Cataracts: The Eyes Have It

The Crystalline Lens

The crystalline lens is a natural lens located in the interior of the eye, behind the iris, able to focus images of the external world onto the retina depending on their distance. The crystalline lens is a biconvex lens of variable focusing power, namely a lens able to modify its optical (or focusing) power by changing its shape, a phenomenon known as accommodation. The ability of the crystalline lens to modify its shape (curvature) – and hence its optical (or dioptric) power – depends on the work of the ciliary body, an eye structure which is connected to the crystalline lens through a system of fibrils, called zonular fibers, and that works as a real muscle.

The crystalline lens is composed of three different layers:
1) an external membrane called capsule
2) the lens itself – called central nucleus
3) and an intermediate layer called cortex, situated between the central nucleus and the capsule.

At a young age and in the absence of pathologies, the crystalline lens is an elastic and perfectly transparent tissue; the loss of elasticity gives rise to presbyopia (the inability to focus on near objects), whereas the loss of transparency, which is caused by a process of opacification of the lens, gives rise to an eye condition known as cataract.

The opacification of the crystalline lens makes vision cloudy and, depending on the seriousness and localization of the opacification, the resulting visual impairment may be quite significant. Cataract formation is very common in older age (age-related cataract), but there are several other factors that can determine the formation of different types of cataract, such as 1) congenital cataract, already present at birth, 2) secondary cataract, caused by pre-existing pathologies – affecting the eyes (e.g. glaucoma, uveitis etc.) or the whole organism (e.g. diabetes), 3) cataract related to severe nearsightedness, due to pre-existent pathological myopia, 4) traumatic cataract, such as that deriving from eye injury or surgery, 5) radiation or phototoxic cataract, which follows prolonged exposures to strong sunlight or UV-radiations (e.g. solar lamps, laboratory instruments etc.) without adequate protection, and 6) drug-induced cataract (e.g. steroids-induced cataract). Family history plays also a very important role in the development of cataract.

Steroid-induced Cataract or Posterior Subcapsular Cataract (PSC)

Among drug-induced cataracts, steroid-induced cataract assumes a very relevant importance due to the wide use of steroids (also known as corticosteroids or glucocorticosteroids) in medicine.

Steroid-induced cataract differs from the other types of cataract for its origin, peculiar anatomical location and aspect. With regards to its anatomical location, steroid-induced cataract formation occurs always in the posterior cortex, just within the posterior capsule, and for this reason it is called a posterior subcapsular cataract (PSC). PSC presents a characteristically irregular shape and a dishomogeneous structure consisting of whitish-yellowish opaque granules interspersed with very tiny vacuoles. PSC usually develops in both eyes at the same time.

Corticosteroids (Also Known As Glucocorticoids Or Steroids)

Corticosteroids (or glucocorticoids) belong to the wide class of chemical compounds called steroids, which are ubiquitous in animals and plants, where they have very important biological functions. In animals, steroids can be classified into five categories: Estrogens, progestagens, androgens, mineralcorticoids and glucocorticoids. All corticosteroids can be produced in different tissues of the body and can present the most various functions. Every single compound is produced by a specific body compartment (tissue, organ) and acts in a specific way on – and then in – specific cells called target cells, which can be near or far from the production site. Once entered in a cell, steroids can trigger different cellular mechanisms; most of these mechanisms act very often on the regulation of DNA.

The most common glucocorticoid in nature is cortisol (or hydrocortisone), from which derive cortisone and corticosterone. Glucocorticoids are powerful anti-inflammatory and immunosuppressive agents and are the most widely used drugs to treat inflammations – also ocular inflammations – and prevent rejections after organ transplantation. The usefulness of glucocorticoids in medicine brought pharmaceutical industries to synthesize new molecules with different functional groups and hence different properties.

Corticosteroids And Direct/Indirect Undesired Effects On Eye Health

The use of glucocorticoids presents different contraindications and adverse reactions that may affect eyes directly or indirectly, such as for example the onset of diabetes, a metabolic disorder that can have very serious consequences on the retina, and the enhancement of the intraocular pressure (IOP) that can cause glaucoma, an eye pathology that can cause extremely serious damages to the optic nerve and hence vision. Other side effects deriving from the use of glucocorticoids are the reactivation of the Herpes simplex virus and the reduction of the healing process of the cornea after damage or refractive surgery. The most common and known side effect due to the use of corticosteroids is the development of posterior subcapsular cataract (PSC): Cortison, desametason and prednisone are the most common drugs that, among others, induce PSC formation. 

Corticosteroids And The Induction Of Posterior Subcapsular Cataract (PSC)

The correlation between the prolonged use of corticosteroids and PSC formation is known since 1960. Corticosteroids are widely used drugs and they are real life-savers in many situations, such as for example bronchial asthma and “anaphylactic shock”, to contrast serious inflammations (cortisone is the most commonly used drug for rheumatoid arthritis) and to inhibit rejections in patients who underwent organ transplantation.

