Macular corneal dystrophy is a rare, inherited eye condition that progressively affects the cornea, the transparent outer layer of the eye. This disorder leads to the accumulation of abnormal deposits within the corneal tissue, causing it to become cloudy. As the clouding advances, it can significantly impair vision. The condition is typically bilateral, affecting both eyes, and vision tends to worsen over time.
Understanding Macular Corneal Dystrophy
The cornea has several layers, with the thick central stroma being primarily affected in macular corneal dystrophy. This is where abnormal substances, specifically mucopolysaccharide deposits (also known as glycosaminoglycans), accumulate.
The precise organization of collagen fibers in the stroma is crucial for transparency and light focusing. The accumulation of these deposits disrupts this organization, leading to a hazy appearance and reduced transparency of the cornea. This clouding scatters incoming light, resulting in blurred vision and often affecting central vision. The progressive buildup of these deposits gradually deteriorates visual clarity.
Signs and Genetic Basis
Symptoms of macular corneal dystrophy emerge in early childhood or adolescence. Individuals may notice reduced visual sharpness and glare sensitivity. Eye pain and discomfort can also occur.
Upon examination, doctors observe characteristic gray-white opacities within the corneal stroma, which gradually expand and merge over time, leading to widespread haziness. The condition is an autosomal recessive disorder, meaning an individual inherits two mutated gene copies, one from each parent. Carriers typically do not show symptoms but can pass the gene.
The CHST6 gene (chromosome 16q22) is associated with macular corneal dystrophy. It provides instructions for an enzyme that produces keratan sulfate, essential for corneal transparency. Mutations in this gene lead to abnormal enzymes, causing poorly sulfated or unsulfated keratan sulfate to accumulate in the cornea.
Diagnosis and Management
Diagnosing macular corneal dystrophy involves a thorough eye examination and specialized tests. A slit lamp examination allows observation of characteristic gray-white opacities and overall haziness within the corneal stroma. Corneal topography, a mapping technique, can provide detailed images of the cornea’s shape and thickness, highlighting any irregularities or thinning that may be present. Genetic testing is frequently used to confirm the diagnosis by identifying specific mutations in the CHST6 gene.
Current management strategies for macular corneal dystrophy focus on addressing symptoms and improving visual function. In earlier stages, non-surgical options like rigid gas permeable contact lenses may help improve vision by creating a smoother refractive surface. For advanced cases where vision is significantly impaired by corneal clouding, corneal transplantation is the primary surgical treatment.
Two main types of corneal transplants are performed: penetrating keratoplasty (PKP) and deep anterior lamellar keratoplasty (DALK). PKP involves replacing the entire thickness of the diseased cornea with a clear donor cornea. DALK, a partial-thickness transplant, replaces only the diseased corneal stroma, leaving the patient’s own Descemet’s membrane and endothelium intact. While both procedures aim to restore vision, DALK may carry a lower risk of disease recurrence in the graft compared to PKP, as the underlying disease can sometimes return in the transplanted tissue.
Living with Macular Corneal Dystrophy
Living with macular corneal dystrophy often involves adapting to progressive vision changes. The disease is known to worsen over time, and individuals may require multiple corneal transplants throughout their lives as the opacities can recur in the transplanted tissue. Ongoing ophthalmological care is important for monitoring disease progression, managing symptoms, and determining the optimal timing for interventions.
To help individuals cope with vision loss, a range of low vision aids and rehabilitation services are available. These can include specialized magnifying devices, electronic reading aids, and adaptive strategies for daily tasks. Connecting with support groups or organizations dedicated to rare eye diseases can provide valuable emotional and practical support. These resources offer a platform for individuals and families to share experiences, access information, and navigate the challenges associated with macular corneal dystrophy.