Physiology · MU Sofia

90. Color vision. Eye movements and binocular vision.

Covers how the three cone types with short, medium and long wavelength sensitivity support trichromatic colour vision, then follows colour signals from retinal ganglion cells through the lateral geniculate nucleus to the visual cortex. It also describes dichromacy and monochromacy, the extraocular muscles with their cranial nerves, and saccades, smooth pursuit and vergence. It closes with the advantages of binocular vision and binocular summation, and ends with recap questions.

Inside: 1 section · 8 labelled pictures · 29 flashcards · 5 min

Topic 89 of 104 in the MU Sofia syllabus for Physiology (Dental Medicine, Year 2). The free AceMed note covers it in 1 section, about 707 words (5 min of reading), with 29 flashcards.

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  1. Colour vision. Eye movements and binocular vision.

Colour vision. Eye movements and binocular vision.

Colour vision is the ability to perceive different wavelengths of light as distinct colors. This ability is primarily due to the presence of cone cells in the retina. There are three types of cones, each sensitive to a different range of wavelengths, corresponding to red, green, and blue light. The different types of cones are named based on the wavelengths to which they are most sensitive:

  • Short-wavelength (S) cones: Detect blue light
  • Medium-wavelength (M) cones: Detect green light
  • Long-wavelength (L) cones: Detect red light

This system is called trichromatic colour vision. The brain perceives color based on the relative activation levels of these three cone types. For example, when yellow light strikes the retina, both M and L cones are stimulated.

Colour Processing

  • Retina: Colour processing begins at the level of ganglion cells in the retina. Specific ganglion cells receive input from different combinations of cone types and respond to particular colour contrasts, such as red-green or blue-yellow.
  • Lateral Geniculate Nucleus (LGN): The signals from the ganglion cells are transmitted to the LGN, Different layers of the lateral geniculate nucleus get input from different cone cells. Inner layers 1 & 2 has magnocellular cells (large cells) and layers 3, 4 & 5 have parvocellular cells (small cells), where they are further processed

and segregated into separate pathways for red-green and blue-yellow color information.

  • Visual Cortex: The LGN projects to the visual cortex, where the information from different colour pathways is combined and interpreted, allowing us to perceive a wide range of colors.

Colour Deficiencies

  • Dichromacy: Occurs when one type of cone is missing, resulting in the inability to distinguish certain colors.
  • Monochromacy: Occurs when two or all three types of cones are missing, resulting in complete color blindness.

Eye movements are essential for maintaining clear vision and tracking objects in the visual field. These movements are controlled by six pairs of extraocular muscles, which are innervated by three cranial nerves:

  • Oculomotor nerve (CN III): Controls the superior rectus, inferior rectus, medial rectus, and inferior oblique muscles.
  • Trochlear nerve (CN IV): Controls the superior oblique muscle.
  • Abducens nerve (CN VI): Controls the lateral rectus muscle.

Types of Eye Movements

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