Cataracts are the number one cause of blindness in the world. In France, it affects more than 20% of the population over 65, and 60% of those over 85. Its prevalence is constently increasing due to longer lifespans. In the absence of surgical treatment, a patient with cataracts may experience a total or partial clouding of the lens, that causes a gradual and irreversible reduction in vision. In rare cases, it may appear in only one eye (unilateral cataract) but it generally affects both eyes (bilateral cataract). The visual discomfort it causes depends on both the intensity and location of the clouding of the lens.
What do we mean by lens?
The lens is situated behind the iris and is completely transparent. It is elastic and biconvex in shape. This form, or shape, depends on the ciliary muscle, which differs from person to person. It changes shape to allow vision at varying distances and it is this that brings focus to the retina. The lens is composed of a central core of protein fibers which is surrounded by a transparent and elastic envelope : the capsule. In this small "pouch", there are two parts which we can identify anatomically : the anterior capsule and the posterior capsule. In a patient with cataracts, the lens loses its transparency and flexibility and also changes colour according to its severity (brown, red, white, etc...). Light can no longer be transmitted effectively to the retina, therefore the image produced is no longer clear. When the cataract is large, it can be seen by the naked eye, in the pupil.
Symptoms most often appear with age, although cataracts can occur at any time of life. Cataracts are painless and are characterized by purely visual symptoms, the main one being a gradual decrease in vision, sometimes over several years, despite an appropriate correction with glasses or lenses.
Progressive clouding of the lens can manifest as :
- blurred vision
- a decrease in visual acuity
- impaired colour vision (yellowing, or difficulty distinguishing close colours)
- glare, halos around light sources which can make driving at night difficult
- optical aberrations
- a decrease in the vision of contrasts
- the need to increase the light sources for certain activities (reading, sewing...)
The impact of these symptoms on daily activities can become significant and very bothersome.
Different types of cataract :
We will classify the different types of cataracts according to the anatomical zone of the lens in which the cataract appears.
Nuclear cataract : the opacities are located in the nucleus of the lens. Its evolution leads to growing myopia and sometimes the splitting of images.
Cortical cataract : the opacities are located at the periphery, on the cortex of the lens.
Cortico-nuclear cataract : all the layers of the lens are more or less equally clouded. It is the most common form of senile cataract. The patients feel they need more light to see.
Subcapsular cataract : The opacities are located under the posterior or anterior capsule of the lens. This cataract gives the sensation of having a veil before the eyes and of being dazzled.
The different forms of cataracts are also named according to their cause of occurence.
Senile cataract : it is the most common cataract. It appears with ageing, at around 65/70 years old, although it can affect much younger individuals. The nucleus and cortex are opacified (cortoco-nuclear cataract). It often affects far vision first before interfering with near vision.
Traumatic cataract : it often occurs in young people and children following a force trauma (e.g. a punch, champagne cork, ball sports : watch out for badminton and squash!). It is typically posterior subcapsular. It can also follow an eyeball injury or the introduction of a foreign body into the eye. It can sometimes appear long after being hit.
Pathological cataract : they include cataracts alongside another ocular pathology : strong myopia, chronic uveitis (they are called "complicated cataracts") or to a general metabolic pathology such as insulin-dependent diabetes (posterior subcapsular cataracts) for example. There may be iatrogenic cataracts due to prolonged use of certain drugs (corticosteroids) or in the aftermath of radiation therapy.
Congenital cataract : it can be present from birth (0,03% of births) and requires early management to avoid amblyopia.
Secondary cataract or capsular fibrosis : it occurs frequently after cataract surgery. It is not considered a complication of the first operation. It is due to the clouding of the lens envelope within a few months or years after the primary procedure. It is easily diagnosed with a slit lamp examination and treated at once with the YAG laser (capsulotomy).
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