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Biomedical subjects

D J O'Leary

Publications and source records attributed to D J O'Leary.

At least 19 recordsLinked to original sources
PubMed2005

Comparison of pulsatile ocular blood flow in Indians and Europeans.

PURPOSE: To compare pulsatile ocular blood flow (POBF) in Europeans and Indians and provide reference values for a group of healthy Indians. PATIENTS AND METHODS: Measurement with the POBF Tonograph was performed on healthy Indian subjects in India (n=252). A further 80 subjects (40 of Indian descent and 40 Europeans) underwent measurements in Cambridge, England. The instrument used for measurement was the same for both the studies. RESULTS: The mean POBF in the Indians in India was found to be 1176 microl/min. The mean POBF value in the Europeans was found to be 1033 microl/min and that for Indians in England was 1061 microl/min. The difference between the POBF within groups was significant (one-way ANOVA P<0.05) with the POBF of Indians in India being higher than Europeans and Indians in the UK. The difference between the Europeans and Indians in the UK did not reach statistical significance. CONCLUSIONS: POBF values in Indians living in India were found to be considerably higher than the previously published normal value of 650 microl/min in European studies and other studies for other racial groups. The reason for this apparent difference may be instrument-related rather than genetic because such a large difference was not observed when a comparison was performed in the UK. In addition, the results for both groups in our comparative study were still considerably higher than reported in previous studies. The POBF of Indians in India is slightly higher than the POBF of people of Indian ethnic origin in England.

Adolescent↗
PubMed2004

Effect of corneal parameters on measurements using the pulsatile ocular blood flow tonograph and Goldmann applanation tonometer.

AIMS: To investigate the effect of central corneal thickness and corneal curvature on intraocular pressure measurements using the pulsatile ocular blood flow tonograph and the Goldmann applanation tonometer, and to assess the agreement between the pulsatile ocular blood flow tonograph and the Goldmann applanation tonometer in intraocular pressure measurement. METHODS: 479 subjects underwent intraocular pressure measurements with the Goldmann applanation tonometer and the pulsatile ocular blood flow tonograph. Of these, 334 patients underwent additional measurement of central corneal thickness with an ultrasonic pachymeter and corneal curvature measurement with a keratometer. RESULTS: The intraocular pressure measurements obtained with both the Goldmann applanation tonometer and the pulsatile ocular blood flow tonograph varied with central corneal thickness and mean keratometric reading. Intraocular pressure measured using the Goldmann applanation tonometer increased by 0.027 mm Hg per micro m increase in central corneal thickness. Intraocular pressure measured using the pulsatile ocular blood flow tonograph increased by 0.048 mm Hg per micro m increase in central corneal thickness. For an increase of 1 mm of mean corneal curvature there was rise in intraocular pressure of 1.14 mm Hg measured by the Goldmann applanation tonometer and of 2.6 mm Hg measured by the pulsatile ocular blood flow tonograph. When compared to the Goldmann applanation tonometer, the pulsatile ocular blood flow tonograph underestimated at low intraocular pressure and overestimated at higher intraocular pressure. CONCLUSION: Central corneal thickness and corneal curvature affected measurements obtained with the pulsatile ocular blood flow tonograph more than they affected measurements obtained with the Goldmann applanation tonometer.

Adolescent↗
PubMed2001

Ring-closing metathesis of olefinic peptides: design, synthesis, and structural characterization of macrocyclic helical peptides.

Heptapeptides containing residues with terminal olefin-derivatized side chains (3 and 4) have been treated with ruthenium alkylidene 1 and undergone facile ring-closing olefin metathesis (RCM) to give 21- and 23-membered macrocyclic peptides (5 and 6). The primary structures of peptides 3 and 4 were based upon a previously studied heptapeptide (2), which was shown to adopt a predominantly 3(10)-helical conformation in CDCl(3) solution and an alpha-helical conformation in the solid state. Circular dichroism, IR, and solution-phase (1)H NMR studies strongly suggested that acyclic precursors 3 and 4 and the fully saturated macrocyclic products 7 and 8 also adopted helical conformations in apolar organic solvents. Single-crystal X-ray diffraction of cyclic peptide 8 showed it to exist as a right-handed 3(10)-helix up to the fifth residue. Solution-phase NMR structures of both acyclic peptide 4 and cyclic peptide 8 in CD(2)Cl(2) indicated that the acyclic diene assumes a loosely 3(10)-helical conformation, which is considerably rigidified upon macrocyclization. The relative ease of introducing carbon-carbon bonds into peptide secondary structures by RCM and the predicted metabolic stability of these bonds renders olefin metathesis an exceptional methodology for the synthesis of rigidified peptide architectures.

