Biomedical subjects

Joanna A Phipps

Publications and source records attributed to Joanna A Phipps.

6 recordsLinked to original sources

PubMed2006

Rod photoreceptor dysfunction in diabetes: activation, deactivation, and dark adaptation.

PURPOSE: To examine photoreceptor function in diabetes in detail by evaluating photoreceptor light activation, deactivation of the photoresponse, and recovery of the photoreceptor after bleaching (dark adaptation) in rats made diabetic with streptozotocin (STZ). METHODS: Animals were assigned to treated and control groups. Light activation in rod photoreceptors was established using a paired-flash electroretinogram (ERG) protocol, and the leading edge of the a-wave was modeled with the mechanisms mediating phototransduction. Deactivation of the photoreceptor response was evaluated at three luminous exposures (1.4-2.2 log cd.m/s-2) using a variable interstimulus interval (ISI) paradigm. Dark adaptation was evaluated at 90-second intervals for 30 minutes after approximately 20% pigment bleach. At each time point, a paired-flash signal (1.4 log cd.s/m-2) was used to extract rod responses. RESULTS: Diabetic animals showed decreased amplitudes of the photoreceptor response 12 weeks after diabetes induction. No difference was found in the rate of deactivation of the photoresponse in diabetic rats. Normalized amplitudes showed that diabetic animals had significantly faster dark adaptation (P<0.01) than did controls. CONCLUSIONS: Although photoreceptor activation was abnormal, deactivation was unaltered after 12 weeks of diabetes. The faster relative recovery found in diabetes after bleach, in the presence of normal pigment dynamics, may reflect a decrease in outer segment lengths.

Animals↗

PubMed2005

Dysfunction of retinal neurons and glia during diabetes.

Diabetic retinopathy is the leading cause of blindness in those of working age. It is well known that the retinal vasculature is altered during diabetes. More recently, it has emerged that neuronal and glial dysfunction occurs in those with diabetes. Current research is directed at understanding these neuronal and glial changes because they may be an early manifestation of disease processes that ultimately lead to vascular abnormality. This review will highlight the recent advances in our understanding of the neuronal and glial changes that occur during diabetes.

Animals↗

PubMed2004

Flicker perimetry losses in age-related macular degeneration.

PURPOSE: To compare static and flicker perimetry outcomes in patients with early age-related macular degeneration (AMD). METHODS: Perimetry was performed in the central visual field of one eye of each of 25 patients with good visual acuity (> 6/12) and early AMD using static and flickering targets. These results were compared with data obtained from a single eye of 34 age-matched control subjects, 33 of whom were retested at 1 to 3 months after their initial visits. RESULTS: In all cases, patients with early AMD had greater mean defects for flickering than static targets, returning a significantly larger group average in response to flicker (4.3 +/- 0.6 dB) than to static (1.8 +/- 0.6 dB; P < 0.005). Greater pattern defect losses were also present in AMD-affected eyes with flicker compared with static perimetry (P < 0.02). These give a higher diagnostic sensitivity for flicker (68% vs. 42%, P < 0.05) at 90% specificity. Sensitivity can be increased to 84% +/- 6% (specificity 92% +/- 4%) if the criterion for failure is a more than 10-dB loss in the foveal region (1 degrees -3 degrees ). CONCLUSIONS: Flickering targets expose foveal deficits in early AMD better than do static targets. Flicker perimetry is an easy, short procedure that may be useful for monitoring the progression of AMD.

Aged↗

PubMed2004

Paired-flash identification of rod and cone dysfunction in the diabetic rat.

PURPOSE: To investigate the onset of retinal neural dysfunction in the streptozotocin (STZ)-induced diatebic rat. METHODS: A cohort of 20 Sprague-Dawley rats were randomly assigned to treatment (STZ 50 mg/kg, n = 10) and control (citrate buffer, n = 10) groups and observed for 12 weeks. Diabetes was confirmed by blood glucose (>15 mmol/L) and HBA(1c) (>7.0%). Treated animals received 2 to 3 U insulin daily. Retinal function was monitored using paired-flash electroretinograms (ERGs) at baseline and various time points between 2 days and 12 weeks after treatment, to allow isolation of rod and cone components. Protocols compared photoreceptor and inner retinal responses (rod and cone) at each time point. RESULTS: Losses in the function of rod photoreceptors and the inner retina were seen 2 days after STZ injection, with recovery in some components by 4 weeks and a secondary loss of function at 12 weeks. Some inner retinal responses (cone response and rod oscillatory potentials (OPs) remained consistently depressed over the entire 12 weeks. CONCLUSIONS: Retinal neural dysfunction was observed as early as 2 days after STZ injection. These acute changes reflect either STZ toxicity or hyperglycemia as a result of pancreatic compromise. Consistent loss over the 12 weeks of the cone response and OPs suggests a vulnerability of the inner retina to STZ-related effects. The 12-week losses in function of retinal neurons are consistent with a generalized diabetic neuropathy, since impaired function developed simultaneously in both inner and outer retinal neurons.

Animals↗

PubMed2003

Loss of cone function in age-related maculopathy.

PURPOSE: To evaluate cone visual function of subjects with age-related maculopathy (ARM). METHODS: Cone thresholds in 16 patients with ARM and 14 age-matched control subjects were compared. All subjects had visual acuity of 6/12 or better in the studied eye. A range of contrast thresholds were measured to evaluate diverse aspects of cone visual function under steady state conditions (spatiotemporal, color and luminance, and photopic sensitivity) or after bleaching (adaptation dynamics). RESULTS: ARM produced a diffuse loss across all cone steady state visual functions in 31% to 44% of subjects. The adaptation time constant of cone recovery was significantly prolonged in most (69%) ARM eyes. A cross-correlational analysis found adaptational kinetics to be independent of other steady state losses, with cone photopigment regeneration being the most affected visual function in ARM (chi(2) = 4.03, P < 0.05). CONCLUSIONS: The results show that cone-adaptational kinetics are affected in ARM more so than are steady state thresholds. Given that cone recovery is easy to examine in a clinical setting, this test may provide a useful index of photopic function in patients with ARM.

Adaptation, Ocular↗

PubMed2001

Fast psychophysical procedures for clinical testing.

INTRODUCTION: Psychophysical methods are used in clinical settings to obtain estimates of visual performance. Such methods should be fast and accurate, yet robust to the corrupting effects of false responses. METHODS: In this paper, we develop these concepts and investigate the efficiency of two maximum likelihood methods (bestPEST and ZEST) for use in clinical applications. The performance of both methods will depend on whether a criterion-free paradigm (alternate forced choice) is adopted. RESULTS: Our data show that the number of trials needed to obtain reliable thresholds with a yes/no paradigm can be as few as six to eight, provided no false responses are given within the first few trials. In addition, we show that the reliability and short-term variability of the endpoint of the methods is compatible with clinical applications. CONCLUSION: We show that a yes/no maximum likelihood method using a small number of presentations will yield reliable and accurate estimates of threshold in a clinical setting.

Journal Article↗