Histologic Changes and Wound Healing Response Following 10-Pulse Noncontact Holmium:YAG Laser Thermal Keratoplasty

BACKGROUND

Noncontact holmium:YAG laser thermal keratoplasty (Ho:YAG LTK) is a promising new technology for correction of hyperopia and astigmatism. We studied the acute histologic changes and wound healing response following Ho:YAG LTK performed with treatment parameters encompassing those used in clinical studies.

METHODS

We performed 10-pulse noncontact Ho:YAG LTK on three human corneas 1 day before their removal at penetrating keratoplasty and on six New Zealand white rabbit corneas followed for up to 3 months. Tissues were studied with light and transmission electron microscopy and immunohistochemistry.

RESULTS

The amount of acute tissue injury increased according to the pulse radiant energy. In human corneas, changes in the irradiated zones included epithelial cell injury and death, loss of fine filamentous structure in Bowman's layer, disruption of stromal lamellae, and keratocyte injury and death. In the rabbit corneas, similar acute changes were noted. By 3 weeks, epithelial hyperplasia and stromal contraction were present. Wound healing in the rabbits included repair of the epithelial attachment complex, keratocyte activation, synthesis of type I collagen, partial restoration of stromal keratan sulfate and type VI collagen, and retrocorneal membrane formation.

CONCLUSIONS

Noncontact Ho:YAG LTK produces acute epithelial and stromal tissue changes and in rabbit corneas stimulates a brisk wound healing response.

Changes in pupil size induced by phacoemulsification and posterior chamber lens implantation: consequences for multifocal lenses

PURPOSE

Because the optical performance of eyes implanted with multifocal intraocular lenses will theoretically depend upon the size and position of the pupil relative to the near and distance zones of the lens, we designed a study to determine whether preoperative pupil size is useful in predicting the postoperative pupil size of patients having phacoemulsification with posterior chamber lens implantation.

SETTING

Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, Texas.

METHODS

We prospectively measured pupil sizes preoperatively and postoperatively in 71 consecutive patients who had phacoemulsification with posterior chamber lens implantation. Pupil sizes were photographed under five lighting and viewing conditions that simulated a range of normal functional situations.

RESULTS

The mean change in preoperative to postoperative pupil size was less than 0.5 mm in all five testing conditions. However, changes in pupil diameter of 1.0 mm or more were noted in approximately 10% of patients in each testing situation. Sex, iris color, and the presence or absence of intraoperative iris trauma were not predictive factors for determining which patients sustained large postoperative changes in pupil size.

CONCLUSIONS

Preoperative pupil size does not predict postoperative size with sufficient consistency to ensure a good match between pupil diameter and the zone sizes of multizone multifocal intraocular lenses.

How to evaluate and implement new technologies in an era of managed care and cost containment

New technologies often enable clinical laboratorians to overcome the challenges we face. These technologies sometimes become available with amazing punctuality, addressing recent problems and keeping the physician-customer satisfied for another day. Traditionally, developments such as a new cancer marker have been implemented into routine use with little circumspection because the benefits diagnostically and financially were perceived to far outweigh the risk that the new test or technology was not as effective as described. The notion of subsequently removing older tests inferior to the new one has hardly been considered. The challenges confronting clinical laboratorians today, however, are affecting that typical pattern dramatically. Four of the most pervasive challenges are comprehensively examined in the 1995 Clinical Chemistry Forum. One of these key areas--the proper implementation of modern technology in the form of new tests or new approaches to producing clinical laboratory results--is the main topic of this review.

Secondary cataract formation following pediatric intraocular lens implantation: 6-month results

Secondary membrane formation is the most common complication of posterior chamber intraocular lens (PC IOL) implantation in children. The purpose of this study was to determine the effect of various methods of managing the posterior capsule and anterior vitreous on the rate of posterior capsular opacification in children implanted with PC IOLs. We retrospectively studied 16 eyes of 12 children (age 1.5-12 years) implanted with PC IOLs; the follow-up period was at least 6 months. The posterior capsule and anterior vitreous were managed in a variety of ways: in 5 eyes the posterior capsule was left intact, and 11 eyes underwent posterior capsulorehexis (PCCC)-6 cases without and 5 cases with anterior vitrectomy. In two eyes of each of the last two groups, posterior optic capture was performed. Visually significant secondary cataract developed in all five eyes with intact posterior capsules and in the four eyes that had undergone PCCC without vitrectomy and without posterior optic capture. The optical axis remained clear in all eyes that had undergone vitrectomy and in all eyes treated with posterior optic capture. Each procedure, posterior optic capture and anterior vitrectomy appears to be effective in preventing or delaying posterior opacification in lens implantation in infants and children. However, a longterm follow-up is required to determine the efficacy and safety of these two approaches.

