified for transplantation. The use of at least some pseudophakic corneas may substantially increase the potential donor pool.

Therapeutic drug monitoring in methadone maintenance: choosing a matrix

Methadone maintenance is the premier pharmacological treatment for opioid addiction, but it is rarely informed by evidence-based practice guidelines for dosage monitoring and adjustment. Such guidelines are crucial because the pharmacokinetics of methadone vary greatly among patients, and this variation may account for differences in treatment outcome. We review the pharmacokinetics of methadone and factors that may alter it (including drug interactions, disease states, and idiosyncratic differences among patients). Also reviewed are prospects for therapeutic drug monitoring (TDM) of methadone in plasma, urine, sweat, and saliva. Due to its ease of collection and its presumed representation of the bioavailable free-fraction of methadone, saliva may be a promising matrix. However, saliva methadone concentrations are influenced by salivary pH, and future studies are needed to determine how to control for that. Administrative, medical, and social implications of methadone TDM are briefly discussed.

Medical complications of female genital mutilation

More than 130 million women are subjected to genital mutilation. Despite increasing efforts to reduce the practice, there are many obstacles to eliminating this 2,000-year-old practice, which is based on strong cultural traditions. As college health clinicians provide care to more international students from countries where female genital mutilation is performed, increased awareness and knowledge of the procedure will enable clinicians to understand and manage its complications. We report a case of obstructive uropathy resulting in hydronephrosis secondary to female genital mutilation and review the medical literature regarding this and other complications of genital mutilation "surgery."

A mutant Drosophila insulin receptor homolog that extends life-span and impairs neuroendocrine function

The Drosophila melanogaster gene insulin-like receptor (InR) is homologous to mammalian insulin receptors as well as to Caenorhabditis elegans daf-2, a signal transducer regulating worm dauer formation and adult longevity. We describe a heteroallelic, hypomorphic genotype of mutant InR, which yields dwarf females with up to an 85% extension of adult longevity and dwarf males with reduced late age-specific mortality. Treatment of the long-lived InR dwarfs with a juvenile hormone analog restores life expectancy toward that of wild-type controls. We conclude that juvenile hormone deficiency, which results from InR signal pathway mutation, is sufficient to extend life-span, and that in flies, insulin-like ligands nonautonomously mediate aging through retardation of growth or activation of specific endocrine tissue.

A quality measurement framework for managed care organizations

This article presents a framework for a quality measurement system and its corresponding principles for quality improvement within a managed care environment. The quality measurement system comprises four modes: quality assessment, comparison, improvement, and system evaluation. If these modes are to be effective, the measurement system must incorporate the following five principles: (a) maintain and continually improve the data systems, (b) develop and utilize sound methodology and valid indicators, (c) build a competent measurement team, (d) develop effective strategies for implementation, and (e) protect member confidentiality. This model is helpful in the ongoing development and testing of new measurement systems.

Adult patients with occult bacteremia discharged from the emergency department: epidemiological and clinical characteristics

To determine the epidemiological and clinical characteristics of patients who were discharged from the emergency department (ED) and subsequently proved to have bacteremia, we prospectively assessed all patients examined in the ED during an 18-month period from whose blood cultures a significant organism was isolated. Discharged patients were contacted and reevaluated. Two case-control studies were conducted, in which each study patient was matched with a total of 4 control patients. During the study period, 46,336 patients were examined in the ED; 78% were adults and 22% were children. Blood cultures were performed for 25% of the adult patients and for 44% of the children. Although the occurrence of occult bacteremia in patients who were discharged from the ED is 3.7 times more common in children than in adults, the absolute numbers of discharged adults and children with occult bacteremia are similar. Careful clinical assessment will not prevent discharge of some of these patients; however, these patients in general do well and can be safely recalled for reevaluation and complementation of therapy.

Dyspnea differentiation index: A new method for the rapid separation of cardiac vs pulmonary dyspnea

STUDY OBJECTIVE

To assess the utility of a new parameter in the differentiation of dyspnea of cardiac origin from dyspnea of pulmonary origin.

METHODS

The peak expiratory flow (PEF) rate and the partial pressure of oxygen in arterial blood (PaO(2)) were measured in 71 patients with the chief complaint of dyspnea. The patients were treated in the hospital, and the final diagnosis (cardiac or pulmonary) of the cause of dyspnea was made at discharge. We defined a new measure, the dyspnea differentiation index (DDI), as (PEF x PaO(2))/1,000. We performed a receiver operating characteristic (ROC) curve analysis of the data to define the measure that best distinguished cardiac from pulmonary dyspnea. The curves also allowed us to establish an optimal cut-off point to distinguish between cardiac and pulmonary dyspnea.

