Actually, there's some evidence that THC and other cannabinoids has a protective effect in the case of retinal diseases, and it's also been used as a treatment for glaucoma. While these results aren't proven beyond a shadow of a doubt, the evidence is that they're not only neutral for certain eye diseases, but beneficial. Now, if you had diabetic retinopathy, I'm not sure I would recommend continuing to smoke, but as you are and given the current state of the evidence, I think you're fine to continue.

Note, however, that I am a random person on Reddit and NOT A DOCTOR!

In any case, while I would not recommend taking drugs, if you're going to take them anyway a vapouriser may make it less harmful.

I'm total and I also smoke at least once a week, sometimes more. Someone earlier in the thread laid out the medical benefits. It helps to use a vaporizer. Even if where you live doesn't allow cannabis you can still order a vaporizer from a lot of online retailers. I suggest r/PuffItUp.