Visual System Objectives Eyeball functions Name the structures

Visual System

Objectives Eyeball functions Name the structures and functions of retina Differentiate between cones and rods Draw central visual pathway Predict visual field defects by lesion sites

Visual Perception 1. Refraction of lights by the lens and cornea 2. Convert the electromagnetic energy in light by the retinal photoreceptor cells into nerve impulses 3. Nerve impulses from retinal photoreceptor to visual cortex (occipital lobe) 4. Perception of visual image in the primary visual cortex (V 1). V 1 projects to the adjacent visual association area for advanced processing.

Through the Lens (& Cornea) Refraction of lights Focused image on the retina reversed and inverted Ciliary muscle regulates the lens curvature

Visual field vs. Retinal field Binocular visual field

Retina: Photoreceptors Rods Cones -more (100 million) -less (30 million) -retina, except fovea -central retina, fovea -operate under dim light -operate under bright light -low visual acuity -high visual acuity -process grayscale color -process all color shades *3 types: blue/green/red

Optic Disc – Optic Nerve Ganglion cell axons converge at the optic disc At optic disc, axons turn posteriorly and exit the retina to form optic nerve Not in the middle More towards nasal No photoreceptor Blind spot!

Exercise: Find your blind spot Pick an eye Close the other eye Stare at the cross Move your note around Check if the black dot disappears in a specific location!

Exercise: 2 things to take away! No photoreceptor, no visual information The optic nerve is not in the middle of the retina, so the blind spot is in: Right eye: right visual field Left eye: left visual field Test your right eye Test your left eye

Video: visual pathway https: //www. youtube. com/watch? v=ETIp 8 k. ZPo. Bw From visual field to visual cortex

Quick review Visual field Retina Optic nerve Optic chiasm Lateral Geniculate Nucleus Optic Radiation Visual cortex

Visual Cortex

Visual Field Defect Anopsia A lesion at any point in the visual pathway Causes: tumors, strokes, etc Loss of a specific point in the visual field We will discuss 6 types

Video: visual lesions https: //www. youtube. com/watch? v=463 SLpz 7 bxs to 7: 20

Visual Perceptual Deficit Visual agnosia Lesion in visual association cortex Dorsal: Visual integrated motion, temporal, and spatial information Ventral: Visual memory, object recognition, written information

Visual Perceptual Deficit Left Neglect Apperceptive agnosia Associative agnosia Prosopagnosia Alexia Agraphia Optic aphasia

Left Neglect Fail to respond to the information on the contralateral side to the brain lesion Can happen in either R/L hemisphere, but more common in RH damage 31% - 66% people with RHD show neglect

Left Neglect An example: https: //www. youtube. com/watch? v=d 4 Fh Zs-m 7 h. A 1: 40, 3: 20

Theories about Neglect NOT due to: Primary sensory deficit (e. g. , visual pathway cut) Motor deficit Perceptual disorder Deficit in space representation Attention deficit Most accepted theory Severe neglect: ignore all the sensory inputs from the affected side

Prosopagnosia Impaired ability to recognize faces Famous people Family members In severe cases, people may not distinguish objects from faces An example: https: //www. youtube. com/watch? v=vw. Crxom Pbt. Y

Visual Deficit Assessment Some examples!

Line Bisection Present a horizontal line and ask a person to label the middle of the line

Picture description Present action scenes with details on both L & R side, and ask a person to describe it

Drawing