Final answer:
The next step for the nurse practitioner is to refer the client for immediate evaluation by an ophthalmologist.
Step-by-step explanation:
The next step for the nurse practitioner is to refer the client for immediate evaluation by an ophthalmologist. The client's symptoms, including a gritty feeling in the eyes, diminished visual acuity, changes in color vision, and a feeling of pressure behind the eyes, indicate a potential eye problem. An ophthalmologist specializes in diagnosing and treating eye conditions, and they will be able to perform a thorough examination and provide appropriate treatment or referral.