Biomedical subjects

Olga Overbury

Publications and source records attributed to Olga Overbury.

11 recordsLinked to original sources

PubMed2006

Macular hole: perceptual filling-in across central scotomas.

The present study examined perceptual distortions of a vertical line before and after macular hole (MH) surgery in 25 eyes of 24 patients. Participants' perceptual reports of distortions were classified as solid, bent right/left, thinned at the center, or broken. The majority of patients (72%) reported symmetrical distortions of the line pre-operatively. After surgery, participants with larger MHs were more likely to retain residual distortions. Of particular interest is the group reporting thinning of the line preoperatively, as the center should be perceptually missing. Examination of MH diameters in relation to the line perceptions indicated that the shape of the perceived line can be explained at the retinal level, while its continuity must be perceptually created at the cortical level.

Adult↗

PubMed2006

Defining the nature of motion perception deficits in glaucoma using simple and complex motion stimuli.

PURPOSE: The purpose of this study is to determine the nature of motion perception deficits in primary open-angle glaucoma by measuring the sensitivity of simple (luminance-defined) and complex (texture-defined) motion, the latter requiring supplementary neural processing to be resolved. These findings will help address the possible extent of the cortical damage in glaucoma that has been recently demonstrated by anatomic and physiological studies. They also serve the purpose of establishing which motion paradigms would be most appropriate for assessing glaucoma-related functional loss. METHODS: Direction-identification thresholds for first-order and second-order motion were measured for 26 patients with primary open-angle glaucoma (for both phakic and pseudophakic) and 18 nonglaucomatous observers. RESULTS: The glaucomatous observers showed significantly increased motion thresholds for both first- and second-order motion conditions when compared with nonglaucomatous observers. However, the relative increase in threshold for first-order motion did not differ significantly from that of second-order motion. CONCLUSIONS: These findings imply that there is no measurable higher-level cortical function damage caused by the glaucomatous process because no greater loss in second-order motion was observed. Based on the results, we suggest that motion paradigms used to assess functional loss in primary open-angle glaucoma should consist of simple, first-order type stimuli to minimize potential confounds such as those introduced by both the normal and pathologic aging process on complex motion processing (i.e., perimetry using complex motion stimuli).

Aged↗

PubMed2006

Quebec model for low vision rehabilitation.

The increase in longevity (and secondary morbidity) in the Quebec population adds social and financial pressure to society, as it does elsewhere in Canada and in many western countries. This article gives a brief history of the evolution of vision rehabilitation services in Quebec and describes how services are provided for people with low vision throughout the province. Although numerous groups, associations, centres, and resources are available to assist people with vision impairments, such as the Canadian National Institute for the Blind-Québec, the majority of visual rehabilitation services are provided by government-sponsored rehabilitation centres, namely the Centres régionaux de réadaptation en déficience physique that are located strategically throughout the province. Low vision clinical evaluations in these centres are shared by 36 optometrists throughout the province. Between 5 and 7 ophthalmologists are involved in low vision care, half in university-affiliated hospitals, primarily in Montreal. There may be delays of up to 6 months to be seen in a funded low vision clinic. Statistics obtained from la Régie de l'assurance maladie du Québec show that there are approximately 8,000 requests for low vision aids every year, and that 80% of clients retain at least some level of visual function. Services are covered by Medicare and low vision aids are provided at no cost, although ophthalmologists cannot prescribe low vision aids through the Medicare-funded system. We must ensure that the capacity of our system continues to provide adequately for clientele in the future.

Health Resources↗

PubMed2006

Differences between recognition and resolution acuity in patients undergoing macular hole surgery.

