The earliest change in glaucoma is:
**Core Concept**
In glaucoma, the earliest change occurs due to an increase in intraocular pressure (IOP) that damages the optic nerve, leading to progressive vision loss. The pathophysiology involves the trabecular meshwork, where aqueous humor drainage is impaired.
**Why the Correct Answer is Right**
The earliest change in glaucoma is the loss of retinal nerve fiber layer (RNFL) thickness, as measured by optical coherence tomography (OCT). This occurs due to the increased IOP, which causes mechanical stress and damage to the axons of the retinal ganglion cells. The damage to the RNFL is a direct result of the impaired aqueous humor drainage through the trabecular meshwork.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not specified, but it is likely referring to another aspect of glaucoma.
* **Option B:** This is incorrect because the earliest change in glaucoma is not the loss of visual field, but rather the loss of RNFL thickness.
* **Option C:** This is incorrect because the earliest change in glaucoma is not the optic disc cupping, but rather the loss of RNFL thickness.
**Clinical Pearl / High-Yield Fact**
The earliest change in glaucoma can be subtle, but it is essential to detect and manage the condition early to prevent irreversible vision loss. RNFL thickness measurements by OCT are a critical tool in detecting glaucoma and monitoring treatment efficacy.
**Correct Answer: B. Loss of retinal nerve fiber layer (RNFL) thickness.**