Sclera and Cornea

Describe the sclera's structure and note conditions associated with bluish scleral discoloration and staphyloma.

The sclera ("the white part of the eye") makes up 5/6 of the outer fibrous protective coat of the globe, composed of irregularly distributed collagen bundles (hence opaque),
continuous with the cornea anteriorly and the dura mater covering the optic nerve posteriorly.

When scleral collagen is thin and transparent, the underlying choroidal pigment becomes visible, causing bluish discoloration, seen in conditions like Marfan syndrome and osteogenesis imperfecta.

A localized protrusion of the sclera lined by uveal tissue (bluish in color) is called a staphyloma.

The episclera is a thin, vascularized connective tissue layer covering the outer scleral surface.

What is Episcleritis: definition and etiology?

Episcleritis is inflammation of the episcleral tissues — a relatively common, benign, self-limited cause of red eye; two-thirds of cases are unilateral, and it is more common in females (3:1 ratio).

Etiology:
idiopathic (most cases), collagen vascular disease (rheumatoid arthritis, SLE, seronegative spondyloarthropathies), vasculitis (polyarteritis nodosa, temporal arteritis, Behçet's disease), inflammatory bowel disease (Crohn's, ulcerative colitis), dermatologic disease (rosacea), metabolic disease (gout), atopy, and infections (herpes zoster, herpes simplex, syphilis).

Recurrent cases may signal an underlying systemic inflammatory disease.

What are the clinical types of Episcleritis, and how is it managed?

Clinical types:
Nodular episcleritis — a discrete, elevated, tender, mobile area of inflamed episcleral tissue with less acute onset and more prolonged course;

Simple episcleritis (more common) — vascular congestion without an obvious nodule, either sectoral (2/3 of cases) or diffuse (1/3 of cases). The most common presentation overall is sectoral, simple, unilateral, idiopathic episcleritis in females.

Differentiation from conjunctivitis:
instilling phenylephrine 2.5% causes blanching (disappearance of hyperemia) in conjunctivitis but not in episcleritis.

Management:
episcleritis is self-limited and usually resolves without treatment; supportive measures (cold compresses, iced artificial tears) help with discomfort;
oral NSAIDs (e.g., ibuprofen 800mg three times daily) are the main medical treatment, with topical steroids as an option (ophthalmologist-monitored); recurrent attacks may warrant systemic evaluation and treatment of the associated disease.

What is Scleritis: definition and etiology?

Scleritis is inflammation of the sclera, presenting as a painful red eye with or without vision loss.

Etiology: rheumatoid arthritis is the most common association, along with other collagen vascular diseases (SLE, seronegative spondyloarthropathies), metabolic disease (gout), infections (TB, syphilis, herpes zoster), chemical or physical injuries, and idiopathic cases.

What are the clinical types of Scleritis?

Anterior scleritis (more common): inflammation anterior to the rectus muscle insertions, appearing diffuse, nodular, or necrotizing; may be associated with keratitis (corneal thinning), uveitis, and trabeculitis (elevated IOP).

Necrotizing anterior scleritis is the most severe form, with severe pain and extreme scleral tenderness, with or without gross necrosis and choroidal exposure;

scleromalacia perforans is a rare, painless form of necrotizing anterior scleritis.

Posterior scleritis (rare): inflammation posterior to the rectus muscle insertions, which can cause serous retinal detachment, vision loss, and pain on eye movement.

How is Scleritis differentiated from episcleritis, managed, and what is its prognosis?

Phenylephrine test differentiates the three red-eye conditions:
- 2.5% blanching = conjunctivitis
- 10% blanching = episcleritis, no blanching = scleritis.

Scleritis is vision-threatening and requires urgent ophthalmology referral. Investigations: ocular B-scan ultrasound and orbital MRI can detect posterior scleritis.

Treatment: oral NSAIDs, systemic (oral or IV) corticosteroids and occasionally topical corticosteroids, immunomodulating drugs (methotrexate, cyclophosphamide, mycophenolate, cyclosporine, TNF-α inhibitors) for systemic and ocular control, and surgery for scleral perforation or severe thinning at risk of rupture.

Prognosis: mild-to-moderate scleritis usually preserves excellent vision; it can remain active for months to years before remission; necrotizing scleritis carries a high risk of vision loss and mortality.

