Hélène Kergoat

Use of the retinal vessel analyzer in ocular blood flow research

Acta Ophthalmol. 2010: 88: 717–722

Ocular perfusion pressure in glaucoma

This review article discusses the relationship between ocular perfusion pressure and glaucoma, including its definition, factors that influence its calculation and epidemiological studies investigating the influence of ocular perfusion pressure on the prevalence, incidence and progression of glaucoma. We also list the possible mechanisms behind this association, and discuss whether it is secondary to changes in intraocular pressure, blood pressure or both. Finally, we describe the circadian variation of ocular perfusion pressure and the effects of systemic and topical medications on it. We believe that the balance between IOP and BP, influenced by the autoregulatory capacity of the eye, is part of what determines whether an individual will develop optic nerve damage. However, prospective, longitudinal studies are needed to better define the role of ocular perfusion pressure in the development and progression of glaucoma.

Use of colour Doppler imaging in ocular blood flow research.

The main objective of this report is to encourage consistent quality of testing and reporting within and between centres that use colour Doppler imaging (CDI) for assessment of retrobulbar blood flow. The intention of this review is to standardize methods in CDI assessment that are used widely, but not to exclude other approaches or additional tests that individual laboratories may choose or continue to use.

Visual retinocortical function in dementia of the Alzheimer type

Background: Some histological investigations have reported anomalies in the primary visual pathways of individuals with dementia of the Alzheimer type (DAT), while others have suggested that these visual structures are spared by the disease process. Objectives: This study was conducted to address this issue of substantial controversy. We determined in vivo whether DAT alters the functioning of the primary visual pathways by evaluating pattern-reversal electroretinograms (ERGs) and cortical visual evoked potentials (VEPs). Methods: Twenty-seven individuals with mild to moderate DAT and 27 age- and sex-matched control subjects were included in the investigation. ERG and VEP recordings were obtained from all participants with the use of a clinical electrodiagnostic system. Stimulus conditions were biased towards a preferential response from the magnocellular and parvocellular subdivisions of the visual system. Results: Amplitude and latency of the ERG were not affected by DAT. The VEP amplitude was not attenuated in DAT individuals, but there was a delay in the latency of the VEPs arising from both magnocellular and parvocellular streams of visual processing. Conclusion: Our results indicate that while the inner retina appears to be spared by the disease process, the visual function is altered upstream in the retinocortical visual pathways of individuals with DAT.

Neuroretinal function is normal in early dementia of the Alzheimer type

We recently demonstrated that retinal ganglion cell function, optic nerve head parameters and the retinal nerve fiber layer thickness are not altered in early dementia of the Alzheimer type (DAT). Our current objective was to assess whether the function of cells located more distally in the retina is also unaffected by the disease. We evaluated 23 individuals with early to moderate DAT and 23 healthy age-matched subjects, all displaying clinically normal visual function. Scotopic and photopic flash electroretinograms (fERGs) and oscillatory potentials (OPs) were recorded. The amplitude and latency of the retinal potentials did not differ between DAT and control subjects. Our current results showing normal fERGs and OPs in early DAT indicate that the underlying neurons giving rise to these signals are not impaired by the disease process. These data support and extend our recent findings suggesting that visual deficits in DAT do not stem from neuroretinal dysfunction.

Consequences of an increase in the ocular perfusion pressure on the pulsatile ocular blood flow.

Purpose. In previous studies we have demonstrated that physical exertion constricted the major retinal arteries, increased the redness of the optic nerve head, and attenuated scotopic white flash oscillatory potentials. These anatomic and functional changes in the human retina suggested that blood flow to the innermost retinal layers was modified in some way to cause these changes. The objective of this study was to determine whether physical exertion also affected blood flow in the choroid, the exclusive source of blood to the outermost layers of the retina. Methods. Eighteen healthy adults volunteered for this study. An OBF Tonograph system (OBF Laboratories UK Ltd., Malmesbury, Wiltshire, U.K.) was used to derive the pulsatile ocular blood flow, which reflects the pulsatile component of blood flow in the choroid, at rest and 20 minutes after biking at a heart rate of 140 beats/min. Results. At the systemic level, biking increased the blood pressure and the heart rate. At the ocular level, the duration of the systolic and diastolic phases of the intraocular pulse was shortened, and the pulse amplitude and volume were reduced. Despite the attenuation of the intraocular pulse parameters, the pulsatile ocular blood flow increased by some 18% after exercise largely because of the much larger increase in heart rate. The ocular perfusion pressure increased, whereas the intraocular pressure decreased. Conclusions. Physical exertion in the form of aerobic exercise increased the pulsatile component of blood flow in the choroid. Because the choroid is the sole blood supply to the outer retina, it was concluded that the degree of perfusion of the photoreceptors necessary for vision is increased by physical exertion. This increased choroidal blood flow is presumably to sustain vision as blood is directed to the large muscle groups involved in the physical activity.

