Eye Anatomy, Visual Assessment, and Common Eye Disorders

Eye findings become easier to interpret when the structure explains the symptom. The cornea is the transparent front surface and supplies much of the eye’s refractive power. Because it is densely innervated, a corneal abrasion or keratitis can cause intense pain, tearing, and photophobia. The lens fine-tunes focus by changing shape; clouding of the lens produces a cataract and gradually reduces clarity and contrast. The iris controls the pupil. The ciliary muscle changes lens shape for near vision, while the ciliary processes produce aqueous humour. Aqueous flows from the posterior chamber through the pupil into the anterior chamber, then drains mainly through the trabecular meshwork and Schlemm canal, with additional uveoscleral outflow. If drainage is obstructed, intra-ocular pressure (IOP) rises. In angle-closure glaucoma, the iris moves forward and blocks the drainage angle rapidly; in primary open-angle glaucoma, the angle remains anatomically open but outflow resistance increases over time. The vitreous humour fills the large posterior cavity behind the lens. Age-related vitreous changes can create floaters, but a sudden shower of floaters with flashes may indicate traction on the retina. The...