Biomedical subjects

Gregory R Jackson

Publications and source records attributed to Gregory R Jackson.

8 recordsLinked to original sources

PubMed2006

The Scotopic Sensitivity Tester-1 and the detection of early age-related macular degeneration.

PURPOSE: Previous research shows that dark adaptation is a marker of early age-related macular degeneration (ARMD), even when visual acuity remains good. This study evaluates whether a commercially available, off-the-shelf device for measuring dark adaptation, the Scotopic Sensitivity Tester-1 (SST-1), which uses a full-field stimulus, detects early ARMD as defined by fundus appearance. Fundus appearance is the gold standard method for defining the presence of ARMD. METHODS: Dark adaptation was measured using the SST-1 in 12 young adults (mean age 23 years), 17 old adults with normal retinal health (mean age 69) and 19 old adults with early ARMD (mean age 74). Normal retinal health and presence of early ARMD were defined by masked grading of dilated fundus photographs using the Wisconsin Age-Related Maculopathy Grading System. RESULTS: Older adults in normal retinal health exhibited slower dark adaptation as compared with young adults. No difference in the rate of dark adaptation was found between early ARMD patients and older adults in normal retinal health. CONCLUSIONS: Although the SST-1 differentiated between young and older adults, it failed to detect dark adaptation abnormalities in early ARMD when referenced against older adults in normal retinal health. This may be attributable to the full-field stimulation used by the SST-1, which may be better suited for characterizing retinal degenerations affecting large retinal areas than for focal macular diseases like ARMD.

Adult↗

PubMed2006

Effect of short-term, high-dose retinol on dark adaptation in aging and early age-related maculopathy.

PURPOSE: To examine the effect of a short course of high-dose retinol (preformed vitamin A) on dark adaptation in older adults with normal retinal health or early age-related maculopathy (ARM). METHODS: The study design was a randomized, double-masked, placebo-controlled experiment. Adults > or = 50 years of age whose fundus photographs for the eye to be tested psychophysically fell within steps 1 to 9 of the Age-Related Eye Disease Study (AREDS) Grading System were randomly assigned to a 30-day course of 50,000 IU oral retinol or a placebo. At baseline and 30-day follow-up, dark adaptation was tested and the Low Luminance Questionnaire (LLQ), an instrument for assessing difficulty with vision in reduced lighting, was administered. Primary outcomes of interest were rod- and cone-mediated parameters of dark adaptation, with scores on the LLQ's six subscales as secondary outcomes. RESULTS: The sample consisted of 104 participants with 52 each in the intervention and placebo groups. There were no group differences in baseline variables. At 30-days, the dark-adaptation parameters of cone time-constant, cone threshold, rod-cone break, and rod threshold did not differ. The retinol intervention group had significantly larger (i.e., steeper) rod slopes, indicating faster sensitivity recovery, than did the placebo group (P = 0.0419). There were no group differences in scores on the LLQ subscales driving, extreme lighting, emotional distress, general lighting, or peripheral vision. The retinol group had a higher score by five points on the mobility subscale compared with the placebo group (P = 0.0141). Those who had the most self-reported change on the mobility subscale at day 30 were more likely to have greater change in the speed of dark adaptation, as indicated by the rod slope parameter (r = 0.24, P = 0.0141). CONCLUSIONS: A short-term, high-dose course of retinol increased the rate of rod-mediated dark adaptation in older adults who were in the early phases of ARM or were exhibiting normal retinal aging. These results are consistent with the hypothesis that depositions and other structural changes in the retinal pigment epithelium and Bruch's membrane in aging and early ARM cause a localized retinoid deficiency.

Aged↗

PubMed2005

Impact of aging and age-related maculopathy on inactivation of the a-wave of the rod-mediated electroretinogram.

This study examined the impact of aging and age-related maculopathy (ARM) on the inactivation of phototransduction in rod photoreceptors by measuring the recovery of the a-wave using a paired flash electroretinogram technique. Measurements were made on 32 older adults in normal retinal health, 25 with early ARM, 7 with late ARM, and 20 young adults for comparison purposes. ARM presence and severity were defined by the Wisconsin Age-Related Maculopathy Grading System based on grading of fundus photographs. The inactivation of rod phototransduction exhibited an aging-related slowing. Those with early ARM did not exhibit inactivation slowing over and above what would be expected based on normal retinal aging. Persons in the late stages of ARM exhibited dramatic slowing in inactivation kinetics.

