**Core Concept**
Topical beta blockers, such as timolol and betaxolol, are used to reduce intraocular pressure in glaucoma patients. However, they can also cause systemic side effects due to absorption through the ocular tissue.

**Why the Correct Answer is Right**
The correct answer is related to the systemic absorption of topical beta blockers, which can lead to various complications. Beta blockers can cause bronchoconstriction in individuals with asthma or chronic obstructive pulmonary disease (COPD) due to unopposed alpha-1 receptor stimulation. This is because in the lungs, the beta-2 receptors are predominantly responsible for bronchodilation, while the alpha-1 receptors cause bronchoconstriction.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a contraindication of topical beta blockers. In fact, diabetes is a common indication for glaucoma treatment, and topical beta blockers are often used in diabetic patients.
**Option B:** This option is incorrect because topical beta blockers do not significantly affect blood glucose levels. However, systemic beta blockers can have a paradoxical effect on glucose metabolism, but this is not a contraindication for topical use.
**Option C:** This option is not a contraindication for topical beta blockers. In fact, topical beta blockers can be used in patients with a history of heart failure, but with caution and under close monitoring.

**Clinical Pearl / High-Yield Fact**
It is essential to note that patients with a history of asthma or COPD should be warned about the potential risk of bronchoconstriction with topical beta blockers. A thorough medical history and pulmonary function tests (PFTs) should be performed before initiating topical beta blocker therapy.

**Correct Answer: D. Asthma/COPD.