RESULTS

Patients with pulmonary dyspnea had a significantly lower mean PEF than patients with cardiac dyspnea (144 +/- 66 vs 267 +/- 97 L/min, respectively; p < 0.001). They also had a lower DDI than patients with cardiac dyspnea (8.4 +/- 4.0 vs 18.4 +/- 7.9 L-mm/min, respectively; p < 0.001). These two measures, PEF and DDI, also best distinguished pulmonary from cardiac dyspnea. PEF was able to diagnose the correct cause of dyspnea in 72% of patients, and DDI was correct in 79% of patients. This compares favorably to the performance of the emergency department physicians, who were able to predict the correct diagnosis in only 69% of patients.

CONCLUSION

These results demonstrate that the PEF by itself is useful in differentiating between cardiac and pulmonary causes of dyspnea, but that the calculation of DDI is superior in this regard.

Photorefractive keratectomy to correct myopic or hyperopic astigmatism with a cross-cylinder ablation

PURPOSE

To assess the efficacy and safety of a combined ablation of the steep and flat meridian to correct astigmatism with the excimer laser.

METHODS

Twenty-two eyes with myopic, mixed, or hyperopic astigmatism (mean preoperative spherical equivalent refraction -4.30 +/- 4.70 D [range, -12.50 to +1.50 D] and mean preoperative cylinder magnitude -3.40 +/- 1.40 D [range, -1.50 to -6.00 D]) underwent PRK with the Nidek EC-5000 excimer laser. The surgical strategy involved ablating half the amount of the cylinder (in diopters) along steepest meridian, the other half in a subsequent step along the flattest meridian; thereafter, the spherical equivalent was corrected.

RESULTS

Six months postoperatively, mean spherical equivalent refraction was -0.07 +/- 0.87 D and mean cylinder was -0.44 +/- 0.36 D. Mean spectacle-corrected visual acuity was 0.86 +/- 0.13 compared to 0.75 +/- 0.22 preoperatively. Mean corneal haze was 0.67 +/- 0.31. No patient lost 2 or more lines of spectacle-corrected visual acuity and there were no complaints about night halos or glare.

CONCLUSIONS

Unlike other ablation strategies, the cross-cylinder method creates a smooth transition (low dioptric gradient) between the treated and untreated cornea. This is achieved by first treating the cylinder and making the corneal surface spherical and then ablating the spherical component of the refractive error.

Algorithm to correct hyperopic astigmatism with the Nidek EC-5000 excimer laser

BACKGROUND

The efficacy of a new ablation algorithm for the correction of hyperopic astigmatism with the Nidek EC-5000 excimer laser was evaluated.

METHODS

Twenty-five eyes with mean preoperative hyperopia of +3.76 +/- 1.70 D and a mean hyperopic cylinder of 2.20 +/- 0.80 D underwent photorefractive keratectomy (PRK) using a new algorithm with the Nidek EC-5000 excimer laser (software version 3.0). The new algorithm differed from previous algorithms in that less tissue was removed for the same amount of diopters, and there was less of a dioptric gradient between the optical zone and the transition zone. Mean preoperative spectacle-corrected visual acuity was 0.8 +/- 0.09. Minimum follow-up was 6 months.

RESULTS

Mean postoperative spectacle corrected visual acuity (geometric mean) increased significantly to 0.89 +/- 0.1. The mean sphere decreased by 3.08 D and the mean cylinder by 1.60 D.

CONCLUSION

Hyperopic PRK using the Nidek EC-5000 excimer laser with this new algorithm for hyperopic astigmatism appears to be safe and effective.

Evaluation of four maternal smoking questions

OBJECTIVE

The authors evaluated four questions about maternal smoking during pregnancy for use on birth certificates.

METHODS

Question 1 (yes/no format) and Question 2 (trimester-specific design) were tested among 1171 women who delivered at two Kaiser Permanente medical centers in northern California. Responses to Questions 1 and 2 were compared with smoking information provided by participants in telephone interviews conducted during pregnancy. Question 3 (multiple choice format) and Question 4 (month- and grouped month-specific design) were tested among 900 women who enrolled in a statewide prenatal screening program and who delivered in 20 hospitals in four Central Valley counties. Responses to Questions 3 and 4 were compared with mid-pregnancy serum cotinine levels. The authors evaluated the four questions in terms of conciseness, response rate, data accuracy, and type of data requested.

RESULTS

Questions 1 and 2 were the most concise. Response rates could not be calculated for Questions 1 and 2. Response rates were 86.0% for Question 3 and 74.2% for Question 4. Sensitivity was 47.3% for Question 1, 62.1% for Question 2, 83.8% for Question 3, and 86.7% for Question 4. The types of data requested by Questions 2 and 4 seem to best satisfy the needs of the broad audience of birth certificate users.

CONCLUSIONS

No single question was clearly superior. The authors propose a combination of Questions 2 and 4, which asks about average number of cigarettes smoked per day in the three months before pregnancy and in each trimester of pregnancy.

Efficacy of cobalt chelates in the rabbit eye model for epithelial herpetic keratitis

PURPOSE

A new class of antiviral agent, cobalt chelates (the CTC series), was evaluated for treating epithelial herpetic keratitis, consequent stromal disease being the major infectious cause of blindness in industrial nations.

