Patient with open angle glaucoma with 7D of myopia, complains of blurring of vision on administration of pilocarpine. What is the reason for the blurring?
**Core Concept**
In patients with open-angle glaucoma and pre-existing myopia, the use of pilocarpine can lead to an increase in the depth of the anterior chamber due to the contraction of the ciliary muscles, resulting in a decrease in the vitreous volume and a subsequent increase in the curvature of the cornea. This can cause a myopic shift, leading to a change in the refractive error.
**Why the Correct Answer is Right**
The myopic shift caused by pilocarpine is due to the contraction of the ciliary muscles, which increases the curvature of the cornea and decreases the vitreous volume. This change in the refractive error can lead to a blurring of vision in patients with pre-existing myopia. The ciliary muscles are responsible for controlling the shape of the lens, and their contraction leads to an increase in the curvature of the cornea.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because pilocarpine does not cause an increase in intraocular pressure (IOP) in patients with open-angle glaucoma.
**Option B:** This option is incorrect because pilocarpine does not cause a decrease in the depth of the anterior chamber in patients with open-angle glaucoma.
**Option C:** This option is incorrect because pilocarpine does not cause a change in the refractive error due to a change in the shape of the lens in patients with open-angle glaucoma.
**Clinical Pearl / High-Yield Fact**
Pilocarpine can cause a myopic shift in patients with pre-existing myopia due to the contraction of the ciliary muscles, resulting in a decrease in the vitreous volume and an increase in the curvature of the cornea.
**Correct Answer:** D.