Cataract: Etiology, Classification, Symptoms, Diagnostics, and Treatment

A cataract is a clouding of the natural lens of the eye, which is a component of the optical system of the eyeball. This pathology leads to a significant reduction in visual acuity and subsequently to the complete loss of visual functions.

Anatomy

The lens is a transparent, biconvex anatomical structure located between the iris and the vitreous body. The lens has the shape of a biconvex lens and comprises elastic tissue. Its diameter is approximately 9–10 millimeters.

The main part of the lens consists of transparent protein fibers that ensure its transparency and flexibility. The lens changes its shape due to the action of the ciliary muscles, allowing the eye to focus on objects at various distances. This is called accommodation. The lens must remain transparent so that light can pass through to the retina without distortion. Clouding of the lens, as in the case of cataracts, can lead to a decrease in visual acuity.

Etiology

There are many factors contributing to the development of cataracts. They can be both congenital and acquired.

1. Age-related changes. With increasing age, degenerative changes — known as phacosclerosis — occur in the tissues of the lens. Most people over the age of 60 experience this condition.
2. Hereditary factors. Genetic predisposition can play a role in the development of cataracts.
3. Injuries. Mechanical damage to the eyeball (penetrating injuries or contusions) can lead to clouding of the lens layers.
4. Ultraviolet radiation. Prolonged exposure to sunlight can accelerate the development of cataracts.
5. Systemic diseases. Diabetes mellitus, rheumatoid arthritis, atopic dermatitis, and other chronic diseases can contribute to cataract development.
6. Medications. Prolonged use of corticosteroids, gold compounds, and other medications may increase the risk of lens clouding.
7. Primary eye diseases. Chronic anterior uveitis, angle-closure glaucoma, and high myopia can trigger cataract development.
8. Intrauterine infections (rubella, cytomegalovirus, or syphilis). This leads to varying degrees of lens opacification.

Classification and clinical presentation

By localization of opacities

Depending on the localization of the opacities in the lens fibers, the following types can be distinguished:

1. Nuclear cataract. Hardening of the lens nucleus, accompanied by its yellowing and increased refractive power. This leads to significant “myopization” of the eyeball.
2. Cortical cataract. The initial signs of clouding occur in the cortical layers of the lens near the equator. The central parts of the lens remain transparent for a long time; thus, visual acuity is not altered.
3. Posterior subcapsular cataract. Characterized by an early and rapidly progressing decrease in acuity.
4. Vision cataract. This type of opacity is specific to the waterlogging of lens fibers in the form of subcapsular vacuoles, predominantly located above the posterior capsule.
5. Polar cataract (anterior and posterior). This is lens opacification in the form of a circular spot of whitish or gray color, located at the anterior or posterior pole of the lens under the capsule. The area of opacity is most often adhered to the capsule.
6. Total cataract. Opacity affecting all layers of the lens.

By degree of maturity

According to the degree of maturity, the following forms of senile cataract are distinguished:

• Initial. There are minor opacities in the lens; on biomicroscopy, a cross-section of all lens layers can be obtained, visual acuity (in the absence of retinal changes) is over 0.1, the reflex from the fundus in transmitted light is slightly weakened, and the optic disc and macular zone can be visualized by ophthalmoscopy.
• Immature. Opacities are more significant; on biomicroscopy, a cross-section of all lens layers cannot be obtained, visual acuity is below 0.1, but object vision is preserved, the reflex from the fundus in transmitted light is weakened, the macular zone is not clearly ophthalmoscoped, and the optic disc is ophthalmoscoped through a dense flounce.
• Mature. Significant opacities; on biomicroscopy, a cross-section cannot be obtained even from the anterior cortical layers of the lens, object vision is absent, correct light projection is determined (if there are no retinal changes), the reflex from the fundus in transmitted light is absent, and the fundus is not accessible for ophthalmoscopy.
• Overmature. Pronounced opacities in all layers of the lens with a mother-of-pearl sheen; the cortical layers have a homogeneous structure, sometimes the nucleus is visible, shifted downward (sunsetting sign), there may be folds on the anterior capsule, and the anterior chamber is deeper than in the fellow eye.
• Swelling. Significant homogeneous opacities in all lens layers; the depth of the anterior chamber is less than in the fellow eye.

Diagnosis of cataract

Cataract diagnosis is based on clinical examination and evaluation of symptoms. The main diagnostic criteria include:

1. Symptoms. Blurred or unclear vision, loss of brightness of colors, increased sensitivity to light and glare in bright light, and difficulties with reading and driving, especially at night.
2. Ophthalmological examination. For cataract diagnosis, the patient’s examination is carried out with a wide pupil (mydriasis) in transmitted light. Against the background of a pink reflex, lens opacities appear black, as some of reflected rays are absorbed by the cloudy lens fibers. Biomicroscopy with a slit lamp is used to determine the localization of opacities.

