A cataract is the clouding of the crystalline lens, a biconvex structure of varying dioptic power located inside the ocular bulb. It is the most frequent worldwide cause of loss of vision in adults and the elderly.
This pathology has been known for thousands of years. Nevertheless, up until the mid-17th century cataracts were though to be clots of “rotten humours” behind the pupil that could block the emanation of visual spirits from the eye, thus interfering with vision.
One of the most frequent interventions during this “lengthy pre-history” was the reclinatio cataractae, which consisted of inserting a sharp instrument through the sclerocorneal limbus and push this “rotten humour” down into the vitreous body.
Once it became clear that the clouding resided in the crystalline lens itself, treatment options became more rational: in the second half of the 18th century two different surgical techniques were proposed, the precursors to the modern ICCE (IntraCapsular Cataract Extraction) and ECCE (ExtraCapsular Cataract Extraction), by Drs. Daviel and Sharp.
ICCE was invented in 1961 by Dr. Krawicz, ECCE was invented in the early 1980s and the modern FACO in the late 1980s (Kelman).
Cataracts can occur at any age: the pathology is classified on the basis of the age of the patient when it first emerged and the presence of factors which may have led to its onset: the various types include congenital cataract, senile cataract, traumatic cataract, and secondary cataract.
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:
Visual simulation in patients with transparent crystalline lens
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 ambylopia ex anopsia. Cataracts alone never lead to blindness.
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: The cataracts act like a filter and affect the transmission of the various wavelengths, leading to impaired colour vision, especially for blue and violet, and the perception of objects as yellower than they really are.
Reduced sensitivity to contrast: some patients continue to have good vision but have evident subjective disorders, leading to a reduction in the quality of vision. A contrast sensitivity test may be useful and is sometimes more reliable that variations in vision in order to assess the evolution of the cataract in the early phases of the disease.
Dazzling and perception of halos around lights: More frequent in anterior cortical cataracts, it is linked to the increase of diffused light at the margins of cataracts.
Restriction of visual field: When peripheral cataracts are particularly dense, they act as a diaphragm and restrict the field of vision. Additionally, cataracts reduce the intensity of the light that reaches the retina and lead to concentric isoptere shrinkage. This causes difficulties in differential diagnosis, since in the presence of a patient with cataracts and glaucoma, one must determine which of the two disorders caused the restriction of the visual field.
Visual simulation in patient with crystalline lens affected by cataract
The main characteristic of the crystalline lens, along with its accommodation, is transparency.
Cataracts cause a loss of transparency, caused by a change in the submicroscopic structure of the components of the lens. There are many, sometimes contradictory theories to explain the causes of this physiopathological phenomenon (more than 2 out of 3 eyes are affected by opacification after the age of 65).
Known risk factors include age, diabetes mellitus (diabetics suffer from cataracts at three times the rate of non-diabetics), traumatic eye injuries, long-term cortisone treatment, and hereditariness (evident in congenital categories).
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, there are two main techniques used for the surgical extraction of cataracts: phacoemulsification (FACO) and, much less frequently, extracapsular extraction (ECCE).
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 anesthesia modalities can be used: general (ex: newborn children), local, intracameral, or topical anesthesia (with anesthetic eye drops).
Post-operation therapy consists of anti-inflammatory and antibiotic eye drops and requires oral antibiotic therapy.
There are currently 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.
This intervention involves making a long corneal incision (about 11 mm) through which the cataracts is extracted. At the end of the intervention the IOL can be implanted in the capsular bag. The corneal incision is closed using Nylon 10/0.