Dystrophy of the cones is a rare disease that affects the cones of the retina, with symptoms that can vary, but often include a decrease in the ability to see in bright light and a loss of visual clarity. Identifying this disease early is crucial to managing its symptoms and improving the quality of life of those affected.
Cones and rods
Retinal photoreceptors are divided into cones e sticks. The two types of photoreceptor cells have structural differences, which are related to important functional characteristics. Moreover, all rods contain the same photopigment, the rhodopsin, whereas the cones have three different types of light-sensitive pigments (the iodopsins), which ensure the discrimination of the various colours (each retinal cone contains only one of the three photopigments).
Features and Functions
Cones and rods are very specialised cells that have the specific function of receiving light stimulus and transforming it into an electrical signal that is transmitted to the brain.
In the visual process, photoreceptors perform complementary functions and their work in synchrony is necessary for good quality vision
- I cones are located in the central part of the retina, the fovea, and are responsible for colour perception, so-called 'photopic vision', and for distinct vision. Cones average between 6.3 and 6.4 million. There are three types of cones, with absorption peaks at 420, 530 and 560 nm, corresponding to the three colours blue, green and red respectively. Therefore, cones are capable of perceiving colours.
- I sticks have a very high sensitivity to light and enable them to see even at night and in low light intensity, so-called 'scotopic or twilight vision'. These photoreceptors, however, are unable to construct good quality images and are incapable of distinguishing colours. In fact, the rods are involved in achromatic vision, which is only characterised by white, black and shades of grey.
Dystrophy of the cones
The cone dystrophy is a degenerative disease that affects the cone cells of the retina, responsible for central vision and colour perception.
It can occur in individuals of all ages, although in many cases the symptoms begin to manifest during childhood or adolescence, while onset in adulthood is rarer.
Differential diagnosis
Other diseases can affect the retina and impair vision, such as age-related macular degeneration or retinitis pigmentosa, but while macular degeneration results in a progressive loss of central vision and retinitis pigmentosa initially impairs peripheral vision, cone dystrophy is characterised by the fact that it primarily impairs sharp colour perception and detailed vision.
This difference is crucial for a correct diagnosis and for designing an appropriate treatment plan that meets the specific needs of affected patients.
Causes of Coni Dystrophy
Genetic Factors
The genetic predisposition is one of the main factors in the onset of cone dystrophy. Numerous studies have shown that specific mutations in certain genes can cause the disease.
To date, about ten genes associated with cone dystrophy have been identified. The gene most frequently involved is ABCA4which also causes Stargardt's disease, and involves autosomal-recessive transmission: the genetic defect must be inherited from each of the parents, both of whom are healthy carriers, in order to manifest symptoms. Other genes frequently associated with cone dystrophy are CRX and GUCY2D, responsible for several autosomal dominant forms (where one copy of the defect is sufficient to manifest the disease) and RPGR (which also causes two-thirds of X-linked retinitis pigmentosa, and predominantly affects males). Rarer forms involve the GUCA1A gene, which is associated with both cone dystrophy and rod-cone dystrophy. It is likely that some mutations in the genes that cause retinitis pigmentosa and macular dystrophies are also responsible for cone dystrophies.
Individuals with a family history of cone dystrophy should consider genetic counselling to assess risk. Genetic testing can identify the presence of mutations that might indicate a predisposition to the disease.
Environmental Influences
Although cone dystrophy has mainly genetic causes, certain environmental influences can aggravate the condition.
Prolonged exposure to bright light without protection can accelerate retinal cone degeneration. Therefore, it is advisable to use sunglasses with UV protection to reduce retinal damage.
Furthermore, exposure to certain toxins or chemicals may contribute to the development and progression of cone dystrophy.
Possible concauses
Diabetes or certain diseases, such as retinitis pigmentosa or other retinal degenerative diseases, can predispose individuals to cone dystrophy.
Common Symptoms of Dystrophy
Symptoms of cone dystrophy can vary, but there are common signs that can help in the diagnostic process.
The most obvious symptom of cone dystrophy is the change in colour vision. Patients may have difficulty distinguishing between different shades, especially in bright light.
In addition to altered colour perception, there is often a loss of sharpness in central vision. This can make it difficult to read, drive or perform activities that require detailed vision.
These changes may occur gradually, making it important to monitor eyesight regularly for significant changes.
The photophobiaor sensitivity to bright light, is another common symptom. Patients may find bright environments annoying and prefer softer light conditions.
Wearing sunglasses or photochromic lenses can help manage sensitivity and improve visual comfort.
Diagnosis and Evaluation
An accurate diagnosis of cone dystrophy is crucial to initiate effective treatment.
Diagnostic procedures for cone dystrophy include various ophthalmological examinations.
- OCT (Optical Coherence Tomography): Provides detailed images of the retina, helping to identify damage or abnormalities in the cones.
- Electroretinogram (ERG)It measures the electrical responses of the retina to light, highlighting possible dysfunctions in the cones.
- Visual Field Test: Assesses central and peripheral vision, identifying areas of visual loss.
Early diagnosis is essential for managing cone dystrophy. Early intervention can slow down the progression of the disease and preserve vision.
Scheduling regular eye examinations, especially for those with a family history of the disease, is essential to detect any abnormalities early.
Early diagnosis also increases the chances of success of experimental therapies, which often require intervention in the early stages.
Treatment Options
There is currently no therapy available that can halt the progression of the disease or restore sight. The visual prognosis is, unfortunately, negative. Therapy aims to slow down the degenerative process, treat complications and help patients cope with the psycho-social impact of blindness.
I current medical treatments for cone dystrophy focus mainly on managing symptoms and improving quality of life.
The use of corrective glasses, special contact lenses and visual aids can help improve residual vision.
Food supplements, such as antioxidants and vitamins, can support ocular health and slow down the progression of the disease.
Le experimental therapies represent hope for the future treatment of cone dystrophy.
Gene therapy is one of the most promising areas, with the aim of correcting the genetic mutations responsible for the disease.
The long-term management of cone dystrophy requires a comprehensive approach that includes regular eye care and psychological support.
Adaptations to work and home life, such as the use of technological devices and reading apps, can improve patients' autonomy.
Participating in support groups can provide a sense of community and help share strategies for coping effectively with the disease.
On the subject of maculopathies see also:
- Hereditary Maculopathies: Perspectives - Oculista Italiano
- Retinitis pigmentosa: new gene discovered - Oculista Italiano
- Hereditary maculopathies: genes & C - Oculista Italiano
Yates WB, Grigg JR, Nash BM, Ma A, Rajagopalan S, et al. Longitudinal study in autosomal recessive PROM1 inherited retinal disease. Ophthalmic Genet. 2025 Jun 10:1-14. doi: 10.1080/13816810.2025.2510306. Epub ahead of print. PMID: 40494823.
English 
Italian 
Spanish