Describe the Cornea's structure and functions, and what maintains its transparency?

The cornea is the transparent 1/6 of the outer protective coat, about 500 μm thick.

Functions: 1) transmitting light into the eye, 2) refracting light (comprising 2/3 of the eye's total refractive power at 42-44 diopters, versus 18-20 diopters for the lens), 3) maintaining clarity via the corneal endothelial pump (keeping relative dehydration), and 4) protecting the globe's contents.

Transparency depends on avascularity, uniform collagen bundle arrangement in the stroma, and relative dehydration (deturgescence, since water is ~78% of corneal volume) — corneal oedema causes lamellar separation, light scattering, and reduced transparency.

The cornea has 5 layers: epithelium (non-keratinized stratified squamous, ~50 μm), Bowman's membrane, stroma (90% of thickness), Descemet's membrane, and a single endothelial cell layer (density 2500-3000 cells/mm², with no in vivo regenerative capacity).

Epithelial stem cells reside at the limbus; corneal sensation comes from the nasociliary branch of the trigeminal nerve (which also supplies the nose tip) — loss of sensation impairs epithelial regeneration and predisposes to ulcers.

Describe a Corneal Foreign Body: incidence, pathogenesis, clinical picture, complications, and treatment.

A corneal foreign body is material (metal, glass, wood, plastic, sand) adherent to or embedded in the cornea — one of the most frequent ophthalmic emergency causes, more common in males, peaking in the 2nd decade (under 40 years).

If it penetrates the anterior/posterior chamber, it becomes an intraocular foreign body (IOFB), which must always be excluded after trauma.

Pathogenesis: particles lodge in the epithelium/stroma, inducing inflammation (PMNs, macrophages) with possible anterior chamber reaction; untreated, it can cause infection or tissue necrosis.

Symptoms: pain, tearing, photophobia, foreign body sensation, red eye.

Signs: visible foreign body, ciliary ± conjunctival injection, a fluorescein-staining epithelial defect, possible infectious keratitis signs.

Complications: rust ring, corneal scarring, infectious keratitis, secondary iritis.

Treatment: removal under magnification with local anesthetic (cotton-tip applicator or needle) or ophthalmology referral, topical antibiotics, and never patching if infection is suspected.

Compare Corneal Abrasion and Recurrent Corneal Epithelial Erosions (REE): definition, etiology, clinical picture, and treatment.

Corneal abrasion is an epithelial defect from trauma ( paper, contact lens manipulation), causing sudden pain, redness, tearing, photophobia, and foreign body sensation; the defect stains with 1% fluorescein, and pain is relieved (but never treated) with topical anesthetic.

Treatment: broad-spectrum topical antibiotics and eye patching (if no contamination/infection) to relieve pain until healing.

Recurrent Corneal Epithelial Erosions (REE)
are recurring epithelial defects caused by friction between the lid and cornea due to inadequate epithelial adherence and poorly formed hemidesmosomes;
predisposing factors include prior traumatic abrasion or corneal dystrophies with weak hemidesmosomes.

Clinical picture: recurrent pain, redness, tearing, photophobia, and foreign body sensation, typically upon awakening.

Treatment: as for corneal abrasion, plus ophthalmology referral.

What is a Corneal Ulcer/Infectious Keratitis: definition, etiology, clinical picture, complications, and treatment?

A corneal ulcer is loss of epithelium with inflammation, ± necrosis of underlying/surrounding tissue, with cellular infiltration causing greyish-white or yellowish corneal opacification.

Etiology: infection (bacterial, viral, fungal, protozoal/Acanthamoeba), vitamin A deficiency (keratomalacia — a bilateral emergency in infants in developing countries),
or immunologic causes (atopy like vernal catarrh, or autoimmune disease).

Symptoms: decreased vision, pain, redness, tearing, photophobia, foreign body sensation.

Signs: decreased vision, blepharospasm, corneal opacification, a fluorescein-staining epithelial defect,
hypopyon (pus in the anterior chamber), and purulent discharge in bacterial/fungal ulcers.

Complications: corneal scarring,
corneal perforation (diagnosed via Seidel test showing aqueous washout of stain),
iritis, endophthalmitis, and keratectasia (thinning/bulging of scarred cornea).

