Soccer cleat sizes do not indicate widths, and this can make it difficult to obtain a good fit. Since many medium width cleats will run either wide or narrow, you can use a side-by-side comparison to identify volume differences among different pairs of shoes.
The two pairs of cleats pictured illustrate a narrow lasted cleat, the Adidas Predator Absolion TRX TF, on the left of each photo, and a wide lasted cleat, the Nike Mercurial Victory II, on the right of each photo. The differences in width are highlighted.
Comparing the uppers, notice how the throatline (opening) of the Nike is so much wider than the Adidas. Also notice the difference in toebox shape and width. The Adidas is more tapered around the toes and the Nike is more rounded, accommodating a wider forefoot.
In evaluating the lower, you can also see how much wider the forefoot and waist are in the Nike than the Adidas.
If your patients are having difficulty finding the perfect fit, showing them this method should help. These principles also apply to other shoes (tennis, basketball, football, etc.) that only come in medium widths.