Retinitis pigmentosa (RP) is a group of inherited eye diseases that cause progressive vision loss. This condition affects the retina, the light-sensitive tissue at the back of the eye, by targeting the photoreceptor cells known as rods and cones. The progression impacts vision in a gradual manner, unfolding over many years.
Early Signs of Progression
The initial indication of retinitis pigmentosa is often a decline in night vision, a symptom known as nyctalopia. This manifests as difficulty seeing in dim light or struggling to adapt when moving from a bright to a darker environment. This occurs because the disease first impacts the rod photoreceptors, which are responsible for vision in low-light conditions.
Shortly after or alongside night vision problems, individuals may notice a gradual loss of their peripheral, or side, vision. This can lead to difficulties such as bumping into furniture or not seeing objects unless they are directly in front. This narrowing of the visual field is a key early sign of the disease’s advancement. During this early stage, daytime vision may remain largely unaffected, which can lead to these symptoms being overlooked.
The Typical Path of Vision Loss
As the disease progresses, the loss of peripheral vision becomes more pronounced, creating what is commonly referred to as “tunnel vision.” This condition narrows the field of view, making activities like navigating crowded spaces or driving increasingly challenging. This happens as photoreceptor cells degenerate from the outer edges of the retina inward. The rate of this visual field loss can vary, but studies show an average annual decline between 7.5% and 10.7%.
Other visual disturbances often develop as the condition advances. Many people experience photopsia, the sensation of seeing flashing or twinkling lights. Another common symptom is photophobia, an increased sensitivity to bright light, linked to the deterioration of cone cells. A decline in the ability to perceive colors can also occur during the mid-stages of the disease.
The progression is typically slow and steady, taking place over several years or decades. Research suggests that, on average, a person with RP may meet the vision standard for legal blindness by a median age of 55. In the late stages, vision may be limited to a small central island or only the ability to perceive light.
Variability in Progression
The progression of retinitis pigmentosa is not uniform. RP is a genetic disease caused by mutations in more than 100 different genes, and the specific gene involved impacts the disease’s characteristics. This genetic diversity is the primary reason the rate and severity of vision loss differ so dramatically between individuals.
The pattern of inheritance also plays a significant role in how the condition progresses. The three main inheritance patterns are autosomal dominant, autosomal recessive, and X-linked. The autosomal dominant form of RP, inherited from a single affected parent, tends to have a slower rate of visual field loss, with some studies estimating an annual decline of around 2.7%.
In contrast, autosomal recessive and X-linked forms of RP often progress more rapidly. Research indicates that autosomal recessive RP may have a mean rate of visual field loss around 10.3% annually, while X-linked RP progresses at about 7.2% per year. The X-linked forms are frequently associated with an earlier onset of symptoms and a more severe overall loss of vision.
Tracking the Progression of RP
Eye care professionals use several specialized tests to monitor the advancement of retinitis pigmentosa. One of the most common is visual field testing, or perimetry, which maps a person’s peripheral vision. This test helps quantify the extent of tunnel vision and track how the field of view changes over time, providing valuable data on the rate of decline.
Another important tool is the electroretinogram, or ERG. This test measures the electrical responses of the retina’s cells, including the rods and cones, when stimulated by light. A reduced or non-detectable ERG response is a characteristic feature of RP and can confirm dysfunction in the photoreceptors before extensive vision loss is apparent.
To view the retinal structure in detail, clinicians use optical coherence tomography (OCT). This non-invasive imaging test provides high-resolution, cross-sectional pictures of the retina’s layers. OCT allows doctors to see the thinning of the photoreceptor layer and helps identify associated complications like macular edema, which is swelling in the central part of the retina.