Eye Anatomy: Conjunctiva Structure and Function

Anatomy

• The conjunctiva is a thin mucous membrane covering the surface of the eye.
• The parts of the conjunctiva include:
  • Palpebral conjunctiva, which lines the eyelids
  • Bulbar conjunctiva, which covers the eyeball
  • The fornix, which is the fold where the palpebral and bulbar conjunctiva meet

Histology

• The conjunctiva consists of stratified squamous and columnar epithelium.
• This epithelium is non-keratinized.
• Goblet cells are present.

Bulbar Conjunctiva

• The bulbar conjunctiva is freely movable over the sclera, except close to the cornea.

Blood Supply

• The palpebral conjunctiva's blood supply comes from marginal and peripheral arcades, originating from the medial and lateral palpebral arteries.
• The bulbar conjunctiva's blood supply comes from the anterior and posterior conjunctival arteries.

Lymphatic Drainage

• The medial one-third of the superior conjunctiva and the medial two-thirds of the inferior conjunctiva drain into the submandibular nodes.
• The lateral two-thirds of the superior conjunctiva and the lateral one-third of the inferior conjunctiva drain into the pre-auricular nodes.

Nerve Supply

• The ophthalmic division and branches of the maxillary division of the fifth cranial nerve provide the nerve supply.

Functions

• Functions of the conjunctiva include:
  • Tear production
  • Supplying oxygen to the cornea
  • Defense mechanisms such as and intact epithelial barrier, lacrimation, a rich blood supply, mucin clumping, and immunologic mechanisms like mast cells, leucocytes & IgA

Microbiology

• The conjunctiva is never free from organisms.
• Factors that prevent bacterial propagation include: relatively low temperature, evaporation of lacrimal fluid, moderate blood supply, and tears not being a good culture medium.
• Bandaging the eye raises the temperature and arrests the movement of eyelids, which can increase the bacterial content.
• Normal flora on the conjunctiva includes: Staph. epidermidis, diphtheroids, P. acne, N. catarrhalis and C.xerosis.
• Viruses that can be found include: herpes virus and adenovirus.

Clinical Features of Diseases

• Redness and stickiness are clinical features.
• A foreign body sensation and lacrimation can occur.
• Occasionally photophobia can occur.
• Vision is generally normal.

Environmental Causes of Red Eyes

• Exposure to airborne allergens, air pollution, smoke, dry air, dust, airborne fumes, chemical exposure (chlorine), and overexposure to sunlight (without UV-blocking sunglasses) can cause red eyes.
• Red eyes occur when blood vessels on the surface of the eye expand.

Causes of Red Eyes

• Common eye conditions that cause red eyes include: dry eyes, eye allergies, pink eye (conjunctivitis), contact lens wear, and digital eye strain.
• Serious eye conditions that can cause red eyes include: eye infections, eye trauma or injury, recent eye surgery (LASIK, cosmetic eye surgery, etc.), uveitis, acute glaucoma, and corneal ulcer.

Causes of Red Eye

• Conjunctiva related causes include: conjunctivitis, dry eye, pterygium, subconjunctival haemorrhage, and trauma.
• Cornea related causes include abrasion, foreign body, laceration, corneal ulcer, keratitis, and contact lens wear.
• Sclera related causes include episcleritis and scleritis.
• Iris and ciliary body related causes include iritis and iridocyclitis.
• Anterior chamber related causes include hyphema and acute angle closure glaucoma.
• Eyelid related causes include triachiasis, entropion and ectropion.
• Orbit related causes include orbital cellulitis and acute dacryocystitis.

Conjunctivitis

• Conjunctivitis is the inflammation of the conjunctiva characterized by redness and discharge.
• The etiology of conjunctivitis can be divided into infective and non-infective causes.
• Infective causes include:
  • Viral: Adenovirus, measles, varicella, HSV,HZ
  • Chlamydial: Trachoma, inclusion conjunctivitis
  • Bacterial: Staph, Strept, gonococcus, T.B, syphilis, Leprosy
  • Fungi: Candida
• Non-infective causes include:
  • Allergic: seasonal, perineal, vernal/ spring catarrah, atopic
  • Chemical: acids, alkalis
  • Miscellaneous: Keratoconjunctivitis sicca, ocular pemphigus, caterpillar hair

Viral Infections of Conjunctiva

• Adenovirus conjunctivitis
• Herpes simplex keratoconjunctivitis
• Herpes zoster conjunctivitis
• Molluscum contagiosum conjunctivitis
• Poxvirus conjunctivitis
• Myxovirus conjunctivitis
• Parammyxovirus conjunctivitis
• ARBOR virus conjunctivitis

