Final answer:
Decreased vision and eye pain in an adult is considered an ophthalmic emergency as it could indicate conditions like acute glaucoma or sever infectious keratitis, which require immediate attention to avoid serious outcomes such as blindness. The other options relate to non-emergent conditions such as eyestrain, allergies, and minor irritations.
Step-by-step explanation:
The ophthalmic emergency in question is option a. Decreased vision and eye pain in an adult. This symptom could signal acute glaucoma, retinal detachment, or sever infectious keratitis, all of which require immediate medical attention to prevent serious complications, including blindness. On the other hand, options b, c, and d describe symptoms more consistent with common, non-emergent issues such as refractive errors, allergies, and minor irritation from external elements respectively.
Inflammation of the conjunctiva, particularly with purulent discharge, indicates conjunctivitis, which can be caused by various agents, including bacteria or viruses. While it can be highly uncomfortable, it is not typically an emergency unless accompanied by other, more severe symptoms. Keratitis, the inflammation of the cornea, can lead to scarring and even perforation, which may result in blindness if not treated promptly and is often considered emergent. Viral conjunctivitis may present with itchy, watery eyes, but is often associated with an upper respiratory infection and is less acute.
Common vision problems such as farsightedness (hyperopia), which causes difficulty in maintaining a clear focus on near objects and may lead to eye strain, are not emergencies. Presbyopia, which is a gradually developing inability to focus on close objects typically occurring in middle age, causes many over 55 to need reading glasses due to the lens of the eye losing its elasticity, not because of changes in the cornea, eyeball length, or retinal thickness.