Martin is in search of proof, proof that his mother lied to him, that the things he cannot see are there as he imagines them to be. He needs photographs described to him because he thinks what you see is the truth. He believes that seeing is believing and that sighted people are never misled. Martin is immature; he sees the world in black and white as being wrong or right. He is still the 10-year-old child who mistrusted his mother and the world around him. He has not let go of the belief that his mother lied to him; he still lives in the same time zone, looking for proof.
Proof is black and white; in reality there are greys. You cannot have proof with people. For example, you can have proof in science and maths; you can prove how a maths equation works and how you get the answer and it has been proven that water consists of hydrogen and oxygen but it is not so easy to prove if a person is lying or not. People do not behave consistently, we are not predictable. You cannot predict what a person will do as we are all very different. .
The basis of friendship and love is trust. Without trust you cannot have a truly loving relationship or a close supportive friendship. When a person doesn't trust anyone they isolate themselves, becoming very angry and self obsessed. That is exactly how Martin is at the start of the movie. However, he does change when he meets Andy because he begins to trust him. Andy becomes the first person Martin ever trusts enough to enable a friendship to start to grow. He had trusted the vet to care for Bill but he had never allowed himself to relax enough or trust the vet enough to allow the seeds to grow. .
Martin trusts Andy when he describes their surroundings and the movie. They share a laugh, which from what we have seen is the first time Martin actually is happy. It is obvious that he enjoys Andy's company, he lies to protect Andy, and he relishes their shared moments.