Adenoviral Conjunctivitis

• Adenoviruses are the most common causes of viral conjunctivitis.
• They are non-enveloped, double-stranded DNA viruses that replicate within the nucleus of host cells.
• Humans are the general reservoir.
• Types of adenoviral conjunctivitis include:
  • Epidemic keratoconjunctivitis (EKC)
  • Nonspecific acute follicular conjunctivitis
  • Pharyngoconjunctival fever (PCF)
  • Chronic relapsing adenoviral conjunctivitis, which is a hypersensitivity reaction

Epidemic Keratoconjunctivitis (EKC)

• It is a type of acute follicular conjunctivitis mostly associated with superficial punctate keratitis and usually occurs in epidemics.
• It is caused by adenoviruses type 8 & 19 and is markedly contagious.
• The incubation period after infection is 8 days.
• The virus is shed from the inflamed eye for 2-3 weeks.
• Symptoms include: redness of sudden onset, profuse watering with mild mucoid discharge, ocular discomfort and foreign body sensation, and (mild) photophobia that becomes marked when the cornea is involved.
• Signs and Symptoms include:
  • Hyperaemia prominent
  • Chemosis
  • Follicles (lower fornix & palpebral conjunctiva)
  • Papillary reaction
  • Petechial subconjunctival hemorrhages (severe adenoviral conjunctivitis).
  • Pseudomembrane lining (lower fornix & palpebral conjunctiva)
• Corneal epithelial microcystic diffuse fine non-staining lesions
• Superficial punctate keratitis (SPK)

Nonspecific Acute Follicular Conjunctivitis

• It is the most common form of acute follicular conjunctivitis.
• It is caused by adenovirus serotypes 1 to 11 & 19.
• It is a milder form of acute follicular conjunctivitis.
• Treatment is similar to EKC.

Pharyngoconjunctival Fever (PCF)

• It is an adenoviral infection commonly associated with subtypes 3 & and 7, but serotypes 2, 4 and 14 have also been documented.
• PCF primarily affects children and appears in epidemic form.
• Treatment is similar to EKC.
• Clinical features include: acute follicular conjunctivitis associated with pharyngitis, fever & pre-auricular lymphadenopathy, and superficial punctate keratitis in 30% of cases.

Acute Hemorrhagic Conjunctivitis

• It is characterized by multiple conjunctival hemorrhages, conjunctival hyperaemia & mild follicular hyperplasia.
• It is caused by Picornaviruses (enterovirus type 70).
• It is very contagious and transmitted by direct hand-to-eye contact.
• Incubation period lasts 1-2 days.
• Symptoms include: pain, redness, watering, mild photophobia, transient blur of vision, and lid swelling.
• Signs include: conjunctival congestion, chemosis, multiple hemorrhage in bulbar conjunctiva, mild follicular hyperplasia, lid edema, pre-auricular lymphadenopathy, and corneal sign: fine epithelial keratitis.

Treatment of Viral Conjunctivitis

• Supportive treatment for amelioration of symptoms is the only treatment required.
• Use cold compresses, and sun glasses to decrease glare.
• NSAID and lubricant eyedrops decrease discomfort.
• Topical antibiotics prevent superadded bacterial infections.
• Highly contagious patients may be infectious for up to 11 days after onset.
• Transmission usually occurs from eyes to fingers to eyes, as well as through contaminated tonometers, contact lenses and eye drops

Acute Herpetic Conjunctivitis

• It, an accompaniment of the 'primary herpetic infection', mainly occurs in children and adolescents.
• It is commonly caused by herpes simplex virus type 1 and spreads by kissing or other close personal contacts.
• HSV type 2 associated with genital infections may also involve the eyes in adults as well as children, though rarely.
• Treatment:
  • Usually self-limiting
  • Topical antiviral drugs control the infection effectively and prevent recurrences
  • Supportive measures are similar to EKC
• Clinical features include:
  • Usually unilateral affection
  • It may occur in 2 forms:
    • Typical form: follicular conjunctivitis and other primary infection such as vesicular lesions of face & lids
    • Atypical form: follicular conjunctivitis without lesions of face and eyelid, resembles epidemic keratoconjunctivitis, may enolve through phases of nonspecific hyperaemia, follicular hyperplasia and pseudomembrane formation
• Preauricular lymphadenopathy always occurs
• Treatment usually involves self-limiting methods and topical acyclovir.

