4.1 Anatomy and physiology of the human visual system

The human visual system is a complex network of structures and processes that enable us to perceive the world around us. From the intricate anatomy of the eye to the neural pathways that transmit visual information, our ability to see is a marvel of biological engineering.

Understanding how our eyes and brain work together to process visual input is crucial for developing effective augmented and virtual reality systems. By mimicking or enhancing natural visual processes, we can create more immersive and realistic experiences in AR and VR applications.

Eye Anatomy

Retinal Structure and Function

Top images from around the web for Retinal Structure and Function

• 

  Vision | Anatomy and Physiology View original

  Is this image relevant?

• 

  13.10 Sensory Perception – Fundamentals of Anatomy and Physiology View original

  Is this image relevant?

• 

  Vision | Anatomy and Physiology I View original

  Is this image relevant?

• 

  Vision | Anatomy and Physiology View original

  Is this image relevant?

• 

  13.10 Sensory Perception – Fundamentals of Anatomy and Physiology View original

  Is this image relevant?

1 of 3

Top images from around the web for Retinal Structure and Function

• 

  Vision | Anatomy and Physiology View original

  Is this image relevant?

• 

  13.10 Sensory Perception – Fundamentals of Anatomy and Physiology View original

  Is this image relevant?

• 

  Vision | Anatomy and Physiology I View original

  Is this image relevant?

• 

  Vision | Anatomy and Physiology View original

  Is this image relevant?

• 

  13.10 Sensory Perception – Fundamentals of Anatomy and Physiology View original

  Is this image relevant?

1 of 3

• Retina is the light-sensitive tissue lining the back of the eye that converts light into electrical signals
• Consists of several layers, including the photoreceptor layer, bipolar cell layer, and ganglion cell layer
• Photoreceptors are specialized cells in the retina that detect light and initiate the process of vision
  • Two main types: rods (sensitive to low light levels) and cones (responsible for color vision)
• Fovea is a small, central area of the retina with the highest concentration of cone photoreceptors
  • Responsible for sharp, detailed vision (visual acuity)
  • Allows for activities requiring fine detail perception (reading, threading a needle)

Neural Pathways in the Eye

• Optic nerve is a bundle of nerve fibers that carries visual information from the retina to the brain
  • Consists of axons from the retinal ganglion cells
  • Exits the back of the eye and travels to the lateral geniculate nucleus (LGN) in the thalamus
• Retinal ganglion cells are the output neurons of the retina that send visual information to the brain via the optic nerve
  • Receive input from bipolar cells and amacrine cells in the retina
  • Axons converge at the optic disc, forming the optic nerve (blind spot due to lack of photoreceptors)

Visual Processing

Cortical Processing of Visual Information

• Visual cortex is the part of the cerebral cortex responsible for processing visual information
  • Located in the occipital lobe at the back of the brain
  • Consists of multiple areas with different functions (V1, V2, V3, V4, and V5/MT)
• Primary visual cortex (V1) is the first cortical area to receive visual input from the LGN
  • Performs initial processing of basic visual features (edges, orientation, and motion)
  • Sends information to higher visual areas for more complex processing (object recognition, color perception)

Visual Field and Acuity

• Peripheral vision refers to the ability to see objects and movement outside the direct line of sight
  • Processed by rod photoreceptors, which are more sensitive to light but have lower visual acuity
  • Important for detecting motion and navigating the environment (spotting a car in the side mirror)
• Visual acuity is the ability to see fine details and resolve small objects
  • Highest in the fovea, where cone photoreceptors are densely packed
  • Measured using a Snellen chart with progressively smaller letters (20/20 vision)

Color Perception

• Color perception is the ability to distinguish different wavelengths of light as distinct hues
  • Mediated by cone photoreceptors, which come in three types: red (long-wavelength), green (medium-wavelength), and blue (short-wavelength)
  • Combinations of cone activation allow for the perception of a wide range of colors (mixing red and green light produces yellow)
• Color processing occurs in higher visual areas, such as V4
  • Involves comparing signals from different cone types to determine hue, saturation, and brightness
  • Certain genetic conditions can lead to color blindness (difficulty distinguishing red and green)

Eye Functions

Accommodation and Focusing

• Accommodation is the eye's ability to change its focus to see objects at different distances clearly
  • Involves changing the shape of the lens using the ciliary muscles
  • When focusing on a nearby object, the lens becomes more curved (thickens)
  • When focusing on a distant object, the lens becomes flatter (thins)
• Presbyopia is an age-related condition in which the lens loses its flexibility, making it difficult to focus on close objects
  • Typically develops in middle age and can be corrected with reading glasses or bifocals

Binocular Vision and Depth Perception

• Binocular vision is the use of both eyes together to create a single, fused image
  • Allows for depth perception and the ability to judge distances
  • Each eye sees a slightly different view of the world (binocular disparity)
  • The brain combines these two images to create a sense of depth (stereopsis)
• Binocular cues for depth perception include retinal disparity and convergence
  • Retinal disparity is the difference in the position of an object on the retinas of the two eyes
  • Convergence is the inward turning of the eyes when focusing on a nearby object (cross-eyed)
• Monocular cues for depth perception can be used with one eye, such as linear perspective and occlusion (overlapping objects)