Stromal Corneal Dystrophies

The cornea is composed of several distinct layers, each with a specific function. The stroma, making up about 90% of corneal thickness, provides its strength and shape. Corneal dystrophies are a group of inherited conditions characterised by the abnormal accumulation of material within one or more corneal layers. These deposits gradually reduce corneal transparency, resulting in blurred vision and other visual disturbances.

This page focuses on three prominent stromal dystrophies: lattice, granular and macular. While all are genetic, they differ in the type of material deposited, their appearance and their clinical course.

Lattice corneal dystrophy

What it is. Lattice dystrophy is characterised by the accumulation of amyloid deposits within the corneal stroma. These form a network of fine, branching, refractile lines resembling a lattice or crisscross pattern, giving the condition its name.

Genetics. Typically autosomal dominant: an affected individual usually has one affected parent, with a 50% chance of passing the condition to each child. Several mutations, often in the TGFBI (transforming growth factor beta induced) gene, are responsible.

Appearance and symptoms. The characteristic lattice lines are the hallmark. Between the lines the cornea may initially be clear but becomes hazy over time.

• Recurrent corneal erosions are a significant and often painful feature. The surface epithelial cells do not adhere well to the underlying abnormal stroma, leading to episodes of sharp pain, light sensitivity, tearing and foreign-body sensation, especially on waking.
• Gradual blurring of vision as the lattice lines and intervening haze become denser.

Progression. Symptoms usually begin in the first or second decade of life. The severity and rate of vision loss vary. Recurrent erosions can be a major problem, affecting quality of life.

Treatment. For recurrent erosions: lubricating drops and ointments, bandage contact lenses, and sometimes anterior stromal puncture or phototherapeutic keratectomy (PTK) with an excimer laser to smooth the corneal surface. For vision loss, corneal transplantation may be necessary — DALK is often preferred if the endothelium is healthy, as it preserves the patient’s own endothelial cells; penetrating keratoplasty may be considered if DALK is not suitable. The dystrophy can recur in the donor graft over many years.

Granular corneal dystrophy (type I and type II / Avellino)

What it is. Granular dystrophy is characterised by the deposition of hyaline material in the corneal stroma.

• Type I (classic granular dystrophy) presents with distinct, crumb-like or sugar-like white granules in the anterior to mid-stroma. The cornea between the granules typically remains clear, especially in earlier stages.
• Type II (Avellino, or granular–lattice dystrophy) is a combined form exhibiting features of both granular and lattice dystrophies. Patients develop both granular deposits and amyloid lattice lines.

Genetics. Both types are autosomal dominant and also caused by mutations in the TGFBI gene — different mutations from those typically causing pure lattice dystrophy.

Appearance and symptoms. In type I, discrete, sharp-bordered white opacities. Vision is often good until later in life, when the granules become more numerous and coalesce, or if surface erosions occur (less common than in lattice dystrophy). Glare can be an early symptom. In type II, a mix of granular opacities and finer lattice lines; visual symptoms and erosions are more variable.

Progression. Symptoms usually appear in the first or second decade. Vision loss is generally slow and may not become significant until the fourth or fifth decade for type I. Avellino dystrophy can be more aggressive.

Treatment. Often not required in early stages if vision is good. Glasses may suffice for glare or mild change. If recurrent erosions occur — more common in type II — treatment is similar to that for lattice dystrophy. For significant vision loss, PTK can sometimes remove superficial opacities; if deeper or denser, DALK or penetrating keratoplasty may be necessary. Recurrence in the graft is possible.

Macular corneal dystrophy

What it is. Macular dystrophy is characterised by the accumulation of glycosaminoglycans (mucopolysaccharides) within the corneal stroma. Unlike lattice and granular dystrophies, the deposits are less well defined, causing a diffuse, ground-glass haziness throughout the entire stroma, from limbus to limbus.

Genetics. The least common of the three but often the most severe visually. It is autosomal recessive: an individual must inherit a copy of the mutated gene — typically CHST6 — from both parents. Parents are usually carriers without symptoms.

Appearance and symptoms. Diffuse clouding of the corneal stroma, often with slightly denser greyish-white spots (macules) scattered within the haze. The cornea between these spots is also hazy, unlike the clear intervening cornea often seen in early granular dystrophy.

• Corneal thinning is often present.
• Significant vision loss often occurs earlier than in lattice or granular dystrophy, typically by the second or third decade.
• Light sensitivity and glare are common.
• Recurrent erosions are less common than in lattice dystrophy.

Progression. Symptoms usually start in the first decade of life, and visual impairment is often severe by young adulthood.

Treatment. Because of the diffuse nature and depth of the opacities, superficial treatments such as PTK are usually not effective. Penetrating keratoplasty has traditionally been the primary treatment, as the entire corneal thickness is affected. DALK may be attempted, but achieving a clear separation plane down to Descemet’s membrane is more challenging with diffuse stromal involvement. Recurrence in the graft is possible but may occur later than with TGFBI-related dystrophies.

General considerations

For all these dystrophies, genetic counselling can be beneficial for affected individuals and their families. Regular ophthalmic examination is essential for monitoring progression and managing symptoms. While these conditions can be visually challenging, advances in corneal surgery — particularly lamellar techniques such as DALK — and effective management of recurrent erosions offer significant hope for maintaining and restoring vision.