How do you tell the difference between bacterial and viral conjunctivitis?

The key differences are in the discharge type and associated findings. Bacterial conjunctivitis produces thick, purulent (yellow-green) discharge with eyelid crusting, while viral conjunctivitis has watery, clear discharge and is often accompanied by a tender preauricular lymph node and upper respiratory symptoms. Viral conjunctivitis is much more contagious and is typically caused by adenovirus.

What is the difference between a stye and a chalazion?

A stye (hordeolum) is an acute, painful, red infection of an eyelid gland, usually caused by staphylococcal bacteria. A chalazion is a chronic, painless, firm nodule that forms when a meibomian gland becomes blocked without active infection. Styes are treated with warm compresses and sometimes antibiotics. Chalazia that persist despite warm compresses may require incision and drainage.

What causes dry eye disease?

Dry eye has two main mechanisms: aqueous deficiency (the lacrimal gland produces insufficient tears) and evaporative dry eye (tears evaporate too quickly, often from meibomian gland dysfunction). Risk factors include aging, hormonal changes, certain medications (antihistamines, antidepressants), prolonged screen use, and autoimmune conditions like Sjogren's syndrome. Diagnosis uses Schirmer testing and tear break-up time.

Conjunctivitis and External Eye Disease: COA Exam Guide

Overview of External Eye Disease

External eye diseases affect the structures on and around the front of the eye, including the conjunctiva, eyelids, and tear film. These are among the most common conditions you will encounter in clinical practice. As a COA, you need to recognize their distinguishing features, understand basic management principles, and communicate findings accurately to the physician.

Types of Conjunctivitis

Conjunctivitis is inflammation of the conjunctiva, the thin transparent membrane covering the sclera and lining the inner eyelids. It is the most common cause of a "red eye" in outpatient settings.

Bacterial Conjunctivitis

Bacterial conjunctivitis typically presents with:

Thick, purulent (pus-like) discharge, often yellow or green
Crusting of eyelids, especially upon waking
Usually starts in one eye and may spread to the other
Eyelids may stick together in the morning

Common causative organisms include Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae. In neonates, Neisseria gonorrhoeae and Chlamydia trachomatis are important causes that require urgent treatment.

Viral Conjunctivitis

Viral conjunctivitis is the most common form overall and is highly contagious. Key features include:

Watery, clear discharge
Often associated with upper respiratory infection symptoms
Tender, palpable preauricular lymph node
Frequently begins in one eye, then involves the other within days

Adenovirus is the most common cause. Epidemic keratoconjunctivitis (EKC) is a severe adenoviral form that can produce subepithelial corneal infiltrates lasting weeks to months.

Prescribing antibiotic drops for viral conjunctivitis. Antibiotics do not treat viral infections and contribute to antibiotic resistance. Supportive care with artificial tears and cool compresses is the appropriate management for uncomplicated viral conjunctivitis.

Allergic Conjunctivitis

Allergic conjunctivitis is characterized by:

Itching as the primary and most distinctive symptom
Bilateral involvement (both eyes affected simultaneously)
Watery discharge with possible mucous strands
Chemosis (conjunctival edema/swelling)
Associated with hay fever, asthma, or eczema

Feature	Bacterial	Viral	Allergic
Discharge	Purulent, thick	Watery, clear	Watery, stringy mucus
Itching	Minimal	Minimal	Intense
Laterality	Often unilateral initially	Often unilateral initially	Bilateral
Lymph node	Usually absent	Preauricular present	Usually absent
Contagious	Moderate	Highly	No

Blepharitis

Blepharitis is chronic inflammation of the eyelid margins. Two main forms exist:

Anterior blepharitis: affects the lash base, often caused by staphylococcal bacteria or seborrheic dermatitis. Findings include collarettes (crusty debris around lash bases) and lid margin redness.
Posterior blepharitis (meibomian gland dysfunction): involves the oil-producing glands within the eyelid. Gland orifices appear capped or blocked, and expressed secretions are thick or granular rather than clear and oily.

Treatment centers on consistent lid hygiene: warm compresses to soften blockages, gentle lid scrubs, and sometimes antibiotic or anti-inflammatory drops or ointments.

Dry Eye Disease

Dry eye disease results from insufficient tear production or excessive tear evaporation. Patients report burning, foreign body sensation, and paradoxically, reflex tearing. Think of it like a windshield with poor wiper fluid. The surface gets scratchy and uncomfortable, and the wipers overcompensate with bursts of watery fluid that do not actually clean the surface properly.

Diagnostic tests include Schirmer testing (measures aqueous tear production) and tear break-up time (TBUT) (measures tear film stability). Treatment ranges from artificial tears for mild cases to punctal plugs and prescription drops like cyclosporine for moderate to severe disease.

Stye vs. Chalazion

The key distinction between a stye and chalazion is timing and tenderness. A stye is acute and painful; a chalazion is chronic and typically painless. When documenting, note the size, location (upper vs. lower lid, medial vs. lateral), and whether the lesion is tender to palpation.

Stye (hordeolum): acute, painful, red bump on the eyelid caused by bacterial infection of a lash follicle (external) or meibomian gland (internal). Treated with warm compresses and sometimes topical antibiotics.
Chalazion: chronic, usually painless, firm nodule in the eyelid from a blocked meibomian gland. If warm compresses do not resolve it within weeks, incision and curettage may be needed.

Key Takeaways

Bacterial conjunctivitis produces purulent discharge; viral is watery; allergic features intense itching
Viral conjunctivitis is highly contagious and often accompanied by a preauricular lymph node
Blepharitis is managed with lid hygiene: warm compresses and lid scrubs
Dry eye testing includes Schirmer test and tear break-up time
Styes are acute and painful; chalazia are chronic and painless
Proper infection control is essential when handling patients with suspected viral conjunctivitis