Biomedical subjects

L B Szczotka

Publications and source records attributed to L B Szczotka.

13 recordsLinked to original sources

PubMed2001

Tears contain the complement regulator CD59 as well as decay-accelerating factor (DAF).

Previous studies have shown that DAF (or CD55), a cell surface inhibitor of autologous C3 activation, is present in tears and that > 90% of the C3 convertase regulatory activity in tear fluid resides in this protein (Lass JH et al., Invest Ophth Vis Sci 1990; 31:1136-48). This study investigated whether (i) the membrane cofactor protein (MCP or CD46), an additional factor that regulates C3 activation, and (ii) the membrane inhibitor of reactive lysis (MIRL or CD59), a cell surface regulator that acts to prevent formation of the membrane attack complex, are also present in tears, and if so, are functional. Two-site immunoradiometric assays showed that MCP is present in tears at low levels (42 + 8 ng/ml, n = 8) while CD59 is present at levels (222 + 78 ng/ml, n = 14) comparable to those of DAF (325 + 289 ng/ml, n = 12). The concentrations of CD59 (i) were increased two-fold or more in closed eye tears, and (ii) were decreased in reflex tears. Western blotting showed that CD59 protein in tears migrates with an apparent mol. wt similar to membrane CD59 protein. Phenyl-Sepharose adsorption and Triton X-114 partitioning of tear CD59 as well as of tear DAF however, showed that both proteins are devoid of GPI anchors. Assays using cobra venom factor-activated human serum and guinea pig erythrocytes showed that CD59 is functionally active in inhibiting autologous C5b-9-mediated lysis and, under constitutive conditions, accounts for > 85% of the C9 inhibitory activity in tear fluid.

CD55 Antigens↗

PubMed2001

A summary of the findings from the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. CLEK Study Group.

BACKGROUND: This summary of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study includes the study design and results to date. METHODS: The CLEK Study is a longitudinal, observational study of 1,209 patients with keratoconus. The study's main outcome measures are corneal scarring, visual acuity, corneal curvature, and quality of life. RESULTS: These patients' mean age at baseline was 39.3 +/- 10.9 years, and they had moderate to severe keratoconus. Ninety-five percent of the patients had steep keratometric readings of at least 45 D, and 78% had best-corrected visual acuity of 20/40 or better in both eyes. Sixty-five percent of the patients wore rigid gas-permeable contact lenses in both eyes, and most of those (73%) reported that their lenses were comfortable. Most rigid gas-permeable contact lens wearers were fitted with apical touch (88%). Fifty-three percent had corneal scarring in one or both eyes, and corneal scarring was associated with corneal staining, contact lens wear, age, the presence of a Fleischer's ring, and a steeper cornea. Corneal scarring was associated with decreased high- and low-contrast visual acuity. CONCLUSIONS: These results characterize keratoconus patients as rigid gas-permeable contact lens wearers with moderately steep corneas. Corneal scarring is associated with decreased vision in keratoconus.

Adult↗

PubMed2000

Decay-accelerating factor in tears of contact lens wearers and patients with contact lens-associated complications.

PURPOSE: Complement activation fragments have been detected in the anterior segment during 1) eye closure, 2) contact lens wear, and 3) in some contact lens-associated pathologies. The decay-accelerating factor (DAF), a membrane-associated complement regulatory protein that inhibits the central C3 amplification convertases of the cascade, is present on both the ocular surface and in tears. In this study, we measured levels of tear DAF in asymptomatic contact lens patients and in patients who presented with contact lens-associated complications. METHODS: Tears were collected from 55 patients using capillary pipettes. Subjects included normal non-contact lens wearing controls (N = 14), asymptomatic soft (N = 13) and rigid gas permeable (N = 5) wearers, and individuals with contact lens-induced acute red eye (CLARE) (N = 4), ulcerative keratitis (N = 3), giant papillary conjunctivitis (GPC) (N = 8), contact lens peripheral ulcers (N = 3), and infiltrative keratitis (N = 5). Levels of DAF were assessed using a two-site immunoradiometric assay using anti-DAF monoclonal antibodies. RESULTS: The mean concentration of DAF in normal controls was found to be 149+/-78 ng/ml, 117+/-59 ng/ml, and 111+/-86 ng/ml for noncontact lens patients, and asymptomatic soft and rigid gas permeable lens wearers, respectively. In the conditions of CLARE, infiltrative keratitis, and GPC, DAF concentrations were significantly reduced compared with normal noncontact lens controls. Compared with asymptomatic soft lens patients, the condition of infiltrative keratitis showed a significant reduction in tear DAF. CONCLUSIONS: This study documents a trend toward decreased levels of tear DAF in patients with the contact lens associated inflammatory conditions CLARE, GPC, and infiltrative keratitis. Tears of patients with infiltrates show the most significant reduction of tear DAF. The reductions may be associated with enhanced complement activation contributing to the pathogeneses of infiltrative keratitis and associated ocular surface diseases.

