Fundus albipunctatus is a rare, inherited disorder of the retina, the light-sensitive tissue at the back of the eye. It is named for its distinct feature: many small, whitish-yellow dots scattered across the fundus, or the eye’s interior surface. The condition is a form of congenital night blindness, where vision impairment in low light is present from birth.
The disorder is defined by these retinal flecks and impaired vision in dim lighting. The spots are distributed throughout the retina but typically spare the fovea, the area for sharp, central vision. While its exact prevalence is unknown, it is recognized from childhood and affects males and females equally.
Symptoms and Visual Experience
The defining symptom is nyctalopia, or night blindness, noticed in childhood. This is not a total inability to see in the dark, but a significantly impaired ability to see in low-light. A related characteristic is severely delayed dark adaptation, where the eyes take an exceptionally long time to adjust after moving from a bright to a dark setting.
While a person with normal vision adapts in minutes, someone with this condition can take hours to achieve their best night vision. This delay occurs because the retina’s photoreceptor cells regenerate much slower than normal. This impacts tasks like navigating a house at night or driving at dusk.
Although the primary complaints relate to night vision, some individuals experience other issues. A reduction in central vision sharpness can occur with age if the macula is involved. Less common symptoms include sensitivity to bright light (photophobia) or a reduced field of vision, with severity varying among individuals.
Genetic Origins and Causes
Fundus albipunctatus is a genetic disorder, not caused by lifestyle or environmental factors. It is inherited in an autosomal recessive pattern, meaning an individual must inherit two copies of a mutated gene, one from each parent. The parents are carriers who each have one copy of the gene and do not show symptoms.
Most cases are caused by mutations in the RDH5 gene, which provides instructions for making the enzyme 11-cis retinol dehydrogenase. This enzyme is part of the visual cycle, the process that converts light into nerve signals. This cycle relies on recycling a form of vitamin A called 11-cis retinal.
When the RDH5 gene is mutated, the enzyme’s function is impaired, slowing the regeneration of 11-cis retinal. This slowdown directly causes delayed dark adaptation and night blindness. Researchers believe the buildup of unprocessed materials from this cycle leads to the formation of the white-yellow flecks.
The Diagnostic Process
An ophthalmologist diagnoses this condition through specialized eye exams. A fundus examination uses an ophthalmoscope to view the back of the eye, revealing the hallmark whitish-yellow spots. These spots are scattered throughout the retina but typically spare the central fovea.
An electroretinogram (ERG) measures the retina’s electrical response to light. Initially, the ERG shows a reduced response from the rod cells, which are responsible for night vision. However, after the patient remains in darkness for a prolonged period, a second ERG shows that rod responses have recovered to near-normal levels. This delayed recovery pattern is distinctive for the condition.
Dark adaptometry can also be used to directly measure the time vision takes to adjust to darkness. For a definitive diagnosis, genetic testing can identify mutations in the RDH5 gene from a blood sample. Confirming the mutation solidifies the clinical diagnosis and is useful for genetic counseling.
Management and Prognosis
The long-term outlook is favorable, as the condition is stationary or very slowly progressive. The primary symptom of night blindness remains stable throughout life and does not lead to total blindness. Since there is no cure, management focuses on adapting to the visual limitations.
Management strategies center on practical support and lifestyle adjustments. This includes using high-wattage light bulbs and nightlights at home to improve visibility. Individuals may also benefit from mobility aids or assistive technologies for low vision, especially in unfamiliar, poorly lit environments.
Vitamin A supplementation has been considered due to its role in the visual cycle, but this is not a standard treatment and its effectiveness is debated. It should only be explored under a doctor’s supervision, as high doses of vitamin A can be toxic. Regular monitoring by an ophthalmologist is recommended to track any potential changes in vision.