Ophthalmology is a clinical medical discipline that studies the diagnosis and treatment of diseases of the visual system, covering common conditions such as cataracts, glaucoma, and diabetic retinopathy, and involving techniques like refractive correction, corneal transplantation, and laser therapy. The visual system includes structures such as the eyeball, cornea, lens, and retina, while the accessory organs include the eyelids, conjunctiva, and lacrimal apparatus. The main subspecialties cover areas such as corneal diseases, vitreoretinal diseases, and neuro-ophthalmology.