Eye Lens Disorders: Common Eye Diseases and Their Impact on Vision

The eye’s elastic lens, which has a diameter of 9 to 10 mm, is approximately 4 mm thick at rest and is located directly behind the pupil, between the vitreous humor and the iris. It consists of long, thin lens fibers. The lens nucleus is located in the center. It is surrounded by the lens cortex.

Light entering the eye is refracted by the lens and projects a more or less sharp image onto the retina. The optic nerve transmits these signals to the brain.

Changes in the curvature of the lens therefore determine the eye’s ability to focus on near and distant objects. The goal of lens adjustment is to project the image as sharply as possible onto the retina.

How a Lens Works: Refraction of Light and Projection onto a Specific Point

Near Accommodation

The ciliary muscle (Musculus ciliaris) is located on the outer surface of the ciliary body. When shifting from distance to near focus (near accommodation), the elastic zonular fibers that connect the eye’s lens to the ciliary body relax. Due to its high elasticity, the lens curves into a spherical shape. It refracts the incoming light to project a sharp image onto the retina.

Distance Accommodation

When shifting from near to far focus (far accommodation), the ciliary muscle relaxes and the zonular fibers tighten. This tension causes the lens to flatten. Due to the reduced curvature, the light entering from the object (located at a greater distance) is refracted less strongly. The sharp image on the retina is produced by this flattening.

The unit of measurement diopter (dpt) indicates the intensity with which the eye’s lens refracts the light passing through it. This ability of the lens to adjust to near and far vision begins to decline as early as adolescence. The lens nucleus hardens over the course of a person’s life, and the lens loses its elasticity (presbyopia).

Presbyopia is not a disease. Due to the loss of function in the eye’s lens, it becomes increasingly difficult to see nearby objects clearly. Reading glasses correct presbyopia.

As vision slowly deteriorates over the course of years, the person affected perceives a hazy veil in front of their eyes. Those affected can still distinguish between light and dark and determine the direction of incoming light.

Vision of a healthy eye (left), next to it, vision of an eye affected by cataracts

Twilight poses fewer problems for the lens than daylight, since the pupil dilates in low-light conditions, allowing the eye to “look past” the cloudiness of the lens.

Sunlight and other strong light sources, on the other hand, are diffracted by the clouded lens and cause glare. Sunglasses or avoiding bright light are therefore recommended for those affected.

Age-related cataracts

Age-related cataracts (cataracta senilis) account for 90% of cases and are the most common form. As a result of the natural aging process, metabolic processes in the eye’s lens can no longer be maintained. This form of cataract is promoted not only by enzymatic changes and nutritional deficiencies, but also by ultraviolet light.

The progression of age-related cataracts is divided into different stages:

• Early-stage cataract (Cataracta incipiens)

In the early stage, when cataracts are just beginning (Cataracta incipiens), the affected person notices a slight clouding of the lens that is barely bothersome.

• Advanced cataract (Cataracta provecta)

Increased clouding of the eye’s lens occurs in the immature stage of cataracts (Cataracta provecta) and already impairs vision in the affected eye.

• Mature Cataract (Cataracta matura)

The clouding of the eye’s lens in the mature cataract stage (Cataracta matura) is so advanced that the patient can only perceive light and shadow.

Another complication is swelling of the eye’s lens. The pressure exerted on the iris can trigger an acute increase in intraocular pressure (glaucoma attack) similar to that seen in glaucoma.

• Hypermature cataract (Cataracta hypermatura)

In the final stage of clouding, the lens cortex liquefies and the hard lens nucleus sinks downward. The displacement of the lens (also known as lens ectopia) can lead to glaucoma, which destroys the eye’s nerve fibers.

Traumatic cataract

Clouding of the eye’s lens caused by an injury is also classified as an acquired cataract. 

Depending on the cause, they have different names:

• Contusion cataract: Caused by a blow to the eye, such as being hit by a snowball
• Heat-induced cataract: Caused by intense heat exposure
• Electrical cataract: Caused by high-voltage electrical accidents
• Radiation cataract: Caused by ionizing radiation
• Fire cataract: Caused by exposure to infrared radiation

Secondary cataract resulting from another disease

Certain diseases can also cause cataracts: diabetes mellitus, metabolic disorders, and various kidney, skin, and muscle diseases can negatively affect vision and lead to cataracts as a secondary condition.

While treatment can halt the clouding of the eye’s lens, it cannot reverse it. The lens can also become cloudy following eye surgery or due to other eye diseases: for example, after inflammation of the iris or with prolonged use of medications such as cortisone.

Diagnosis and Treatment of Cataracts

Although an advanced cataract can be detected without technical equipment, clouding of the lens is diagnosed during a slit-lamp examination with the pupil dilated.

Slit-lamp examination

Medication cannot treat cataracts. Therefore, cataract surgery is necessary to restore vision. During the procedure, the cloudy natural lens is replaced with an artificial lens.

Surgical Procedures, Risks, and Postoperative Care

The most common surgical procedures are:

• Intracapsular lens extraction

In intracapsular lens extraction, the eye’s natural lens is removed from the eye. This procedure is often used in cases of chronic inflammation. A serious long-term complication of this procedure is the potential for retinal detachment.