Molluscum Contagiosum Conjunctivitis

• A waxy, umbilicated eyelid nodule often presents and may be multiple.
• Ispilateral chronic, mucoid discharge and follicular conjunctivitis occur.
• Treatment involves destruction of the eyelid lesion

Membranous and Pseudomembranous Conjunctivitis

• It can be unilateral or bilateral conjunctivitis.
• It involves a pseudo membrane or fibrinous membrane either on the palpebral or bulbar conjunctiva.
• Fibrinous exudate make-up may or may not be firmly adherent to the epithelium of the conjunctiva
• Causes of membranous conjunctivitis:
  • Bacterial causes such as Corynyebacteruim diphtheriae, Beta Hemolytic streptococci, Streptococcus pneumoniae, Neisseria gonorrhea, Staphylococcus aureus and Escherichia coli.
  • Chemical and thermal burns
  • Viral Causes
• Diphtheritic infection chiefly occurs in children who are not immunized.
• Streptococcal conjunctivitis occurs in children associated with measles, scarlet fever, whooping cough, or influenza.
• Clinical presentation includes:
  • mild cases showing swelling of the lids with mucopurulent or sanguineous discharge
  • On everting the lid palpebral conjunctiva is seen to be covered by a peelable white membrane, appearing as a pseudo membranous conjunctivitis
  • In severe cases, lids are brawny (hefty) with semi-solid exudates which impair mobility and prevent formation of free discharge; It compresses the vessels and tends to necrotize the cornea and underlying conjunctiva
  • Membrane separates less easily and may tend to bleed, forming membranous conjunctivitis
• Treatment includes:
  • Antibiotics, broad spectrum antibiotic topical eyedrops and oral/intravenous antibiotic after determining organism and depending on severity.
  • If cornea is involved, use cyclopegics.

Ophthalmia Neonatorum

• It is defined as an acute mucoid, purulent or mucopurulent discharge from one or both eyes in the first month of life.
• Ophthalmia neonatorum is a preventable disease occurring in a newborn due to contamination from maternal genital tract.
• The disease is still prevalent as a public health problem in conditions of poor hygiene and limited access to healthcare.
• Ophthalmia neonatorum can be severe because at birth there are relatively minimal tears, an absence of lymphoid tissue, and thin and delicate conjunctiva and cornea.
• Causative organisms include: Chlamydia oculogenitalis, Streptococcus pneumoniae, Neisseria gonorrhoeae, Staphylococci, Gram negative coliforms, Herpes simplex virus, and chemical causes.
• A bacteriological examination should be done in every case.

Neisseria gonorrhoeae

• It manifests earliest, within 48 hours.
• It is a virulent strain that causes mucopurulent/purulent discharge.
• Both eyes are involved and are asymmetrical.
• There is a thick yellow pus discharge.
• Marked chemosis is a distinguishing feature.
• During examination, surgeon must wear protective goggles and use lid retractors.
• There is a dense infiltration of the bulbar conjunctiva and tense lids.
• Later, lids become soft and are more easily everted.
• Conjunctiva is puckered, with intense congestion.
• Now, free discharge of pus, serum and often blood.
• Pseudomembrane in the fornices.
• Gonococcus can invade the normal cornea, increasing the risk of corneal ulceration if untreated.
• Occasionally, if already infiltrated perforation may occur.
• Ulceration usually occurs in the oval area just below the center of the cornea, the position of the lid margin when the eyes are closed and rotated upwards.
• Sudden perforation with extrusion of contents can occur.

C.trachomatis inclusion conjunctivitis

• It manifests relatively late, usually over a week after birth.
• It is a relatively common cause of ophthalmia neonatorum.
• Bacterial examination is usually negative.
• Characteristic intracellular inclusion bodies are seen.
• Follicles develop after 3 months of age.
• Complicating superficial keratitis is common.
• If untreated, chlamydia otitis and pneumonia may develop later.

Chemical toxicity

• It was used to be seen within few hours of prophylactic topical treatment with silver nitrate solution 1% instilled into each eye (Crede's method).
• It is rarely seen today as erythromycin and tetracycline have replaced it.

Summary of Ophthalmia Neonatorum

• Depending on the onset of symptoms, the differential diagnosis includes:
  • Within the first 48 hours: N.Gonorrhoeae which can be treated with a single dose of Ceftriaxone injection (125mg i.m.) and Tobramycin or Neomycin-bacitracin eye ointment.
  • Within the first 48 hours: Chemical toxicity, which treated by washing eyes and applying Erythromycin ointment.
  • 48-72 hours: Other bacteria, treat with Tobramycin or Neomycin-bacitracin eye ointment.
  • 5-7 days: Herpes simplex virus, treat with Acyclovir eye ointment 3%.
  • More than a week: C.trachomatis, treat with Erythromycin eye ointment.