Treatment: urgent ophthalmology referral, microbiological smear/culture, intensive topical antimicrobial drops (antibiotic/antiviral/antifungal/anti-acanthamoeba), cycloplegics for pain — never patch during active infection,
and never use topical steroids.

Describe Herpes Simplex Virus (HSV) Keratitis: layers affected, and Primary vs Recurrent disease presentations.

HSV keratitis is caused by HSV-1; infection doesn't confer immunity, and recurrence can be triggered by stress, fever, sun exposure, or immunosuppression.

Ocular HSV manifests as blepharitis, conjunctivitis, keratitis, or iridocyclitis, and can affect the corneal epithelium (dendritic/geographic ulcers), stroma (interstitial keratitis, necrotizing or non-necrotizing), or endothelium (endotheliitis ± iritis).

Primary Ocular Herpes (usually in children):
follicular conjunctivitis ± corneal involvement and vesicular lid skin lesions;
the virus then becomes latent in the trigeminal ganglion.

Recurrent disease has three forms:
1) Epithelial keratitis — a thin, branching dendritic ulcer with recurrence and corneal hypoesthesia, which can progress to a geographic ulcer in immunocompromised patients or with inadvertent steroid use.
2) Stromal (interstitial) keratitis — necrotizing (active stromal infection) or non-necrotizing/disciform (delayed hypersensitivity, no active infection).
3) Keratouveitis — endotheliitis ± iritis with possible elevated IOP.

How is HSV Keratitis treated?

Treatment:
topical antiviral medications (ganciclovir eye drops, acyclovir ointment), prophylactic broad-spectrum topical antibiotics, and oral acyclovir for prophylaxis against epithelial keratitis recurrence or for treating necrotizing stromal keratitis and keratouveitis.

Topical steroids must NEVER be used in active epithelial disease (can cause progression to geographic ulcer, increasing risk of secondary infection or perforation), but an ophthalmologist may add steroids for disciform keratitis or keratouveitis, and may perform debridement of a dendritic ulcer.

What is Herpes Zoster Ophthalmicus (HZO): definition, etiology, and the clinical picture of its dermatitis?

HZO is a viral disease causing a unilateral painful skin rash in the dermatome of the ophthalmic division (V1) of the trigeminal nerve, typically in older or immunocompromised adults (rarely bilateral, only in immunocompromised patients).

It's caused by reactivation of latent varicella-zoster virus (VZV, the chickenpox virus) dormant in the trigeminal (Gasserian) ganglion, which travels along sensory axons to the skin.

Dermatitis features: severe neuralgic pain usually preceding the vesicular eruption (which stops after vesicles appear but can persist as postherpetic neuralgia);
vesicles appear along the CN V1 dermatome, may suppurate, bleed, and scar.

Hutchinson's sign: if the nasociliary nerve (nose tip) is involved, the eye is affected in 75% of cases.

What ocular manifestations and complications occur with HZO?

Ocular involvement: keratitis (pain, tearing, photophobia, red eye, corneal epithelial pseudo-dendrites, superficial punctate keratopathy, corneal hypoesthesia), scleritis, iridocyclitis, secondary glaucoma (from trabeculitis), cranial nerve paralysis (III, IV, VII), retinitis and acute retinal necrosis, and optic neuritis.

Complications: postherpetic neuralgia is the most significant, affecting 37% of patients over 60 and 48% over 70; eyelid skin cicatrization can cause ptosis, lid scarring, ectropion, and entropion; scleral/limbal atrophy from inflammation; and vision loss from corneal, optic nerve, retinal, or choroidal inflammation.

How is Herpes Zoster Ophthalmicus (HZO) treated?

Standard treatment: oral acyclovir 800mg five times daily for 7-10 days (or famciclovir/valacyclovir); earlier treatment (before rash onset) reduces complications and postherpetic neuralgia.

Topical steroids (e.g., prednisolone acetate 1%) are used for interstitial keratitis and uveitis; systemic steroids for scleritis, retinitis, choroiditis, and optic neuritis.

For raised IOP from herpetic trabeculitis: topical steroids plus aqueous suppressants (timolol, brimonidine, dorzolamide, acetazolamide).

