Biomedical subjects

R E Gundel

Publications and source records attributed to R E Gundel.

9 recordsLinked to original sources

PubMed1996

Anterior hydrogel lens deposits: polished vs. unpolished surfaces.

Traditionally, lathe cut hydrogel lenses receive both back and front surface polishing to eliminate any surface irregularities that might serve as potential attachment sites for lens deposits or even microorganisms. However, with the advent of newer more technologically advanced lathing equipment, the need for lens polishing may require renewed justification. This study sought to compare, by scanning electron microscopy (SEM), anterior lens surface deposit formation on polished and unpolished 55% water hydrogel lenses. A total of 10 subjects wore in 1 eye (control) a lens with both front and back lens surfaces polished and on the other eye (test) a lens with only the back lens surface polished for a period of 2 weeks on a daily wear basis. Each lens was then scanned (using SEM), with 3 separate regions photographed at 30x using a 10 kV electron source. Using a Wilcoxon Signed-Ranks test on the differences between average deposit ratings for the polished and the unpolished lenses, by subject pair, we failed to reject the null hypothesis that the difference was zero.

Biofilms↗

PubMed1996

Standardized rigid contact lens fitting protocol for keratoconus.

Keratoconus is typically managed by a variety of rigid contact lens fitting techniques and lens designs. The two most fundamental fitting techniques are apical corneal touch (including divided or three-point touch) and apical clearance. In the course of designing a multi-center study of keratoconus patients, a standardized keratoconus fitting protocol was developed. All contact lens parameter options are uniform except for base curve and secondary curve radii, which are determined by interpretation of fluorescein patterns using the CLEK Study trial lens set and protocol. The initial trial lens's base curve is the average keratometric reading; sequentially steeper lenses are applied until definite apical clearance is observed. We have evaluated the feasibility of this standardized fitting protocol on 30 keratoconus patients. Our results suggest that we have developed a standardized contact lens fitting set and fitting protocol to simplify contact lens management in patients with mild to moderate keratoconus.

Contact Lenses↗

PubMed1996

Feasibility of fitting contact lenses with apical clearance in keratoconus.

Despite the wide variety of rigid contact lens fitting philosophies for the visual correction of keratoconus, questions remain, including which approach-flat, divided support, or steep-contributes the most toward the preservation of a clear cornea. One goal of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Pilot Study was to determine the feasibility of managing early keratoconus patients with apical clearance rigid contact lenses. Of 30 keratoconus patients identified with at least 1 nonscarred cornea, 17 patients (30 eyes) were randomly assigned to a steep lens fitting protocol. After trial fitting with a standardized lens design demonstrating minimum apical clearance, lenses were dispensed whose base curve was 0.2 mm steeper than the minimum apical clearance lens. Patients were re-evaluated on a quarterly schedule concluding at 12 months. Changes in keratometry between baseline and 12 months identified unequal steepening of the flat and steep corneal curvatures, suggestive of corneal molding. Best corrected rigid lens visual acuity measures illustrated no significant changes over the course of the study. Clinically significant corneal compromise was transiently observed in some patients. Only 1 of 22 eyes completing the pilot study and fitted with apical clearance developed mild corneal scarring.

Adolescent↗

PubMed1993

Parameter consistency in disposable lenses.

An evaluation of parameter consistency and edge defects as they might relate to premature lens fracture was undertaken for 2 disposable lens types, 50 Johnson & Johnson Acuvue lenses and 50 Wesley-Jessen FreshLook lenses. Diameter measurements varied from 13.97 to 14.48 mm (mean = 14.28 mm, SD = 0.138 mm) for Acuvue and 14.30 to 14.63 mm (mean = 14.41 mm, SD = 0.064 mm) for FreshLook. Based on previously reported information, these diameter variations for Acuvue may be sufficient to affect lens fitting characteristics. Calculated back surface sagittal depth varied from 3.27 to 3.38 mm (mean = 3.32, SD = 0.029 mm) for Acuvue and 3.68 to 3.87 mm (mean = 3.75 mm, SD = 0.039 mm) for FreshLook. Center thickness was generally consistent across the power range evaluated (-0.50 to -4.00 D) for the FreshLook lenses, and appeared to increase significantly for low minus powers for the Acuvue lenses. Twenty-one (44%) Acuvue lenses and 6 (12%) FreshLook lenses showed edge defects that might contribute to premature lens fracture.

