Jennifer R. Lewis

Comparative Study of Fibrillar Collagen Arrangement in the Corneas of Primates and Other Mammals

This study is a comparative study of the relationship between corneal structure, morphology, and function in a range of mammalian species. X‐ray scattering patterns were gathered at regular spatial intervals over the excised cornea (and in most cases also the scleral rim) of humans, marmosets, horses, cows, pigs, rabbits, and mice. All patterns were analyzed to produce quantitative information regarding the predominant orientation of fibrillar collagen throughout the tissue. The predominant direction of corneal collagen varies between mammals. This variation is not related to the size, shape, or thickness of the cornea or the frequency with which the animal blinks. A relationship does, however, appear to exist between corneal collagen arrangement and visual acuity. An excess of collagen directed toward one or both sets of opposing rectus muscles is a feature of animals that have an intermediate to high level of visual acuity. There is a significant variation in the arrangement of corneal collagen between different mammalian species. This finding may be related to differences in the frequency of action and the forces generated by the various extraocular muscles during eye movement and image fixation. Anat Rec, 2007.

Depth Profile Study of Abnormal Collagen Orientation in Keratoconus Corneas

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Relationship among fMRI, contrast sensitivity and visual acuity

The purpose of this study was to ascertain whether visual acuity or contrast sensitivity function (CSF) is proportional to visual cortical function based on fMRI volume and level of activation or Z-score. Forced choice procedures were utilized to measure the monocular log minimal angle of resolution (logMAR) visual acuity and CSF. The CSF data were collapsed into a single index by the use of weighted mean contrast sensitivity (WMCS), being defined as the mean of the products of each spatial frequency multiplied by its corresponding contrast sensitivity. fMRI data had been obtained with a 1.5 T GE Signa scanner with visual stimuli including 1.0 and 2.0 c/deg vertical sinusoidal gratings. Subjects consisted of eight normal adults and five amblyopic patients, with the amblyopic subjects added to gauge whether the outcome was due to a restricted range of scores or the small number of study participants. In normal subjects, the fMRI volume and level of activation exhibited no statistically significant correlation with visual acuity at P<0.05. Statistically significant correlations were obtained between WMCS and fMRI volume (R=0.765, P=0.027) and fMRI level of activation (R=0.645, P=0.007), with right eye stimulation using the 1.0 c/deg grating. On the whole, statistically significant correlations between WMCS and fMRI parameters were maintained when subject age was held constant and when data from the five amblyopic subjects were included to expand the range of values and increase the number of data sets for analysis. fMRI volume and Z-score were more closely associated with the CSF, as defined by WMCS, than visual acuity. The results suggest that the CSF reflects the underlying visual cortical cells responsible for fMRI volume and the level of activation.

Normative database of donor keratographic readings in an eye-bank setting

PURPOSE: To generate a normative donor topographic database from rasterstereography images of whole globes acquired in an eye‐bank setting with minimal manipulation or handling. SETTING: Eye‐bank laboratory. METHODS: In a retrospective study, rasterstereography topographic images that had been prospectively collected in duplicate of donor eyes received by the Central Ohio Lions Eye Bank between 1997 and 1999 were analyzed. Best‐fit sphere (BFS) and simulated keratometry (K) values were extracted. These values were recalculated after application of custom software to correct any tilt of the mapped surfaces relative to the image plane. The mean value variances between right eyes and left eyes, between consecutive scans, and after untilting were analyzed by repeated‐measures analysis of variance and t tests (P≤.05). RESULTS: A keratographic database of 556 pair‐matched right and left eyes was generated. Normal distributions were observed in frequency histograms of each value (P>.05, Kolmogorov‐Smirnov). There was no difference between right and left eyes or consecutive scans (P>.05). The mean values changed when the images were tilt‐corrected (P<.05). The right eye BFS, Kflat, and Ksteep values of 42.03 diopters (D) ± 1.88 (SD), 42.21 ± 2.10 D, and 43.82 ± 2.00 D, respectively, increased to 42.52 ± 1.73 D, 43.05 ± 1.99 D, and 44.57 ± 2.02 D, respectively, after tilt correction. CONCLUSIONS: Keratometric parameter frequency distributions from the donor database of tilt‐corrected data were normal in distribution and comparable to parameters reported for normal eyes in a living population. These findings show the feasibility and reliability of routine donor‐eye topography by rasterstereography. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.

Effect of soft contact lenses on optical measurements of axial length and keratometry for biometry in eyes with corneal irregularities.

PURPOSE To assess the repeatability and reliability of IOLMaster (Carl Zeiss Meditec, Inc., Dublin, CA) axial length and keratometry measurements (K readings) with a soft contact lens on normal eyes. The method is designed for eyes with corneal irregularities or after endothelial keratoplasty. METHODS Biometry was performed on 20 healthy right eyes of volunteer subjects with mean age, 27.3 +/- 4.9 years; axial length, 24.77 +/- 1.04 mm; and K reading, 43.48 +/- 1.69 D. Axial length and keratometry were measured and repeated with -0.5 D SofLens38 (Bausch & Lomb, Rochester, NY) and Acuvue2 (Johnson & Johnson, New Brunswick, NJ) soft contact lenses. Repeatability and reliability were evaluated. Contact lens thickness was measured directly by corneal optical coherence tomography (OCT). RESULTS Axial lengths increased 59 +/- 10 microm with SofLens38 and 134 +/- 13 microm with Acuvue2, and these changes correlated with the OCT contact lens thicknesses (P = 0.995). The axial length variability remained constant (P = 0.18), measuring 24 +/- 10 microm for SofLens38 and 23 +/- 8 microm for Acuvue2 compared with 20 +/- 7 microm with no lens. K readings of 43.08 +/- 1.66 D with SofLens38, 42.79 +/- 1.57 D with Acuvue2, and 43.48 +/- 1.69 D with no lens corresponded to differences of -0.40 +/- 0.12 D with SofLens38 and -0.69 +/- 0.19 D with Acuvue2. The K-reading variability increased slightly from 0.04 to 0.09 D with either lens. CONCLUSIONS Low-power soft contact lenses enable reliable and repeatable IOLMaster axial length and K-reading measurements. Correcting for the measurable lens thickness and lens effects, a <0.5-D error in the Sanders-Retzlaff-Kraff (SRK) II power formula is predicted.