Physiology · MU Sofia

89. Central processing of visual information. Light adaptation. Visual acuity

Traces the visual pathway from the retina through the optic chiasm and optic tracts to the superior colliculus, pretectum, suprachiasmatic nucleus, lateral geniculate nucleus and visual cortex. Explains photopic, mesopic and scotopic vision, and the pupillary, photoreceptor and neural mechanisms of light adaptation. Closes with optical and neural factors behind visual acuity, its measurement by minimum angle of resolution, and the factors that affect it.

Inside: 4 sections · 6 labelled pictures · 25 flashcards · 6 min

Topic 88 of 104 in the MU Sofia syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 4 sections, about 896 words (6 min of reading), with 25 flashcards.

In this note

  1. Central processing of visual information. Light adaptation. Visual acuity.
  2. Light Adaptation
  3. Visual Acuity
  4. Recap Questions

Central processing of visual information. Light adaptation. Visual acuity.

The visual pathway begins in the retina and continues to the brain, where visual information is processed and interpreted. The axons of the ganglion cells in the retina converge to form the optic nerve. The two optic nerves meet at the optic chiasm, where some fibers decussate (cross over to the other side). Fibers from the nasal hemiretina decussate, while those from the temporal hemiretina remain ipsilateral. After the optic chiasm, the fibers continue as the optic tracts, which carry visual information to several areas of the brain:

  • Superior colliculus of the midbrain: For control of eye movement. The midbrain participates in the control of eye movements and contains relay nuclei of the auditory and visual systems.
  • Pretectum of the midbrain: For control of the pupillary light reflex. For example, in the pupillary light reflex, light striking the retina activates parasympathetic preganglionic nerves in the Edinger-Westphal nucleus, leading to contraction of the sphincter muscle and pupillary constriction.
  • Suprachiasmatic nucleus of the hypothalamus: For control of diurnal rhythms (circadian rhythm) and hormonal changes.
  • Lateral geniculate nucleus (LGN) of the thalamus: For visual perception.

Optic Tract to the Lateral Geniculate Nucleus to the Visual Cortex

Fibers from the optic tract that terminate in the LGN synapse with optic radiating neurons, which project to the visual cortex in the occipital lobe. The LGN has six layers, each with a specific function related to the level of the synapse. Different layers of the LGN receive input from different cone cells. The visual cortex is responsible for analyzing visual information received from the LGN and has specialized

neurons that respond to various features, such as dark or light objects. From the primary visual cortex, signals are sent to secondary visual areas, including the visual association cortex, which further processes visual information, including 3D position, gross form, motion, and color.

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