Macrotextures (as defined in Ars Magica sourcebook HoH:S p64) allow species to be manipulated to interact with the sensory organs in different ways, and allows for correcting vision impairment. That said I haven’t seen a spell to do so yet, and can imagine that it would be common enough once ageing starts to irrevocably alter the Magi of the Order. Interesting that eyeglasses are a period feature in some regions, and there is a quite famous Book of Optics written in the mid 11th century.
A reasonable goal is to design a spell which can be used all the time in an item and avoid warping the target, perhaps through a low level effect and enchanting into a familiar bond.
Eyes of the Exuberant Youth
Rego Imagonem 4, R: Personal, D: Concentration, T: Individual
This spell alters the visual species which will strike the caster’s eyes so that they are adjusted to correct for any visual impairment apart from blindness. The effect might have to be tuned when first cast to maximize clarity and assign the correct focus.
(Base 3, +1 Concentration)
If placed into a familiar bond or a tailored magical device there should be a selection made for many uses, or for constant effect (YSMV).
When created as an item:
Eyeglasses for the Wizened Sage – sturdy silver set of eyeglasses set with clear crystal lenses. The glasses are enchanted with the the Eyes of Exuberant Youth above. The user can refocus and change the style and mixture of macrotexture by concentrating, so that the eyeglasses might be handed down between Magi.
Effect mods = Final effect level Rego Imagonem 17 – Device is constant, as it is designed with a Sun duration (+1 mag more), uses an environmental trigger (+3), two uses per day (+4), and targets the species at the wearer’s eyes. The effect is designed at Range Touch (+1 mag more) so it can affect the species travelling through the lenses of the glasses.