I am currently writing an independent project investigating the teaching and learning of algebra for students with a visual impairment. I am struggling to find literature specifically about teaching mathematics to VI. Are there any relevant journals or authors that I'm missing?
I do not have any sources, but I do have some critical arguments on this topic that can produce insight into this and related problems in mathematics.
Rather than limiting ourselves to the blind, let us assume that we wish to teach math to someone who is unable to see or hear. The question "How do we teach math to someone who is unable to see or hear?" is surprisingly similar to the question "How do we communicate with people who are deaf blind?"
The reason these two questions are similar is because, as the old adage goes, math is a language. Math, as a human activity, is a way of using language according to certain rules. The first rules we introduce a student to, be they blind, deaf, deaf blind, or otherwise, are those of arithmetic.
Though there are arguments, and you can find many of them, which claim that geometry plays some fundamental role in elementary mathematics, there is nothing in our intuitive notions of geometry which reflect the formal rigor which is found in a mathematical study of geometry. Furthermore, the rigor which is the cornerstone of mathematics is found immediately in the most elementary arithmetic operation: addition.
The simplest arithmetical act of addition is addition by one, which is given the technical name "succession". The principle problem in teaching any student about math is to introduce them to the rules that must be followed in order to add one.
A tool which is surprisingly useful at introducing this rule to a student is the abacus (it is also one of the most efficient tools to use when introducing a positional numeral systems). Though, for the deaf blind some minor modifications significantly improve the learning experience. Rather than having an abacus whose beads are lose and easy moved by bumps or brushings of fingers, it is best to put a piece of felt underneath the frame of beads so that the beads are held firm by the felt, but can still be moved so as to operate the abacus.
The essential part of learning the rules of arithmetic is to recognize that a process each of whose steps might be something simple like "add one" can transform one configuration of beads into a surprisingly different configuration, and that all of these states can be understood as abbreviations for successive actions of "add one".
While we use geometric terms to describe the shapes of physical objects, these terms are rarely, if ever, used in a mathematical sense. Rather, they are introduced just as words like "fluffy" or "soft" are introduced: to communicate an informal similarity between observations of events.
The remaining complexities of mathematics are introduced alongside the introduction of ever more sophisticated communication techniques. Ultimately, there are often a large number of unique and nonuniform methods of communication that combine to give the deafblind the power to connect with others.
Here's an article/video that I found helpful as I teach math to a visually impaired student:
Best of luck to you and your students!
You can find articles and videos on teaching math to low vision and blind students from the Texas School for the Blind and Visually Impaired. https://www.tsbvi.edu/ In particular, you can find informative videos from Susan Osterhaus on that site. She is an instructor with 25+ years of teaching experience with blind and visually impaired students mostly in K-12.
The tsvi site also has manipulatives and other resources for sale.
Additionally the blindmath listserv has information - mostly on how to address reading math. The listserv is essentially a forum for math students (principally college level) and professionals to address different questions and issues.