Hyperopia correction by noncontact holmium:YAG laser thermal keratoplasty. Clinical study with two-year follow-up

BACKGROUND

Thermal keratoplasty to correct hyperopia has been attempted with nonlaser and laser devices. Problems have included long-term regression and irregular induced astigmatism. The present clinical study was performed to investigate the safety, efficacy, and stability of a noncontact mode of holmium: YAG laser energy delivery and a modified laser thermal keratoplasty treatment procedure for correction of low hyperopia.

METHODS

Seventeen patients underwent noncontact holmium: YAG laser thermal keratoplasty in their nondominant eyes for correction of hyperopia of up to 3.00 diopters. Treatment parameters included simultaneous delivery of eight holmium: YAG laser spots in a symmetrical octagonal array with a centerline diameter of 6mm, 10 pulses of laser light at 5-Hz pulse repetition frequency, and pulse energies of 159 to 199mJ. Follow-up was 2 years in 15 of 17 patients.

RESULTS

In the 15 eyes examined at 2 years after surgery, mean uncorrected distance Snellen visual acuity improved from 20/125-1 to 20/50-2. The mean change in spherical equivalent of subjective manifest refraction was -0.79 diopter. Eleven of these 15 eyes (73%) had a mean refractive correction of -1.1 diopters (range, -0.38 to -2.63 diopters); regression between 14 days and 2 years was 0.2 diopter. Four eyes (27%) had no persistent refractive correction (within +/- 0.25 diopter). Mean induced refractive astigmatism was 0.18 diopter. None of the eyes lost two or more lines of spectacle-corrected distance vision. The amount of refractive correction at 2 years after surgery was correlated to the treatment pulse energy and the volume of the opacified corneal tissue observed immediately after treatment.

CONCLUSIONS

This technique of noncontact laser thermal keratoplasty produced safe, effective, and persistent corrections of low hyperopia in the majority of treated eyes.

How to evaluate and implement new technologies in an era of managed care and cost containment

New technologies often enable clinical laboratorians to overcome the challenges we face. These technologies sometimes become available with amazing punctuality, addressing recent problems and keeping the physician-customer satisfied for another day. Traditionally, developments such as a new cancer marker have been implemented into routine use with little circumspection because the benefits diagnostically and financially were perceived to far outweigh the risk that the new test or technology was not as effective as described. The notion of subsequently removing older tests inferior to the new one has hardly been considered. The challenges confronting clinical laboratorians today, however, are affecting that typical pattern dramatically. Four of the most pervasive challenges are comprehensively examined in the 1995 Clinical Chemistry Forum. One of these key areas--the proper implementation of modern technology in the form of new tests or new approaches to producing clinical laboratory results--is the main topic of this review.

Corneal topographic changes after noncontact holmium:YAG laser thermal keratoplasty to correct hyperopia

PURPOSE

To analyze the changes in corneal curvature induced by laser thermal keratoplasty (LTK) to correct hyperopia.

SETTING

Cullen Eye Institute, Baylor College of Medicine, Houston, Texas.

METHODS

We performed LTK on nine hyperopic eyes using a noncontact holmium: YAG (Ho:YAG) laser. Five eyes received a single ring of eight spots at the 6 mm zone (Group A); four received a second ring of eight at the 7mm zone (Group B). Computerized videokeratography (CVK) was obtained preoperatively and 1, 30, 90, 180, and 360 days postoperatively. We calculated the net dioptric changes in the following CVK values: corneal curvature at the 1, 3, 5, and 7 mm zones; effective corneal refractive power (Eff RP); and spherical equivalent of subjective manifest refraction (SE SMR). We classified difference maps according to the pattern of induced change.

