He has already aged out of ECI services, but let the district know you are aware of the federal Child Find program and ask about services through that. You'll probably need to learn the educational diagnostic codes for your child's condition, because without that label, I'm afraid you won't get squat. If the school's evaluation won't get him the services you feel he needs to be successful, the school is obligated to provide and IEE, which is an independent evaluation funded by the school. This is federal law, and make sure you let them know you are aware of it. When they say "This cannot happen" be sure to ask them to show you where that is state in the IDEA (Individuals with Disabilities Education Act). Texas has a reputation for ignoring those pesky federal laws, particularly when it comes to schools.
Silly, aren't we? Assuming the schools are out for our child's best interest and have a shred of common sense in them?
Also, read this website so you know your child's rights: http://www.wrightslaw.org
And get on local listservs with other parents dealing with similar vision impairments. You'll learn a lot from other parents.
If you don't get what he needs, please invite your state representative to join you at any meetings with the school. It's amazing how the presence of a reporter, lawyer or legislator at an ARD meeting can change things, and your child may have all sorts of great services heaped on him at least for a while.