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ABSTRACT: Purpose. To test the hypothesis that in healthy human eyes the lamina cribrosa (LC) insertion into the pia mater increases with age. Methods. The optic nerve heads (ONHs) of donor eyes fixed at either 5 or 50 mm Hg of IOP were sectioned, stained, and imaged under bright- and dark-field conditions. A 3-dimensional (3D) model of each ONH was reconstructed. From the 3D models we measured the area of LC insertion into the peripapillary scleral flange and into the pia, and computed the total area of insertion and fraction of LC inserting into the pia. Linear mixed effect models were used to determine if the measurements were associated with age or IOP. Results. We analyzed 21 eyes from 11 individuals between 47 and 91 years old. The LC inserted into the pia in all eyes. The fraction of LC inserting into the pia (2.2%-29.6%) had a significant decrease with age (P = 0.049), which resulted from a nonsignificant increase in the total area of LC insertion (P = 0.41) and a nonsignificant decrease in the area of LC insertion into the pia (P = 0.55). None of the measures was associated with fixation IOP (P values 0.44-0.81). Differences between fellow eyes were smaller than differences between unrelated eyes. Conclusions. The LC insertion into the pia mater is common in middle-aged and older eyes, and does not increase with age. The biomechanical and vascular implications of the LC insertion into the pia mater are not well understood and should be investigated further.
Investigative ophthalmology & visual science 09/2012; 53(11):6870-9. · 3.43 Impact Factor
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ABSTRACT: PurposeTo investigate the time taken for Swedish Interactive Threshold Algorithm (SITA)-standard (SITA-s) data management from first
stimulus to printed results.
MethodsProspective case series. Twenty-one subjects underwent visual field testing of the right eye with both SITA-s and Humphrey
Full Threshold (FTT). The order of the tests (SITA-s and FTT) were randomized for each subject.
ResultsThe time-to-finish calculation and saving was significantly longer for SITA-s (41%, p<0.001) than FTT. The patient testing time and total testing time was 47% and 39% shorter with SITA than with FTT, respectively
(p<0.001).
ConclusionThe data processing of the SITA-s compromises by 8% (p<0.001) some of the advantages of the faster patient testing time.
Annals of Ophthalmology 04/2012; 37(2):91-94. · 0.16 Impact Factor
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ABSTRACT: To determine whether brand-name glaucoma drops differ from generic equivalents in bottle design, viscosity, surface tension, and volume in North America.
Experimental study.
We studied 5 bottles each of 11 kinds of glaucoma drops.
Density-based calculations of drop volume were assessed using 0.1 mg analytic balance. Viscosity was measured using rotational rheometery. Bottle tip diameter was measured using 0.05 mm Vernier calipers. Surface tension was measured using a Fisher Scientific (Ottawa, ON) tensiometer.
For the American brand-name Timoptic XE, the average drop volume was 38 ± 3.1 μL versus 24 ± 1.5 μL of Timolol GFS (p < 0.0001). For the Canadian brand-name Timoptic XE, the average drop volume was 42 ± 4.0 μL versus 25 ± 2 μL of timolol maleate EX (p < 0.0001). The Canadian brand-name Timoptic drop volume was 28 ± 1.4 μL versus 35 ± 1.9 μL Apo-Timop (p < 0.01). At a 0.1 per second shear rate, the viscosity of Canadian Timoptic XE was 20 times higher than that of its generic equivalent, whereas the viscosity of American Timoptic XE differed from the generic by a factor of 100. The surface tension of Canadian Timoptic XE was 31% higher than that of the generic (p < 0.001), whereas the surface tension of American Timoptic XE was 21% higher than that of the generic (p < 0.001). The bottle tips of the Canadian and American Timoptic XE measured about 3.5 times larger than those of their generics.
American and Canadian Timoptic XE eye drops vary significantly from the generics in drop volume, viscosity, surface tension, and bottle tip. Canadian brand-name Timoptic delivered significantly smaller drop volumes than generic Apo-Timop. Careful consideration should be given to drop viscosity and bottle design when generic ophthalmic products are evaluated for interchangeability and market entry.
Canadian Journal of Ophthalmology 02/2012; 47(1):55-61. · 1.47 Impact Factor
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ABSTRACT: To evaluate the prevalence of undetected glaucoma in a Toronto population.