Alkenes↗
PubMed2001

Facility of accommodation in myopia.

PURPOSE: Myopes have been shown to have abnormal accommodative characteristics. This study investigated the characteristics of accommodation facility in myopic and emmetropic students. METHODS: Distance and near positive and negative accommodation response time components of facility were measured over a 1 min period using a -2.00 D/zero lens pair for distance responses and a +/-2.00 D lens pair for near responses. 79 students (37 myopes and 42 emmetropes) aged 18-27 years acted as subjects. Subjects were masked, and the results were analysed in a masked fashion. RESULTS: Mean distance facility was significantly lower (9.7 cycles per minute (cpm)) in the myopic group compared with the mean distance facility in the emmetropic group (15.6 cpm; p < 0.005). There was no significant difference in the near facilities of the two groups (11.5 cpm in myopes vs 12.9 cpm in emmetropes). Positive accommodation response time for distance vision was greater than 4 s in 45% of myopes and in 9% of emmetropes. CONCLUSIONS: Our findings confirm that myopes tend to have abnormal accommodation responses to blur. Distance facility, but not near facility of accommodation is more frequently reduced in myopes than in emmetropes.

Accommodation, Ocular↗
PubMed2000

Scalar coupling across the hydrogen bond in 1,3- and 1,4-diols.

[reaction: see text] Scalar coupling between hydroxyl groups sharing a 1,4- or 1, 3-intramolecular hydrogen bond can be readily detected using standard 2D NMR techniques. Analyses of isotopically perturbed 2D J-resolved spectra have revealed (h2)J to be on the order of 0.3 Hz in systems such as diols 2 and 3. A standard 2D COSY experiment, modified to detect small coupling constants, is shown to be a convenient method for detecting (h2)J in these systems. Couplings derived from density functional finite perturbation theory (DFT/FPT) are found to be in general agreement with experimental data.

Alcohols↗
PubMed2000

Free-space accommodative response and minus lens-induced accommodative response in pre-school children.

PURPOSE: The purpose of this study was to investigate and compare the accommodative accuracy of pre-school children between free-space accommodative stimulus and minus lens-induced accommodative stimulus. METHODS: The accommodative responses of 59 pre-school children, ages 2 to 5 years, were measured objectively with a Canon Autoref R-1 under two different conditions, giving an optical accommodative stimulus of 1 D; first, viewing a target placed 100 cm away (free-space stimulus), and second, viewing a distant target through a -1.00 D lens. RESULTS: The mean lag of the accommodative response for the free-space accommodative stimulus is 0.24 D, while the mean lag of the accommodative response with the minus lens-induced accommodative stimulus is 0.69 D. The lag of accommodative response for free-space accommodative stimulus is significantly lower than the lag of accommodative response for minus lenses. CONCLUSIONS: Pre-school children can accommodate more accurately toward a free-space accommodative stimulus, as compared with minus lens-induced accommodative stimulus.

Accommodation, Ocular↗
PubMed1998

Size and number of epithelial cells washed from the cornea after contact lens wear.

Using the technique of Fullard and Wilson, tear samples were collected atraumatically from the corneas of 14 rigid gas permeable (RGP) contact lens wearers, 14 soft contact lens (SCL) wearers, and 22 controls who did not wear contact lenses. Samples were analyzed for the number, size, and contiguity of the cellular contents. Both RGP and SCL groups had, on average, significantly fewer cells per sample than controls (median values were 11 and 12 cells vs. 44). The difference remained significant even after a correction of three cells was applied to account for cells adherent to the lenses. Approximately 80% of epithelial cells from both lens wear and control eyes were found in isolation, whereas 20% were contiguous with 1 or 2 other cells. This result is compatible with the majority of epithelial cells having exfoliated from the surface of the cornea after detaching from their neighbors, rather than detaching in sheets of cells. The cell length and cell area were analyzed. RGP wearers had significantly smaller cells than controls, whereas SCL wearers had slightly (but significantly) larger cells. These results may reflect changes in the exfoliation mechanism of the corneal epithelium in contact lens wear.

Cell Count↗
PubMed1998

Corneal response to orthokeratology.