METHODS

Effects of CTC complexes were monitored in cell cultures and in a rabbit eye model, either infected with herpes simplex virus type 1 (HSV-1) or uninfected. Several antiviral concentrations of CTC complexes nontoxic to Vero cells were administered to rabbit eyes with HSV-1-induced keratitis. Corneal surface virus titers were measured, and corneal lesions of epithelial keratitis were monitored by slit-lamp microscopy and scored. Recovery rates and incidence were compared in eyes treated with CTC complexes, placebo, or clinically formulated trifluorothymidine (Viroptic), using nonparametric statistics.

RESULTS

All CTC complexes inhibited HSV-1 replication in vitro, CTC-96 being best. CTC-96, CTC-23, and CTC-67 eliminated (<1 plaque-forming unit[pfu]) corneal surface HSV-1 (otherwise >10(5) pfu) in order of descending potency, but CTC-82 was ineffective. CTC-96 (either 5 microg/ml six times daily or 10 microg/ml five times daily) accelerated herpetic dendritic keratitis recovery better than or the same as trifluorothymidine (10 mg/ml nine times daily). CTC complexes were nontoxic to Vero cells continuously exposed to < or =25 microg/ml; 50 microg/ml of CTC 96 nine times daily did not irritate uninfected rabbit eyes.

CONCLUSION

Topical CTC-96 applications were at least as effective as Viroptic in diminishing disease signs and corneal surface virus at concentrations less than one-thousandth that of Viroptic.

High immunization rates versus missed immunization opportunities in a private pediatric office

OBJECTIVE

This prospective study examines coverage levels for immunization of two-year-old children in a large private pediatric practice, and delineates the frequency of missed opportunities for vaccination.

SETTING

A private single-specialty group pediatric practice in a suburban locale.

DESIGN

With the aid of our office billing computer, 218 children between the ages of 21 and 24 months who had ever received medical care in our practice were identified. A manual chart review was performed to identify those children no longer receiving care from us. Of the 189 patients remaining, the immunization records in the patients' charts were compared to the State of Delaware immunization registry to identify those who had not received the full panel of recommended vaccines. Those charts were examined to identify reasons for underimmunization. No patient recall was performed. The charts of underimmunized children were reexamined five months later to determine how many had become fully immunized.

RESULTS

On initial review, 86 percent of 21-24 month old children in our practice had received all recommended vaccines. Only 15 percent of the underimmunized children had had a missed opportunity for vaccination in the initial chart review. About half of the underimmunized patients received their missing vaccines over the next five months, yielding an eventual immunization rate of 94 percent. Only two of the 11 children still underimmunized by the end of the study (aged 26 to 29 months) had appeared for an 18 month or a 24 month well child visit; only four of the 11 had had a missed opportunity to receive immunizations during the five month study period. A subsequent chart review showed that 90 percent of our patients were up-to-date at 24 months of age.

CONCLUSIONS

Achievement of a 90 percent immunization rate for two year old children is possible in a large private practice. Most underimmunized children in our practice had failed to appear for recommended well visits; a minority experienced missed opportunities for immunization.

Assessment of high and low contrast visual acuity after photorefractive keratectomy for myopia

BACKGROUND

Our aim was to assess visual acuity using standardized charts and illumination conditions after photorefractive keratectomy.

METHODS

High and low contrast visual acuity were measured on Bailey-Lovie logarithm of the minimum angle of resolution (LogMAR) charts under high and low illumination conditions on 105 photorefractive keratectomy patients who had been treated with the Summit (N = 60) or the VISX (N = 45) excimer laser.

RESULTS

Best corrected visual acuity was reduced in the treated eye compared with the untreated control eye under all test conditions, with the greatest differences under conditions of low contrast and low illumination. Reduction of acuity under low contrast and low illumination was related to small optic zone sizes and steep ablation edge profiles found in Summit-treated eyes. In the VISX-treated eyes, high contrast acuity was reduced in the presence of central topographical irregularities, subepithelial haze, and higher myopic corrections.

CONCLUSIONS

Testing conditions such as those described here may be useful in quantifying vision degradation in suboptimal viewing conditions and among patients with vague complaints.

Zonal Photorefractive Keratectomy for Presbyopia

PURPOSE

We performed zonal excimer laser photorefractive keratectomy in three eyes of three presbyopic patients using a specially designed mask, with a minimum follow-up of 24-months.

METHODS

Two females (ages 59 and 48) and one male (age 55) were included in the study. The procedure was performed with a mask designed by one of the authors (GMN), applied to the Aesculap-Meditec Mel 60 excimer laser. The mask consists of a mobile diaphragm formed by two blunt blades. The aim in all the eyes was a presbyopic correction of 3.00 D.

RESULTS

After an initial regression of 1.00 D, the presbyopic correction remained stable during the 36-month follow-up. The patients read at least J3 at normal reading distance without correction. Since the ablated zone was only about 15% of the total area of a 3.0 mm pupil, all three patients were also able to read with their preoperative presbyopic correction (using the untreated 85% of the pupillary area).