Adult↗

PubMed2004

Impact of aging and age-related maculopathy on activation of the a-wave of the rod-mediated electroretinogram.

PURPOSE: To examine the impact of aging and age-related maculopathy (ARM) on the activation of phototransduction in rod photoreceptors by measuring the a-wave of the flash, full-field electroretinogram (ERG). METHODS: Enrollees consisted of older adults (> or = 60 years of age) in normal retinal health (n = 41) and those with early (n = 39) or late ARM (n = 7), in whom disease presence and severity were defined based on grading of stereoscopic color fundus photographs according to the Wisconsin Age-Related Maculopathy grading system. Young adults (ages 16-30 years; n = 27) were enrolled for comparison purposes. Previously established procedures were used to estimate the ERG response to two families of flash intensities. By computer subtraction of responses, the isolated rod response was identified. Each participant's ensemble rod responses were fit with the following equation to describe the response (R) as function of flash intensity (I), and time (t): R(I,t) = [1 - exp[-I x S x (t - td)2]] x RmP3, where S is sensitivity, td is the delay before onset of the a-wave, and Rm(P3) is the maximum amplitude. RESULTS: In analyses of older adults, there was no impact of early ARM presence or severity on log S, Rm(P3), or td after adjustment for age and intraocular lens presence. Differences between young and old normal subjects in log S, RmP3, and td disappeared when analyses were limited to older adults with intraocular lenses. CONCLUSIONS: When the light absorption of the aged lens is taken into account and reliable definitions of normal retinal aging and ARM are used, the activation of the a-wave as measured by the rod-mediated full-field ERG is not affected by early ARM, nor is it impacted by normal retinal aging.

Adolescent↗

PubMed2003

Visual dysfunction, neurodegenerative diseases, and aging.

The four most common sight-threatening conditions in older adults in North America are cataract, ARM, glaucoma, and diabetic retinopathy. Even in their moderate stages, these conditions cause visual sensory impairments and reductions in health-related quality of life, including difficulties in daily tasks and psychosocial problems. Many older adults are free from these conditions, yet still experience a variety of visual perceptual problems resulting from aging-related changes in the optics of the eye and degeneration of the visual neural pathways. These problems consist of impairments in visual acuity, contrast sensitivity, color discrimination, temporal sensitivity, motion perception, peripheral visual field sensitivity, and visual processing speed. PD causes a progressive loss of dopaminergic cells predominantly in the retina and possibly in other areas of the visual system. This retinal dopamine deficiency produces selective spatial-temporal abnormalities in retinal ganglion cell function, probably arising from altered receptive field organization in the PD retina. The cortical degeneration characteristics of AD, including neurofibrillary tangles and neuritic plaques, also are present in the visual cortical areas, especially in the visual association areas. The most prominent electrophysiologic change in AD is a delay in the P2 component of the flash VEP. Deficits in higher-order visual abilities typically are compromised in AD, including problems with visual attention, perceiving structure from motion, visual memory, visual learning, reading, and object and face perception. There have been reports of a visual variant of AD in which these types of visual problems are the initial and most prominent signs of the disease. Visual sensory impairments (e.g., contrast sensitivity or achromatopsia) also have been reported but are believed more reflective of cortical disturbances than of AD-associated optic neuropathy.

Age Factors↗

PubMed2002

Early age-related maculopathy and self-reported visual difficulty in daily life.

