While doing your rounds, you meet a 4 day old newborn girl, named Caitlyn, who is brought to the emergency department due to redness and swelling of the eyes. Physical examination shows bilateral eye erythema and purulent discharge. The infant was born at home to a mother who received no prenatal care and is unable to provide any medical history. Some days later, 41-year-old Joshua comes to the ophthalmology clinic complaining of black spots and blurry vision that started about two weeks ago. He mentions that the spots go away when he closes his left eye. On examination, visual acuity is 20/100 in the right eye and 20/20 in the left. Fundus examination is pictured. His medical history includes a diagnosis of HIV infection 8 years ago.
Based on the initial presentation, both Caitlyn and Joshua have some form of inflammatory, infectious or traumatic eye condition. But first, a bit of physiology real quick. If we zoom into the wall of the eye, it is made up of three major layers. There’s a fibrous outer layer that contains the cornea and sclera. The outer surface of the sclera is covered by a mucous membrane, called conjunctiva, which also lines the inside of the eyelids. The middle vascular layer is called uvea and consists of the iris, pupil, choroid, and ciliary body. Finally, the neural layer consists of the retina which helps convert light into neural signals that travel via the optic nerve to the brain for visual processing.
Okay, let’s start with stye, also known as hordeolum, which is a common bacterial infection of the sebaceous glands of the eyelids. For your exams, remember that the most common pathogen is Staphylococcus aureus. Styes present as painful, red, pus-filled lumps and are usually located at the lid margin, in which case they are known as external styes, or under the conjunctival side of the eyelid, also called internal styes. For your exams, keep in mind that for unknown reasons, styes tend to be more common in individuals with acne vulgaris and diabetes mellitus. Diagnosis is clinical and treatment usually involves warm compresses, massage and topical antibiotics, usually dicloxacillin.
Now, it’s important to differentiate a stye from a chalazion. A chalazion results from the obstruction of sebaceous glands of the eyelids, without any infection. It presents as a slow-growing, painless, rubbery nodule, usually in the middle of the eyelid. Diagnosis is clinical and no treatment is necessary, since it's usually self-resolving.
Next is conjunctivitis, which is inflammation of the conjunctiva. For your exams, remember that there are two main types of conjunctivitis, infectious and non-infectious. Infectious conjunctivitis can be further divided into viral and bacterial conjunctivitis. Viral conjunctivitis is the most common one and is typically caused by adenovirus but can be also due to herpes simplex virus or varicella-zoster virus. Bacterial conjunctivitis can be gonococcal, which is caused by Neisseria gonorrhoeae, or chlamydial, which is caused by Chlamydia trachomatis. For your test, remember that gonococcal conjunctivitis tends to be more severe and might be accompanied by various complications. That's because gonococci can penetrate further into the cornea, causing corneal edema, ulceration or even scarring and perforation. In some cases, gonococci could get even deeper and involve the interior of the eye, causing endophthalmitis, or make it into the systemic circulation and spread throughout the body. Now, non-infectious conjunctivitis includes allergic conjunctivitis, which is usually caused by airborne allergens, like pollen, and nonallergic conjunctivitis, caused by chemical or mechanical irritation of the conjunctiva. A high-yield fact is that in newborns, chemical conjunctivitis is most often caused by the use of ophthalmic silver nitrate for prophylaxis against ocular gonococcal infection.