**Core Concept:**
Macular edema and glaucoma are two ocular complications of diabetes mellitus that can lead to vision loss. Macular edema refers to the accumulation of fluid in the central part of the retina (macula), causing blurred vision. Glaucoma is a group of eye diseases characterized by elevated intraocular pressure, which can damage the optic nerve and lead to visual field loss. Insulin-dependent diabetes is a severe form of diabetes mellitus that requires daily insulin administration.

**Why the Correct Answer is Right:**
Among the given options, the least resort to treat both macular edema and glaucoma is option D, "IOP lowering agents (e.g., prostaglandin analogs)." These agents, such as latanoprost and travoprost, act as prostaglandin F2alpha analogs and lower intraocular pressure by increasing the outflow of aqueous humor from the eye. This is crucial in managing glaucoma, as elevated intraocular pressure is a major risk factor for optic nerve damage in glaucoma patients.

**Why Each Wrong Option is Incorrect:**

A. "Topical corticosteroids": These drugs have anti-inflammatory and immunosuppressive effects but are not specifically indicated for lowering intraocular pressure in glaucoma patients. They can lead to increased intraocular pressure and exacerbate the condition.

B. "Topical beta-blockers": These drugs (e.g., timolol) are primarily used to lower intraocular pressure in glaucoma patients, not for macular edema treatment.

C. "Topical alpha-agonists": Alpha-agonists (e.g., epinephrine) are used to increase intraocular pressure, which is counterproductive in the context of treating both macular edema and glaucoma.

**Clinical Pearl:**

Topical prostaglandin analogs are the least harmful choice among the given options to treat both macular edema and glaucoma. They possess the advantage of having fewer systemic side effects compared to corticosteroids and can be used in patients with diabetes and macular edema.