PURPOSE: To determine whether early age-related maculopathy (ARM) is associated with visual difficulty in daily activities beyond the difficulty that would be expected based on normal retinal aging; to determine whether scotopic sensitivity and visual acuity are associated with visual difficulties in these older adults. STUDY DESIGN: Comparative, cross-sectional questionnaire study. SUBJECTS: Ninety-two older adults with early ARM in at least one eye as defined by one or more large (>63 microm) drusen and/or focal hyperpigmentation but no choroidal neovascularization or geographic atrophy, acuity of 20/60 or better, and a reference group of 55 older adults in the same age range without these fundus features and acuity of 20/35 or better in each eye. METHOD: Tests of visual acuity and scotopic sensitivity and a general health questionnaire were carried out. The Activities of Daily Vision Scale (ADVS) was administered to assess self-reported visual difficulties in everyday tasks and expressed on a scale of 0 (extreme difficulty) to 100 (no difficulty). Fundus photographs were taken and graded to characterize the presence and severity of ARM to determine eligibility. RESULTS: For purposes of analysis, the early ARM group was divided into those whose fellow eye (FE) was 20/60 or better and those whose FE was worse than 20/60. ADVS subscale scores were substantially lower in the early ARM group with FE worse than 20/60 (medians, 58-83) compared with the normal retinal health group (medians, 97-100). Even for those with early ARM with FE 20/60 or better, four of five subscale scores were lower (medians, 81-97), albeit slightly in some cases, than those of the reference group. For both ARM subgroups, the night driving subscale had the lowest scores of all subscales. Persons with early ARM with FE 20/60 or better were more likely to report difficulty on the night driving (odds ratio [OR], 4.3; 95% confidence interval [CI], 1.6-11.4), near vision (OR, 5.0; 95% CI, 1.9-12.9), and glare disability (OR, 2.7; 95% CI, 1.1-6.3) subscales compared with those in normal retinal health, adjusting for age, gender, medical comorbidities, and lens density. For early ARM patients with FE worse than 20/60, there was widespread reporting of difficulty on all subscales (ORs ranging from 4.7-52.9). Poor scotopic sensitivity was highly associated with difficulty on the night driving subscale (OR, 6.6; 95% CI, 1.2-35.5) but not with any other subscale. Acuity worse than 20/25 in both eyes was significantly associated with difficulty on all ADVS subscales; when this acuity impairment was present in one eye only, associations were still significantly present on some subscales, although they were weaker. CONCLUSIONS: Persons in the early phases of ARM, even when their fellow eye has relatively good acuity, are more likely to experience difficulty in night driving, near vision tasks, and glare disability compared with those in good retinal health. Scotopic dysfunction, a functional marker of early ARM, is linked to reported night driving problems. Even when acuity impairment occurs in one eye only, patients report difficulties with day driving and near and far vision tasks.

Activities of Daily Living↗

PubMed2002

Photoreceptor degeneration and dysfunction in aging and age-related maculopathy.

The relative rate of rod and cone degeneration is a fundamental characteristic of any disorder affecting photoreceptors, including aging and age-related maculopathy (ARM). The human macula consists of a small cone-dominated fovea surrounded by a rod-dominated parafovea. In aging and early ARM, rods degenerate before cones, a decline in scotopic (rod-mediated) sensitivity is more prominent than a decline in photopic (cone-mediated) sensitivity, and the time course of dark adaptation of rods slows dramatically. The topography of rod dysfunction and loss in early ARM matches the location of pathology in the retinal pigment epithelium (RPE)/Bruch's membrane complex visible in the ocular fundus. Rod dysfunction and loss in aging and ARM may be due to retinoid deficiency at the level of the photoreceptors cause by impaired retinoid translocation across the RPE/Bruch's membrane complex, a hypothesis deserving of further investigation.

Aging↗

PubMed2002

Aging-related changes in the multifocal electroretinogram.

The multifocal electroretinogram (MERG) was recorded in the central 36 degrees-diameter field in 26 young (19-30 yr) and 20 old (60-74 yr) adults in normal retinal health according to a fundus grading scale. The mean amplitude densities of the first-order and second-order responses in this retinal region were lower for old adults compared with young. The aging-related reduction of the first-order amplitude density was greatest at the fovea and decreased as a function of eccentricity. Similarly, the amplitudes of the first negative and positive peaks of the first-order MERG waveform were reduced with age, and the pattern of reduction followed a similar eccentricity dependency. The aging-related changes in the MERG waveform may be due to slowed temporal adaptation in the aged retina.

Adult↗