A cross-sectional survey.
Toronto residents aged 50 years or older.
Telephone calls were randomly made to Toronto residents. Those who indicated they did not have glaucoma were invited to the Toronto Western Hospital for a comprehensive ophthalmic assessment, including best corrected visual acuity testing, applanation tonometry, pachymetry, gonioscopy, disc assessment, frequency doubling technology, and Heidelberg retinal tomography. Patient suspected to have glaucoma were asked to return for further evaluation, including a 24-2 Humphrey automated visual field test, repeat Heidelberg retinal tomography, repeat disc assessment, and possibly a diurnal tension curve. The diagnosis of glaucoma was made based on standardized criteria modified from those used by the Rotterdam Study and Foster and associates.
Among 975 eligible respondents, 73 (7.5%) stated that they had glaucoma. Of the remaining 902 negative respondents, 271 booked clinical appointments, and 180 completed the clinical assessment; their mean age was 61.6 years. Of the participants, 7 (3.9%) were diagnosed with glaucoma: 5 (2.8%) had primary open-angle glaucoma (3 with low-pressure and 2 with high-pressure glaucoma); 1 had (0.6%) chronic angle-closure glaucoma; and 1 (0.6%) had pseudoexfoliation glaucoma. A further 8 (4.4%) participants were classified as probably having open-angle glaucoma and 33 (18.3%) as being suspected to have glaucoma. Narrow angles were found in 27 participants (15%), and 37 (20.6%) had family histories of glaucoma.
The prevalence of undetected glaucoma appears to be high in Toronto. Further studies involving larger numbers of participants are required to confirm this finding.
Canadian Journal of Ophthalmology 08/2011; 46(4):352-7. · 1.47 Impact Factor
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ABSTRACT: Purpose. To present a series of retinal disease cases that were imaged by spectral domain optical coherence tomography (SD-OCT) in order to illustrate the potential and limitations of this new imaging modality. Methods. The series comprised four selected cases (one case each) of age-related macular degeneration (ARMD), diabetic retinopathy (DR), central retinal artery occlusion (CRAO), and branch retinal vein occlusion (BRVO). Patients were imaged using the Heidelberg Spectralis (Heidelberg Engineering, Germany) in SD-OCT mode. Patients also underwent digital fundus photography and clinical assessment. Results. SD-OCT imaging of a case of age-related macular degeneration revealed a subfoveal choroidal neovascular membrane with detachment of the retinal pigment epithelium (RPE) and neurosensory retina. Using SD-OCT, the cases of DR and BRVO both exhibited macular edema with cystoid spaces visible in the outer retina. Conclusions. The ability of SD-OCT to clearly and objectively elucidate subtle morphological changes within the retinal layers provides information that can be used to formulate diagnoses with greater confidence.
Journal of Ophthalmology 01/2011; 2011:764183.
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Ophthalmology 11/2010; 117(11):2237. · 5.45 Impact Factor
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ABSTRACT: Glaucoma is characterized by loss of retinal nerve fibers, structural changes to the optic nerve, and an associated change in visual function. The major risk factor for glaucoma is an increase in intraocular pressure (IOP). However, it has been demonstrated that a subset of glaucoma patients exhibit optic neuropathy despite a normal range of IOP. It has been proposed that primary open angle glaucoma could be associated with structural abnormalities and/or functional dysregulation of the vasculature supplying the optic nerve and surrounding retinal tissue. Under normal conditions, blood flow is autoregulated, i.e., maintained at a relatively constant level, in the retina and ONH, irrespective of variation in ocular perfusion pressure. A number of factors released by the vascular endothelium, including endothelin-1 and nitric oxide, are suggested to play an important role in the regulation of local perfusion in the retina and ONH. Most work to-date has investigated homeostatic hemodynamic parameters in glaucoma, rather than the measurement of the hemodynamic response to a provocation. Future work should comprehensively assess blood flow in all the ocular vascular beds and blood vessels supplying the eye in response to standardized stimuli in order to better understand the pathophysiology of glaucomatous optic neuropathy.