CONCLUSION

Although only three eyes were treated with the zonal presbyopia mask presented here, the visual and refractive outcome appears promising in view of the relatively long follow-up time.

Long-term Results of Photorefractive Keratectomy for Hyperopia and Hyperopic Astigmatism

PURPOSE

This study was conducted to determine the safety and efficacy of using the Nidek EC-5000 excimer laser for photorefractive keratectomy to correct hyperopia and hyperopic astigmatism.

METHODS

We treated 67 eyes of 44 patients for hyperopia and hyperopic astigmatism with the Nidek EC-5000 excimer laser. The algorithm provided an ablation zone of 5.5 mm diameter with the addition of a tapered transition zone of 3.5 mm diameter, for a total ablation of 9 mm diameter.

RESULTS

Uncorrected visual acuity (geometrical mean) changed from 0.16 to 0.37 at 12 months; corrected visual acuity (geometrical mean) changed from 0.8 to 0.89; mean sphere decreased by 2.08 D from 3.76 to 1.40 D (range, 1.70 to 1.68 D) and cylinder by 1.40 D from 2.20 to 1.00 D. Refractive results for < or = 3.00 D were reasonably accurate and stable, but for > +3.00 D, undercorrection and regression over l year were the rule.

CONCLUSION

Hyperopic PRK proved to be a safe technique in regard to the risk of loss of visual acuity with no central corneal opacities and with a generally rapid recovery of baseline spectacle-corrected visual acuity, but the predictability of correction greater than +3.00 needs improvement.

Radial and staggered treatment patterns to correct hyperopia using noncontact holmium:YAG laser thermal keratoplasty

PURPOSE

To compare the effects of two treatment patterns in the correction of hyperopia by noncontact holmium:YAG laser thermal keratoplasty (LTK).

SETTING

Divisione Oculistica, Ospedale S. Gerardo, Monza, Italy.

METHODS

Using two treatment patterns, we performed noncontact LTK in one session in 16 eyes of 8 patients with isometropic hyperopic refractive errors; mean preoperative subjective cycloplegic refraction was +4.90 diopters (D) +/- 1.17 (SD). The treatment consisted of 24 spots in three concentric rings of eight spots each; ring diameters were 6.0, 7.0, and 8.0 mm, respectively. Each spot received seven pulses of laser energy at 30 mJ/pulse. We treated one eye of each patient with a radial pattern (the spots of the three rings aligned on the eight semimeridians) and the fellow eye with a staggered pattern (the spots of the contiguous rings at 22.5 degrees from each other). Follow-up at 1, 15, 30, 90, 180, and 360 days included subjective cycloplegic refraction, uncorrected (UCVA) and spectacle-corrected visual acuity (SCVA), computerized videokeratography (CVK), and Scheimpflug camera examination.

RESULTS

One year postoperatively, the mean subjective cycloplegic refraction was +2.75 +/- 1.6 D in the eyes treated with the radial pattern and +3.40 +/- 1.6 D in those treated with the staggered pattern; the mean change in subjective cycloplegic refraction was 2.15 and 1.50 D, respectively. Mean UCVA improved by five lines in the radial group and by four lines in the staggered group. Mean SCVA returned to preoperative levels by day 15 in the radial group and at 1 year in the staggered group; at 1 year, SCVA improved by one line in the radial group and remained unchanged in the staggered group. No eye lost one or more lines of SCVA. Refractive astigmatism was essentially unchanged in both groups. Scheimpflug photography and CVK indicated larger and more uniform corrected zones in the radial group.

CONCLUSIONS

Radial and staggered patterns effectively corrected low hyperopia, although both were subject to a certain amount of regression. The radial pattern produced faster postoperative recovery of SCVA and demonstrated greater refractive stability.

Excimer Laser Photorefractive Keratectomy for Presbyopia: 24-month Follow-up in Three Eyes

BACKGROUND

For some patients, standard optical correction for presbyopia is not satisfactory. Using a specially designed mask, we developed a procedure for correcting presbyopia with excimer laser photorefractive keratectomy (PRK).

METHODS

A mask consisting of a mobile diaphragm formed by two blunt blades was used to ablate a 10 to 17 microm deep semilunar-shaped zone immediately below the pupillary center, steepening the corneal curvature in that area. Three eyes of three presbyopic patients were treated, aiming at a near addition of +3.00 D. Follow-up time was 24 months.

RESULTS

After an initial regression of 1.00 D during the first 6 months, the presbyopic correction remained stable for the duration of the follow-up period, enabling uncorrected near vision of J3 in all three eyes. Uncorrected distance visual acuity was not altered. Contrast sensitivity (Regan) was slightly decreased only at the 11% level. Videokeratography confirmed corneal steepening in the ablated area.

CONCLUSION

The visual and refractive outcome of excimer laser PRK for presbyopia with the Aesculap-Meditec MEL 60 is promising, especially in view of the 2-year follow-up.