PURPOSE: The present investigation compared recognition acuities (ETDRS chart) with resolution acuities (Landolt-C chart) in a sample of patients with idiopathic macular holes (MH). Traditionally, visual acuity in a clinical setting is measured with a letter chart. Yet, the ability to recognize a letter differs from a resolution task, such as detecting the direction of a gap in a ring. It was hypothesized that resolution acuity would be more impaired than recognition acuity in patients with MH, because component cues in letter optotypes are not available in Landolt-Cs. METHOD: Visual acuities of 23 patients with MH (age range, 52-82) were tested, using standard ETDRS and Landolt-C charts. Optical coherence tomography was used to confirm the diagnosis of MH. RESULTS: Acuities correlated strongly, before and after surgery (r = 0.92 and r = 0.95, respectively). However, paired t-tests determined that resolution acuity was significantly more impaired at both time points than was recognition acuity (P < 0.001). Using Bland-Altman plots, the limits of agreement between the two acuity types indicated that resolution acuity differed from recognition acuity by up to five lines before surgery and up to 3 lines after surgery. CONCLUSIONS: ETDRS and Landolt-C acuities differ in a clinically significant way in patients before and after MH surgery. Measuring recognition acuity by reading letters may lead to an overestimate of visual ability at the retinal level in patients with MH by including compensatory top-down cognitive processes that are unavailable for resolution tasks.

Aged↗

PubMed2005

Visual function assessment and metamorphopsia after macular hole surgery.

The purpose of this study was to develop a new resolution acuity measure for patients after macular hole surgery. Fifty eyes of 44 patients who had undergone successful treatment were tested. Visual acuity was measured with the Snellen, Early Treatment of Diabetic Retinopathy Study and Landolt-C charts. A Line Resolution Test was performed as part of their follow-up exam where a vertical line was presented. Participants were categorized by their perception of the line as solid, bent or broken. The line could be distorted into a sine-wave pattern in order to determine the participants' detection threshold for the distortion. Chart acuities did not differ among the three groups, as categorized by their line perception. Only the distortion measure was sensitive enough to differentiate the solid- from the broken-line group. The distortion measure assesses resolution power of the macula in smaller increments than acuity charts. This hyperacuity approach is more appropriate in the assessment of functional outcome after microsurgery.

Aged↗

PubMed2004

Red-green chromatic mechanisms in normal aging and glaucomatous observers.

PURPOSE: This study was designed to determine whether normal aging and glaucoma are associated with red-green (R/G) chromatic processing abnormalities, a function that is primarily performed by the parvocellular visual pathway. METHODS: Chromatic processing mechanisms were examined in 98 glaucomatous observers (between the ages of 49 and 93 years; mean age, 70.8 +/- 9.4 [SD]) and 67 normal observers (between the ages of 49 and 88; mean age, 70.6 +/- 10.6 years) with the use of the minimum-motion and motion-nulling paradigms. Phakic glaucomatous (n = 60; mean age, 68.7 +/- 8.9 years) and normal (n = 32; mean age, 69.8 +/- 10.6 years) and pseudophakic glaucomatous (n = 38; mean age, 74 +/- 9.4 years) and normal (n = 35; mean age, 71.4 +/- 10.6 years) subjects were tested to evaluate the effects of lenticular aging on color perception. RESULTS: Phakic observers (normal or glaucomatous) displayed significantly different minimum-motion values than did both their younger counterparts and all the pseudophakic subjects. These results suggest that normal aging with the presence of a natural lens is accompanied by a significant decrease in green-light sensitivity, an effect that is not exacerbated by glaucoma and is primarily related to optical factors. The data also revealed no differences in color motion perception between groups, indicating that the higher cortical mechanisms of the parvocellular pathway implicated in the analysis of information about the middle and long wavelengths of the visible spectrum are not selectively affected by the disease process and normal aging. CONCLUSIONS: Normal aging and glaucoma do not produce significant R/G chromatic processing deficits at retinal and postretinal levels when optical factors are excluded. The authors propose the hypothesis that glaucoma-related effects on motion perception and blue-on-yellow perimetry should be viewed as evidence of loss of ganglion cells that necessitates integration of information over larger retinal areas and more receptor cells than in the R/G chromatic system. Ganglion cells with large receptive fields involve more neural connections and are less numerous than those that respond to R/G information. The functional consequence of this could be that the loss of a single ganglion cell with a larger receptive field would have a greater impact on visual function than the loss of a ganglion cell with a smaller receptive field, such as the ones that process R/G information. The authors believe that glaucoma-induced functional loss is best viewed as related to receptive field structure and function rather than to anatomic cell-type damage.