PURPOSE: The technique of orthokeratology produces a corneal response to the mechanical pressures exerted by rigid contact lenses. This paper reports a study which investigated the topographic and pachometric corneal changes induced by orthokeratology. METHODS: Six young myopic subjects (11 eyes) wore "accelerated orthokeratology" lenses (OK-74; Contex Inc., Sherman Oaks, CA) in a high Dk material (AirPerm; Dk = 88) for 28 days. Corneal and epithelial thickness were measured topographically using the Holden-Payor optical micropachometer, and corneal topography was monitored using the EyeSys system. RESULTS: Refractive error change reached 1.71 +/- 0.59 D reduction in myopia after 28 days. After 1 day of lens wear, statistically significant central corneal flattening was noted, which progressed to reach 0.22 +/- 0.07 mm (1.19 +/- 0.38 D) at 28 days. A trend toward central epithelial thinning was apparent, reaching statistical significance on day 28 (7.1 +/- 7.1 microm; 9.6%). Midperipheral corneal thickening was also found approximately 2.5 mm from the corneal center, which was statistically significant by day 14 (13.0 +/- 11.1 microm; 2.4%). Calculations using Munnerlyn's formula indicate that changes in corneal sagittal height based on topographical thickness changes across the flattened central 5.25-mm zone can account for the refractive changes observed. CONCLUSIONS: These findings suggest that the initial corneal response to orthokeratology may be explained by redistribution of corneal tissue, rather than by overall bending of the cornea.

Adult↗
PubMed1998

Nutritional requirements of the corneal epithelium and anterior stroma: clinical findings.

PURPOSE: To monitor the health of the epithelium and the anterior stroma when porous membranes are implanted into the feline cornea and to determine membrane diffusivity characteristics needed to maintain corneal integrity. METHODS: Filtration membranes in a range of effective pore sizes of less than 15 nm (groups 1 and 2, n = 11), 25 nm (group 3, n = 8), 50 nm (group 4, n = 16), and 100 nm (group 5, n = 15) were implanted into an interlamellar corneal pocket of the stroma. The implanted membranes ranged in thickness from 6 nm to 15 nm and were between 8 mm and 12 mm in diameter. Animals were monitored for clinical signs of intolerance to the implants. RESULTS: At 1 month, thinning and ulceration had occurred in the epithelium and the anterior stroma of all animals in groups 1 and 2; epithelial changes, anterior stromal thinning, and ulceration had developed in 75% of animals of group 3; 50% of animals showed vascularization and only 7% showed epithelial degeneration in group 4; and local anterior stromal thinning was observed in 7% of animals in group 5, indicating clinical acceptance of the implanted membrane. In the long term (greater than 50 days), 30% and 73% of the group 4 and 5 corneas, respectively, were clinically quiet. Analysis of the failure times indicated an inverse relation between failure rate and pore size: less than 15 nm > 25 nm > 50 nm > 100 nm. The difference between the 100-nm and 50-nm membranes was significant (P = 0.03). CONCLUSIONS: A corneal implant must have a porosity greater than that provided by 50-nm membranes. The 100-nm membranes used in this study establish the porosity needed to satisfy the nutritional requirements of the cornea.

Animals↗
PubMed1997

Optometric findings in velocardiofacial syndrome.

Velocardiofacial syndrome (VCFS) is a congenital genetically determined condition with skeletal, heart, and facial anomalies. Almost all children have learning problems, despite an often normal or above average IQ. We have examined 10 children with a prior diagnosis of VCFS. All were mildly to moderately hyperopic. Most had poor accommodation, and convergence was clinically poor. About 30% had tortuous retinal vessels. VCFS may be detected in the optometry clinic, and optometric management may ameliorate the learning problems in some cases.

Abnormalities, Multiple↗
PubMed1997

Changes in the interpupillary distance with age and its effect on the near fusion free position.

PURPOSE: The effect of the rate of the interpupillary distance (IPD) change with age on the near fusion free position was investigated in the present study. METHODS: Three hundred and fifty-two children aged from 2 to 16 years of age were tested. Interpupillary distance was estimated with a modified Viktorin's method and the near fusion free position was measured with a modified Maddox Wing. RESULTS: The results reveal a significant difference in IPD growth rate between females and males and between children aged below and above 5 years. Most children below 5 years of age were orthophoric, but heterophoria became more common above 5 years of age. CONCLUSION: The present study suggests that the oculomotor control system for convergence can compensate for age changes in IPD.