CD55 Antigens↗

PubMed2000

Efficiency and accuracy of two computerized topography software systems for fitting rigid gas permeable contact lenses.

PURPOSE: The world of computerized videokeratoscopy is continually evolving. Computerized videokeratoscope contact lens programs boast the capability to accurately design final rigid gas permeable (RGP) lens parameters and simulate contact lens fluorescein patterns. We evaluated the EyeSys System 2000 Pro-Fit software (v. 4.0) and Humphrey Atlas MasterVue Contact Lens Module (v. A6) for efficiency and accuracy in fitting RGP contact lenses on normal subjects. METHODS: Balanced manifest refractions, slit lamp examinations, and computerized topographical analysis with RGP module lens fitting were performed and compared for all eyes. Lens parameters were chosen after an optimal simulated fluorescein pattern was achieved by either accepting the initially recommended default lens or a modification. Final lens parameters were based on clinical performance. RESULTS: With the Humphrey Atlas software, which uses a default topographic tear clearance fitting protocol set by the manufacturer, 24/50 (48%) eyes required modifications to the default fitting parameters based on the simulated fluorescein patterns. Nine of 50 eyes (18%) required further modifications once the RGP lens was dispensed. The EyeSys Pro-Fit software, which allows a custom tear clearance fitting protocol set by the user as default, required modifications to 20/35 eyes (57.1%) from default fittings provided by the system. Six of 35 eyes (17.1%) required subsequent modifications once the RGP lens was dispensed. Comparison of the EyeSys to Humphrey modules revealed no significant difference in efficiency (P=0.51), defined as any changes required to the default parameters; however, the user made more modifications to the EyeSys module from the default setting. There was no significant difference in final success rates between EyeSys (82.9%) and Humphrey (82%) systems (P=1.00). CONCLUSION: Although both topography guided contact lens modules offered accuracy in RGP fitting, a user programmed default (EyeSys) protocol did not improve efficiency in RGP lens parameter selection compared to a manufacturer programmed default module (Humphrey). The need for a knowledgeable contact lens fitter remains to guide the systems in achieving the optimal fit.

Contact Lenses↗

PubMed2000

Peripheral corneal contour measured by topography influences soft toric contact lens fitting success.

PURPOSE: Empirical fitting success is important to expanding the soft toric contact lens market. Previous study has lead to the hypothesis that lens flexure may alter expected fitting relationships and back vertex power (BVP) in situ. In this study, baseline topographic features as potential variables in predicting soft toric fitting success were analyzed. METHODS: One-hundred forty-nine eyes were empirically fit with back surface toric soft lenses after placido-based videokeratography was performed. Measurements recorded from baseline instantaneous maps included: flat simulated keratometry (Sim-K) value (in diopters) and axis, steep Sim-K value (in diopters) and axis, eccentricity of the flat meridian, and the form of corneal astigmatism. Astigmatism was classified as types I-V based upon differences between central and peripheral corneal toricity. RESULTS: Ninety-three of 149 (62.4%) eyes were successfully fit empirically with the first trial lens. One-hundred thirty-five of 149 (90.6%) eyes were ultimately successful after unsuccessful trial lenses were adjusted and reordered. There were no differences between the empirically fit success and failure groups in instrument reported eccentricity, Sim-K values, or Sim-K axes (P>0.05). Of 115 eyes classified for form of corneal astigmatism, 76 (66%) were classified with high or irregular peripheral astigmatism (types IV and V). There was a significant association between fitting success and the form of corneal toricity (P=0.0327). Thirty-nine of 115 (34%) eyes were classified as corneal types I-III (spherical or minimally toric corneal periphery) and were associated with empirical fitting success (P=0.0092). CONCLUSION: Empirical soft toric fitting success can be anticipated in spherical corneas, central astigmatism, or corneas with peripheral toricity which matches the central toricity. However, high and irregular peripheral corneal toricity occurs in the majority of astigmatic patients. Corneal topography is a valuable tool to assess peripheral astigmatism which may be one factor influencing unexpected lens performance.