• Extracapsular lens extraction

Extracapsular lens extraction is the most commonly used procedure. In this procedure, the posterior lens capsule remains in the eye. The surgeon removes only the anterior lens capsule and the cloudy material of the natural lens.

Sometimes, the lens becomes cloudy again after surgery. This is caused by residual capsule fragments that lead to a renewed obstruction of the pupil. This secondary cataract is treated with laser therapy. The artificial lens implanted is not as elastic as the natural lens. Therefore, it cannot adapt to the curvature of the eye. The resulting loss of refractive power is corrected with contact lenses or glasses.

During follow-up care, the patient receives eye drops containing antibiotics and corticosteroids to prevent inflammation and infection.

In lens ectopia, the lens dislocates into the anterior chamber or the vitreous cavity.

In most cases, an irregular displacement of the lens in only one eye is acquired, for example, as a result of an injury.

Bilateral lens ectopia—a displacement of the lenses in both eyes—is usually associated with congenital malformations or a genetic predisposition.

Types of Lens Ectopia

There are various forms of lens ectopia:

• Lens luxation (Luxatio lentis)

In lens luxation (Luxatio lentis), the lens is completely displaced due to the rupture of the lens suspensory ligaments. The dislodged lens therefore lies at the bottom of the vitreous body or, less commonly, in the anterior chamber of the eye. 

The displacement of the lens into the vitreous body and the breakdown of lens fibers often lead to inflammation. Since the cornea is the only structure left to refract light in the absence of the lens, hyperopia (farsightedness) results.

• Subluxation (Subluxatio lentis)

In subluxation (subluxatio lentis), the eye lens partially shifts out of the pupil due to loosening of the zonular fibers. The lens, which is usually reduced in size (microphakia), takes on a spherical shape (spherophakia). Because the spherical lens has too strong a refractive power, this results in nearsightedness (myopia).

• Lens tremor (iridodonesis)

In lens tremor, the lens suspension is weakened. This results in abnormal mobility of the lens within the eye.

Mild lens dislocations may be asymptomatic. With more severe displacement of the lens, double vision may occur. Visual acuity deteriorates significantly due to the reduction in refractive power. This results in nearsightedness.

The causes of lens ectopia vary:

• Connective tissue or metabolic disorders: Such as Marfan syndrome, Weill-Marchesani syndrome, or homocystinuria.
• Age-related changes: Such as in advanced cataracts, where liquefaction of the lens cortex causes the hard lens nucleus to sink downward.
• Chronic combined inflammation: of the iris and ciliary body (iridocyclitis)
• Eyeball contusion (contusio bulbi): For example, caused by a punch. This can result in a contusion rosette. A contusion rosette is characterized by a star-shaped opacity in the lens cortex and a deposit of scattered iris pigments. 
• Tumors in the eyeball
• Mechanical overstretching of the lens fibers: In cases of an oversized eyeball (myopia magna)

The dislocated lens can cause damage to the cornea, which in turn can lead to corneal opacity. The displaced lens is surgically removed (lensectomy). The patient is then fitted with an artificial lens.

A rare disorder of the eye lens is a fissure in the eye. This can be congenital or result from eye injuries or surgeries. Depending on its size and severity, the fissure affects the patient’s vision.

Disorders of the lens are among the most common eye diseases and can develop over the course of a person’s life as a result of many conditions. In particular, clouding of the lens—as seen in cataracts or glaucoma—often leads to a significant deterioration in vision and, if left untreated, can result in blindness. The eye’s lens is crucial for correctly focusing light rays to produce a sharp image on the light-sensitive layer of the retina. Changes to the cornea and the lens affect the cornea’s refractive power and accommodation, which can impair vision.

Common eye diseases such as glaucoma are often associated with elevated intraocular pressure, which can also damage the optic nerve. At the same time, age-related farsightedness and presbyopia play a major role, as the natural lens’s ability to accommodate decreases, making it difficult to see up close. Astigmatism and farsightedness also cause light rays to be incorrectly focused or to converge before reaching the retina. In such cases, vision aids such as glasses or contact lenses help improve vision and restore sharp focus.

Other changes in the eye, such as aphakia or lens dislocation, affect the stability of the lens, which is anchored in the eye by zonular fibers. Structures such as the vitreous humor, the macula, or the point in the center of the retina are also crucial for visual perception. These conditions can also be exacerbated by diabetes mellitus, as fluid can seep into the retina or the retina can be damaged and detach from its underlying layer. In rare cases, such problems occur even in children and young adults.

Treatment today is usually performed on an outpatient basis and utilizes modern techniques involving the implantation of an artificial lens or intraocular lens. Toric lenses can also be implanted in cases of corneal curvature. After surgery, such as for a secondary cataract, vision is often significantly improved. It is important that such conditions are detected and treated early, ideally through regular preventive checkups with an ophthalmologist. The risk of lens clouding increases significantly, especially after age 60, which is why regular checkups are crucial. This is the only way to achieve long-term improvement in your vision and prevent severe vision loss.