Correlation of an exercise-induced increase in systemic circulation with neural retinal function in humans

Although the effects of physical exertion on intraocular pressure and systemic blood pressure are well established, the retinal response to such physiologic stress has not been examined. We studied the effect of short-term intense exercise on the principal waves in the scotopic and photopic flash electroretinograms, as well as the lower-amplitude oscillatory potentials. Sixteen healthy volunteers between 20 and 30 years of age participated in this experiment. The electroretinograms and oscillatory potentials were recorded with a Nicolet CA-1000 clinical averager, using DTL-type fiber electrodes. All retinal potentials were taken immediately before and after a minimum 20-min period of stationary bicycling that increased the heart rate to about 140 beats per minute. The electroretinograms were recorded from eyes with dilated pupils, 10 min after white-light adaptation of the right eye, and 30 min after dark adaptation of the left eye. Red flashes and dim white flashes were used to elicit photopic and scotopic electroretinograms, respectively. While no changes were recorded for any of the electroretinogram components recorded under photopic conditions, the amplitude of OP5 was decreased and the implicit time of OP4 was delayed after exercise for scotopic conditions. We concluded that exercise caused component-specific changes in the scotopic oscillatory potentials. Since it is well known that oscillatory potentials are vulnerable to ischemia, scotopic oscillatory potentials may be used as simple noninvasive indices of the reactivity of the retinal vascular autoregulatory system during exercise.

Oculo-visual changes and clinical considerations affecting older patients with dementia

Dementia is associated with various alterations of the eye and visual function. Over 60% of cases are attributable to Alzheimers disease, a significant proportion of the remainder to vascular dementia or dementia with Lewy bodies, while frontotemporal dementia, and Parkinsons disease dementia are less common. This review describes the oculo‐visual problems of these five dementias and the pathological changes which may explain these symptoms. It further discusses clinical considerations to help the clinician care for older patients affected by dementia.

Assessment of Visual Function in Institutionalized Elderly Patients

OBJECTIVE To describe the visual function and ocular health of frail elderly patients institutionalized in a tertiary care university-affiliated geriatric hospital. DESIGN Retrospective file review. SETTING A university-affiliated geriatric hospital. PARTICIPANTS 440 patient files. MEASUREMENTS The archived clinical files of patients from the long-term care beds of the Institut universitaire de gériatrie de Montréal, who had died between April 2000 and 2004 were reviewed. Pertinent medical and visual characteristics were extracted and entered into a database for analysis. RESULTS The age of the patients ranged from 65 to 104 years. The major ocular conditions observed were cataract, pseudophakia, conjunctivitis-blepharitis, age-related macular degeneration, and glaucoma. Of the 231 patients referred for a partial or full eye examination, visual acuity was available in 178. Visual impairment was considered absent in 87 patients; mild in 52; moderate in 17; and 22 patients were legally blind. Of the 105 patients referred for a full eye examination, an evaluation of the refraction, visual acuity, and ocular health was possible in 89, irrespective of their cognitive status. CONCLUSION These data demonstrate that the vast majority of severely disabled elderly patients examined retained good visual acuity into advanced age. The most prevalent ocular conditions observed are treatable, thereby emphasizing the importance of regular eye care for the institutionalized frail elderly. The results clearly demonstrate that it is possible to perform a complete evaluation of visual function and ocular health in the elderly institutionalized patient, independent of age, cognitive status, or communication disorders.

Changes in the retinocortical evoked potentials in subjects 75 years of age and older

OBJECTIVE Current trends are showing a rapid increase in the elderly population, particularly the subgroup that is 75 years of age or more. Considering the fact that several ocular diseases are more prevalent among the elderly, it is increasingly important to investigate normal visual function in this subgroup of our population. The objective of this study was to determine the effects of advanced aging on visual retinocortical function by evaluating the electrophysiological responses of the most rapidly increasing segment of the geriatric population. METHODS Fifty-eight healthy subjects between the ages of 20--32 years (n=30) and 75--88 years (n=28) participated in this study. We recorded their pattern electroretinograms (ERGs) and cortical visual evoked potentials (VEPs) under stimulus conditions biased toward the preferential response of the magnocellular and parvocellular subdivisions of the visual system. RESULTS Elderly subjects showed reduced ERG amplitudes relative to young participants. The amplitude of the VEPs also decreased with age, while their latency increased. The effect of senescence was most apparent under stimulus conditions combining the magnocellular and parvocellular pathway contributions and less pronounced when the stimulus conditions were biased to favor the response of either system. CONCLUSIONS Our results demonstrate that visual retinal and cortical function deteriorates with old age. Our data further indicate that senescence has widespread effects on the visual system, altering the functioning of both the magnocellular and parvocellular visual pathways.