Astigmatism↗

PubMed1999

Rigid contact lens fitting relationships in keratoconus. Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group.

PURPOSE: Although the influence of flat-fitting contact lenses on corneal scarring in keratoconus is frequently debated, the current standard of care with regard to the apical fitting relationship in keratoconus remains undocumented. METHODS: Patients were examined at baseline in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study (N = 1209). Patients wearing a rigid contact lens in one or both eyes (N = 808) had their habitual rigid contact lenses analyzed, and the fluorescein patterns and base curves were compared to the first definite apical clearance lens (FDACL). The FDACL is the flattest lens in the CLEK Study trial lens set that exhibits an apical clearance fluorescein pattern. For patients wearing a rigid contact lens in both eyes, one eye was selected randomly for analysis. RESULTS: Twelve percent of the rigid contact lens-wearing eyes were wearing lenses fitted with apical clearance based upon the clinician's fluorescein pattern interpretation. The remainder (88%) was wearing lenses fitted with apical touch. For mild (steep keratometric reading <45 D) keratoconus corneas, the mean estimate of the base curve to cornea-fitting relationship was 1.18 D flat (SD +/- 1.84 D); moderate (steep keratometric reading: 45 to 52 D) corneas were fitted on average 2.38 D flat (SD +/- 2.56 D); and severe (steep keratometric reading > 52 D) corneas were fitted an average of 4.01 D flat (SD +/- 4.11 D). CONCLUSIONS: Despite the potential risk for corneal scarring imposed by flat-fitting rigid contact lenses, most CLEK Study patients wear flat-fitting lenses. Overall, rigid lenses were fitted an average of 2.86 D (SD +/- 3.31 D) flatter than the FDACL.

Contact Lenses↗

PubMed1998

Contact lenses after LASIK.

BACKGROUND: The corneal shape is significantly altered after LASIK, necessitating new contact lens designs and fitting techniques for optimal postoperative contact lens performance. METHODS: Procedures for fitting soft and rigid gas-permeable lenses are described on the basis of the authors' experience. Topographic map options are explored to assess the best curvature and contour data to assist in RGP lens fitting. RESULTS: Standard soft and rigid lenses are often used with success after LASIK. When fitting standard and reverse geometry RGP lenses, axial topographic maps provide the best curvature values to assist in the fitting of RGP lenses. CONCLUSIONS: Although patients may be apprehensive to pursue contact lens fitting after elective LASIK refractive surgery, new fitting techniques should turn a potentially difficult fitting into a teachable science.

Contact Lenses↗

PubMed1998

Comparison of axial and instantaneous videokeratographic data in keratoconus and utility in contact lens curvature prediction.

PURPOSE: Instantaneous radius of curvature data in corneal videokeratoscopy better represents corneal shape and local curvature changes in keratoconus than axial maps, especially in the periphery. Knowledge of instantaneous radius is especially important in keratoconus for analysis of the cone apex, which is often decentered. In this study, we quantitatively compared axial and instantaneous displays of videokeratographic data in keratoconus, with emphasis on apex curvature and position. We assessed the utility of instantaneous data for rigid gas permeable (RGP) contact lens curvature selection and compared it with data derived from the original axial displays in keratoconus. METHODS: We performed modern placido-based videokeratography on 35 eyes with clinically diagnosed keratoconus. We derived the apex curvature, the position of the apex relative to the center of the map, and the steep simulated keratometry (SIM-K) reading from axial and instantaneous videokeratographic displays. We also collected the RGP base curves for 28 eyes that were fit with a minimal apical bearing or clearance RGP contact lens. RESULTS: The instantaneous apex was consistently located closer to the center of the map than the axial apex. Means (and standard deviations) for the best fit RGP base curve, axial steep SIM-K, axial apex curvature, instantaneous steep SIM-K, and instantaneous apex curvature were 52.00 D +/- 5.92 D, 50.93 D +/- 5.94 D, 54.81 D +/- 7.14 D, 49.19 D +/- 5.54 D, and 56.86 D +/- 7.89 D, respectively. Statistical comparisons revealed axial steep SIM-K to best represent the RGP base curve for the entire group. Similarly, in the subset of patients with apex decentrations within 1 mm of the map center, the axial steep SIM-K best represented the RGP base curve. In the remaining decentered cone subset, the axial apex curvature best represented the base curve. CONCLUSIONS: Axial and instantaneous maps differ significantly in apical position and apex curvature in keratoconus. Although instantaneous radius may better represent corneal shape, axial curvatures better predict the final RGP base curve in keratoconus patients.

