13th December 2023

Anterior segment disease

Vision loss attributed to anterior segment pathology can be divided into:

• Cornea
• Anterior chamber-related
• Lens

Cornea

A corneal ulcer is a defect of the corneal epithelium and underlying stroma. This is a potentially vision-threatening ocular emergency. Even with prompt treatment, patients can suffer significant morbidity from corneal perforation, scarring, secondary glaucoma and permanent vision loss.

Aetiology:

• Infectious
  • Bacterial infection (most common). Organisms include Staphylococcus species (eyelids) and Pseudomonas aeruginosa (contact lens users).
  • Viral: Herpes viruses are a common cause of viral keratitis. There may be a history of previous herpetic keratitis, recent cold sore (herpes simplex), or recent/concurrent shingles (herpes zoster) affecting the ophthalmic branch (V1) of the trigeminal nerve.
  • Parasitic: Acanthamoeba is a free-living protozoan found in freshwater and soil that can cause corneal ulcers in contact lens wearers. It characteristically causes pain out of proportion to clinical signs due to infiltration of corneal nerves. For this reason, it is often missed in the early stages.
  • Fungal: Less than 10% of all corneal infections. They are most often precipitated by corneal trauma or exposure to organic matter.
• Non-infectious
  • Exposure keratopathy: incomplete eyelid closure (facial nerve palsy; stroke) results in exposure of the inferior third of the cornea, with drying of the tear film and subsequent corneal surface breakdown.
  • Neurotrophic cornea: Corneal sensation is supplied by the trigeminal branch (V1) of the trigeminal nerve. Loss of sensation is a high-risk factor for corneal breakdown. Causes may be local (prolonged contact lens use; herpes virus), systemic neuropathy (diabetes; amyloidosis) or lesion anywhere along the path of V1.
  • Autoimmune: vasculitic corneal ulcers often affect the peripheral cornea and cause rapid and circumferential corneal changes.

Risk Factors

• Contact lens wear
• Severe dry eyes
• Trauma/abrasion
• Nutritional deficiency (malabsorption, liver cirrhosis, alcohol excess)
• Systemic collagen vascular disease
• Corneal exposure secondary to incomplete lid closure (facial nerve palsy)
• Loss of corneal sensation

Clinical Presentation

Slit-lamp examination demonstrates an epithelial defect with an underlying yellow/grey infiltrate. A dendritic appearance is characteristic for herpes simplex keratitis. The presence of a hypopyon (white fluid level within the anterior chamber) indicates sight-threatening disease.

Management

All patients presenting with a red eye and a history of contact lens use should be discussed with the local ophthalmic team. Active corneal ulcers require a corneal scrape for gram staining, microbial culture and sensitivity, viral and acanthamoeba PCR to determine underlying aetiology. Definitive management is directed against the underlying cause.

Image Source: Wikimedia Commons (2015). Parasite140120-fig1 Acanthamoeba keratitis, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Parasite140120-fig1_Acanthamoeba_keratitis.png (Accessed on: 15  May 2022).

Image Source: Wikimedia Commons (2017). Dendritic corneal ulcer, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Dendritic_corneal_ulcer.jpg (Accessed on: 15  May 2022).

Image Source: Wikimedia Commons (2017). Hypopyon 1, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Hypopyon_1.jpg (Accessed on: 15  May 2022).

Anterior chamber

Acute angle-closure glaucoma (AACG) is an ophthalmic emergency. The normal range for intraocular pressure is 10 to 22 mmHg. Aqueous humor production begins in the ciliary body, flows through the pupil, and exits the eye through the trabecular meshwork and Schlemm’s canal in the anterior chamber angle (between the iris and the cornea). In acute angle-closure glaucoma, the intraocular pressure increases rapidly due to obstruction of the drainage angle and blockage of aqueous humor outflow. Predisposing factors include an anatomically narrow anterior chamber angle, increasing lens size and an anteriorly located iris-lens diaphragm. AACG is often precipitated by pupillary dilatation. As the pupil enlarges, the peripheral iris contacts the lens, preventing the flow of aqueous through the pupil (pupillary block). This leads to bulging of the iris (iris bombe), crowding of the anterior chamber angle by the iris and obstruction of aqueous humor outflow. The intraocular pressure rises acutely, leading to symptomology.

Risk Factors

• Age: The average age at presentation is 60. This is felt to be due to the increasing size of the lens with age
• Gender: F:M ratio 4 to 1
• Ethnicity: more common in Southeast Asians, Chinese, and Inuit heritage
• Family history: An anatomically narrow anterior chamber angle is usually inherited

Clinical Presentation

• Reduced vision associated with haloes
• Severe headache
• Nausea & vomiting
• Abdominal pain
• Red, injected eye
• Cloudy cornea
• Fixed, semi-dilated pupil (iris ischaemia)
• Intraocular pressures commonly >50mmHg (normal 11-2mmHg)
• Glaucomatous or swollen optic disc

Management

The medical treatment for AACG aims to:

1. Decrease production of aqueous humor
2. Restore aqueous outflow
3. Relieve pupillary block

Initial medical therapy includes a combination of the following medications:

• Intravenous acetazolamide 500 mg, topical beta-blocker (timolol 0.5%) and alpha 2-agonist (apraclonidine 1%) to block the production of aqueous humor.
• Topical pilocarpine 1% to 2% to constrict the pupil and increase the outflow of aqueous humor.
• If the intraocular pressure remains elevated after an hour, intravenous mannitol 1 gram/kg can be given (if there is no contraindication) to rapidly reduce the volume of aqueous humor.

Definitive treatment is by laser peripheral iridectomy (PI) after the acute episode subsides. Iridectomy relieves the pupillary block by allowing the flow of aqueous humor through the iris. The contralateral eye usually has the same predisposing anatomy and carries up to 80% risk of developing an attack of AACG if untreated. Hence, PI is usually performed in both eyes following a first presentation.

Prognosis

The outcome for patients with AACG is good following treatment if recognised early. In the early stages, corneal clouding may be subtle and overlooked. Patients may be mistakenly worked up for intracranial or abdominal symptoms. Delay in treatment can lead to damage to the optic nerve and vision loss.

Image Source: Wikimedia Commons (2011). Acute Angle Closure-glaucoma, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Acute_Angle_Closure-glaucoma.jpg (Accessed on: 15  May 2022).

Lens

Cataracts cause a painless, slow deterioration of vision. There may be difficulty with focusing and glare experienced with bright lights. Some patients experience a ‘second sight’ – whereby the increased refractive power of an enlarging cataract produces an improvement with near-tasks such as reading. Inevitably, over time, vision progressively declines as the cataract becomes cloudy. Patients are more likely to present to their local optician than an acute practitioner. Certain conditions predispose to accelerated and/or early onset cataract formation:

• Diabetes mellitus
• Corticosteroid use
• Myotonic dystrophy

Cataract extraction is the management of choice.

References 

• Ahram DF, Alward WL, Kuehn MH. The genetic mechanisms of primary angle closure glaucoma. Eye (Lond). 2015 Oct;29(10):1251-9.
• Collignon NJ. Emergencies in glaucoma: a review. Bull Soc Belge Ophtalmol. 2005;(296):71-81.
• Shahid H, Salmon JF. Malignant glaucoma: a review of the modern literature. J Ophthalmol. 2012;2012:852659.