Factors affecting epithelial hyperplasia after photorefractive keratectomy

PURPOSE

To determine the effect of patient age, postoperative time, ablation zone diameter and depth, attempted correction, and corneal topography on postoperative corneal epithelial thickness after photorefractive keratectomy (PRK).

SETTING

Private clinic and university hospital, Stockholm, Sweden.

METHODS

This retrospective, unmasked study comprised 136 myopic patients treated unilaterally with PRK. Seventy eyes had been treated with the Summit excimer laser 27 months +/- 7 (SD) earlier using ablation zone diameters of 4.1 to 5.0 mm. Sixty-six eyes had been treated with the VISX excimer laser 6 +/- 3 months earlier using a 6.0 mm zone diameter. The untreated fellow eyes served as controls. Epithelial thickness was measured at a standardized central corneal area with a modified optical pachymeter, and corneal topography was determined using computerized videokeratoscopy.

RESULTS

In the Summit group, the epithelial layer in the PRK eyes was 12.0 microns (21%) thicker than in the control eyes (P < .001; 95% confidence interval [CI] 9.35 to 14.3 microns). This thickness differential correlated significantly with increased ablation depth and attempted correction. In the VISX group, the epithelium in the treated eyes was 7.0 microns (7%) thinner (P = .0009; 95% CI -1.9 to -6.7 microns) and thickness did not correlate with ablation depth or attempted correction. There was no correlation between epithelial hyperplasia and patient age or postoperative follow-up. With the laser groups combined, epithelial hyperplasia was greater with smaller zone sizes and a greater rate of change in power at the edge of the ablation zone.

CONCLUSION

The factors associated with an increase in epithelial thickness were small ablation zones, greater attempted corrections, and deeper ablations. Larger, smoother ablation profiles may result in less epithelial hyperplasia.

Failure of Mechanical Epithelial Removal to Reverse Persistent Hyperopia After Photorefractive Keratectomy

BACKGROUND

Residual hyperopic overcorrection after photorefractive keratectomy (PRK) using early algorithms is a rare but serious complication. Anecdotal evidence suggests that epithelial removal can stimulate epithelial hyperplasia, thereby reducing overcorrection. The aim of this study was to determine if epithelial removal effectively reduced hyperopia after PRK for myopia and, concurrently, to correlate the healing response with the refractive outcome.

METHODS

Enrolled were seven eyes of seven patients (mean age, 44 +/- 13 years) who had undergone PRK with a mean manifest refractive error of +2.21 +/- 0.74 diopters (D). All had undergone PRK an average of 24 +/- 9 months previously. Epithelial removal was performed over the excimer-treated zone with a surgical blade. Subjective refraction, epithelial thickness, corneal topography, and subepithelial haze were measured up to 1 year postoperatively.

RESULTS

Reduction in hyperopia between the baseline and 1-year visit was not statistically significant (mean difference, 0.55 D reduction; p = .102). That epithelial removal did not stimulate a wound-healing response is further supported by the absence of change in epithelial thickness over the first month and the small amounts of subepithelial haze. Central corneal power was reduced by a mean of 0.64 D after 1 month (p < .05).

CONCLUSIONS

Epithelial removal alone did not reduce the hyperopic overcorrection present after PRK, nor did it stimulate epithelial hyperplasia in the majority of these eyes. However, a trend toward improvement was noted with time was noted.

A comparative study of epithelial hyperplasia after PRK: Summit versus VISX in the same patient

Epithelial hyperplasia has been found to occur after photorefractive keratectomy in eyes treated with small (5 mm or less) ablation zone diameters with the Summit laser, but not with large zones (6 mm) with the VISX laser (Gauthier et al. 1995a). The aim of this study was to further investigate the effect of surgical parameters on epithelial hyperplasia by comparing eyes treated with the same zone diameter but two different lasers. We examined 11 subjects who had photorefractive keratectomy for myopia performed with 5 mm ablation zones with the Summit excimer laser in one eye and the VISX 20/20 laser in the fellow eye an average of 21 months previously. Epithelial thickness and corneal topography were measured. The mean epithelial thickness was not statistically different (p = 0.083) between the eyes treated with the Summit (66 +/- 12 microns) and VISX (60 +/- 14 microns) lasers. Postoperative corneal dioptric power showed a similar profile between the two eyes at the edge of the zone, with the VISX-treated corneas being more shallow centrally. There was a trend towards greater epithelial thickness with deeper ablations. This study supports the hypothesis that epithelial hyperplasia is dependent on ablation zone diameter and ablation depth.

Role of epithelial hyperplasia in regression following photorefractive keratectomy

AIM

To determine the relation between epithelial hyperplasia and regression of effect after photorefractive keratectomy (PRK).

METHODS

Seventy unilaterally treated patients with PRK were examined. All eyes had been treated with the Summit excimer laser 27 (SD 7) months previously with zone diameters of 4.1 to 5.0 mm. The untreated fellow eyes served as controls. Epithelial thickness was measured centrally with a thin slit optical pachometer and manifest subjective refraction was performed.

