Of course you should wear a pair of sunglasses in summer. The UV rays in summer are especially intense than that in other seasons. Our pupil will dilate to let in more light when we are in a darker situation and will narrow when we are in a brighter situation to limit the light that enters our eyes. This is the natural protection of our eyes. But wear a pair of sunglasses will not prevent this natural protection.
I think they will not prevent the natural protection. Our eyes are flexible in this part. Our eyes have to work for us for the rest of our life. If this can prevent the pupils from dilating or narrowing to prevent our eyes, what can they do to react to other serious changes? The muscles in our eyes control the pupil to dilate and narrow according to the environment. If the muscles weren't damaged by sunglasses, they still can do this for us at any time. So you really don't need to worry about this.
Sweetie, harsh sunlight, UV rays and glare are harmful to our eyes. We may get some kinds of eye diseases such as cataract, macular degeneration and etc. in our later lives. We often wear sunglasses when we are in the outside. We will take off sunglasses when we enter the house. Usually we will stay at most 4-5 hours in the outside one day. So we just wear sunglasses for at most 5 hours a day. This will not prevent the natural protection of our eyes. So don't worry about that.