Microcirculation (New York, N.Y.: 1994) 10/2010; 17(7):568-81. · 2.37 Impact Factor
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ABSTRACT: Scleral thickness, especially near the optic nerve head (ONH), is a potential factor of interest in the development of glaucomatous optic neuropathy. Large differences in the dimensions of the sclera, the principal load-bearing tissue of the eye, have been observed between individuals. This study aimed to characterize the effects of these differences on ONH biomechanics. Eleven enucleated human globes (7 normal and 4 ostensibly glaucomatous) were imaged using high-field microMRI and segmented to produce 3-D individual-specific corneoscleral shells. An identical, idealized ONH geometry was inserted into each shell. Finite element modeling predicted the effects of pressurizing the eyes to an IOP of 30 mmHg, with the results used to characterize the effect of inter-individual differences in scleral dimensions on the biomechanics of the ONH. Measurements of the individual-specific corneoscleral shells were used to construct a 2-D axisymmetric idealized model of the corneoscleral shell and ONH. A sensitivity analysis based on this model quantified the relative importance of different geometrical characteristics of the scleral shell on the biomechanics of the ONH. Significant variations were observed in various measures of strain in the idealized lamina cribrosa (LC) across the seven normal corneoscleral shells, implying large differences in individual biomechanics due to scleral anatomy variations alone. The sensitivity analysis revealed that scleral thickness adjacent to the ONH was responsible for the vast majority of variation. Remarkably, varying peripapilary scleral thickness over the physiologically measured range changed the peak (95th percentile) first principal strain in the LC and radial displacement of the ONH canal by an amount that was equivalent to a change in IOP of 15 mmHg. Inter-individual variations in scleral thickness, particularly peripapillary scleral thickness, can result in vastly different biomechanical responses to IOP. These differences may be significant for understanding the interactions between IOP and scleral biomechanics in the pathogenesis of glaucomatous optic neuropathy. The relationship between scleral thickness and material properties needs to be studied in human eyes.
Experimental Eye Research 09/2010; 93(1):4-12. · 3.26 Impact Factor
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ABSTRACT: The biomechanical environment of the optic nerve head (ONH), of interest in glaucoma, is strongly affected by the biomechanical properties of sclera. However, there is a paucity of information about the variation of scleral mechanical properties within eyes and between individuals. We thus used biaxial testing to measure scleral stiffness in human eyes. Ten eyes from 5 human donors (age 55.4+/-3.5 years; mean+/-SD) were obtained within 24h of death. Square scleral samples (6mm on a side) were cut from each ocular quadrant 3-9 mm from the ONH centre and were mechanically tested using a biaxial extensional tissue tester (BioTester 5000, CellScale Biomaterials Testing, Waterloo). Stress-strain data in the latitudinal (toward the poles) and longitudinal (circumferential) directions, here referred to as directions 1 and 2, were fit to the four-parameter Fung constitutive equation W=c(e(Q)-1), where Q=c(1)E(11)(2)+c(2)E(22)(2)+2c(3)E(11)E(22) and W, c's and E(ij) are the strain energy function, material parameters and Green strains, respectively. Fitted material parameters were compared between samples. The parameter c(3) ranged from 10(-7) to 10(-8), but did not contribute significantly to the accuracy of the fitting and was thus fixed at 10(-7). The products cc(1) and cc(2), measures of stiffness in the 1 and 2 directions, were 2.9+/-2.0 and 2.8+/-1.9 MPa, respectively, and were not significantly different (two-sided t-test; p=0.795). The level of anisotropy (ratio of stiffness in orthogonal directions) was 1.065+/-0.33. No statistically significant correlations between sample thickness and stiffness were found (correlation coefficients=-0.026 and -0.058 in directions 1 and 2, respectively). Human sclera showed heterogeneous, near-isotropic, nonlinear mechanical properties over the scale of our samples.