RESULTS

The epithelium was 21% thicker in the treated eye (p < 0.0001). The relation between refractive regression and epithelial hyperplasia was significant (r = 0.41; p < 0.001).

CONCLUSIONS

Epithelial hyperplasia after PRK correlated with the myopic shift (including hyperopia reduction) after treatment with the Summit laser. A model is proposed suggesting that both subepithelial and epithelial layers contribute to regression in the Summit treated eyes with 18 microns of epithelial hyperplasia contributing each dioptre of regression.

Identification and characterization of a novel surface antigen gene induced in mast cells activated through the high affinity IgE receptor

In an effort to isolate novel genes involved in inflammation and/or mast cell activation, we have used a combination of differential screening and subtractive hybridization to isolate genes whose expression are induced upon activation of a transformed rat mast cell line. One of the isolated clones, pMCA-32, contained an open reading frame of 278 amino acids that included a putative hydrophobic transmembrane domain, a cysteine rich Ig-like extracellular domain, and a cytoplasmic domain containing three consensus SH2-domain phosphotyrosine binding sites. The MCA-32 gene is also highly conserved between rat and mouse, with the two coding regions being 73% identical. Although the MCA-32 coding region did not contain an obvious signal peptide, MCA-32 protein was detected on the surface of rat mast cells, and the cloned cDNA produced a cell surface protein when expressed in COS-7 cells. MCA-32 RNA from both mouse and rat undergoes alternative splicing, producing an mRNA containing an in-frame deletion of the TM domain, suggesting that a form of MCA-32 protein may be secreted. MCA-32 mRNA expression was up-regulated upon activation of RBL-2H3 cells and was highly abundant in primary peritoneal mast cells. Expression of MCA-32 RNA was only observed in primary and transformed mast cells from rat, while in the mouse MCA-32, RNA was also produced in significant amounts by a number of transformed monocyte cell lines. Thus, MCA-32 is a novel surface protein whose structure and expression suggest roles in the development and/or activation of mast cells and monocytes.

Identification and characterization of a novel surface antigen gene induced in mast cells activated through the high affinity IgE receptor

In an effort to isolate novel genes involved in inflammation and/or mast cell activation, we have used a combination of differential screening and subtractive hybridization to isolate genes whose expression are induced upon activation of a transformed rat mast cell line. One of the isolated clones, pMCA-32, contained an open reading frame of 278 amino acids that included a putative hydrophobic transmembrane domain, a cysteine rich Ig-like extracellular domain, and a cytoplasmic domain containing three consensus SH2-domain phosphotyrosine binding sites. The MCA-32 gene is also highly conserved between rat and mouse, with the two coding regions being 73% identical. Although the MCA-32 coding region did not contain an obvious signal peptide, MCA-32 protein was detected on the surface of rat mast cells, and the cloned cDNA produced a cell surface protein when expressed in COS-7 cells. MCA-32 RNA from both mouse and rat undergoes alternative splicing, producing an mRNA containing an in-frame deletion of the TM domain, suggesting that a form of MCA-32 protein may be secreted. MCA-32 mRNA expression was up-regulated upon activation of RBL-2H3 cells and was highly abundant in primary peritoneal mast cells. Expression of MCA-32 RNA was only observed in primary and transformed mast cells from rat, while in the mouse MCA-32, RNA was also produced in significant amounts by a number of transformed monocyte cell lines. Thus, MCA-32 is a novel surface protein whose structure and expression suggest roles in the development and/or activation of mast cells and monocytes.

[Photorefractive keratectomy (PRK). The limits of our knowledge]

The confines of our knowledge with respect to excimer laser photorefractive keratectomy are particularly manifest in two areas: the effects of the excimer on the corneal tissue, especially in the course of the wound healing process; and the optical aberrations caused by the laser treatment through structural alterations in a previously clear cornea. The criteria currently used to evaluate the outcome of excimer refractive surgery are not adequate. More stringent and nuanced assessments are needed to expand the frontiers of our knowledge.

Indications, results, and complications of refractive corneal surgery with lasers

The use of lasers to correct refractive errors has become an established clinical procedure in many countries. Excimer laser photorefractive keratectomy (PRK) has been performed on an estimated 400,000 to 500,000 eyes worldwide. For myopia up to about 6.0 D, PRK appears to be generally safe, exhibiting acceptable accuracy, predictability, and stability. Complications of PRK can occur intraoperatively, and early or late postoperatively. For higher degrees of myopia, laser in situ keratomileusis may prove to be a more appropriate procedure, but long-term follow-up is needed. Hyperopic PRK and holmium:yttrium-aluminum-garnet thermokeratoplasty are still considered investigational methods, and for newer technologies, such as solid-state lasers, human trials are being launched.

