Final answer:
An older adult client with diabetes mellitus reporting a gradual loss of peripheral vision is likely experiencing open-angle glaucoma, a condition where increased intraocular pressure causes optic nerve damage leading to peripheral vision loss.
Step-by-step explanation:
The correct answer to the student's question is b. Open-angle glaucoma. A gradual loss of peripheral vision is a characteristic manifestation of open-angle glaucoma, which is a common eye condition particularly among older adults. In open-angle glaucoma, increased intraocular pressure can lead to damage to the optic nerve, resulting in the progressive loss of peripheral vision, often without other noticeable symptoms until significant vision loss has occurred.
While age-related macular degeneration (AMD) is a major cause of blindness and involves the death of cells in the macula leading to a loss of central vision, it does not primarily affect peripheral vision. This contrasts with open-angle glaucoma, where the primary issue is with peripheral visual fields. It's important to note that diabetes can exacerbate the risk of various eye conditions, including both glaucoma and macular degeneration, due to the potential for damage to small blood vessels within the eye.