Visual Pathways & Eye Physiology

• Sera, a 64-year-old woman unable to read her Bible
• Module: Eye, Problem: 3.03

Supplementary Sessions

• Resource sessions include anatomy of the optic pathways and extra-ocular muscles, physiology of vision, and eye examination focusing on pupillary reflexes and accommodation reflex.
• Fixed resources include anatomy of the eye, utilizing the Anatomy Lab

Visual Pathways:

• The main components of the visual pathway need to be identified
• Lesions at these components can then be investigated, to reveal the cause of visual defects and complications
• Components such as the Retina, Receptors and Neurones, Optic disc, Fovea & Macula, Visual pathway containing the Optic nerve & its coverings, Optic chiasma, Optic tract, Lateral geniculate body as well as the Optic radiation must all must be understood
• Anatomical pathways of reflexes must be understood
• Including the corneal reflex, direct and consensual light reflex and accommodation

Physiology of vision

• To understand how the eye works, one must be able to explain the processes involved in vision
• Describe how defects of image formation are corrected
• Understand the components and importance of receptor cells
• Discuss retinal photopigments, characteristics, and their role in color vision, night vision, and dark adaptation
• Explain how the eye achieves focusing, accommodation, binocular vision, and horizontal, vertical, and diagonal gaze, including involved muscles and eye structures
• Describe the assessment of visual function using visual acuity and visual fields
• Explain how different visual field defects occur due to damage in neural pathways from the retina to the visual cortex

Causes of poor vision

• Poor vision can be broken down into the following key areas:
• Visual pathway
• Focusing and light-transmitting media like cornea, aqueous humour, lens, and vitreous humour
• Fundus structures like optic disc, retina, and choroid
• The transmitting system, consisting of the optic nerve, chiasm, tract, and radiation
• Cortical centers of recognition
• It is important to differentiate the cause of poor vision such as:
• Sudden vs Gradual
• Painful vs Painless
• Common causes of vision loss are:
• Corneal opacities, cataracts, and myopia

Painless White Eye

• Cataracts are the primary focus for the causes of a painless eye
• Other common causes of cataracts
• Age related
• Congenital
• Secondary (diabetes, glaucoma, steroids, etc
• Traumatic
• Cataracts can cause symptoms such as:
• Blurred or hazy vision
• Glare
• Halos
• Cataracts can be classified by:
• Nuclear
• Cortical
• Subscapular
• Cataracts can be treated with phacoemulsification

Examination of the eye

• The eye is accessible to examination to identify abnormalities
• Assess systemic diseases
• Testing includes
• Ocular history combined with Opthalmologic examination
• Key aspects of the examination include:
• Visual Function - Central vision, visual acuity, peripheral vision, visual fields
• Non-Visual Function - Binocular alignment and extraocular movements
• Evaluation of Anatomical structures:
• Eyelids
• Pupils
• Ocular motility
• Anterior segment
• Intraocular preassure
• Fundus