"To see or not to see: that is the question." The "Protection-Against-Schizophrenia" (PaSZ) model: evidence from congenital blindness and visuo-cognitive aberrations

Abstract

The causes of schizophrenia are still unknown. For the last 100 years, though, both "absent" and "perfect" vision have been associated with a lower risk for schizophrenia. Hence, vision itself and aberrations in visual functioning may be fundamental to the development and etiological explanations of the disorder. In this paper, we present the "Protection-Against-Schizophrenia" (PaSZ) model, which grades the risk for developing schizophrenia as a function of an individual's visual capacity. We review two vision perspectives: (1) "Absent" vision or how congenital blindness contributes to PaSZ and (2) "perfect" vision or how aberrations in visual functioning are associated with psychosis. First, we illustrate that, although congenitally blind and sighted individuals acquire similar world representations, blind individuals compensate for behavioral shortcomings through neurofunctional and multisensory reorganization. These reorganizations may indicate etiological explanations for their PaSZ. Second, we demonstrate that visuo-cognitive impairments are fundamental for the development of schizophrenia. Deteriorated visual information acquisition and processing contribute to higher-order cognitive dysfunctions and subsequently to schizophrenic symptoms. Finally, we provide different specific therapeutic recommendations for individuals who suffer from visual impairments (who never developed "normal" vision) and individuals who suffer from visual deterioration (who previously had "normal" visual skills). Rather than categorizing individuals as "normal" and "mentally disordered," the PaSZ model uses a continuous scale to represent psychiatrically relevant human behavior. This not only provides a scientific basis for more fine-grained diagnostic assessments, earlier detection, and more appropriate therapeutic assignments, but it also outlines a trajectory for unraveling the causes of abnormal psychotic human self- and world-perception.

Keywords: Protection-Against-Schizophrenia (PaSZ); blindness; cognition; continuous diagnostic criteria; early detection; schizophrenia; vision therapy; visual aberrations.

Figure 1

The “Protection-Against-Schizophrenia” (PaSZ) Model. The continuous PaSZ model depicts the relative risk for schizophrenia as a function of the continuous variable visual capacity. Whereas both “absent” vision (congenital blindness) and “perfect” vision (“supernormal” vision) may be associated with a decreased risk for schizophrenia, the model suggests that the risk for developing schizophrenia increases from both ends of the visual capacity continuum toward a “peak risk” (Landgraf et al., ; Silverstein et al., 2013). The location of this peak risk has yet to be determined experimentally. However, the peak has important implications for the understanding of the etiology, development, and therapy of the disorder: individuals suffering from visual impairment (located to the left of the peak), who never developed “normal” vision, may reduce their risk for developing schizophrenia through a decline in visual capacity. Individuals suffering from visual deterioration (located to the right of the peak), who previously had “normal” visual skills, may reduce their risk for developing schizophrenia through an improvement in visual capacity. Note that the model does not make a concrete assumption on the association between vision capacity and risk for schizophrenia (linear, exponential, etc.). Instead, we suggest that extensive longitudinal and epidemiological investigations, also controlling for age-related visual capacity decline (Ofan and Zohary, ; Cattaneo et al., 2008), are necessary to elaborate this issue. In this context, visual capacity may comprise but is not limited to measures of visual acuity (near/far), sensitivity to light, motion, and color, visual field size, and stereoscopic vision. To the best of our knowledge, this is the first model that uses a continuous (more vs. less psychotic) rather than a categorical (“normal” vs. “mentally disordered”) approach to represent psychiatrically relevant human behavior. Abbreviations: PaSZ = Protection-Against-Schizophrenia; SZ = schizophrenia; Prodromals = individuals identified at ultra-high risk for developing schizophrenia; 1st episode patients = patients with schizophrenia that have had one (identified) psychotic episode; Chronic patients = patients with schizophrenia that have had at least three (identified) psychotic episodes.

Figure 2

The Progressive Vision-Space-Body-and-Cognitive-Identity (ViSBI) model of schizophrenia. Source: Reprinted with kind permission from Bentham Science Publishers. Note. The progressive ViSBI model stresses vision-related deteriorations from prodrome to chronic syndrome that may lead to schizophrenia. The model comprises four complexes: “Vision,” “Space,” “Body,” and “cognitive Identity. ”The “Vision,” “Space,” and “Body” complexes are reviewed in the sections on “The Vision Perspective on Schizophrenia“ in the current paper. The “Cognitive Identity” complex (shadowed in gray) is hypothesized as a part of the model (see Landgraf et al., 2012). Complexes are sub-divided into specific research areas (e.g., in the “Vision” complex: oculomotricity and scanning) and disease progression status (prodromal, first episode, and chronic schizophrenia patients). Tasks listed in each row indicate deficient performance of the corresponding patient group. Some areas have not been investigated in schizophrenia patients (“suggestions for further research”). The “Visual Input” triangle in the middle indicates that (congenital) blindness may prevent these mechanisms from taking place because visual perceptual input is required for this pattern of aberrations to occur. Abbreviations: prodromal = individuals identified at ultra-high risk for developing schizophrenia; first episode = patients with schizophrenia that have had one (identified) psychotic episode; chronic = patients with schizophrenia that have had at least three (identified) psychotic episodes; SPEM = smooth pursuit eye movements; n-back = spatial n-back task.