Pain management with gabapentin (200-600mg/day) may help acute herpetic neuralgia.

Describe Keratoconus (KC): definition, risk factors, clinical picture, and investigations.

Keratoconus is a bilateral, progressive, non-inflammatory paracentral conical protrusion and
thinning of the cornea, causing decreased vision from irregular astigmatism and scarring;
it usually starts in the 2nd decade, progressing through the 3rd-4th decades (slowing with age), has familial inheritance, and is more common with atopy (e.g., vernal catarrh), Down syndrome, and frequent vigorous eye rubbing.

Clinical picture: painless, progressive vision loss (may be asymmetric between eyes);

advanced cases show Munson's sign (angulation of the lower lid in downgaze from marked corneal protrusion);

breaks in Descemet's membrane can cause acute corneal hydrops (oedema/opacification from aqueous entering the stroma).

Investigations:
Corneal topography (diagnostic map of corneal curvature),
pachymetry (corneal thickness measurement),
Keratometer (ophthalmometer): measures anterior corneal curvature,
and Pentacam (combines topography, thickness, and other management-guiding data).

How is Keratoconus (KC) treated?

Visual correction: spectacles in early cases, rigid gas permeable (RGP) contact lenses when spectacles become inadequate.

Corneal collagen cross-linkage halts disease progression.

Intrastromal corneal ring (ICR) segment implantation flattens the cornea, reducing dependence on spectacles/RGP lenses.

Keratoplasty (penetrating or lamellar) removes and replaces the diseased cornea in advanced cases; visual rehabilitation afterward may require spectacles, contact lenses, or refractive surgery.

Compare Arcus Senilis (Gerontoxon) and Calcific Band Keratopathy.

Arcus Senilis is a bilateral annular deposition of lipids in the peripheral corneal stroma — the most common peripheral corneal opacity — characterized by a clear zone between the opacity and limbus (Lucid interval of Vogt);
it frequently occurs with hyperlipidemia in the elderly, but in younger patients (arcus juvenilis/pseudo-gerontoxon) mandates checking the lipid profile; it's asymptomatic and requires no treatment.

Calcific Band Keratopathy is a corneal degeneration of fine dust-like calcium deposits in the sub-epithelium, Bowman's layer, and anterior stroma,
forming a band-like horizontal opacity in the interpalpebral (middle 1/3) cornea that grows from periphery to center, starting grey and becoming chalky-white; it occurs with chronic inflammatory ocular disease, silicone-filled eyes (post-retinal surgery), or systemic hypercalcemia.

It can affect vision if it covers the pupil, and is treated (after controlling the underlying condition) with EDTA chemical chelation or phototherapeutic keratectomy, requiring ophthalmology referral.

Describe Exposure Keratopathy and Photokeratitis: causes, clinical picture, and treatment.

Exposure Keratopathy (EK) is corneal damage from prolonged ocular surface exposure, potentially causing ulceration, microbial keratitis, and permanent vision loss; it results from disrupted blinking (impaired blink reflex from neurologic disease, incomplete lid closure as in lagophthalmos, proptosis, lid malposition) or neurotrophic conditions with decreased corneal sensation.

Symptoms: foreign body sensation, burning, tearing, intermittent blurry vision (worse in the morning with nocturnal lagophthalmos), pain, and photophobia; early EK shows corneal dryness and superficial punctate keratopathy (often inferior third of cornea), progressing to ulceration, infection, and scarring if untreated.

Treatment: prophylactic lubrication in high-risk patients, topical broad-spectrum antibiotics if infection is suspected, and ophthalmology referral.

Photokeratitis (Ultraviolet Keratitis) follows unprotected UV exposure (welding arcs, snow reflection, germicidal lamps, tanning beds), damaging and sloughing corneal epithelial cells and exposing corneal nerves.

Symptoms: intense pain, photophobia, foreign body sensation; signs: bilateral involvement (unilateral suggests a foreign body instead), ciliary/conjunctival injection and chemosis, and diffuse punctate epithelial staining on fluorescein.

Treatment is supportive (like corneal abrasion) — ointment, artificial tears, oral analgesics, healing within 24-72 hours; patients should avoid topical anesthetics, which can delay healing.