Adolescent↗
PubMed1990

Incision depth affects the recovery of corneal sensitivity and neural regeneration in the cat.

To assess the effect of incision depth on the recovery of corneal sensitivity and neural regeneration, adult domestic cats underwent either 8-mm circular nonpenetrating keratotomies or penetrating autografts. The contralateral eye served as control. Corneal sensitivity was determined at various intervals after surgery. The depth of incision in the nonpenetrating keratotomies, assessed by optical pachometry, ranged between 49 and 91% of total corneal thickness. The animals were ranked based on the depth of incision and the average sensitivity within the keratotomy over the 1-yr recovery period. A significant negative correlation was found between incision depth and the recovery of sensitivity (Spearman rank-order correlation r = -0.84, P less than 0.05). Some recovery of sensitivity was found in the center and periphery of the incised zone when incision depth was less than 53% of total corneal thickness. With deeper incisions, the center of the incised zone remained insensitive throughout the measurement period, while the periphery of the incised zone showed a slight recovery of corneal sensitivity, proportional to incision depth. The recovery of corneal sensitivity was higher in a small annular region just distal to the incision site. When incision depth exceeded approximately 53%, gold chloride impregnation showed that the resultant reinnervation was confined to single intraepithelial axons or localized regions of irregular epithelial fibers. With shallower incisions, the deeper stromal trunks were spared, resulting in the persistence of a reduced subepithelial plexus and basal epithelial leashes. We have shown that when an incision severs all stromal trunks, the neural regeneration is insufficient for functional recovery of corneal sensitivity at the center of an 8-mm keratotomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Cell content of tears following overnight wear of a contact lens.

The cell content of the precorneal tears of eight subjects was sampled following overnight wear of a contact lens in one eye. This was compared with morning samples taken from the other eye, and afternoon samples taken several days later from both eyes. In the morning the median number of desquamated epithelial cells in the precorneal tears was 62 cells in the lens-wearing eye and 119 cells in the control eye. The difference was not statistically significant. In the afternoon the medians were 18.5 cells in one eye and 7.5 cells in the other. There were relatively few leucocytes in the afternoon, the median was 2 leucocytes in one eye and 9 in the other. In the morning the median was 8,154 leucocytes in the lens-wearing eye and 6,500 in the control eye. The data show that large numbers of leucocytes are present on the ocular surface during sleep. There was no evidence that the number of leucocytes or the number of epithelial cells was altered by the presence of the contact lens.

Adult↗
PubMed1987

Indirect monitoring of carbon-13 metabolism with NMR: analysis of perfusate with a closed-loop flow system.

NMR studies of living cells and of perfused organs almost invariably require a major effort in the design of either the probe or the support system. For enriched 13C studies of metabolism, it is sometimes possible to use a simpler approach, one amenable to use in narrow-bore high-resolution NMR spectrometers. Since some of the metabolic changes are reflected by changes in the chemical composition of the media, it may be necessary to provide only for NMR measurements of the perfusate. A simple apparatus is described which allows NMR measurement of the perfusate. A commercially available concentric NMR tube, modified to incorporate flow, is inserted in the flow loop and placed in the spectrometer. An example is given of the metabolism of 13C-enriched glucose to lactate by chick embryo fibroblasts grown in a hollow fiber bundle assembly.

Animals↗
PubMed1987

Effect of cross cylinder power on cylinder axis sensitivity.

Astigmatic errors (0.50 D to 1.50 D in 0.25 D steps) were induced in each of 5 subjects, and cylinder axis thresholds were assessed from 12 reversals of a 2.5 degrees stepsize staircase for 0.50 D and 1.00 D cross cylinders (CC). Equivalent power thresholds were 0.077 D (0.05 SD) for the 0.50 D CC and 0.104 D (0.05 SD) for the 1.00 D CC. Findings are significantly different from predictions of a "linear" blur detection model, but are consistent with a model assuming constant blur thresholds and power-dependent distortion thresholds. Our results support the use of minimal CC power in refining cylinder axis.

Adult↗
PubMed1986

Chromatic and luminance difference contribution to stereopsis.

Stereoacuity has been measured at various luminance difference levels and also at the isoluminance point, where the target and the background have equal luminances. The results of the experiment show that acuity at isoluminance is three times worse than the value obtained when there is maximum contrast between target and background. possible reasons for these findings were investigated. Results of control experiments show that neither chromatic aberration nor defective accomodative response could be responsible for this finding.

Color↗