Pterygium
Encyclopedia
Pterygium most often refers to a benign growth of the conjunctiva
. A pterygium commonly grows from the nasal
side of the sclera
. It is usually present in the palpebral fissure
. It is associated with, and thought to be caused by ultraviolet
-light exposure (e.g., sunlight
), low humidity, and dust. The predominance of pterygia on the nasal side is possibly a result of the sun's rays passing laterally through the cornea
, where it undergoes refraction and becomes focused on the limbic
area. Sunlight passes unobstructed from the lateral side of the eye, focusing on the medial limbus after passing through the cornea. On the contralateral (medial) side, however, the shadow of the nose medially reduces the intensity of sunlight focused on the lateral/temporal
limbus
.
(actinic elastosis
) and fibrovascular proliferation. It has an advancing portion called the head of the pterygium, which is connected to the main body of the pterygium by the neck
. Sometimes a line of iron
deposition can be seen adjacent to the head of the pterygium called Stocker's line. The location of the line can give an indication of the pattern of growth.
The exact cause is unknown, but it is associated with excessive exposure to wind
, sunlight
, or sand
. Therefore, it is more likely to occur in populations that inhabit the areas near the equator
, as well as windy locations. In addition, pterygia are twice as likely to occur in men than women.
Some research also suggests a genetic predisposition due to an expression of vimentin
, which indicates cellular migration by the keratoblasts embryological development, which are the cells that give rise to the layers of the cornea. These cells also exhibit an increased P53 expression likely due to a deficit in the tumor
suppressor gene. These indications give the impression of a migrating limbus
because the cellular origin of the pterygium is actually initiated by the limbal epithelium.
The pterygium is composed of several segments:
with side shields and/or wide brimmed hats and using artificial tears throughout the day may help prevent their formation or stop further growth. Surfers and other water-sport athletes should wear eye protection that blocks 100% of the UV rays from the water, as is often used by snow-sport athletes.
As it is a benign growth, pterygium typically does not require surgery unless it grows to such an extent that it covers the pupil
, obstructing vision
or presents with acute symptoms. Some of the irritating symptoms can be addressed with artificial tears. However, no reliable medical treatment exists to reduce or even prevent pterygium progression. Definitive treatment is achieved only by surgical removal. Long-term follow up is required as pterygium may recur even after complete surgical correction.
If there is recurrence after surgery or if recurrence of pterygium is thought to be vision threatening, it is possible to use strontium (90Sr)
plaque therapy. 90Sr
is a radioactive substance that produces beta particle
s, which penetrate a very short distance into the cornea at the site of the operation. It suppresses the regrowth of blood vessels that occur with return of the pterygium. The treatment requires some local anaesthetic in the eye and is best done at the time of, or on the same day as the pterygium excision.
The 90Sr
plaque is a concave metal disc about 1-1.5 cm in diameter that is hollow and filled with an insoluble strontium salt. The side placed on the eye is a very thin and delicate silver film that will contain the strontium but allow the beta particles to escape. The dose of radiation to the conjunctiva is controlled by the time that the plaque is left in contact with the surface. The integrity of the plaque surfaces is paramount to prevent exposure to patients and so is wipe tested to see if radioactive matter is escaping. Obviously this test must be done very very gently.
Conjunctival auto-grafting is a surgical technique that is effective and safe procedure for pterygium removal. When the pterygium is removed, the tissue that covers the sclera known as the conjunctiva is also extracted. Auto-grafting replaces the bare sclera with tissue that is surgically removed from the inside of the patients’ upper eyelid. That “self-tissue” is then transplanted to the bare sclera and is fixated using sutures, tissue adhesive, or glue adhesive.
Amniotic membrane transplantation is an effective and safe procedure for pterygium removal. Amniotic membrane transplantation offers practical alternative to conjunctival auto graft transplantation for extensive pterygium removal. Amniotic membrane transplantation is tissue that is acquired from the innermost layer of the human placenta and has been used to replace and heal damaged mucosal surfaces including successful reconstruction of the ocular surface. It has been used as a surgical material since the 1940s, and has been shown to have a strong anti-adhesive effect.