Patient Satisfaction Following Photorefractive Keratectomy for Myopia

This study was conducted to evaluate the subjective response of patients who underwent photorefractive keratectomy (PRK) for myopia with the Summit Technology UV 200 LA excimer laser (Summit Technology, Inc., Waltham, Mass.) (3.5 to 5.0 mm diameter ablation zone) 36 months previously. One-hundred thirteen patients with preoperative myopia between -1.50 diopters (D) and -6.50 D with an ablation diameter of 3.5 mm to 5.0 mm answered a questionnaire at the 36-month examination. Sixty-two percent of patients had both eyes treated. Halo problems were experienced always by 34% of patients in the group, 26% sometimes, and 40% never. Permanent night vision problems were experienced by 40%; 30% reported them sometimes and 30% reported no problems at all. Sixty percent never needed to use glasses after treatment, 30% sometimes did, and 10% always wore glasses. Seventy percent of patients thought the results were very good; the remaining 30% experienced different degrees of halo and night vision problems.

Epithelial Alterations Following Photorefractive Keratectomy for Myopia

BACKGROUND

A retrospective observational study was conducted to test the hypothesis that there is clinically measurable epithelial hyperplasia after photorefractive keratectomy (PRK), and to determine its effect on the epithelial oxygen uptake rate.

METHODS

One hundred myopic eyes who had been previously treated unilaterally with PRK were examined. Fifty eyes were treated with the Summit excimer laser (Summit Technology, Waltham, Mass) 27 +/- 7 months previously with ablation zone diameters of 4.1, 4.3, 4.5, or 5.0 mm. Fifty eyes were treated with the VISX excimer laser (VISX Inc, Sunnyvale, Calif) 5 +/- 4 months previously with one ablation zone diameter of 6.0 mm. The untreated eyes served as controls. Epithelial thickness was measured at a standardized central area within the ablation zone with a modified optical pachometer. Oxygen uptake rate was measured in a subgroup of 30 eyes (20 Summit and 10 VISX).

RESULTS

The epithelium after PRK was 24% thicker than in the control eye in the Summit group (mean difference 13 +/- 10 microns; p < .01) and 7% thinner in the VISX group (mean difference -4 +/- 10 microns; p < .01). A higher oxygen uptake rate correlated with a thicker epithelium (r = 0.42; p < .05).

CONCLUSIONS

The epithelium was significantly thicker after PRK between 13 and 37 months after treatment with the Summit excimer laser using ablation zone diameters of 4.1 to 5.0 mm. The epithelium was thinner between 1 and 15 months after treatment with the VISX laser using an ablation zone diameter of 6.0 mm. An increase in oxygen uptake rate reflected the metabolic rate of a greater number of cells in the hyperplastic layer.

Twenty-four-month follow-up of excimer laser photorefractive keratectomy for myopia. Refractive and visual acuity results

PURPOSE

To evaluate the 24-month refractive outcome of excimer laser photorefractive keratectomy (PRK) performed on normal, sighted myopic eyes; and to assess the evolution of postoperative refraction, the accuracy of predicted correction, and the results in terms of uncorrected visual acuity.

METHODS

Photorefractive keratectomy was performed on 495 eyes, with a preoperative refraction ranging from -1.25 to -7.50 diopters (D). Ablation zone diameters of 4.3 and 4.5 mm were used. All patients were treated with a standard topical steroid regimen postoperatively. Minimum follow-up time was 24 months.

RESULTS

Mean refraction (spherical equivalent +/- standard deviation) at 24 months was -0.27 +/- 0.74 D, which was significantly (P < 0.01) different from the mean at 12 months (0.01 +/- 0.78 D). There was also a significant (P = 0.01) difference between the 12- and 18-month (-0.15 +/- 0.82 D) mean refractions. But there was no significant difference between the means at 18 and 24 months postoperatively. Subgroup analysis at 24 months showed that patients with low to moderate myopia (up to -3.90 D) had significantly better refractive outcomes than those with higher myopia. Also at 24 months, 91% of the eyes had an uncorrected visual acuity of at least 20/40, and 81.5% had an uncorrected visual acuity of at least 20/30. Correspondingly, 87.5% of the eyes were within 1.00 D of emmetropia, and 71.7% were within 0.50 D. Only 0.4% lost one line of best-corrected visual acuity, no eye lost two lines or more.

CONCLUSIONS

Refraction after PRK is slow to stabilize, but appears to reach stability by 18 to 24 months after surgery. The refractive results are reasonably predictable and compare well with those achieved with radial keratotomy.