Journal of biomechanics 06/2010; 43(9):1696-701. · 2.66 Impact Factor
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ABSTRACT: The biomechanical environment within the optic nerve head, important in glaucoma, depends strongly on scleral biomechanical properties. Here we use a range of measured nonlinear scleral stress-strain relationships in a finite element (FE) model of the eye to compute the biomechanical environment in the optic nerve head at three levels of intraocular pressure (IOP). Three stress-strain relationships consistent with the 5th, 50th and 95th percentiles of measured human scleral stiffness were selected from a pool of 30 scleral samples taken from 10 eyes and implemented in a generic FE model of the eye using a hyperelastic five-parameter Mooney-Rivlin material model. Computed strains within optic nerve head tissues depended strongly on scleral properties, with most of this difference occurring between the compliant and median scenarios. Also, the magnitudes of strains were found to be substantial even at normal IOP (up to 5.25% in the lamina cribrosa at 15 mmHg), being larger than previously reported values even at normal levels of IOP. We conclude that scleras that are "weak", but still within the physiologic range, will result in appreciably increased optic nerve head strains and could represent a risk factor for glaucomatous optic neuropathy. Estimations of the deformation at the optic nerve head region, particularly at elevated IOP, should take into account the nonlinear nature of scleral stiffness.
Annals of biomedical engineering 04/2010; 38(4):1586-92. · 2.41 Impact Factor
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ABSTRACT: To investigate the hypotheses that the topography of the optic nerve head (ONH) significantly changes during the day in untreated primary open-angle glaucoma (uPOAG) and healthy volunteers; and that there is a significant association with diurnal variations of intraocular pressure (IOP) and mean ocular perfusion pressure (MOPP).
Fourteen uPOAG and 14 age-matched normals were included. IOP, blood pressure, and ONH topography were measured between 7:00 AM and 10:00 PM. MOPP was calculated. A mixed-effect repeated measures analysis was done. Variance component analysis was done for glaucoma and normal groups separately based on the mixed-effect models.
The cup volume, rim volume, and cup shape measure in the temporal (T) and temporal-inferior (TI) sectors were significantly different between the 2 groups (P<0.05). The highest variance component was owing to "patients" whereas "time" had the smallest contributed percentage. Cup volume (T and TI) and reference height (RH) showed a significant (P<0.001) diurnal change in uPOAG. Rim volume (T and TI) showed a significant diurnal change in normals (P≤0.01). There was no significant (P>0.05) association between the change in IOP, MOPP, and ONH topography in either group. There was a significant association between cup volume and RH in both groups (P<0.001, global and T). There was a significant association between MOPP and RH in both groups (P<0.001).
The ONH topography significantly changed during the day in both groups. The change in ONH topography was associated with the change in reference height, which in turn was associated with MOPP. These findings suggest that the time of the day and the level of perfusion pressure should be considered when evaluating ONH topography using the HRT. Repeated measures are recommended when evaluating ONH topography.
Journal of glaucoma 04/2010; 20(1):44-50. · 1.74 Impact Factor
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ABSTRACT: To determine whether a 30-degree head-up sleeping position decreases nocturnal intraocular pressure (IOP) compared with lying flat in patients with glaucoma.
Prospective, nonrandomized comparative case series.
Seventeen eyes of 17 patients with glaucoma with controlled IOP and new disc hemorrhage.
Patients with a new disc hemorrhage despite well-controlled IOP were evaluated in a sleep laboratory on 2 separate nights, the first night lying flat and the second night in a 30-degree head-up position. Intraocular pressure and blood pressure (BP) were measured every 2 hours from 6 PM to 8 AM. For the 6 PM, 8 PM, 10 PM, and 8 AM measurements (awake period) the subjects were sitting for both nights. For the midnight, 2 AM, 4 AM, and 6 AM measurements (sleep period), the subjects were supine for the first night and 30 degrees head up for the second night.
Difference in IOP during the sleep period (midnight to 6 AM) between lying flat and 30-degree head-up positions.
Seventeen eyes of 17 patients were included. There were no significant differences (P=0.68) between the 2 study visits in IOP during the awake period (6 PM, 8 PM, 10 PM, and 8 AM) when patients were sitting upright. During the sleep period (midnight to 6 AM) the mean IOP was 3.2 mmHg lower in the 30-degree head-up position compared with the flat position (P=0.03; 95% confidence interval, 0.25-6.1 mmHg). Sixteen of 17 patients (94.1%) had lower IOP in the 30-degree head-up position. The reduction in IOP in the 30-degree head-up position was 20% or more in 35% of patients (6/17). There were no differences in BP or ocular perfusion pressure between the 2 positions.
The 30-degree head-up sleeping position lowers IOP compared with the flat position. Although this effect varies between individual patients, mean IOP was 20% lower in one third of patients in this series.