Using an amniotic graft facilitates epithelialization, and has anti-inflammatory as well as surface rejuvenation properties. Amniotic membrane transplantation can also be fixated to the sclera using sutures, or glue adhesive.
Amniotic membrane transplantation with Tisseel glue application and Mitomycin-C has shown excellent cosmetic outcomes with a surface free of redness, stitching, or patches, which makes the ocular surface suitable for vision correction surgery sooner.
Conjunctiva
The conjunctiva covers the sclera and lines the inside of the eyelids. It is composed of rare stratified columnar epithelium.-Function:...
. A pterygium commonly grows from the nasal
Human nose
The visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils...
side of the sclera
Sclera
The sclera , also known as the white or white of the eye, is the opaque , fibrous, protective, outer layer of the eye containing collagen and elastic fiber. In the development of the embryo, the sclera is derived from the neural crest...
. It is usually present in the palpebral fissure
Palpebral fissure
Palpebral fissure is the anatomic name for the separation between the upper and lower eyelids. In adults, this measures about 10mm vertically and 30mm horizontally.It can be reduced in horizontal size by fetal alcohol syndrome and in Williams Syndrome...
. It is associated with, and thought to be caused by ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
-light exposure (e.g., sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
), low humidity, and dust. The predominance of pterygia on the nasal side is possibly a result of the sun's rays passing laterally through the cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
, where it undergoes refraction and becomes focused on the limbic
Corneal limbus
The corneal limbus is the border of the cornea and the sclera . The limbus is a common site for the occurrence of corneal epithelial neoplasm....
area. Sunlight passes unobstructed from the lateral side of the eye, focusing on the medial limbus after passing through the cornea. On the contralateral (medial) side, however, the shadow of the nose medially reduces the intensity of sunlight focused on the lateral/temporal
Temple (anatomy)
Temple indicates the side of the head behind the eyes. The bone beneath is the temporal bone as well as part of the sphenoid bone.-Anatomy:Cladists classify land vertebrates based on the presence of an upper hole, a lower hole, both, or neither in the cover of dermal bone which formerly covered the...
limbus
Corneal limbus
The corneal limbus is the border of the cornea and the sclera . The limbus is a common site for the occurrence of corneal epithelial neoplasm....
.
Pathology
Pterygium in the conjunctiva is characterized by elastotic degeneration of collagenCollagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
(actinic elastosis
Actinic elastosis
Actinic, or solar, elastosis is an accumulation of abnormal elastin in the dermis of the skin, and in the conjunctiva of the eye, which occurs as a result of the cumulative effects of prolonged and excessive sun exposure, a process known as photoaging.-Clinical features:Actinic elastosis usually...
) and fibrovascular proliferation. It has an advancing portion called the head of the pterygium, which is connected to the main body of the pterygium by the neck
Neck
The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...
. Sometimes a line of iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
deposition can be seen adjacent to the head of the pterygium called Stocker's line. The location of the line can give an indication of the pattern of growth.
The exact cause is unknown, but it is associated with excessive exposure to wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
, sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
, or sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
. Therefore, it is more likely to occur in populations that inhabit the areas near the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
, as well as windy locations. In addition, pterygia are twice as likely to occur in men than women.
Some research also suggests a genetic predisposition due to an expression of vimentin
Vimentin
Vimentin is a type III intermediate filament protein that is expressed in mesenchymal cells. IF proteins are found in all metazoan cells as well as bacteria. IF, along with tubulin-based microtubules and actin-based microfilaments, comprise the cytoskeleton...
, which indicates cellular migration by the keratoblasts embryological development, which are the cells that give rise to the layers of the cornea. These cells also exhibit an increased P53 expression likely due to a deficit in the tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
suppressor gene. These indications give the impression of a migrating limbus
Corneal limbus
The corneal limbus is the border of the cornea and the sclera . The limbus is a common site for the occurrence of corneal epithelial neoplasm....
because the cellular origin of the pterygium is actually initiated by the limbal epithelium.
The pterygium is composed of several segments:
- Fuchs' Patches (minute gray blemishes that disperse near the pterygium head)
- Stocker's Line (a brownish line composed of iron deposits)
- Hood (fibrous nonvascular portion of the pterygium)
- Head (apex of the pterygium, typically raised and highly vascular)
- Body (fleshy elevated portion congested with tortuous vessels)
- Superior Edge (upper edge of the triangular or wing-shaped portion of the pterygium)
- Inferior Edge (lower edge of the triangular or wing-shaped portion of the ptyerygium).
