Biomedical subjects

M K Smolek

Publications and source records attributed to M K Smolek.

24 records · Page 2Linked to original sources

PubMed1993

Interlamellar cohesive strength in the vertical meridian of human eye bank corneas.

PURPOSE: Previously, human corneal stromal interlamellar cohesive strength in the horizontal meridian was shown to be twice as strong peripherally as centrally (approximately 2.90 x 10(-1) versus 1.40 x 10(-1) N/mm). In the current study, stromal samples excised from the vertical meridian were studied to determine if meridional differences also exist. Precise knowledge about corneal stromal structure is warranted, because anisotropy can influence postoperative healing strength and corneal shape. METHODS: Limbus-to-limbus stromal strips with a constant 2.2-mm width were obtained from the vertical meridians of 52 eyebank corneas (8 single, 22 pairs). Cohesive strength was recorded as samples were split at a constant 1.6 mm/s at 50% stromal depth. RESULTS: The mean cohesive strength in the inferior periphery was found to be only two thirds the strength observed in the nasal or temporal periphery (1.96 x 10(-1) N/mm versus approximately 2.94 x 10(-1) N/mm @ 5 mm). The mean cohesive strength in the inferior periphery was also significantly less than the strength of the superior periphery (1.85 x 10(-1) N/mm +/- 8.83 x 10(-3) SEM versus 2.34 x 10(-1) +/- 1.37 x 10(-2) @ 4 mm from the central cornea; P = 0.0027). Unlike the samples from the horizontal meridian, which could be described by a profile symmetric about the central cornea, force profiles for the vertical data could be characterized with distinct, classifiable patterns that were generally asymmetric. Fellow corneas from a single donor tended to have strength profiles belonging to the same class (P = 0.035; chi-square), although some paired eyes exhibited profiles from distinctly different classes. CONCLUSIONS: These data strongly support the concept of an anisotropic collagen macrostructure that is more complex than previously believed. This inherent structural anisotropy may become a significant determinant of corneal shape during ectatic disease and some forms of keratorefractive surgery.

Adult↗

PubMed1992

A biomechanical evaluation of rabbit corneas in M-K and Dexsol.

We compared the average force required to separate normal corneas at a 50% stromal depth, with the force required to separate corneas stored for 2, 5, 7, 10, and 14 days in either McCarey-Kaufman or Dexsol corneal storage medium. The required interlamellar separation force was calculated by standardizing the width of the test strips. The average required force for 35 fresh rabbit corneas (no storage) was 9.1 +/- 1.5 g/mm. There was no significant change in the required separation force after storage in either medium for up to 14 days.

Animals↗

PubMed1990

Interlamellar adhesive strength in human eyebank corneas.

The interlamellar biomechanical properties of stromal collagen are relatively unknown, yet may be highly significant with respect to wound healing and the efficacy of certain keratorefractive surgical procedures. Interlamellar adhesive strength was measured as the tearing force required to separate corneal lamellae at a 50% stromal depth in 16 human eyebank corneas. The mean value for the central cornea was found to be 14.2 (+/- 0.5 SEM) g-wt/mm of tissue width. Histology showed a smooth separation between the lamellae along the tearing plane in the central cornea. We believe that the adhesive strength measured in the central cornea may be primarily the force needed to break interlamellar proteoglycan bonds between collagen lamellae, because no torn lamellae were found in this region. The mean adhesive strength and the SEM increased toward the periphery in a symmetrical fashion. The mean adhesive strength in the far periphery was 31.6 (+/- 3.7 SEM) g-wt/mm at 5 mm nasally, and 28.4 (+/- 3.2 SEM) g-wt/mm at 5 mm temporally, and was approximately twice the mean central value. The rising value of the mean adhesive strength with increasing distance from the central cornea was believed to be due to a more highly disorganized collagen network in which greater numbers of lamellae passed obliquely in depth through the tearing plane. These lamellae would contribute their tensile strength to the adhesive strength measurement along the tearing plane. Histology from the peripheral cornea confirmed the existence of depth-varying collagen lamellae and the torn ends of lamellae that passed across the tearing plane.

Adhesiveness↗

PubMed1986

Nonius horopter in projected viewing.

Nonius horopter measurements were made on three normal subjects using both physically displaced (real viewing) and stereogrammetrically displaced (projected viewing) test objects. Three subjects with ocular anomalies were tested using the projected viewing arrangement with and without 5% overall magnifier before the right eye, and seven complete measurements of the projected viewing horopter were made on a fourth subject with an ocular anomaly over the period of 1 month. These latter individual plots showed large irregularities that changed location from day to day. Plotting the mean and standard error of the means of these seven sets of data produced a smoothing out of the horopter locus. Plotting each individual horopter setting in the sequence of measurement and monitoring eye position indicated that all of the irregularities and regional horopter changes found are most likely introduced by changes in fixation disparity (vergence eye movements).

Depth Perception↗

PubMed1983

A comparison of two horopter criteria.

Both the binocular nonius and classical nonius criteria were applied to a group of subjects in order to compare the resulting horopters. Results indicated that monocular visual directions shifted along with changing binocular disparities when using the binocular nonius technique. This method constitutes a modification of the frontal plane criterion, since binocular portions still can be set equidistant to the fixation object. Comparing equidistance (binocular nonius) with equidirection (nonius) indicated that the 2 loci were essentially the same. Shifts in the nonius horopter induced by a small overall magnifier could not be predicted for 2 out of 7 subjects; one of these with aniseikonia and the other with intermittent exotropia. Irregularities in all horopter data could be accounted for by shifts in the vergence angles during the experiment.

Aniseikonia↗

PubMedDate not supplied

Videokeratography for quantitative surface analysis of used soft contact lenses.

The greater utilization of soft contact lenses calls for the development of new and objective methods of evaluating the optical performance of the different lens types, in situ. We used videokeratography to examine the surface topography of soft contact lenses that had been worn for more than 1 year on 27 eyes of 23 patients, and compared the resulting color-coded maps and topographic indices as well as contact lens-corrected visual acuities, with those obtained with new replacement lenses on the same eyes. Visual inspection of the color-coded maps revealed differences in the surface characteristics of the used and new lenses. Comparison of quantitative indices including the SAI (Surface Asymmetry Index), IAI (Irregular Astigmatism Index), SRI (Surface Regularity Index), and SDP (Standard Deviation of Powers) showed that asymmetry, surface irregularity, potential visual acuity (derived from the SRI), and corneal power distribution were significantly poorer with the used lenses than with the new (P = 0.0001). The videokeratoscope is useful for evaluating the soft contact lens surface in situ, as an indicator of optical quality; it also permits the objective evaluation of lens cleaning techniques.

Adolescent↗