RESULTS

At 1 year, steepening at the 1, 3, 5, and 7 mm CVK zones was 0.5 diopter (D), 0.6 D, 0.1 D, and -0.42 D, respectively, in Group A and 1.5 D, 1.5 D, 1.1 D, and 0.54 D, respectively, in Group B. Effective corneal refractive power increased 0.6 D in Group A and 1.5 D in Group B. Mean change in SE SMR was -0.6 D in Group A and -1.4 D in Group B. Most regression occurred during the first 90 days. Difference maps showed five bow-tie, two irregularly irregular, one semicircular, and one homogeneous patterns.

CONCLUSIONS

Noncontact Ho:YAG LTK produced peripheral corneal flattening and central corneal steepening. A greater change in curvature was produced using a two-ring treatment.

Corneal topographic changes and induced astigmatism resulting from superior and temporal scleral pocket incisions

BACKGROUND AND OBJECTIVE

To determine the corneal topographic changes that are induced by superior and temporal 5-mm scleral pocket incisions.

PATIENTS AND METHODS

The authors retrospectively reviewed the records of 43 patients who underwent phacoemulsification with posterior chamber lens implantation through unsutured 5-mm scleral pocket incisions, 24 superiorly and 19 temporally. Corneal curvature was measured using computerized videokeratography, and the induced astigmatism was calculated with the Holladay-Cravy-Koch formula.

RESULTS

At 4 to 6 weeks, postoperatively there was mild flattening along with the meridian of the incision in both groups. The change was greater with the superior incisions, but the differences between the groups were not statistically significant. Surgically induced astigmatism was 0.7 D (+/-0.1 D) in the eyes that received superior incisions, and 0.3 D (+/-0.1 D) in the eyes that received temporal incisions; this difference was statistically significant (P < .03).

CONCLUSIONS

At 4 to 6 weeks postoperatively, temporal 5.0-mm scleral pocket incisions provide more stable postoperative topography than do superior scleral pocket incisions.

Computerized videokeratography and keratometry in determining intraocular lens calculations

PURPOSE

To compare the accuracy of standard keratometry and computerized videokeratography (CVK) in determining intraocular lens (IOL) power calculations.

METHODS

Using the EyeSys Corneal Analysis System, we prospectively obtained CVK maps on 75 eyes of 69 patients scheduled to have phacoemulsification with implantation of a posterior chamber intraocular lens. Using manifest refraction obtained at 6 weeks postoperatively, we optimized the calculations for the Hoffer Q, Holladay, and SRK/T formulas for standard keratometric and the following six CVK values: average curvatures at the 1 mm, 2 mm, and 3 mm zones, the keratometric equivalent at the 3 mm zone, and the Stiles-Crawford weighted averages over the 3 mm and 6 mm zones. The accuracy of these parameters was determined by calculating the mean absolute error and percentage of patients with accuracy within < or = 0.5 diopter (D), < or = 1.0 D, and < or = 2.0 D.

RESULTS

Keratometrically derived data were slightly more accurate than the CVK-derived values. The average difference in mean absolute error between the keratometric and CVK values was 0.13 D for the Hoffer Q formula, 0.11 D for the Holladay, and 0.08 D for the SRK/T.

CONCLUSIONS

In this population of patients, we found the CVK-derived corneal curvature values to be slightly less accurate than standard keratometry in predicting IOL power. However, CVK provides important corneal curvature data for IOL calculations in patients with abnormal or surgically altered corneal surfaces.

Evaluation of intraocular pressure with Healon and Healon GV in sutureless cataract surgery with foldable lens implantation

PURPOSE

To evaluate transient increases in intraocular pressure (IOP) after use of high-viscosity viscoelastic agents in cataract surgery.

SETTING

Military Hospital, Ulm, Germany.

METHODS

In a prospective, randomized study, we evaluated IOP following cataract surgery using two different viscoelastic substances (Healon, Healon GV). The viscosity of Healon GV is 10 times higher than that of Healon because of higher concentration and molecular weight. Patients having identical phacoemulsification procedures (sutureless clear corneal tunnel incision with foldable silicone lens implantation) (N = 60) and identical viscoelastic removal were assigned to groups of 15 based on viscoelastic used and removal time (20 or 40 seconds). Intraocular pressure was measured preoperatively and at 6, 24, 36, and 48 hours and 1 month postoperatively.

