La cataract is the opacification of the crystalline (the natural lens of the eye) that gradually leads to a decrease in the view. The natural lens, located between theiris (coloured part of the eye) and the pupil, plays a crucial role in focusing light on the retina. In order to have a sharp image, the parts of the eye in front of the retina, including the lens, must be clear and transparent. If the lens is opacified, the image that reaches the retina will be blurred or distorted, resulting in blurred vision. The extent of the visual disorder depends on the degree of opacification of the crystalline lens and may affect one or both eyes.
Causes of cataracts
The crystalline lens is essentially made up of water and proteins and the structure of these proteins allows light to pass through undisturbed. Over the years, due to the normal ageing process that involves the entire organism, there is an aggregation and oxidation of the lens proteins that leads to the gradual lens opacification. Age-related changes are therefore the key factor in cataract formation, but there may also be other causes that contribute to this degeneration: family history, smoking, excessive exposure to sunlight and the presence of systemic diseases such as diabetes mellitus, hypocalcaemia, myotonic dystrophy, Wilson's disease, hypo- and hyperthyroidism.
There are different types of cataract:
-Congenital cataractcharacterised by partial opacity or total lens, occurs at birth and is diagnosed within the first year of life. Approximately 200,000 children worldwide are blind due to congenital cataract, the incidence of the disease is 3 per 10,000 births and in two thirds of cases it is present in both eyes. The causes are: hereditary (in more than a third of cases); gestational or from intrauterine infections; from metabolic disorders; reactions to drugs administered during pregnancy; diabetes; ocular anomalies of different types.
-Nuclear cataract: è the most common, begins with the gradual hardening, yellowing and sclerosis of the nucleus, later expanding into the other layers of the lens. Its onset is linked to theage and is due to the normal ageing process.
-Cortical cataract: is characterised by white wedge-like opacities that begin in the periphery of the lens and radiate towards the centre. This type of cataract is also age-related, but tends to occur more often in people with diabetes.
-Rear subcapsular (PSC): occurs in the posterior pole of the lens and, although in most cases it is spontaneous, PSC can also develop secondary to metabolic causes such as diabetes, or due to inflammation, uveitis and long-term use of topical or systemic corticosteroids. Significant symptoms may not occur until the cataract is well developed. PSC tends to appear in younger patients and progresses more rapidly than other cataract subtypes.
-Anterior subcapsular (ASC): develops due to degeneration of the epithelial cells of the anterior lens, resulting in an opacity on the anterior surface of the lens beneath the capsule. It may occur secondary to trauma, iatrogenic causes or spontaneously.
-Traumatic cataract: determined by head or eye traumaexposure to intense heat, radiation or chemicals. Clearly, there are some individuals who are more at risk than others, due to their work activities, sports or simply their lifestyle.
-Drug-induced cataract: determined by several pharmacological agents administered systemically, inhaled, intraocularly and cutaneously. The time of onset of this type of cataract depends on the drug. The use of anabolic steroids may, for instance, be associated with its formation.
Cataract symptoms
Cataracts develop slowly and painlessly. Due to the insidious nature of its progression, many patients are often unaware and do not complain of any dramatic change in vision. The most commonly reported symptoms are:
–blurred vision and easy glare
–light halos around pinpoint lights
–reduced visual acuity and contrast sensitivity
-difficulties in distinguishing between colours
-increase in myopia
–double monocular vision and viewing multiple images of an object
Cataract symptoms can also refer to other ocular pathologiesso if they are present, it is always advisable to refer to a specialist.
Cataract diagnosis and intervention strategies will be covered in the next issue.
Bibliography
– Jay Thompson, Naheed Lakhani Cataracts. Prim Care Clin Office Pract 42 (2015) 409-423.
Dr. Carmelo Chines
Direttore responsabile
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