The authors have no proprietary or commercial interest in any materials discussed in this article.
Ophthalmology 02/2010; 117(7):1348-51. · 5.45 Impact Factor
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ABSTRACT: Scleral thickness, especially near the region of the optic nerve head (ONH), is a potential factor of interest in the development of glaucomatous optic neuropathy. Our goal was to characterize the scleral thickness distribution and other geometric features of human eyes. Eleven enucleated human globes (7 normal and 4 ostensibly glaucomatous) were imaged using high-field microMRI, providing 80 microm isotropic resolution over the whole eye. The MRI scans were segmented to produce 3-D corneoscleral shells. Each shell was divided into 15 slices along the anterior-posterior axis of the eye, and each slice was further subdivided into the anatomical quadrants. Average thickness was measured in each region, producing 60 thickness measurements per eye. Hierarchical clustering was used to identify trends in the thickness distribution, and scleral geometric features were correlated with globe axial length. Thickness over the whole sclera was 670 +/- 80 microm (mean +/- SD; range: 564 microm-832 microm) over the 11 eyes. Maximum thickness occurred at the posterior pole of the eye, with mean thickness of 996 +/- 181 microm. Thickness decreased to a minimum at the equator, where a mean thickness of 491 +/- 91 microm was measured. Eyes with a reported history of glaucoma were found to have longer axial length, smaller ONH canal dimensions and thinner posterior sclera. Several geometrical parameters of the eye, including posterior scleral thickness, axial length, and ONH canal diameter, appear linked. Significant intra-individual and inter-individual variation in scleral thickness was evident. This may be indicative of inter-individual differences in ocular biomechanics.
Experimental Eye Research 11/2009; 90(2):277-84. · 3.26 Impact Factor
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ABSTRACT: Human optic nerve head (ONH) anatomy is of interest in glaucoma. Our goal was to carry out a morphometric study of the human ONH based on 3D reconstructions from histologic sections. A set of 10 human ONHs (from four pairs of eyes plus two singles) were reconstructed in an iterative procedure that required the resulting geometries to satisfy a set of quality control criteria. Five models corresponded to eyes fixed at 5 mmHg and the other five models to eyes fixed at 50 mmHg. Several aspects of ONH morphology were measured based on surface and point landmarks: the thicknesses of the lamina cribrosa (LC), the peripapillary sclera and the pre-laminar neural tissue (peripapillary and within the cup); the minimum distance between the anterior surface of the LC and the subarachnoid space; the surface area of the anterior and posterior surfaces of the LC; and the diameter of the scleral canal opening. Our results showed that about one third of the anterior LC surface was obscured from view from the front by the sclera. In all eyes the LC inserted into the pia mater, and not only into the sclera. The variations in ONH morphology between eyes of a pair exceeded, or were of the same order as, changes in morphology due to acute changes in IOP. The reconstruction and morphometry techniques introduced are suitable for application to the ONH. Comparison of measurements in eyes fixed at different pressures suggested small effects on geometry of the increase in IOP. A large variability in ONH morphology, even between contralateral eyes of different IOP, was observed. We conclude that reconstruction of human ONH anatomy from 3D histology is possible, but that large inter-individual anatomic variations make morphometric analysis of the ONH very difficult in the absence of large sample numbers. The insertion of the pia mater into the LC may have biomechanical implications and should be further investigated. Emerging clinical imaging techniques such as deep-scanning OCT will be limited to investigation of the central and mid-peripheral regions of the LC due to optical "occluding" by the peripapillary sclera.
