Visual contrast sensitivity in Parkinson's disease is worsened with cabergoline treatment

Conscious perception and the modulatory role of dopamine: no effect of the dopamine D2 agonist cabergoline on visual masking, the attentional blink, and probabilistic discrimination

RATIONALE

Conscious perception is thought to depend on global amplification of sensory input. In recent years, striatal dopamine has been proposed to be involved in gating information and conscious access, due to its modulatory influence on thalamocortical connectivity.

OBJECTIVES

Since much of the evidence that implicates striatal dopamine is correlational, we conducted a double-blind crossover pharmacological study in which we administered cabergoline-a dopamine D2 agonist-and placebo to 30 healthy participants. Under both conditions, we subjected participants to several well-established experimental conscious-perception paradigms, such as backward masking and the attentional blink task.

RESULTS

We found no evidence in support of an effect of cabergoline on conscious perception: key behavioral and event-related potential (ERP) findings associated with each of these tasks were unaffected by cabergoline.

CONCLUSIONS

Our results cast doubt on a causal role for dopamine in visual perception. It remains an open possibility that dopamine has causal effects in other tasks, perhaps where perceptual uncertainty is more prominent.

Enhanced Obstacle Contrast to Promote Visual Scanning in Fallers with Parkinson's Disease: Role of Executive Function

The ability to perceive differences in environmental contrast is critical for navigating complex environments safely. People with Parkinson's disease (PD) report a multitude of visual and cognitive deficits which may impede safe obstacle negotiation and increase fall risk. Enhancing obstacle contrast may influence the content of visual information acquired within complex environments and thus target environmental fall risk factors. 17 PD with a history of falls and 18 controls walked over an obstacle covered in a high and low contrast material in separate trials whilst eye movements were recorded. Measures of visual function and cognition were obtained. Gaze location was extracted during the approach phase. PD spent longer looking at the obstacle compared to controls regardless of contrast (p < .05), however group differences were largest for the low contrast obstacle. When accounting for group differences in approach time, PD spent longer looking at the low contrast obstacle and less time looking at the ground beyond the low contrast obstacle compared to controls (p < .05). The response to obstacle contrast in PD (high-low) was significantly associated with executive function. Better executive function was associated with spending longer looking at the low contrast obstacle and at the ground beyond the high contrast obstacle. Enhancing the contrast of ground-based trip hazards may improve visual processing of environmental cues in PD, particularly for individuals with better executive function. Manipulating contrast to attract visual attention is already in use in the public domain, however its utility for reducing fall risk in PD is yet to be formally tested in habitual settings.

Visual losses in early-onset and late-onset Parkinson's disease

Patients with Parkinson's disease (PD) manifest visual losses. However, it is not known whether these losses are equivalent in both early-onset (EOPD) and late-onset (LOPD) patients. We evaluated contrast sensitivity and color vision in EOPD and LOPD patients and in age-matched controls. Losses occurred in both patient groups but were more pronounced in EOPD, consistent with the notion that non-motor symptoms are affected by age of symptom onset. More studies of visual function in EOPD and LOPD patients are needed to understand how aging is related to the pathophysiology of non-motor PD symptomatology. This would permit earlier diagnosis and, perhaps, better management of the disease.

Ocular and visual disorders in Parkinson's disease: Common but frequently overlooked

Patients with Parkinson's disease (PD) often compensate for their motor deficits by guiding their movements visually. A wide range of ocular and visual disorders threatens the patients' ability to benefit optimally from visual feedback. These disorders are common in patients with PD, yet they have received little attention in both research and clinical practice, leading to unnecessary - but possibly treatable - disability. Based on a literature search covering 50 years, we review the range of ocular and visual disorders in patients with PD, and classify these according to anatomical structures of the visual pathway. We discuss six common disorders in more detail: dry eyes; diplopia; glaucoma and glaucoma-like visual problems; impaired contrast and colour vision; visuospatial and visuoperceptual impairments; and visual hallucinations. In addition, we review the effects of PD-related pharmacological and surgical treatments on visual function, and we offer practical recommendations for clinical management. Greater awareness and early recognition of ocular and visual problems in PD might enable timely instalment of tailored treatments, leading to improved patient safety, greater independence, and better quality of life.