Photorefractive keratectomy for low myopia at 5 mm treatment diameter. A comparison of two excimer lasers

The aim of the study was to evaluate the algorithm and surgical performance of two excimer lasers, the Summit Excimed 200 LA and the VISX 20/20, by assessing visual outcome parameters such as visual acuity and contrast sensitivity, and subjectively estimating dark vision performance. Furthermore, refractive results and centration of the surgically ablated area were assessed. Twenty patients were included in each group. The indications were myopia between -2 to -5 diopters allowing up to -0.75 diopters astigmatism. The treatment diameter was 5 mm. The postoperative treatment was topical dexamethasone for 3 months. The follow-up time was 12 months. The results showed a median refraction +/- 0.0 D in the Summit group and -0.5 D in the VISX group 12 months postoperatively. The uncorrected visual acuity was 0.5 (20/40) or better for 100% of the Summit treated eyes, whereas 85% of the VISX treated eyes achieved 0.5 (20/40) or better. The other visual qualities as contrast sensitivity, dark vision and centration of the ablation zone were the same in both groups. The slightly more myopic outcome of the VISX laser explains the poorer average uncorrected visual acuity in this group. We have, as a result of the refractive results, changed our algorithm in the VISX machine to achieve emmetropia. It is our experience that one should try to reach emmetropia in this young population.

Excimer retreatment of regression after photorefractive keratectomy

Regression of effect is a well-established complication of excimer laser photorefractive keratectomy for the correction of myopia. In 17 eyes retreated with excimer photorefractive keratectomy, minimum follow-up time was six months. Mean (+/- SD) refraction at six months postoperatively was -0.97 +/- 2.10 diopters, significantly different (P < .01) from the pre-retreatment mean of -2.91 +/- 0.86 diopters. The 11 best eyes (six-month refraction < -1.00 diopter) had a mean refraction of +0.32 +/- 0.67 diopter. At six months after retreatment, 64.7% had an uncorrected visual acuity greater than or equal to 20/40, and 58.8% were within 1.00 diopter of emmetropia. Two eyes showed a loss of one to two Snellen lines at six months. There was no significant increase in mean haze after retreatment. While the percentage of eyes with uncorrected visual acuity greater than or equal to 20/40 and the percentage of eyes within 1.00 diopter of emmetropia were lower than in eyes which did not require retreatment, the results of this study indicate that the majority of photorefractive keratectomy regressions can be successfully retreated.

Effect of postoperative steroids on the refractive outcome of photorefractive keratectomy for myopia with the Summit excimer laser

To assess the role of topical steroids following excimer laser photorefractive keratectomy (PRK) for myopia, we compared the refractive outcome in 100 eyes that did not receive steroids in the immediate postoperative period (untreated eyes) with 100 eyes that were treated with topical dexamethasone for three months postoperatively. Photorefractive keratectomy was performed with the Summit laser, using 4.3 mm and 4.5 mm ablation zones. At three months after surgery, the untreated eyes had a mean refraction of -0.97 +/- 1.15 diopters (D), significantly different (P < .01) from the mean refraction (+0.46 +/- 0.74 D) of the steroid-treated eyes. By six months postoperatively, 86% of the untreated eyes had regressed to a myopia of at least 0.50 D, whereas only 23% of the steroid-treated eyes had regressed. In a second study, we compared the results in 25 patients whose first PRK eye was treated with steroids after surgery but whose second eye was not. At three months postoperatively, mean refraction in the steroid-treated eyes was +1.23 +/- 0.71 D, significantly different (P < .01) from the mean of -0.45 +/- 1.29 D in the untreated eyes. The refractive results in PRK eyes treated with the Summit unit and with relatively small ablation zone diameters showed that eyes that received dexamethasone postoperatively were less likely to regress to myopia.

Excimer laser photorefractive keratectomy for myopia. Clinical results in sighted eyes

PURPOSE

To evaluate the refractive results of excimer laser photorefractive keratectomy (PRK) performed on normal, sighted myopic eyes; to assess the role of postoperative topical steroid treatment in patients with PRK; and to study the regression of effect.

METHODS

An argon fluoride 193-nm excimer laser was used. Photorefractive keratectomy was performed on 420 eyes with preoperative refraction ranging from -1.25 to -7.50 diopters (D). Minimum follow-up time was 12 months, and 194 of the eyes were followed for 15 months. Postoperative treatment generally consisted of topical dexamethasone for 3 months, but in a sub-study, some eyes were treated for only 5 weeks.

RESULTS

Mean refraction (spherical equivalent +/- standard deviation) at 12 months was -0.04 +/- 0.84 D and at 15 months -0.22 +/- 0.78 D. At 12 months postoperatively, 86% of the eyes were within 1.00 D of emmetropia, at 15 months 87%. At 12 months, 91% of the eyes had an uncorrected visual acuity of at least 20/40, at 15 months 87%. Eyes treated with dexamethasone for 3 months regressed significantly less than those treated for only 5 weeks (P < 0.01). Dexamethasone also was effective in reversing regression later in the postoperative course. Eyes with preoperative myopia up to 4.90 D had significantly better refractive results at 12 months than eyes with myopia ranging from 5.00 to 7.50 D (P < 0.01).

CONCLUSION

These data show that excimer laser PRK can correct myopia with good predictability. Results at 12 and 15 months tend to suggest stability of postoperative refraction. Regression of effect was more common in higher myopes. Topical steroids postoperatively seem to play a crucial role for the refractive result.