The human eye is nature's version of a camera, yet so much more complex than a camera that all its functions require years of study to understand. For example, within the layers of the retina immediately behind the lens, light impulses are converted into electrical signals which proceed through the optic nerve to the occipital cortex at the back of the brain, where they are “translated”.



Healthy eyes see in 20/20 vision. That is, standing 20 feet away from an eye chart – a series of symbols, or images, printed on a page – people with 20/20 vision can see everything a “normal” eye can see, normal being based on the average visual acuity of a majority of the population.

But the human eye is far from perfect. Defects in the shape of the lens, or inadequate filling of the vitreous humor, can result in inadequate vision. Age and disease also play their part in reducing human vision. Thus, perfect vision at birth may require correction as early as grade school, and will almost certainly require correction by the age of retirement.

Ophthalmologists, or eye doctors, can help patients understand the need for corrective lenses or surgery by using an Eye Anatomy Poster, whose central figure is a cut-away view of the right eye which depicts everything from the rods and cones (specialized structures in the eye the retina uses to process light) to more esoteric items like the canal of Schlemm – or scleral venous sinus, a circular channel that collects fluid from the anterior chamber and sends it to the bloodstream.

With its diagram of the visible light spectrum, and a dissection of the structures of the eyeball, this detailed chart makes it easier to see how the sight of a flower, for example, passes through the retina to the optic nerve and is interpreted by the brain for our enjoyment, edification and understanding.

Additional discussions include the visual field – that all-inclusive area in front of the eye as well as at the extreme periphery – and accommodation, the process by which the parts of the eye increase optical power to maintain a clear image, also called focus.

This accommodation declines with age, so that by roughly age 50 the human eye becomes presbyopic, or unable to focus on objects close to the eye. Other age-related problems include macular degeneration, or AMD, cataracts and glaucoma, caused by a buildup of pressure in the vitreous humor as a result of failure of the scleral venous sinus.

The Glaucoma Disease Education Poster is a superb teaching tool for eye doctors, enabling patient understanding of the exact mechanisms involved in glaucoma and the progressive effects of vision loss over time. The chart also offers diagnosis and treatment options.

Though glaucoma treatment is difficult, current protocols call for lowering pressure either via eyedrops or surgery. Surgeons now know that reducing the pressure of the vitreous humor by 30 percent is successful in retarding loss of vision, even in patients with a type of glaucoma where the eye pressure remains normal (normal-tension glaucoma). This – reducing pressure – is currently the primary goal of any therapy.