Prevention
As it is associated with excessive sun or wind exposure, wearing protective sunglassesSunglasses
Sunglasses or sun glasses are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can sometimes also function as a visual aid, as variously termed spectacles or glasses exist, featuring lenses that...
with side shields and/or wide brimmed hats and using artificial tears throughout the day may help prevent their formation or stop further growth. Surfers and other water-sport athletes should wear eye protection that blocks 100% of the UV rays from the water, as is often used by snow-sport athletes.
Symptoms
Symptoms of pterygium include persistent redness, inflammation, foreign body sensation, tearing, which can cause bleeding, dry and itchy eyes. In advanced cases the pterygium can affect vision as it invades the cornea with the potential of obscuring the optical center of the cornea and inducing astigmatism and corneal scarring.Treatment
Today a variety of options are available for the management of pterygium, from irradiation, to conjunctival auto-grafting or amniotic membrane transplantation, along with glue and suture application.As it is a benign growth, pterygium typically does not require surgery unless it grows to such an extent that it covers the pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
, obstructing vision
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
or presents with acute symptoms. Some of the irritating symptoms can be addressed with artificial tears. However, no reliable medical treatment exists to reduce or even prevent pterygium progression. Definitive treatment is achieved only by surgical removal. Long-term follow up is required as pterygium may recur even after complete surgical correction.
If there is recurrence after surgery or if recurrence of pterygium is thought to be vision threatening, it is possible to use strontium (90Sr)
Strontium
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
plaque therapy. 90Sr
Strontium
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
is a radioactive substance that produces beta particle
Beta particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
s, which penetrate a very short distance into the cornea at the site of the operation. It suppresses the regrowth of blood vessels that occur with return of the pterygium. The treatment requires some local anaesthetic in the eye and is best done at the time of, or on the same day as the pterygium excision.
The 90Sr
Strontium
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
plaque is a concave metal disc about 1-1.5 cm in diameter that is hollow and filled with an insoluble strontium salt. The side placed on the eye is a very thin and delicate silver film that will contain the strontium but allow the beta particles to escape. The dose of radiation to the conjunctiva is controlled by the time that the plaque is left in contact with the surface. The integrity of the plaque surfaces is paramount to prevent exposure to patients and so is wipe tested to see if radioactive matter is escaping. Obviously this test must be done very very gently.
Conjunctival auto-grafting is a surgical technique that is effective and safe procedure for pterygium removal. When the pterygium is removed, the tissue that covers the sclera known as the conjunctiva is also extracted. Auto-grafting replaces the bare sclera with tissue that is surgically removed from the inside of the patients’ upper eyelid. That “self-tissue” is then transplanted to the bare sclera and is fixated using sutures, tissue adhesive, or glue adhesive.
Amniotic membrane transplantation is an effective and safe procedure for pterygium removal. Amniotic membrane transplantation offers practical alternative to conjunctival auto graft transplantation for extensive pterygium removal. Amniotic membrane transplantation is tissue that is acquired from the innermost layer of the human placenta and has been used to replace and heal damaged mucosal surfaces including successful reconstruction of the ocular surface. It has been used as a surgical material since the 1940s, and has been shown to have a strong anti-adhesive effect.
Using an amniotic graft facilitates epithelialization, and has anti-inflammatory as well as surface rejuvenation properties. Amniotic membrane transplantation can also be fixated to the sclera using sutures, or glue adhesive.
Amniotic membrane transplantation with Tisseel glue application and Mitomycin-C has shown excellent cosmetic outcomes with a surface free of redness, stitching, or patches, which makes the ocular surface suitable for vision correction surgery sooner.
External links
- Facts About the Cornea and Corneal Disease The National Eye Institute (NEI)
- Pterygium eMedicine WebMD online article on pterygium (overview, differential diagnoses & workup, treatment & medication, and follow-up)
- Pterygium Surgery with Auto Conjuctival Graft Video from the American Medical Videos Journal