Thank you again.
There are two main statutory protections for employees who miss work for medical reasons. The first is the Family Medical Leave Act, which permits qualifying employees to take up to 12 weeks of protected leave for "serious health conditions." However, the FMLA only applies to employers with 50 employees or more, so it would not apply to your husband's employer and he would not be eligible for protection under this law.
The second potential protection is the Americans With Disabilities Act, which requires employers to "reasonably accommodate" employees with disabilities, which in some cases can mean allowing a disabled employee to take time off work to deal with their medical condition. The problem here is that your husband does not appear to have missed work due to a medical "disability."
Unfortunately, this means that there may be no legal protection for an individual in your husband's circumstance. It would be tremendously unfair to let him go because he missed work for a medical reason, but the law does not prohibit employers from being unfair. A cause of action for wrongful termination only arises if an actual law is broken, and unless the FMLA applies or the employee has a disability, no law is broken if an employee is terminated for seeking medical treatment, as crazy as that sounds.
Perhaps your husband can at least argue that his most recent absence was for an eye condition that rises to the level of a disability (a medical condition which "significantly impairs a major life function") and that he is entitled to reasonable accommodations under the ADA. If he puts this in writing to his employer, that will certainly give them some pause before letting him go, simply because they know they will likely need to deal with litigation. That would really be the only option here. It's imperfect, but unless it can be argued that your husband missed work for a disability he has no protection under the law.
If I can clarify anything at all for you, please do not hesitate to ask. It is my pleasure to assist you further if necessary....