Diseases of the eye and adnexa

This chapter covers disorders affecting the eye and its accessory structures (eyelids, lacrimal glands, conjunctiva, retina, optic nerve, etc.). Conditions range from relatively mild and common problems like conjunctivitis and refractive errors to chronic, vision-threatening diseases such as glaucoma, cataracts, diabetic retinopathy, and age-related macular degeneration.
The codes are anatomically organized, beginning with eyelid disorders and moving inward to deeper structures of the eye. Many conditions specify laterality (right eye, left eye, bilateral), which is essential in ophthalmology. Severity and stage are often captured — for example, different types and stages of glaucoma.
This chapter excludes traumatic injuries to the eye (which fall under the injury chapter S00-T88) and systemic diseases affecting vision when the systemic condition is primary. Accurate coding in this chapter is critical for surgical planning (e.g., cataract extraction), chronic disease monitoring, and visual disability documentation. Because vision directly impacts quality of life, early diagnosis and classification of eye diseases play an important preventive role in healthcare systems.