Aged↗

PubMed2003

Using the arteriolar Pressure Attenuation Index to predict ocular hypertension progression to open-angle glaucoma.

BACKGROUND: Vascular phenomena are considered important to optic nerve and visual field progression in open-angle glaucoma (OAG). A recently described formulation, the Pressure Attenuation Index (PAI), links arteriolar caliber variations to pressure loss along the retinal arteriolar system. OBJECTIVE: To examine whether the PAI could predict ocular hypertension (OHT) progression to OAG. METHODS: The PAI was calculated for 27 eyes of 14 patients with OHT using initial and final digitized optic disc photographs taken during a follow-up interval of 5 to 18 years. Serial stereo color disc photographs and visual fields were analyzed to determine progression. RESULTS: At baseline, the arteriolar tree of 8 subjects with OHT that progressed to OAG (n = 8 eyes) demonstrated a 45.8% greater mean PAI value than that of 7 subjects who did not progress (n = 7 eyes) (mean +/- SEM, 5.31 +/- 0.93 vs 3.64 +/- 0.34; r = 0.83). Progression was independent of baseline cup-disc ratio. The PAI values of subjects with stable OHT remained stable after a median follow-up interval of 12.0 years. The PAI values of subjects with OHT that progressed demonstrated a further increase of 19.97% +/- 11.24% during a median follow-up period of 6.0 years. CONCLUSIONS: The results support the hypothesis that low end-arteriolar pressure predicts the progression from OHT to OAG. The PAI provides a new, early, reproducible, and physiological method to study vascular phenomena in glaucoma.

Adult↗

PubMed2003

The role of lenticular senescence in age-related color vision changes.

PURPOSE: It has been reported that greater age-related losses in sensitivity occur for short-wavelength visual stimuli than for medium- and long-wavelength visual stimuli. The purpose of the current experiment was to determine to what extent optical, receptoral, and postreceptoral factors contribute to these age-related changes in color vision. METHODS: One hundred two observers (ages 18-87) completed a minimum motion task to determine isoluminance between red and green and between red and blue. A motion-nulling task was also performed to assess the L-M postreceptoral chromatic mechanism. RESULTS: No significant age-related changes occurred in red-green isoluminance values. Red-blue isoluminance values showed a significant and systematic decrease with age in observers with phakic eyes. Pseudophakic eyes in older subjects performed this task as well as phakic eyes in young subjects. The motion-nulling results demonstrated small age-related losses in the postreceptoral color mechanisms. CONCLUSIONS: The findings of this experiment, particularly those of the red-blue isoluminance task, indicate that the optical factor of lenticular senescence is the main contributor to the age-related changes observed in color vision. A model based on age-related changes in lenticular absorbance shows good fit with the experimental data of observers with phakic eyes, suggesting that optical factors are the main cause of the age-related changes in these color vision tasks.

Adolescent↗

PubMed2002

Aging and bilateral symmetry detection.

The salience of bilateral symmetry varies as a function of the orientation of the symmetry axis. Vertical symmetry is most salient, followed by horizontal and then oblique orientations. We tested symmetry detection in different age groups to determine whether performance of this intermediate-level visual task is affected by normal, nonpathological aging. We tested forty participants and analyzed the results with respect to age group and symmetry orientation (vertical, horizontal, and 45 degree oblique). There was a vertical symmetry detection advantage for all participants, where sensitivity was highest for vertical symmetry, followed by horizontal symmetry, and then the oblique symmetry. Sensitivity to symmetry did not differ for the two younger age groups (aged 19-39 and 40-60), but declined significantly for the group aged 61-70, and declined again for the oldest group aged 71-80. This age-related difference in sensitivity to symmetry was not reflected in a measure of bias, where there were no differences as a function of age.

