The eye and human visual perception Andrew D. Cummins

Overview Structure and function of the eye Image processing and signal pathways Medical concerns and current research Questions

Q: What is an eye? A: A transducer, a device that converts energy from one form to another. In detail, the eye converts light (electromagnetic) energy into electrochemical energy. Light is transformed into electrical signals that can be interpreted by the brain.

Structure of the eye Source: U. Rochester

Main structures Cornea – first “lens” of the eye – provides majority of the eyes focusing power due to a high optical refraction index at the air/water interface (~n = 1.4). Iris – membrane controlled by muscles that determine the amount of light entering the eye. Lens – provides fine accommodate between near-field (0-3m) and far field (>3m). Ciliary body – composed of a muscle and connective tissues which control the focus of the eye’s lens. Retina – main optical imaging system – composed of photosensitive cells (rods and cones) responsible for light transduction. Sclera – white protective tissue surrounding the eye. Optic Nerve – connects neural retinal tissue to brain pathways.

Function of the eye Focusing light from the outside world, the eye creates an image in much the same way as a digital camera. The anterior (frontal) portion of the eye supports this light gathering function, while the posterior (rear) portion in (especially the retina) turns the light into electrochemical signals sent to the brain. We can therefore separate the eye itself into two main subunits: optics and transducers. Optics: Focusing elements such as the cornea and lens that manipulate light. Transducers: Cells within the retina (rods and cones) that convert harvested light into signals that the brain can interpret.

From eye to brain

The eyes, gateway to the soul, a biological wonder, and a source of infinite inspiration. …However, they are only a small part of how we see. Caeci sunt oculi, cum animus alias res agit. The eyes are blind when the mind is otherwise occupied. -Publilius Syrus

Source: ufl.edu

Overview of visual pathways in the brain Optic nerve Optic radiations (nervous tissue) Optic chiasm some of the afferent interneurons “cross over at this point” Visual cortex of the occipital lobe (back of brain) Lateral geniculate nucleus of the thalamus

Current research The eye is a sensitive organ that is crucial for human perception. A great deal of research is now melding the fields of physical optics to biomedicine. Example: Using lasers to correct corneal defects. This procedure is now commonplace (LASIK, PRK, etc.), but started with research into corneal injury – especially burns.

Current research Corneal thermal Lesions – usually untreatable, but modern research has shown insights into corneal stem cells that might lead to new therapies Source: A. Cummins

Questions ?