Red Eye and its differential diagnosis

Explanation:

Red eyes can be due to either Conjunctivitis, or Corneal injury or intraocular (iris) pathology. Iritis is seen as a Hypopyon, Corneal abrasion is a FB sensation in the eye and conjunctivitis is either painful or itchy.

Iris pathology is elicited best by shining light on the unaffected eye and seeing the patient get discomfort in the affected eye. This is due to consensual reflex constricting not only the eye where light is shone but also the other eye where the irritated iris is now forced to constrict. Also in pathology of the iris, the redness has a clear margin around the cornea where there is no redness (clear limbus). The red vessels cannot be moved over the sclera because they are deep vessels.Also note that in anterior uveitis/iritis, the patient has pain in th eaffected eye even when light is shone in the non affected eye. This is due to consensual reflex (response due to light in the other eye) One can also see a hypopyon ( a hazy settlement of pus cells (leukocytes in the anterior chamber - settled down due to gravity)

On the other hand the redness in conjunctivitis lacks this clear margin and also the vessels are superficial and can be moved over the sclera