A cataract is the clouding of the crystalline lens, a biconvex structure of varying dioptic power located inside the ocular bulb.
The cataract is the most frequent worldwide cause of loss of vision in adults and the elderly.
The classification of this pathology is performed according to the age of onset and the presence of factors that may have determined it: congenital cataract, senile cataract, complicated cataract and secondary cataract.
The opacification of the lens is caused by an alteration of the microscopic structure of the lens components. The theories that arose to explain this pathological phenomenon or, better said, pathophysiological (more than 2 out of 3 eyes out of 3 go towards opacification over the age of 65), are manifold, some even contradictory.
Every year 500,000 cataract operations are performed in Italy and this operation represents about 83% of the work of a normal ophthalmology hospital ward, for a disease that affects one in four people after the age of 70.
The known risk factors are age, diabetes mellitus (the incidence of cataract in diabetics is three times higher than in non-diabetics), bulbar traumas, long-lasting cortisone therapies, inheritance (evident in congenital cataracts).
Signs and symptoms
Cataracts are characterized by visual impairments that can evolve more or less rapidly and be more or less severe depending on the type and degree of advancement of the cataract:
Loss of vision: This is the symptom that most frequently alarms patients and leads them to seek an ophthalmology exam. Loss of vision generally develops slowly, over the course of months or, in the case of senile cataracts, years.
This disorder can be very serious for bilateral congenital cataracts, where it can lead to a permanent ambylopia.
Monocular diplopia: Double vision in the eye affected by cataracts. It can be present in the initial phases of cataracts, when the irregularity of lenticular fibres leads to the diffraction of light rays, with the perception of two or more images even when the other eye is closed..
Ametropia: In nuclear cataracts, progressive myopia (index myopia) is frequent and can reach many dioptres; often, in the initial phases, myopia is not accompanied by a loss of transparency, so that it is possible to achieve 10/10 vision using adequate corrections. Elderly patients show a gradual reduction in presbyopia. Astigmatism and hyperopia are rarer and always less severe, secondary to changes in refraction at the cortical fibre level.
Dyschromatopsia, reduced sensitivity to contrast, dazzling and perception of halos around lights, restriction of visual field.
When is surgery indicated?
In adults, the main motivation for cataract removal is loss of vision. The extent of the loss that justifies intervention is variable and depends on the visual needs of each individual. In general, in the presence of bilateral cataracts an intervention is indicated when loss of vision is such that it significantly impairs the patient’s daily activities. In the presence of lateral cataract, visual acuity is compensated by the healthy eye, but there are problems related to reduced field of vision, reduced stereoscopic vision, and photophobia. In such cases, the ophthalmologist will recommend intervention but will leave the patient free to decide whether to do so or not, underlying the non-urgent nature of the intervention.
The extraction of the crystalline lens is urgent and imperative when the evolution of the cataract may lead to serious complications such as glaucoma or secondary uveitis.
Extraction of the cataract and implant of artificial crystalline lens
Today the most used technique for the surgical extraction of cataract is the phacoemulsification (FACO).
The crystalline lens affected by the cataract is replaced by an artificial crystalline lens (IOL) that can correct the eye’s refraction error. Today, pseudo-accommodative lenses can be installed. These lenses can partially re-establish the eye’s capacity to focus, in order to minimize the use of reading glasses after the intervention.
The intervention is usually performed on an outpatient basis. Various anaesthesia modalities can be used: general (ex: new-born children), local, intracameral, or topical anaesthesia (with anaesthetic eye drops). Post-operation therapy consists of anti-inflammatory and antibiotic eye drops and requires oral antibiotic therapy. Today there are many techniques for the phacoemulsification of the crystalline lens. They all share a common characteristic: the fragmentation of the cataract and the aspiration of its cortical residue. The intervention involves making an incision in the corneal periphery (of about 2 mm), through which the probe that will remove the cataracts is introduced. At the end of the intervention, a special instrument is used to insert a soft IOL in the capsular bag through the same incision. Closing the incision does not require stitches.
Recently, the use of the femtosecond laser has been introduced in cataract surgery: this type of technology makes it possible to perform some delicate phases of the operation using a femtoseconds laser that replaces the surgeon's hand. The laser is guided by a computer that captures images of the patient's eye in real time through optical consistency tomography (OCT). This type of surgery standardizes some early stages of surgery; however, the central stage of surgery is still performed by the surgeon's hand, who also carries out the intraocular lens implantation. A fervent debate is still taking place within the scientific community on the real advantages of the femto-assisted cataract intervention over phacoemulsification surgery.