Time should not be an overriding concern when testing due to the handwriting problem or use of a typewriter. Use of a resource period to complete work is an alternative. With eyesight problems, the student should be given extra time for reading, larger print where possible and in cases where work needs to be copied from a blackboard, a seat at the front of the classroom. Limitations of each individual will be different, but the one thing that can be said is that progressive deterioration is ongoing. The rate of deterioration will vary by individual.
Many students do.
However, when a student feels strongly about not participating, it is usually best not to force participation. If the student says they can't do an exercise or activity, that should be respected. This comes back to the most important consideration - the student's self esteem. Situations should be structured to have the student be a winner. Teachers must learn the student's physical abilities and look for alternatives.