These have an array of small holes through black screens that replace the lenses in a pair of glasses. By reading with the aid of Trayner Glasses for fifteen minutes or so every day, the ciliary muscle is exercised and grows stronger. Vision is clearer while using Trayner Glasses because the ciliary muscle and lens are focusing beyond their habitual range. The unaided vision improves gradually over a few weeks as the muscle gets stronger with the extra use. The Anatomy of Focusing Myopia, or short sight, is the condition where the range of focus of the eye is shortened, making it unable to bring distant objects into focus.
Some people are genetically more predisposed to myopia than others.
Having two short-sighted parents will give a strong risk of developing myopia. The way an individual uses their eyes, as well as their genes, will determine how, or even if, they will become myopic. While the eye grows, hormones control the growth of the rear part of the eye. These growth hormones are released in response to the degree of blur experienced when viewing a distant object. If the distance is too sharp then the eye deems itself too long sighted and growth is increased, lengthening the eye and shortening the sight.