Pterygium

Definition

A pterygium is a pathological condition that affects the anterior segment of the eyeball. It is characterized by fibrovascular proliferation of wing-like, vascularized tissue that starts from the bulbar conjunctiva, crosses the corneoscleral junction (limbus), and extends to the adjacent cornea.

Etiology

Currently, long-term exposure to UV light, changes in lacrimal fluid, cytokine or growth factor imbalances, and p53 mutations are thought to be the major triggers for pterygia.

Anatomic Pathology

A pterygium consists of three parts — head, neck, and body. The head is the invasive part of a triangular-shaped formation, characterized by progressive growth. The neck connects the head to the body and covers the limbus; it is the narrowest part of a pterygium. The body is the broadest conjunctival portion of the pterygium, with its base directed toward the medial corner of the eye. Both early and late stages of the disease may present with an opaque surface of the cornea near the apex of a pterygium (halo).

The key pterygium feature is vessels that appear more dilated than other normal adjacent conjunctival vessels. The formation is typically semitransparent.

Classification

The condition has 3 grades based on the length of a pterygium:

• Grade 1: The initial stage, where the pterygium head is observed near the limbal cornea; visual function or refraction is not affected.
• Grade 2: The pterygium head is located midway between the limbus and the projection of the external border of the normal pupil (3 mm). Irregular corneal astigmatism is observed directly in front of the pterygium head, while the central zone is characterized by minor regular astigmatism. Visual acuity typically remains unaffected.
• Grade 3: The pterygium head is located on the cornea in the projection of the pupil diameter in daylight (3 mm), astigmatism may reach up to 13 diopters; visual function may be impaired due to the thickening of the corneal horizontal meridian.

One more pterygium classification is based on the likelihood of its proliferation:

• 1st degree: Episcleral vessels are clearly visible through the semitrasparent, atrophic membrane. Progression risks are low.
• 2nd degree: This is an active condition. Episcleral vessels are partly visible through the semitrasparent pterygium above the cornea.
• 3rd degree: An opaque, red, sarcotic pterygium proliferates promptly. Episcleral vessels are not visible for examination.

Diagnosis

Medical history: Dry ocular surface, persisting irritation, foreign body sensation, smarting eyes, burning sensations, eyeball hyperemia, increased light sensitivity (photophobia), and decreased contrast sensitivity due to impaired corneal transparency.

Investigations: Corrected visual acuity test, autorefractometry, keratometry, tonometry, and optical coherence tomography (OCT) of the anterior segment of the eye.

Physical examination: Slit-lamp examination of the anterior segment of the eye.

Clinical Manifestations

The diagnosis is based on the following clinical manifestations:

• Fibrovascular proliferation of the conjunctiva within the exposed palpebral fissure;
• Involvement of the corneal surface;
• A triangular or trapezoid-shaped membrane;
• Proliferation starting from the nasal or temporal limbus;
• A white or pink formation depending on the presence of vessels;
• A pigmented epithelial line composed of iron deposits (Stocker’s line) adjacent to a pterygium, which is a marker of a chronic disease.

Treatment

Pterygia may be treated both medically and surgically. Surgical removal of pterygia should be carried out with caution due to the risk of relapse and other complications. The procedure is indicated if a pterygium has not responded to medical therapy, causes constant discomfort, obscures the visual axis, or leads to astigmatism-induced impairment of vision. It may also become too large or restrict ocular motility.

Medical Therapy

An inflamed pterygium may cause irritation, foreign body sensation, and tearing. Most of these symptoms may be relieved with over-the-counter eye drops containing high levels of dexpanthenol or hyaluronic acid. To reduce inflammation, short-term local corticosteroids may be used. These include 0.1 % dexpanthenol eye drops and 0.5 % hydrocortisone eye cream. However, long-term use is not recommended.

Surgical Therapy

Currently, complete pterygium removal combined with conjunctival autografts is considered the industry gold standard, as the procedure is associated with a low relapse rate.

Excision with an amniotic membrane graft may be an alternative technique, but unlike a conjunctival autotransplant, the relapse rate is higher.

Simple excision with bare sclera or conjunctival closure has shown a relapse rate of up to 80 %, which makes it unacceptable.

Peripheral reconstructive lamellar keratoplasty (PALK) is an option in case of corneal opacity.