Algorithms↗

PubMed1998

Repeatability and agreement of two corneal-curvature assessments in keratoconus: keratometry and the first definite apical clearance lens (FDACL). CLEK Study Group. Collaborative Longitudinal Evaluation of Keratoconus.

PURPOSE: This study was conducted to determine the agreement and test-retest repeatability of two methods for measuring corneal curvature in keratoconus: keratometry and the First Definite Apical Clearance Lens (FDACL). Our interest in the FDACL procedure stems from the important contact lens-fitting information and documentation of disease progression provided by the FDACL trial lenses and observation of fluorescein patterns. METHODS: The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is an observational study that has enrolled 1,209 keratoconus patients to characterize the progression of keratoconus, to determine factors associated with its progression, and to assess its impact on quality of life. Ten percent of the patients were randomly selected at baseline for a retest examination. The baseline examination, which included keratometry and FDACL, was repeated in this sample. The FDACL is the flattest lens in the standardized CLEK trial lens set that vaults the apex of the cone. FDACL provides an estimate of the sagittal height of the cone. RESULTS: The correlation of FDACL with the steep keratometric reading (r = 0.89; p = 0.0001) and the flat keratometric reading (r = 0.83; p = 0.0001) were high. Test-retest repeatability as measured by the intraclass correlation coefficient (ICC) was high: FDACL ICC, 0.97; steep keratometric reading ICC, 0.96; and flat keratometric reading ICC, 0.95. Test-retest repeatability of FDACL remained high in advanced disease. CONCLUSION: FDACL provides a repeatable new procedure for determining disease severity in keratoconus.

Adult↗

PubMed1997

Clinical evaluation of a topographically based contact lens fitting software.

BACKGROUND: Second generation corneal topography-based contact lens software programs attempt to fit the cornea based on topographical information rather than simulated keratometry and nomogram-based fits. The EyeSys System 2000 Pro-Fit software (Version 3.1) was clinically evaluated for efficiency in fitting rigid gas permeable (RGP) lenses on 22 normal subjects. METHODS: Balanced manifest refractions, slitlamp examinations, keratometry, computerized topographic analysis and lens fitting, and manual diagnostic RGP fitting were performed on all patients. The topographically fit eyes were compared to corresponding eyes which were manually fit with diagnostic trial lenses. Lens parameters for the topographically fit eye were chosen after an optimal fluorescein pattern was achieved by either accepting the initially recommended Pro-Fit lens or a modification. Final lens parameters were based on clinical performance. Lenses were reordered when there was a need for base curve changes of 0.1 mm or more, power alterations of +/- 0.50 D or more, or for any alteration in diameter, optic zone, or edge lift. RESULTS: Both manual and topographically fit groups achieved 17/22 (77%) eyes successfully fit without any subsequent lens modifications. Time records for the manually fit group averaged 16.5 min, whereas the topographically fit group averaged 8.0 min. CONCLUSIONS: This study reports a 51.4% reduction in chair time when using a topographically based contact lens software program while achieving the same clinical results as in traditional diagnostic RGP fitting, suggesting increased efficiency in fitting RGPs to normal eyes.

Astigmatism↗

PubMed1996

Influence of contact lens wear on the corneal topography of keratoconus.

