Cone-rod dystrophy
Cone-rod dystrophy is a group of inherited eye disorders that cause progressive vision loss due to the deterioration of light-sensing cells in the retina.
Overview
Cone-rod dystrophy affects the retina, the light-sensitive tissue at the back of the eye. The condition is characterized by the gradual breakdown of photoreceptor cells. There are more than 30 types of the disorder, which can occur alone or as part of a larger syndrome.
Symptoms
Symptoms often begin in childhood and progress over time:
- Early signs: Decreased sharpness of vision (visual acuity) and increased sensitivity to light (photophobia).
- Progression: Impaired color vision (dyschromatopsia), blind spots (scotomas) in the center of the visual field, and partial side (peripheral) vision loss.
- Advanced stages: Night blindness, worsening peripheral vision, and involuntary eye movements (nystagmus). Most affected individuals are legally blind by mid-adulthood.
Causes
The retina contains two types of photoreceptors: rods (for low-light vision) and cones (for bright light and color vision). Mutations in more than 30 genes—such as ABCA4, GUCY2D, and CRX—disrupt the structure and function of these cells. In cone-rod dystrophy, cones typically deteriorate before rods, explaining why light sensitivity and color vision impairment are often the first symptoms.
Inheritance
The condition can be inherited in several patterns:
- Autosomal recessive: Both copies of the gene in each cell have mutations. Parents are typically carriers without symptoms.
- Autosomal dominant: One copy of the altered gene is sufficient to cause the disorder.
- X-linked: Rare forms where the gene is located on the X chromosome. Males are affected more frequently than females.