RESULTS

The highest mean IOP elevations in both viscoelastic groups were obtained at 24 hours postoperatively (2.9 mm Hg +/- 4.3 [SD] with Healon and 3.3 +/- 6.3 mm Hg with Healon GV). There were no statistically significant differences between the two viscoelastics and the two removal times during the entire follow-up period (unpaired t-test), but standard deviations were higher in the Healon GV groups at 6 and 24 hours. Two patients in the Healon groups and three in the Healon GV groups required medical treatment for IOP within the first 24 postoperative hours; however, all five patients had an IOP lower than 22 mm Hg on the second postoperative day.

CONCLUSIONS

Based on postoperative IOP, both viscoelastics can be equally well removed from the anterior chamber. Incidence of high IOP using high-viscosity hyaluronic acid is minimized by the described removal technique.

Methods to control astigmatism in cataract surgery

The correction of astigmatism during cataract surgery has evolved due to recent basic and clinical studies. To control surgically induced astigmatism, the surgeon has many options, including varying incision parameters, astigmatic keratotomy, scleral flap recession and resection, toric intraocular lens implantation, and modifying postoperative medical treatment. The recent literature is reviewed, and our current approach for cataract surgery is discussed.

Histological changes and wound healing response following noncontact holmium: YAG laser thermal keratoplasty

PURPOSE

To evaluate acute histological changes and the induced wound healing response in corneal tissue following noncontact holmium:YAG laser thermal keratoplasty (LTK).

METHODS

LTK using 10 pulses and a range of radiant energies was performed on 3 human corneas one day prior ro their removal at penetrating keratoplasty. Rabbit corneas were treated with 10-pulse and 5-pulse LTK and followed for up to 3 months. Tissues were studies with light and transmission electron microscopy and immunohistochemistry.

RESULTS

The amount of acute tissue injury increased with increasing pulse radiant energy. In human corneas, changes in the irradiated zones included epithelial cell injury and death loss of fine filamentous structure in Bowman's layer, disruption of stromal lamallae, and keratocyte injury and death. In the rabbit corneas, similar acute changes were noted. By 3 weeks, epithelial hyperplasia and stromal contraction were present. Wound healing in the rabbit corneas included repair of the epithelial attachment complex, keratocyte activation, synthesis of type I collagen, partial restoration of stromal keratan sulfate and type VI collagen, and retrocorneal membrane formation. Compared to 10-pulse treatments, 5-pulse treatments produced less acute tissue injury and had more rapid restoration of normal stromal architecture.

CONCLUSION

Noncontact LTK produces acute epithelial and stromal tissue changes and in rabbit corneas stimulates a brisk wound healing response. These changes could contribute to postoperative regression of induced refractive correction. Further work is required to determine if reductions in the magnitude of acute tissue injury and induced wound healing response will enhance the efficacy and stability of LTK.

Scanning electron microscopic analysis of foldable acrylic and hydrogel intraocular lenses

OBJECTIVE

To analyze the surface quality of foldable acrylic and hydrogel intraocular lenses (IOLs).

SETTING

Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, and Institute of Anatomy and Cellular Biology, University of Giessen, Germany.

METHODS

We studied eight foldable IOL models with optics made of six different acrylate/methacrylate polymers: Acrylens ACR360 (loptex), AcrySof MA60BM (Alcon), MemoryLens U940A (Mentor), 92S and 92C (Morcher), Hydroview H60M (Storz), HydroSof SH30BC (Alcon), and ISH66 (Corneal). Four IOLs of each design were examined. Light and scanning electron microscopy were performed before and after IOL folding with forceps.

RESULTS

All IOL models had excellent optic and haptic surfaces. The haptic-optic junctions revealed minimal empty spaces or irregularities in three of the five three-piece IOLs and smooth surfaces in all one-piece IOLs. Minimal surface alterations and superficial defects caused by folding were detectable in the two acrylate (acrylic) IOLs (loptex ACR360, Alcon MA60BM) with low water content.

CONCLUSION

Intraocular lenses of acrylate/methacrylate polymers had excellent surface quality. The acrylic IOLs were vulnerable to mild folding or forceps defects; however, these were less marked than those previously noted with poly(methyl methacrylate) IOLs.

