How is intraocular pressure (IOP) defined?

Intraocular pressure (IOP) is defined as the fluid pressure inside the eye. This pressure is primarily determined by the balance between the production and drainage of aqueous humor, the clear fluid that fills the front part of the eye. Maintaining optimal IOP is crucial for the health of the eye, as it helps to preserve the shape of the eye and ensures proper functioning of various eye structures.

When the pressure is too high, it can lead to conditions such as glaucoma, which can cause damage to the optic nerve and result in vision loss. Conversely, if the pressure is too low, it may indicate other eye health issues. Understanding IOP is essential for eye care professionals in diagnosing and managing ocular conditions.

The other options do not accurately represent the definition of IOP, as they pertain to different aspects of ocular anatomy or function, such as muscle pressure, light resistance, or lens focus, which are unrelated to the measurement of pressure within the eye itself.