Cataract

The term cataract refers to the opacification of the lens, i.e. the acquired or congenital loss of transparency of the capsule or its nucleus. In the most frequent cases, the opacification generally occurs gradually and is related to the ageing process. This process is the result of biological and biochemical changes that occur in the lens fibres.

The lens is the natural lens of the eye and is responsible for focusing the light rays on the retina. It is a biconvex and transparent structure that sits directly behind the iris, connected to the ciliary body by ligaments called zonules, formed by numerous fibrils. The lens can be divided into three layers: capsule, cortex and nucleus.

According to the World Health Organization (WHO), cataracts are the leading cause of reversible blindness worldwide, and the second leading cause of low vision.

Types of Cataract

Cataracts can be classified according to their morphology into three types:

• cataract nuclear when the opacification of the lens occurs in the central zone;
• cataract cortical cataract when the opacification occurs in the most lateral area with a radiating appearance;
• cataract posterior subcapsular cataract when opacification occurs beneath the posterior lens capsule.

We can further characterise cataract into four major types according to the aetiology:

• Senile: This is the most common type of cataract, it is estimated that 90% of cataracts are due to age and it is usually bilateral.

• Congenital: Appears at birth due to congenital eye malformations, intrauterine infections, genetic syndromes, radiation exposure and no known cause.

• Traumatic: it is the main cause of unilateral blindness in young active adults. Generally associated with blunt or perforating trauma, however its appearance may be related to other factors such as prolonged exposure to infrared and ionising radiation or electrical shocks. On average, the age range of this type of cataract is about two decades younger than that of senile cataract.

• Secondary: This occurs as a consequence of other systemic diseases and the prolonged use of certain drugs, such as corticosteroids in high doses and for a long time.

The change in visual function depends on the type and severity of the cataract. The signs and symptoms of cataract usually evolve progressively with variable speed and tend to become more pronounced in the more advanced stages. Currently, there is no way to stop or predict cataract progression.

The most frequent signs/symptoms are:

• Decreased visual acuity;
• Feeling of "cloudy" or "blurred" vision;
• Photophobia;
• Glare;
• Decreased sensitivity to contrast;
• Changes in colour vision;
• Visual field alterations.

In nuclear cataract there is an induced myopia, caused by refractive change, due to the more frequent central opacity. Normally distance vision worsens, but in some presbyopic patients (who have difficulty reading) near vision may temporarily improve.

In cortical and subcapsular cataracts, the symptoms may be milder and go unnoticed, since the loss of visual acuity is not so notorious and the most common complaint is related to loss of sensitivity to contrast. The findings of the objective examination performed by the ophthalmologist are always related to the subjective symptoms of the patient.

Cataract has several risk factors besides age, such as smoking, alcohol consumption, exposure to sunlight, Diabetes Mellitus, or continuous use of corticosteroids. Currently there is no effective and proven prevention method for cataract, surgery is the only definitive treatment.

As the clinical picture of cataract is very wide, the diagnosis must be made by an ophthalmologist based on certain tests. Among them we highlight the observation by the ophthalmologist under the bio microscope and the visual acuity and contrast vision. A biometrics specular microscopy, the topography and the OCT are exams that help in the choice of the surgical plan and also in finding situations that may overlap, jeopardising the final result of the surgery.

Cataract surgery is currently the only solution to recover lost sight.

Microsurgery of the cataract, with the aid of femtosecond laser and phacoemulsification and the introduction of an intraocular lens is a very effective surgery, of low risk and rare complications, in the hand of an experienced surgeon and with excellent results.

Good results require careful preparation with regard to the evaluation of the eye's parameters in order to correctly choose the lens to be implanted. It is also important to check for any associated pathologies that could compromise the visual outcome.

The lens to be implanted can be fundamentally of three types, monofocal, extended focus (EDOF) or multifocal.

In the first case the patient can see well in the distance, but will always need close reading glasses.

In the second one the distance vision is also corrected and additionally the intermediate vision.

The multifocal lens will allow total independence from glasses.

All have advantages and some disadvantages, so it is always best to discuss the issue during the consultation.

Once the observation and diagnosis have been made, the ophthalmologist, after agreeing on the type of lens to implant, will order several tests in this regard.

A corneal topography allows one to evaluate the degree of astigmatism and the need to implant a lens that can correct it (toric lens). It also allows the existence of irregularities in the cornea, its curvature and the size of the anterior chamber (that is the space between the back of the cornea and the front of the iris and crystalline lens) as well as the angle between the cornea and the root of the iris. Also, the type of chromatic aberrations present.

The specular microscopy that serves to evaluate the state of the endothelium. The thin layer of cells on the back surface of the cornea which are very important in maintaining the transparency of the cornea. It assesses the number and morphology of the cells.

A biometrics which allows the (axial) length of the eye to be evaluated in order to calculate the power in dioptres of the intraocular lens.

O OCT which allows the condition of the retina to be evaluated. The most important thing in cataract surgery is to evaluate the macula, a small central area of the retina where the image is formed and any alterations that may exist, generally of a degenerative nature.

Cataract treatment is surgical and has a high success rate.

The surgical procedure of choice is cataract surgery by phacoemulsification of the lens and intraocular lens implantation, which can be assisted with femtosecond laser.

Although the purpose of intraocular lens implantation is to replace the lens and eliminate existing opacification, it can also correct previously existing refractive errors(astigmatism, hyperopia and myopia), depending on the type of lens implanted.

On the day of the surgery the eye to be operated on is dilated, that is, drops are placed to dilate the pupil through which the opacified lens can be reached.

Anesthetic drops are placed to numb the surface of the eye.

Afterwards and already in the operating theatre, the patient lies down on the operating table. At the doctor's command, the femtosecond laser performs the circular opening of the lens capsule and also the division of the lens itself into small pieces. He also makes the corneal incisions with precision.

Previously, all these steps were performed manually by the surgeon. One of the advantages of the phentosecond laser is that the circular opening of the capsule is centred in the visual axis, which allows for optimal centring of the intraocular lens. The division of the nucleus allows for brief aspiration of the remnants using minimal phacoemulsification energy, ensuring a clear cornea after surgery.

Finally the lens is inserted and the incision is moistened, dispensing with any suturing.

The patient then goes on with his life, with some recommendations and the temporary daily use of anti-inflammatory and antibiotic eye drops, with his visual function recovered.

The surgery is not without complications. During the operation the capsule, which is essential for the correct implantation of the intraocular lens, may break. If the rupture occurs during the removal of the cataract, remnants of the material may remain in the vitreous. If it occurs during the insertion of the lens it can also fall into the vitreous. Both situations require a vitrectomy to clean the remains of the cataract or to remove the intraocular lens. Both cases resolve definitively without further complications and with equal visual recovery. They are very infrequent and rare in the hands of our experienced surgeons. A somewhat unpleasant situation, which delays visual recovery, is corneal oedema, which sometimes persists for a few days and makes vision difficult.

Another very rare case nowadays with the current technique is the expulsive haemorrhage which, as the name suggests, most often ends in the loss of the vision in that eye.

After surgery, other low-frequency situations also occur, such as cystoid oedema of the macula, in which case low vision can sometimes last for weeks or months before resolving spontaneously.

The posterior vitreous detachment that occurs after surgery can cause a retinal hole which in turn can cause a detachment.

A detachment of the choroid may also occur, usually transient.

Despite the possible complications, the surgery has a visual recovery rate of around 98% and serious complications that jeopardise the final result are very rare.