Topical anesthesia for phacoemulsification: initial 20-case series with one month follow-up

We report the results of our initial 20 phacoemulsification cases performed using topical anesthesia. The preferred topical regimen consisted of preservative-free 0.75% bupivacaine. Intravenous sedation was provided primarily with fentanyl and midazolam. Phacoemulsification was performed through a scleral tunnel incision, and a one-piece poly(methyl methacrylate) or three-piece silicone intraocular lens was implanted. There were no complications with the anesthetic technique. One day postoperatively, 69% of patients with a desired refractive error within 0.75 diopters of emmetropia had an uncorrected visual acuity of 20/40 or better. At one month, all patients had a best corrected acuity of 20/30 or better, and 60%, 20/20 or better. Eighteen patients reported complete intraoperative comfort, and 17 reported complete postoperative comfort. Seven of the 10 patients who had had previous peribulbar anesthesia preferred topical. All 10 "first eye" patients said they would choose topical anesthesia for future surgery. With appropriate case selection, topical anesthesia for phacoemulsification surgery can be used with excellent intraoperative and postoperative results.

Analytical performance characteristics of the T4 method in the Abbott AxSYM immunoassay analyzer

OBJECTIVE

To evaluate the tetraiodothyronine (T4) method in the Abbott AxSYM immunoassay analyzer.

DESIGN

The single-value criteria proposed by Westgard et al. were employed. Assays of control materials established random error (RE) analytical sensitivity, and linearity. Constant error (CE) was established by studying the effects of interferents on T4 quantification. The AxSYM random access immunoassay analyzer was compared with TDx batch analyzer to determine systematic error (SE). Critical concentrations of T4 are 3.0 micrograms/dL and 13.0 micrograms/dL, as these concentrations represent medical decision points. Allowable error at these critical concentrations are 1.0 and 2.6, respectively.

SETTING

Peninsula Regional Medical Center Clinical Laboratories.

RESULTS

Based on Health Care Financing Administration [HCFA] allowable error goals, RE, SE, and CE were acceptable for concentrations of T4 ranging from 3.0 micrograms/dL to 13 micrograms/dL. PE was virtually absent. Total error (TE) = RE + SE was acceptable at 13 micrograms/dL but exceeded allowable error at the lower critical value of 3.0 micrograms/dL. Abbott AxSYM was sensitive to T4 at a concentration of 0.34 microgram/dL. Linearity was excellent and consistent with the manufacturer's claim over a range 1.0 microgram/dL to 24 micrograms/dL. Of the interferents studied only hemoglobin caused a > 15% change in the measurement of T4.

CONCLUSION

The AxSYM immunoasssay analyzer performed to manufacturer's specifications and met HCFA allowable error limits for quantifying T4.

[Surface quality of flexible silicone intraocular lenses. A scanning electron microscopy study]

BACKGROUND

Soft intraocular lenses (IOLs) have been developed to be folded during insertion to allow implantation through a small incision. The surface of the IOL is of great importance in postoperative inflammation and long-term acceptance of the implant. Rough and sharp edges can damage delicate intraocular tissues. The purpose of this study was to analyze new, foldable silicone IOLs for surface quality prior to and following folding.

MATERIALS AND METHODS

Eleven silicone IOLs of different types were included in this study (four one-piece plate-haptic silicone IOLs and seven three-piece silicone IOLs with polypropylene, PMMA or polyimid haptics). We performed scanning electron microscopy on brand-new IOLs prior to and following folding either with forceps or inserter. Special attention was given to the silicone optic surface, optic edges, haptic-optic junctions and the haptic itself. Photographs were taken at 5-350 times magnification.

RESULTS

All IOLS demonstrated a smooth and homogeneous optic surface at low magnification. At high-power magnification (X 350), distinctive surface patterns were evident in some IOLs, which turned out to be artefacts. The edge finish showed surplus silicone material and molding flash in six of 11 IOLs. Positioning holes of the 4 plate-haptic IOLs were, except in one IOL, rounded and not rough. Photographs of the haptic-optic junctions revealed surplus material or clefts between the haptic and optic in six of the 7 three-piece IOLs; the loop ends of two IOLs showed a roughened or irregular surface. We did not detect any IOL changes produced by folding.

CONCLUSIONS

The silicone IOLs tested demonstrated generally acceptable surface properties, but most IOLs had regional surface irregularities of varying magnitude. The clinical impact of these remains to be established, but surplus material or surface defects might result in deposition of inflammatory cells, protein or microorganisms and synechia formation. Folding of the IOLs did not produce superficial defects.