Contact Lenses, Hydrophilic↗

PubMed1992

Quantitative analysis of visual acuity through amber discolored lenses.

Discoloration of hydrogel contact lenses is frequently encountered in clinical practice and often precipitates lens replacement. This investigation sought to determine if lens discoloration was associated with a compromise in low or high contrast, high illumination visual acuity. This association would lead to a more scientific rationale for lens replacement. Amber lens discoloration was achieved using human-worn 55% water hydrophilic contact lenses (Methafilcon-A) heated in a 1% potassium sorbate, low pH saline solution. A spectrum of 6 discolored lenses was obtained with a peak absorbance at 320 nm. Fifteen subjects, between the ages of 22 and 38 years, were tested wearing each of the discolored lenses. None of the differences in high or low contrast acuity between our discolored and nondiscolored lenses were found to be statistically significant using a paired t-test at the 99% significance level.

Adult↗

PubMed1992

Aiding the novice practitioner in contact lens selection.

A comprehensive study was performed to assist the new graduate and novice contact lens practitioner in the choice of the optimal lens for each case scenario, as well as provide guidance for inventory selection. The survey was distributed to the clinical staff at the State University of New York, State College of Optometry, in order to take advantage of the knowledge of the experienced contact lens fitter. There appear to be clinically significant relationships between lens characteristics and performance ratings.

Contact Lenses↗

PubMed1992

Residual hydrogen peroxide as a function of platinum disc age.

Recently there has been considerable attention given to the possible deleterious effects of residual hydrogen peroxide on both the cornea and the crystalline lens of the eye. We measured residual hydrogen peroxide levels of the AOSept disinfection system at regular intervals over a 4 month period. By 1 month the residual hydrogen peroxide level was 21 ppm +/- 9.4 (mean +/- standard deviation); at the end of 2 months it was 36 ppm +/- 17.6. At 3 months, when disc replacement is recommended, the residual hydrogen peroxide level was 43 ppm +/- 4.7 (range: 17-98 ppm). At 4 months the residual hydrogen peroxide level rose to a mean of 48 ppm +/- 18.2. The increase in measured residual hydrogen peroxide between month 1 and each successive month was found to be statistically significant. However, these levels failed to induce an increase in symptomatology or slit lamp findings. As determined by scanning electron microscopy there was an erosion of the platinum coating with time that appeared to coincide with the measured residual peroxide level. Cultures of randomly selected platinum discs at the end of 4 months failed to reveal more than isolated positive findings of Staphylococcus epidermidis. While an increase in residual peroxide with time may lead to greater disinfecting capabilities of this system, the possibility of corneal damage as a direct result of high peroxide levels is of concern.

Adult↗

PubMed1988

Changes in contrast sensitivity induced by spherical hydrogel lenses on low astigmats.

Contrast sensitivity values were taken on seven astigmatic (cylinder correction under 1.00 diopter) and eight spherical myopes using the Vistech VCTS 6500 System. For the astigmatic group, no significant difference in contrast sensitivity was found between the full subjective correction and an equivalent spherical spectacle prescription, despite the absence of cylinder correction. However, comparing the full subjective correction with an equivalent spherical hydrogel lens, we found a significant decrease in contrast sensitivity while wearing lenses for all but the highest spatial frequency tested. Using a group of spherical myopes, we were unable to demonstrate a decrease in contrast sensitivity as a product of hydrogel lens wear alone. Our findings suggest that there is a measurable decrease in contrast sensitivity as a result of fitting low astigmats with spherical hydrogel lenses which cannot be attributed solely to hydrogel lens wear or the absence of cylinder correction.

Adult↗

PubMed1988

Determining appropriate cylinder correction with soft toric lenses.

Several authors have advocated reducing cylinder power when fitting soft toric lenses. One rationale for this reduction is the formation of a tear lens due to incomplete flexure. Using toric lenses of various thickness (0.06-0.14 mm), I was unable to demonstrate the existence of a tear lens under thin or standard thickness Hydron toric lenses. In the absence of such a tear lens, it seems reasonable to use the same cylinder power in a soft toric lens as would be used if prescribing spectacles.

Adolescent↗