Vision central event

FIGURE 8.7 The central event in human vision is absorption of a visible photon by 11-cis-retinal, which then rearranges about one of its double bonds. The chain of alternating (conjugated) single and double bonds permits absorption in the visible. 

When this molecule absorbs light, it rapidly isomerizes (changes its structure) to the all-trans form. This specific chemical reaction is the central event in human vision. The molecule is bound within a protein (the combination is called rhodopsin), the isomerization triggers a series of later processes, ultimately leading to an electrical signal which is sent to the brain. 

Use of diethylpropion for a period longer than 3 months is associated with an increased risk for development of pulmonary hypertension. When used as directed, reported common central nervous system adverse effects included overstimulation, restlessness, dizziness, insomnia, euphoria, dysphoria, tremor, headache, jitteriness, anxiety, nervousness, depression, drowsiness, malaise, mydriasis, and blurred vision. In addition, diethylpropion can decrease seizure threshold, subsequently increasing a patient s risk for an epileptic event. Other organ systems also can adversely be affected, resulting in tachycardia, elevated blood pressure, palpitations, dry mouth, abdominal discomfort, constipation,... 

Figure 29-5. The visual cycle of vitamin A is central to vision. In the retina, light stimulates the conversion of 1 l-c/.s-retinal, part of rhodopsin (Rho), to all-iraws-retinal and activates rhodopsin (Rho ).This initiates the first step of the signal transduction cascade that results in the transmission of the visual signal to the brain.The visual cycle involves biochemical and metabolic events in both the photoreceptors (rods) and the retinal pigment epithelium.

Vision is critical to driving, with some researchers suggesting that vision is required for up to 95% of the sensory input needed to drive (Shinar and Scheiber, 1991). Owsley et al. (1991) have described the driving task as a visually cluttered array, both primary and secondary visual tasks, and simultaneous use of central and peripheral vision. In addition, the driver is usually uncertain as to when and where an important visual event may occur (p. 404). 

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