Experimental Eye Research 09/2009; 90(1):70-80. · 3.26 Impact Factor
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ABSTRACT: Biaxial testing has been used widely to characterize the mechanical properties of soft tissues and other flexible materials, but fundamental issues related to specimen design and attachment have remained. Finite element models and experiments were used to investigate how specimen geometry and attachment details affect uniformity of the strain field inside the attachment points. The computational studies confirm that increasing the number of attachment points increases the size of the area that experiences sensibly uniform strain (defined here as the central sample region where the ratio of principal strains E(11)/E(22)<1.10), and that the strains experienced in this region are less than nominal strains based on attachment point movement. Uniformity of the strain field improves substantially when the attachment points span a wide zone along each edge. Subtle irregularities in attachment point positioning can significantly degrade strain field uniformity. In contrast, details of the apron, the region outside of the attachment points, have little effect on the interior strain field. When nonlinear properties consistent with those found in human sclera are used, similar results are found. Experiments were conducted on 6 x 6 mm talc-sprinkled rubber specimens loaded using wire "rakes." Points on a grid having 12 x 12 bays were tracked, and a detailed strain map was constructed. A finite element model based on the actual geometry of an experiment having an off-pattern rake tine gave strain patterns that matched to within 4.4%. Finally, simulations using nonequibiaxial strains indicated that the strain field uniformity was more sensitive to sample attachment details for the nonequibiaxial case as compared to the equibiaxial case. Specimen design and attachment were found to significantly affect the uniformity of the strain field produced in biaxial tests. Practical guidelines were offered for design and mounting of biaxial test specimens. The issues addressed here are particularly relevant as specimens become smaller in size.
Journal of Biomechanical Engineering 09/2009; 131(9):091003. · 1.90 Impact Factor
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ABSTRACT: To investigate depressive symptomatology among patients with glaucoma and to relate the findings to disease stability.
Cross-sectional postal survey.
The study sample consisted of 258 patients out of a pool of 884 respondents to a survey on health and sleep sent to 1809 glaucoma patients registered in a major tertiary glaucoma centre at the Toronto Western Hospital, Toronto, Ont.
The Center for Epidemiologic Studies Depression Scale questionnaire was mailed along with questions related to demographic information, general health, and sleep quality. Respondents were included if (i) their diagnosis was either primary open-angle glaucoma, normal tension glaucoma, or primary angle-closure glaucoma; (ii) the disease duration was 3 years or more; (iii) clinical examinations were obtained annually; and (iv) perimetric results were reliable. Each patient's condition was classified as stable or progressive on the basis of pointwise decline in visual fields (VFs).
The unadjusted odds ratio for depressive symptoms was found to be 0.4 times less (95% CI 0.19-0.88) in patients with progressive VFs (n = 79) than in patients with stable VFs (n = 179). Adjusting for demographic characteristics, general health, psychiatric comorbidity, and ocular factors did not weaken this association. However, it was reduced by the increased severity of VF defects (moderate and severe).
In this sample of tertiary-care patients, depressive symptoms were found to be less common in patients with progressive than with stable VFs when defects were classified as early, but not when they were classified as moderate or severe.
Canadian Journal of Ophthalmology 05/2009; 44(2):198-204. · 1.47 Impact Factor
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ABSTRACT: To investigate the relationship between industry- vs nonindustry-funded publications comparing the efficacy of topical prostaglandin analogs by evaluating the correspondence between the statistical significance of the publication's main outcome measure and its abstract conclusions.
Retrospective, observational cohort study.
English publications comparing the ocular hypotensive efficacy between any or all of latanoprost, travoprost, and bimatoprost were searched from the MEDLINE database. Each article was reviewed by three independent observers and was evaluated for source of funding, study quality, statistically significant main outcome measure, correspondence between results of main outcome measure and abstract conclusion, number of intraocular pressure outcomes compared, and journal impact factor. Funding was determined by published disclosure or, in cases of no documented disclosure, the corresponding author was contacted directly to confirm industry funding. Discrepancies were resolved by consensus. The main outcome measure was correspondence between abstract conclusion and reported statistical significance of the publications' main outcome measure.
Thirty-nine publications were included, of which 29 were industry funded and 10 were nonindustry funded. The published abstract conclusion was not consistent with the results of the main outcome measure in 18 (62%) of 29 of the industry-funded studies compared with zero (0%) of 10 of the nonindustry-funded studies (P = .0006). Twenty-six (90%) of the industry-funded studies had proindustry abstract conclusions.
Twenty-four percent of the industry-funded publications had a statistically significant main outcome measure; however, 90% of the industry-funded studies had proindustry abstract conclusions. Both readers and reviewers should scrutinize publications carefully to ensure that data support the authors' conclusions.
