A myriad of visual problems based in the eyes may contribute to the symptoms and development of schizophrenia. (Source: Wikimedia Commons, Credit: Marco Castellani)
Two researchers from the New York Eye and Ear Infirmary of Mount Sinai and Rutgers University have found that changes in the structure of the eyes are associated with schizophrenia. Such changes provide another means to understand the disorder beyond changes in the brain (1).
However, as the retina is also part of the nervous system and is connected to the brain, abnormalities in the retina may reflect changes in tissues within the brain. The retina also provides the visual input to the processing areas of the brain, so abnormalities in perception may lead to problems in these processing areas. About 62% of schizophrenic patients suffer from visual distortions of some kind, be it in form, motion, or color (1, 2)
The researchers analyzed existing data to look for trends linking abnormalities in the eyes to schizophrenia. One result they found was that those with schizophrenia often had wider venules in their retina, indicating insufficient blood oxygen supply to the retina and possibly to the brain as well. Additionally, electrical signaling in the retina of some schizophrenics may be abnormal (2).
Visual abnormalities in youth are associated with a diagnosis of schizophrenia later in life. Lowered visual acuity in early childhood as well as strabismus, or misalignment of the eyes, lead to higher rates of schizophrenia when compared to unaffected individuals. Later on in life, schizophrenics are more prone to cataracts and lens opacities than the general population (1, 2).
Thinning of the retina has been linked to other neurological conditions, like Parkinson’s and Alzheimer’s disease. This thinning is correlated with the degree of disability and hallucinations in Parkinson’s diseases. Studies of retinal thinning in schizophrenic patients have also found similar trends, which may explain some of the visual disturbances seen in schizophrenics (2).
Abnormalities in the levels of dopamine in the brain were found in schizophrenics, which may be reflected in the retina as well. Dopamine is a major neurotransmitter for the amacrine cells of the retina. Reduced retinal dopamine in Parkinson’s disease is associated with losses in visual acuity and color vision. This may also be the case in schizophrenia. However, schizophrenics are often given dopamine receptor antagonists for treatment, which may end up affecting visual acuity and lowering contrast sensitivity, as blocking the dopamine receptors and lowering dopamine levels have similar effects on neural signaling (2).
In the acute phase of schizophrenia, or during the first episodes of symptoms, there is actually an increase in dopamine in the retina, which leads to opposite symptoms, namely enhanced contrast sensitivity. The medications have been shown to normalize this effect in the early stages of the disease, but chronic use leads to lower contrast sensitivity. More research is needed to see how these disturbances may contribute to visual disturbances and symptoms of the disease (2).
Another interesting finding was that there has never been a reported case of schizophrenia among the congenitally blind. This may be because the blind have no abnormal visual input, unlike many schizophrenics. Additionally, certain cognitive functions, like comprehension, selective and divided attention, and working and long term memory, are enhanced in the congenitally blind while impaired in schizophrenics. On the other hand, schizophrenics display more abstraction, conceptual inclusiveness, and word inventions than do the congenitally blind. The researchers speculate that changes in the organization of the brain in response to blindness may inherently provide protection against schizophrenia (1, 2)
The researchers hope that studies into the relationship between vision and schizophrenia will provide a better means of understanding the development of the disease. Neuro-based research on the eyes is also faster and cheaper than studies of the brain, providing an easier means of early detection or prediction, as many visual impairments in children are associated with higher rates of schizophrenia in adulthood (1).
References:
- The Mount Sinai Hospital / Mount Sinai School of Medicine. (2015, August 17). Retinal changes may serve as measures of brain pathology in schizophrenia. ScienceDaily. Retrieved August 25, 2015 from sciencedaily.com/releases/2015/08/150817181308.htm
- Steven M. Silverstein, Richard Rosen. Schizophrenia and the eye. Schizophrenia Research: Cognition, 2015; 2 (2): 46 DOI: 1016/j.scog.2015.03.004