Instrumental and laboratory diagnostic methods

• Determination of visual acuity using charts;
• Autokeratometry for assessing refractive changes and astigmatism indicators;
• Tonometry: measuring intraocular pressure to exclude glaucoma;
• Biomicroscopy refers to examination with a slit lamp, which allows the visualization of the lens and cataract stages, as well as the assessment of other eye structures;
• Ophthalmoscopy: examination of the posterior segment of the eye, which can help exclude other pathologies;
• Echobiometry: for assessing the condition of the lens.

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Treatment

Modern cataract treatment methods primarily focus on surgical intervention, as it is the only way to restore normal vision in this pathology.

Surgical methods: phacoemulsification

1. Phacoemulsification. The most common method of cataract removal. It involves the following:

• Using ultrasonic waves to break up the cloudy lens;
• Extracting it through small incisions (usually less than 3 mm);
• Implanting an artificial intraocular lens (IOL) immediately after lens removal.

2. Laser phacoemulsification. This method is similar to traditional phacoemulsification but uses a laser for more precise and safe cataract disintegration. The laser can reduce the risk of complications and improve the procedure’s effectiveness.
3. Research on cataract treatment drops. Currently, research is underway on the possibility of using eye drops for cataract treatment without surgery; however, these methods have not yet gained widespread clinical use.

Intracapsular artiphakia

Intracapsular artiphakia is a condition of the eye where an artificial intraocular lens (IOL) is implanted into the capsular bag in place of the removed lens, typically during cataract surgery.

Intraocular lenses help restore vision in patients with cataracts, as well as in patients with refractive errors (myopia, hypermetropia, astigmatism).

Cataract surgeries with the implantation of IOL in the posterior chamber of the eyeball are performed in patients of various ages, often under local anesthesia in outpatient settings. Thousands of lens replacement surgeries are performed worldwide every day.

IOL selection is based on the patient’s eye parameters (anterior-posterior axis [APA], corneal refractive power, and effective lens position), as well as the properties of the IOL, implantation features, and indications.

Aphakic intraocular lenses are implanted into the capsular bag after phacoemulsification.

The choice of aphakic IOL type depends on numerous factors:

• The patient’s lifestyle;
• Professional activities;
• The presence of other ophthalmic pathologies (retinal diseases, glaucoma).

Types of intraocular lenses

Intraocular lenses are classified as follows based on the focus range:

1. Monofocal lenses. They allow patients to see well at a specific distance. Depending on the calculated optical power of the lenses, they provide good visual acuity either at a distance or up close. If the IOL is calculated for maximum distance vision, glasses are needed for reading and comfortable work at close range.
2. Multifocal (“pseudoaccommodating”) IOLs. They have several optical zones, allowing clear vision at different distances. These lenses have a special optical structure, specifically a mixed diffractive-refractive optical performance, which allows them to mimic the function of the natural crystalline lens. Having multiple foci significantly enhances visual acuity at both near and far distances, greatly reducing the need for corrective glasses. However, the implantation of multifocal IOLs has some disadvantages:

• Possible presence of optical phenomena after surgery (halos, glare);
• Reduced contrast sensitivity at dusk;
• High requirements for the normal condition of the retina and optic nerve;
• Possible prolonged neuroadaptation period.

According to a 2024 meta-analysis published in BMC Ophthalmology, multifocal IOL show good results in carefully selected patients, with satisfaction rates of 85-90%.

3. Toric intraocular lenses. Designed for patients with corneal astigmatism. They have different optical powers in different meridians. The indications for implanting such IOLs are astigmatism of 1.0 diopter and above, combined with cataracts or refractive anomalies.
4. Intraocular lenses with extended depth of focus (EDOF). The lenses feature an extended focus. One mechanism of action of EDOF IOLs is the elongation of one of the focal points over a great distance using diffractive optics, providing better vision at medium distances than monofocal IOLs. This increases image sharpness and contrast and enhances color perception. However, after implantation of such IOLs, patients are recommended to use glasses for work at close range.

Biocompatible materials and IOL construction

Modern intraocular lenses are made from high-tech biocompatible materials that are fully accepted by the body without risk of rejection or allergic reactions. The main materials used for IOL production are:

• Hydrophobic acrylic. The most common material, with excellent optical clarity and minimal tendency to cloud. This material repels water, reducing the risk of protein deposit accumulation on the lens surface.
• Hydrophilic acrylic. A material with high biocompatibility that attracts moisture. Such lenses exhibit a reduced inflammatory response, which is particularly important for patients with concomitant eye diseases.
• Silicone. Provides superior flexibility and foldability for implantation through a micro incision, although it is currently less used due to the tendency to accumulate deposits on the lens surface.

The primary function of an IOL is the precise focusing of light rays on the retina. The optical power of an IOL is measured in diopters and is selected individually for each patient based on detailed measurements of the eye’s anatomical parameters.

The working principle of an intraocular lens is based on the laws of light refraction. When light rays pass through the IOL, it alters their direction to focus precisely on the retina, creating a clear image.

An intraocular lens comprises optics and haptics. The haptic elements participate in the secure fixation of the IOL within the eye in anatomically and physiologically correct positions. The optical part is responsible for visual functions: it refracts and directs light rays onto the retina at the required angle. It can have multiple optical zones on its surface, allowing clear vision both near and far.