Central areolar choroidal dystrophy (CACD) is a rare inherited eye condition that primarily impacts central vision. This condition leads to a gradual and progressive loss of sight, making everyday tasks such as reading and recognizing faces increasingly difficult. Symptoms typically begin to manifest in adulthood, often between the ages of 30 and 60 years. CACD affects both eyes, leading to similar visual changes in each.
Understanding Central Areolar Choroidal Dystrophy
Central areolar choroidal dystrophy is classified as a type of macular dystrophy, meaning it specifically targets the macula, the small central part of the retina responsible for sharp, detailed vision. The condition involves the degeneration of several interconnected layers within the eye. It initially affects the choroid, a layer of blood vessels located beneath the retina, which supplies oxygen and nutrients to the outer retinal layers.
Following this, the retinal pigment epithelium (RPE) also deteriorates. The RPE is a supportive cell layer situated between the choroid and the light-sensing photoreceptor cells. This layer plays a role in nourishing photoreceptors and managing waste products. As these support layers decline, the photoreceptors themselves, which are responsible for detecting light, also begin to waste away.
This progressive loss of cells and blood vessels in the macula ultimately results in the characteristic central vision impairment seen in individuals with CACD.
Recognizing the Symptoms and Progression
Individuals affected by central areolar choroidal dystrophy typically begin to notice changes in their vision in early to middle adulthood. Early symptoms commonly include blurred or distorted central vision. As the condition advances, individuals may develop blind spots, known as scotomas, in the center of their visual field.
The progression of CACD is gradual and can be categorized into four stages. Initially, there are subtle pigmentary changes in the macula, which might go unnoticed. In the intermediate stages, more pronounced pigment clumping and localized retinal pigment epithelium (RPE) atrophy become apparent, potentially causing mild central vision disturbances or difficulty in low-light conditions.
As the disease progresses further, the atrophic areas within the macula enlarge, leading to more noticeable central blind spots that significantly impair vision. In the late stages, there is extensive atrophy of the macula, involving the RPE, choroid, and photoreceptors. This results in severe central vision loss, while peripheral vision generally remains unaffected.
Genetic Roots and Diagnosis
Central areolar choroidal dystrophy is primarily caused by specific changes, or mutations, in the PRPH2 gene. This gene is crucial for the proper structure and function of the eye’s light-sensing photoreceptor cells. The protein encoded by PRPH2 helps maintain the integrity and shape of the outer segments of rods and cones, which are the sites where light is captured and converted into visual signals.
The inheritance pattern for CACD is most commonly autosomal dominant, meaning that a single mutated copy of the gene from one parent is sufficient to cause the condition. Therefore, each child of an affected individual has approximately a 50% chance of inheriting the altered gene. In some rarer instances, autosomal recessive or sporadic patterns have also been observed.
Diagnosing CACD involves a comprehensive eye examination alongside specialized imaging techniques. An ophthalmologist may observe characteristic central macular atrophy and pigmentary changes during a fundus examination. Optical coherence tomography (OCT) provides detailed cross-sectional images of the retina, revealing atrophy of the photoreceptor layer and the RPE-Bruch’s membrane complex.
Fundus autofluorescence (FAF) imaging can highlight areas of RPE dysfunction, often showing a speckled pattern of increased and decreased signal in earlier stages, which progresses to areas of absent signal as atrophy becomes more widespread. Fluorescein angiography, another imaging method, involves injecting a dye into the bloodstream to visualize blood flow and detect characteristic “window defects” in the diseased areas. Genetic testing can confirm the diagnosis by identifying the specific mutation in the PRPH2 gene or other implicated genes.
Current Management and Future Outlook
Currently, there is no cure for central areolar choroidal dystrophy, and existing treatments primarily focus on managing symptoms and supporting individuals to adapt to their vision loss. Supportive care strategies include:
- Using low vision aids, such as magnifiers and electronic devices, which can help individuals with reading and other close-up tasks.
- Vision rehabilitation services, which teach adaptive strategies and maximize remaining vision for daily activities.
- General eye health practices, such as protecting eyes from excessive UV light.
Ongoing research offers promising avenues for future therapies. Gene therapy is a leading area of investigation for inherited retinal diseases like CACD. This approach aims to deliver healthy copies of the mutated PRPH2 gene into the retinal cells to restore proper cellular function and potentially slow or halt disease progression.
Stem cell therapy is another area of active research, exploring the potential to replace damaged retinal pigment epithelium (RPE) cells and photoreceptors. Undifferentiated stem cells can be guided to develop into these specific retinal cell types, with preclinical studies showing encouraging results. Scientists are also investigating neuroprotection strategies, which seek to protect the remaining retinal cells from further degeneration. The development of animal models continues to be instrumental in understanding disease mechanisms and testing novel therapeutic approaches.