American journal of ophthalmology 09/2008; 147(1):33-38.e2. · 3.83 Impact Factor
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ABSTRACT: The aim of the study was to compare the magnitude of vascular reactivity of the retinal arterioles in terms of percentage change to that of the retinal capillaries using a novel, standardized methodology to provoke isoxic hypercapnia. Ten healthy subjects (mean age 25 years, range 21-31) were recruited. Subjects attended a single visit comprising two study sessions separated by 30 min. Subjects were fitted with a sequential re-breathing circuit connected to a computer-controlled gas blender. Each session consisted of breathing at rest for 10 min (baseline), increase of P(ET)CO(2) (maximum partial pressure of CO(2) during expiration) by 15% above baseline whilst maintaining isoxia for 20 min, and returning to baseline conditions for 10 min. Retinal hemodynamic measurements were performed using the Canon Laser Blood Flowmeter and the Heidelberg Retina Flowmeter in random order across sessions. Retinal arteriolar diameter, blood velocity and flow increased by 3.3%, 16.9% and 24.9% (p<0.001), respectively, during isoxic hypercapnia. There was also an increase of capillary blood flow of 34.8%, 21.6%, 24.9% (p< or =0.006) at the optic nerve head neuroretinal rim, nasal macula and fovea, respectively. The coefficient of repeatability (COR) was 5% of the average P(ET)CO(2) both at baseline and during isoxic hypercapnia and was 10% and 7% of the average P(ET)O(2) (minimum partial pressure of oxygen at end exhalation), respectively. The overall magnitude of retinal capillary vascular reactivity was equivalent to the arteriolar vascular reactivity with respect to percentage change of flow. The magnitude of isoxic hypercapnia was repeatable.
Experimental Eye Research 09/2008; 87(6):535-42. · 3.26 Impact Factor
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ABSTRACT: The poor long-term success rate of repeat trabeculectomies in refractory uveitic glaucoma (UG) patients has led to the use of glaucoma drainage devices (GDDs). However, the success and complication rates of GDDs in UG patients utilizing a control group with standard demographic data, design, and surgical technique have never been evaluated.
Fifteen patients (15 eyes) with chronic uveitis and 53 patients (53 eyes) with uncontrolled open-angle glaucoma (OAG) who underwent Ahmed glaucoma valve (AGV) implantation were included in a retrospective, comparative, case-controlled study. Postoperative intraocular pressure (IOP), number of antiglaucoma medications, visual acuity, and complications were compared.
There was a significant difference between the UG versus the OAG group with respect to age only (59.3 years vs 68.4 years, p = 0.006). Regression analysis of the postoperative IOP controlled for age and glaucoma type, and preoperative IOP revealed significantly lower IOP in the UG group at 1 month (p = 0.04; 95% confidence interval [CI] -5.9 to 0.15) and 2 months (p = 0.008; 95% CI -6.0 to 0.97). No significant differences were found at 3, 6, 12, 24, and 30 months. The cumulative success rates at 3 to 30 months for the UG and OAG groups were 80% to 66.6% versus 84.9% to 57% (p = 0.713), respectively. The only complication between the 2 groups that was significantly different was tube removal, which occurred more often in the UG group (p = 0.018).
AGV implantation is an effective and safe procedure in the management of UG, similar to primary OAG.
Canadian Journal of Ophthalmology 09/2008; 43(4):462-7. · 1.47 Impact Factor
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ABSTRACT: Flicker-defined form (FDF) is a temporally driven illusion within which randomly positioned background elements are flickered in counterphase to stimulus elements, creating the illusion of a contour in the region between the background and the stimulus dots. It has been proposed that FDF is dependent on the boundary region between the counterphase flickering dots. Is the stimulus area or the illusory contour itself (region between stimulus and background) paramount to the FDF percept? Circular stimuli were compared to ring stimuli to determine the relative importance of area and contour. The rings were tested in the following configurations: constant maximum diameter/variable area; constant area/variable contour; and constant contour/variable area. For rings with constant diameter, no effect of ring thickness was found. No effect of contour was found for rings of a constant area. For rings of constant contour, the smaller the area the greater the threshold. These results suggest a greater dependence on the area of a stimulus rather than its contour. Area dependence suggests that the theory of contour dependence by a fast extraction system is unlikely. This temporally defined magnocellular-dependent illusion is influenced by slow surface perception mechanisms of the parvocellular system.
Journal of Vision 02/2008; 8(4):15.1-11. · 3.38 Impact Factor
