Hereditary retinal dystrophies

Several lenses, generally positive (converging), assembled on glasses, specially designed to be used at less than 25 cm away in distance. They are not good for seeing far away. They increase the size of the object because they allow to see it clearly when getting very close to it. Binocular vision is not possible with them when they have more than 3 magnifications. They have the advantage of leaving the hands free and they have a larger visual field than magnifying glasses. They are either monofocal or bifocal. The drawbacks are that working distance is very short and fatigue occurs.