Several studies have shown that cataract formation due to the use of corticosteroid presents a dose-effect: The higher the dosage, the higher is the percentage of cataract formation. The effect of PSC formation on children is faster and at a lower dosage. According to many researchers, besides dose-effect, individual susceptibility is also a very important factor, most probably due to genetic variability. In any case, dose-effect of corticosteroids is a problem to which doctors must pay great attention when they prescribe treatments based on steroids to their patients, above all if the treatment is long-term.

Given the existence of different individual susceptibility to the same drug and different susceptibility of the same individual to different drugs, it is not possible to foresee if and when steroids administration will give rise to cataract formation, hence the best thing to do for a patient receiving steroid treatment is to undergo careful eye examinations regularly, in order to monitor the state of health of the crystalline lens over time.

Today the use of steroids is strongly increasing, hence we expect an increase of PCS.

Corticosteroids And Direct/Indirect Undesired Effects On Eye Health

The use of glucocorticoids presents different contraindications and adverse reactions that may affect eyes directly or indirectly, such as for example the onset of diabetes, a metabolic disorder that can have very serious consequences on the retina, and the enhancement of the intraocular pressure (IOP) that can cause glaucoma, an eye pathology that can cause extremely serious damages to the optic nerve and hence vision. Other side effects deriving from the use of glucocorticoids are the reactivation of the Herpes simplex virus and the reduction of the healing process of the cornea after damage or refractive surgery. The most common and known side effect due to the use of corticosteroids is the development of posterior subcapsular cataract (PSC): Cortison, desametason and prednisone are the most common drugs that, among others, induce PSC formation. 

Corticosteroids And Direct/Indirect Undesired Effects On Eye Health

The use of glucocorticoids presents different contraindications and adverse reactions that may affect eyes directly or indirectly, such as for example the onset of diabetes, a metabolic disorder that can have very serious consequences on the retina, and the enhancement of the intraocular pressure (IOP) that can cause glaucoma, an eye pathology that can cause extremely serious damages to the optic nerve and hence vision. Other side effects deriving from the use of glucocorticoids are the reactivation of the Herpes simplex virus and the reduction of the healing process of the cornea after damage or refractive surgery. The most common and known side effect due to the use of corticosteroids is the development of posterior subcapsular cataract (PSC): Cortison, desametason and prednisone are the most common drugs that, among others, induce PSC formation. 

When Cataract Surgery Is Necessary

Steroid-induced cataract can progress quite rapidly and cataract surgery should be performed when the condition becomes troublesome and the person affected feels the need to get rid of it in order to re-establish a clear vision, especially if vision is so blurry to make it difficult if not dangerous to carry out normal daily activities such as going downstairs or driving. It is very important not to wait too long before performing cataract surgery, because in this case the crystalline lens becomes particularly hard and this may give rise to higher risks of complications during the surgical procedure.

Prevention Of Cataract And The Importance Of The Use Of UV Protection

Unfortunately, there are no drugs, eye drops, eye exercises or eyeglasses that can stop or slow down the process of the crystalline lens opacification. Today, the only cure against cataract is cataract surgery, a safe, fast and non-painful routinary surgical procedure that consists in the removal of the opacified crystalline lens and its replacement with a perfectly transparent artificial lens.

The use of sunglasses or clip-on lenses with protection against UV can surely help protect your eyes from UV-light and prevent, or at least delay, cataract formation and also the development of other important ocular pathologies such as maculopathies.

Cataract Surgery: Phacoemulsification

The most advanced cataract surgery procedure available nowadays is called phacoemulsification, which consists in the removal of the opacified crystalline lens and its substitution with a biocompatible artificial lens, called intraocular lens (IOL). Phacoemulsification is a very sophisticated technique that uses ultrasounds to break and eliminate the most central portion of the opacified crystalline lens. The external portion of the crystalline lens, called posterior capsule, is left untouched and works as support for the implant of the new artificial crystalline.

Phacoemulsification is performed in an outpatient modality after local anesthesia and it lasts a few minutes; its performing is minimally invasive, absolutely painless and presents a short post-surgical period (a few days) with no particular discomfort.

Benefits And Possible Risks Of Cataract Surgery

Cataract surgery is a procedure that offers excellent results and nowadays benefits deriving from this technique are really consistent. Vision improves sensibly in the majority of people who undergo this procedure, unless there are serious pre-existing problems affecting the cornea, the retina or the optic nerve.

Very serious complications, such to limit or put vision in danger, are extremely rare; however before undergoing cataract surgery it is very important to talk with your eye doctor about advantages and possible complications of this procedure.

Secondary Cataract (Capsular Fibrosis) And Posterior Capsulotomy

In most cases, months or years after cataract surgery, the posterior capsule(the posterior part of the external membrane of the crystalline lens, called capsule, which hosts the crystalline lens) can also undergo a process of fibrosis and opacification, making vision blurry again. This condition is called secondary cataract (the more precise medical term is capsular fibrosis) and has to be treated with a second short procedure called posterior capsulotomy, a non-invasive laser treatment that lasts a few seconds and is absolutely painless and discomfortless in its post-operative period.