PURPOSE: Corneal videokeratography is frequently used to evaluate keratoconus patients, as it is believed to allow for a more thorough appreciation of the complex curvature changes associated with the anterior corneal surface. The goal of this study was to determine the qualitative and quantitative influence of soft and rigid contact lens wear on the corneal topography of keratoconus. METHODS: 205 keratoconus patients were analyzed by computerized videokeratography for both qualitative corneal topographic patterns and quantitative indices. Fifty-six patients were non-contact lens wearers, 130 wore polymethylmethacrylate (PMMA) or rigid gas permeable (RGP) contact lenses, and 19 wore soft contact lenses. Data from the keratoconus patients were also compared to a control group comprised of normal patients with no history of contact lens wear. RESULTS: All three keratoconus groups had a significantly increased frequency of an asymmetric bowtie/skewed radial axes (AB/SRAX) pattern compared with normals. Differences among the videokeratography patterns for the kertoconus patients included a significant shift from the AB/SRAX videokeratographic pattern to the irregular videokeratographic pattern in the rigid (PMMA or RGP) lens subgroup as well as an increased frequency of the irregular pattern in the soft contact lens group versus the no contact lens group (P < 0.0001). Additional differences between the rigid contact lens and no contact lens keratoconus groups included increased values for the quantitative indices of SAI, SRI, SIM-K, and central K in the rigid contact lens group (P < 0.05). CONCLUSIONS: The increased frequency of qualitative and quantitative corneal irregularity in the rigid contact lens keratoconus group may reflect a mechanical effect of contact lens wear or an advanced disease state in these patients limiting them to rigid lens wear. The advanced disease is evidenced by steeper SIM-K and Central K indices in the rigid contact lens group.

Contact Lenses↗

PubMed1995

Computerized videokeratoscopy contact lens software for RGP fitting in a bilateral postkeratoplasty patient: a clinical case report.

Computerized videokeratoscopy systems now allow interactive rigid gas permeable (RGP) fitting evaluation using fluorescein pattern simulations through updated software programs. We used Computed Anatomy's Topographic Modeling System-1 (TMS-1) Custom Design Contact Lens Program successfully to refit a symptomatic bilateral post-penetrating keratoplasty patient. No trial lenses were used. For each eye the base curve, optic zone size, and edge lift were chosen from the optimal fluorescein pattern designed and titrated on the TMS-1 unit. Lens powers were based on the patient's previous lenses and overrefraction. Dispensed lenses provided a clinically acceptable fit, good comfort, and maximal visual acuity, and no adjustments were necessary. Corneal videokeratoscopy can be successfully employed to titrate an RGP fit, even on irregular corneas.

Astigmatism↗

PubMed1994

Clinical evaluation of a computerized topography software method for fitting rigid gas permeable contact lenses.

Computerized videokeratoscope software programs now have the ability to assist in the design of rigid gas permeable (RGP) contact lenses and simulate fluorescein patterns. We evaluated the performance of Computed Anatomy's Topographic Modeling System (TMS-1) and its Contact Lens Fitting Program (version 1.41) in fitting RGP lenses in 31 subjects. Computerized topographic analysis, balanced manifest refraction, slit lamp examination, and keratometry were performed. Initial lens parameters were ordered according to manufacturer's programmed recommendations for base curve, power, lens diameter, optic zone diameter, and edge lift. Final lens parameters were based on clinical performance. Lenses were recorded for base curve changes of 0.1 mm or more, power alterations of +/- 0.50 D or more, or for any alteration in diameter/optic zone. Twenty-seven patients were analyzed for all five recommended parameters. Thirteen of 27 patients (48%) required no parameter changes. Nine of 27 patients (33%) required one parameter change, four of 27 patients (15%) required two parameter changes, and one patient (4%) needed three parameters altered. The most prevalent change was a power alteration, required in nine of 27 patients (33%); however, comparisons of all initial to final parameters showed no statistically significant differences. Comparison of initial base curves to that which would have been chosen via standard keratometry also showed no significant difference. This study found the TMS-1 default lens recommendations to be clinically unacceptable. This system, however, could be an alternative method of initial lens selection if used to titrate a fit or if software enhancements are incorporated to account for lens movement and flexure.

Astigmatism↗