Anterior Stromal Corneal Dystrophies: Understanding Lattice, Granular, and Macular Dystrophies

The cornea, our eye’s clear front window, is composed of several distinct layers, each with a specific function. The stroma, making up about 90% of the cornea’s thickness, provides its strength and shape. Corneal dystrophies are a group of inherited conditions characterized by the abnormal accumulation of material within one or more layers of the cornea. These deposits can gradually lead to a loss of corneal transparency, resulting in blurred vision and other visual disturbances.

This article focuses on three prominent anterior stromal dystrophies: Lattice Dystrophy, Granular Dystrophy, and Macular Dystrophy. These conditions primarily affect the stroma, the middle layer of the cornea. While they are all genetic, they differ in the type of material deposited, their appearance, and sometimes their clinical course.

1. Lattice Corneal Dystrophy

• What it is: Lattice Dystrophy is characterized by the accumulation of amyloid deposits within the corneal stroma. These deposits form a network of fine, branching, refractile lines that resemble a lattice or crisscross pattern, giving the condition its name.

• Genetics: It’s typically an autosomal dominant condition, meaning an affected individual usually has one parent with the condition, and there’s a 50% chance of passing it on to each child. Several genetic mutations, often in the TGFBI (Transforming Growth Factor Beta Induced) gene, are responsible.

• Appearance & Symptoms:

  • The characteristic lattice lines are the hallmark. Between these lines, the cornea may initially be clear but can become hazy over time.

  • Recurrent Corneal Erosions: A significant and often painful symptom. The surface epithelial cells don’t adhere well to the underlying abnormal stroma, leading to episodes of sharp pain, light sensitivity (photophobia), tearing, and foreign body sensation, especially upon waking.

  • Gradual blurring of vision as the lattice lines and haze become denser.

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

• Treatment:

  • For Recurrent Erosions: Lubricating eye drops and ointments, bandage contact lenses, and sometimes procedures like anterior stromal puncture or phototherapeutic keratectomy (PTK) using an excimer laser to smooth the corneal surface.

  • For Vision Loss: When vision is significantly impaired by stromal opacities, corneal transplantation may be necessary. Deep Anterior Lamellar Keratoplasty (DALK) is often preferred if the endothelium is healthy, as it preserves the patient’s own endothelial cells. Penetrating Keratoplasty (PKP) may be considered if DALK is not suitable. It’s important to note that the dystrophy can sometimes recur in the donor graft over many years.

2. Granular Corneal Dystrophy (Type I and Type II/Avellino)

• What it is: Granular Dystrophy is characterized 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 Dystrophy or Granular-Lattice Dystrophy): This is a combined form that exhibits features of both granular and lattice dystrophies. Patients develop both granular deposits and amyloid lattice lines.

• Genetics: Both types are autosomal dominant and are also caused by mutations in the TGFBI gene (different mutations than those typically causing pure lattice dystrophy).

• Appearance & Symptoms:

  • 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.

  • Type II (Avellino): A mix of granular opacities and finer lattice lines. Visual symptoms and erosions can be more variable, sometimes resembling either granular or lattice dystrophy more closely.

• 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 or later for Type I. Avellino can sometimes be more aggressive.

• Treatment:

  • Treatment is often not required in early stages if vision is good.

  • For glare or mild vision changes, glasses may suffice.

  • If recurrent erosions occur (more common in Type II), treatments similar to those for Lattice Dystrophy are used.

  • For significant vision loss, PTK can sometimes remove superficial opacities. If deeper or denser, DALK or PKP may be necessary. Recurrence in the graft is possible.

3. Macular Corneal Dystrophy

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

• Genetics: This is the least common of the three but often the most severe visually. It is an autosomal recessive condition, meaning an individual must inherit a copy of the mutated gene (typically CHST6) from both parents to develop the condition. Parents are usually carriers without symptoms.

• Appearance & Symptoms:

  • Diffuse clouding of the corneal stroma, often with slightly denser, grayish-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. Vision impairment is often severe by young adulthood.

• Treatment:

  • Due to the diffuse nature and depth of the opacities, superficial treatments like PTK are usually not effective.

  • Penetrating Keratoplasty (PKP) has traditionally been the primary treatment for restoring vision, as the entire corneal thickness is affected.

  • DALK may be attempted by some surgeons, but achieving a clear separation plane down to Descemet’s membrane can be more challenging due to the 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 counseling can be beneficial for affected individuals and their families. Regular ophthalmologic examinations are crucial for monitoring progression and managing symptoms. While these conditions can be visually challenging, advancements in corneal surgery, particularly lamellar techniques like DALK and effective management of recurrent erosions, offer significant hope for maintaining and restoring vision.