Is there a word for the opposite of magnify?

Question

Specifically to do with lenses / magnification, but making something appear smaller rather than larger.

Example:

If her glasses make her eyes look larger:

Her glasses magnify her eyes.

If her glasses make her eyes look smaller:

Her glasses ______ her eyes. (opposite of magnify)

Answer 1

You could use reduce.

You can magnify the size of an image

You can reduce the size of an image

By definition:

make smaller or less in amount, degree, or size

If you are looking something related to lenses use demagnify.

to reduce the size of (something, such as a photographic image or an electron beam)

You could say:

I am going to demagnify this

Or:

I am an expert in demagnification

Answer 2

I've seen this word used as the opposite of magnify, but it's been in specialist fields. That word is minify. However, dictionaries list this word. It seems to have come about analogously using magnify as a model:

2.(with object)
To reduce in actual size or amount; (now) especially to reduce the size of (an image).
From classical Latin min- + -ify, after magnify.
Oxford Living Dictionaries

To make smaller or less significant; reduce.
[min(imum) + (magn)ify.]
American Heritage Dictionary

(tr)
rare
to minimize or lessen the size or importance of (something)
from Latin minus less; for form, compare magnify
Collins Dictionary

1.to make less.
2.to minimize.
Latin min(us ) less + -ify, modeled on magnify
Random House Unabridged Dictionary (dictionary.com)

lessen
Merriam-Webster Dictionary

2.To reduce in apparent size, as for example objects viewed through a lens or mirror shaped so as to increase the field of view, such as a convex or aspheric mirror or a Fresnel lens.
Wiktionary

minification
redirected from minify
A reduction in the apparent size of an object. Example: viewing a distant object through the objective of a galilean telescope. Syn. negative magnification.
Dictionary of Optometry and Visual Science

Minification
Magnification, by a factor of less than one, producing a smaller image.
Wikipedia magnification disambiguation page

Quotes:

Contact lenses neither magnify nor minify the image because they are placed on your cornea.
Physics of the Human Body, 2007

The most common types are reverse telescopes ... which minify objects being viewed but present more information by means of the enlarged visual field.
Dictionary of Optometry and Visual Science, 2014

Figure 3.13b is a photograph taken through a 35-mm lens which minified the optic array by a factor of .70 ...
The Perception of Pictures: Alberti's window, the projective model of pictorial information, 1980.

Some lenses magnify, others make things smaller (minify). How much they magnify or minify can be calculated, but we have to know the actual numbers in your prescription(s)...
From a reddit forum post on optometry board

The lenses in your glasses can magnify or minify the look of your eyes. WHY?!
Facebook post from Adra Eye Care

It also comes up in thesauruses. However as you can see, it seems to be a term that's arisen after magnification to mean its opposite, and is probably not often used outside of specialist domains. In light of that, and since you don't seem to writing a technical or academic piece, you may want to use a more common English word.