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HPA Magazine 9
Inside the human eye is a natural lens, the crystalline lens. Due to its molecular structure, and in normal conditions, the crystalline lens is transparent and refracts light (“bends the light”, i.e. alters its direction). This allows light to pass through the lens, after passing through the cornea and pupil, and focus on the retina, an essential process for vision.
The correct order of the molecules in the lens is essential for its transparency. Therefore, any factors that bring about an alteration of this molecular arrangement will lead to a loss of this transparency, leading to the formation of a cataract.
Consequently, a cataract is a pathology provoked by the appearance of areas with low transparency in the lens. In turn, these areas of low transparency, depending on the extent, degree of opacification (loss of normal transparency) and position in the crystalline lens, will affect normal vision, either partially or totally.
Despite the existence of various risk factors and systemic conditions associated with the occurrence of cataracts (e.g.: diabetes, smoking, over-exposure to ultraviolet radiation, prolonged use of corticoids, family history of premature cataracts, history of ocular trauma, etc.), the main factor is aging. Normally, it begins to be noticed from age 60, when some clouding is normally detected in the natural lens (although this lesser transparency does not necessarily imply a relevant alteration of vision).
The symptoms associated with cataracts are diverse and also depend on the type of cataract. The most common complaints/symptoms are decreased visual acuity, cloudy vision, greater sensitivity to light, double-vision, faded colours, the need for more light when reading, seeing halos around bright objects and more difficulty with night vision. With worsening symptoms and increasing difficulty/incapacity in performing normal day-to-day activities, even using the correct prescription (e.g.: glasses, contact lenses), cataract surgery should be considered. Surgery is the only way to remove a cataract (there is no proof to the efficiency of eye drops or other pharmacological treatment for cataracts).
The decision (informed consent) should always be made after the ophthalmologist clarifies the characteristics of the surgery you will be submitted to, the expected preparation and recuperation and the potential benefits, as well as the possible complications of the surgery.
In cataract surgery, the crystalline lens with opacification is substituted by an artificial lens (Intraocular Lens, or IOL). This artificial lens will fulfil the functions of the natural lens (it will be transparent and help focus light on the retina). The most frequent surgical approach at the moment is the Phacoemulsification of the crystalline lens, followed by the implantation of the IOL. In this procedure (normally with the patient awake, with local/topical anaesthesia), small incisions are made on the cornea through which the surgeon inserts a probe that uses ultrasounds to emulsify and break up the crystalline lens, allowing it to be aspirated. The IOL is then inserted in the capsule bag, (which previously contained the crystalline lens), and substitutes it.
The surgery is mostly performed as an outpatient procedure, and the patient goes home a few minutes afterwards.
The first intraocular lens was developed and implanted in a human eye in 1949 by Harold Ridley. It was an enormous advance in cataract surgery, because for the first time it was possible for patients to recuperate part of their original vision. Since then, there have been important innovations in the manufacturing, characteristics, diversity and technology associated with IOLs.
However, in spite of the diversity, they all have the same basic construction: Optic with refractive capacity (round lens) and Haptic (“arms” that keep the lens in position inside the eye).
AT THE MOMENT, THERE ARE SEVERAL TYPES OF IOLS AVAILABLE TO PATIENTS AND SURGEONS:
Monofocal Lenses: With the same power in all areas of the lens, they allow for good distance vision, but for near vision, corrective glasses are necessary.
Toric Lenses: Different areas of power allow the correction of astigmatism. They add better quality in distance vision, but it is still necessary to use glasses for near vision.
Accommodative Lenses: These lenses alter their form inside the eye, with the aim to allowing for focussing in different distances.
Multifocal Lenses: These lenses have concentric areas with different powers. The objective is to allow for seeing at various distances (close, middle and far). Nowadays, these can also be toric, to correct astigmatism.
The advances in cataract surgery and in the amount and variety of intraocular lenses have contributed not only towards making this procedure safer, more reproducible and reliable, but at the same time providing better visual results, with considerable levels of satisfaction by the patients as well as the surgeons.