Aging↗

PubMed2002

Acute vision impairment: does it affect an anesthesiologist's ability to intubate the trachea?

UNLABELLED: The result of impaired vision on an anesthesiologist's ability to intubate the trachea is unknown. We studied 12 attending staff anesthesiologists as they intubated 2 anesthesia mannequins (A and B) under 6 conditions. The conditions were: 1) usual vision, 2) central-vision loss with 20/500 bilaterally and a 24 degrees central scotoma, 3) peripheral-field loss with 20/20 bilaterally and a 7 degrees visual field, 4) peripheral-field loss with 20/20 bilaterally and a 3.5 degrees visual field, 5) central-vision loss with 20/200 bilaterally and a 12 degrees central scotoma, and 6) right eye ocular media opacity and 20/70 left eye usual acuity. The time to intubation was recorded by stopwatch from gripping the laryngoscope until the anesthesiologist signaled that the endotracheal tube was properly placed in the trachea. The mean +/- SD times to intubation for Mannequins A and B were 16.0 +/- 3.3, 31.9 +/- 10.4, 26.4 +/- 9.0, 26.4 +/- 7.7, 22.4 +/- 5.1, 25.5 +/- 16.9 and 16.6 +/- 6.6, 26.9 +/- 10.0, 21.4 +/- 9.2, 21.4 +/- 5.8, 21.5 +/- 7.7, 17.7 +/- 5.1 s for the 6 conditions, respectively. Multiple analysis of variance revealed a highly significant difference for the time to successful intubation between the anesthesiologists' usual vision and the vision-impaired conditions. There was a significant improvement in time to successful intubation from the first to subsequent intubation attempts. There were also more esophageal intubations in the vision-impaired conditions. This implies that anesthesiologists who develop acute severe vision impairment might have more difficulty intubating the trachea, which could initiate more critical incidents. The results of this study cannot be applied to anesthesiologists with chronic vision impairment. IMPLICATIONS: We found that acute severe vision impairment adversely affects the anesthesiologist's ability to intubate the trachea. This implies that anesthesiologists with acute onset of severe visual handicaps might have more difficulty intubating the trachea, which could initiate more critical incidents.

Acute Disease↗

PubMedDate not supplied

Word-reading thresholds in Alzheimer disease and mild memory loss: a pilot study.

PURPOSE: To determine whether subjects with early Alzheimer Disease (AD) or Mild Cognitive Impairment (MCI) would demonstrate significant abnormalities on tests of word reading threshold (WRT), spatial contrast sensitivity (SCS), and color discrimination (CD). METHODS: Prospective cohort study of 13 AD subjects, 13 subjects with Mild Cognitive Impairment (MCI), and 12 healthy elderly normal controls (ENC). CD was determined using the Farnsworth D-15 method. SCS was tested using a Vistech photographic chart. For WRT determination, pattern-masked words were presented successively at increasing target durations. The threshold was determined as the target duration at which 50% of the words were read. RESULTS: The mean number of errors in Color Discrimination and Spatial Contrast Sensitivity did not differ significantly among the three groups. WRT was significantly longer in the AD group (122.6 +/- 70.8 ms) in comparison with ENC group (53.8 +/- 15.9 ms) (p < 0.001). A WRT threshold limit of 85 msec correctly classified 11/12 ENC subjects and 10/13 AD subjects. Four of the 13 MCI subjects also exceeded this threshold and all four progressed to AD within 2 year follow-up. CONCLUSION: Word Reading Threshold determination discriminates mild AD subjects from ENC, and correlates with severity of cognitive impairment. It may have diagnostic and prognostic utility in early AD and MCI subjects.

Aged↗