A pterygium is a wing-shaped, non-transparent mass originating from conjunctival tissue that extends from the nasal, less frequently from the temporal limbus onto the corneal surface. It is composed of connective and vascular tissue and may cause visual impairment and general discomfort.
Patients with pterygia may not experience any symptoms at all and merely seek medical attention due to cosmetic concerns. They may have observed whitish or flesh-colored tissue to cover determined parts of their cornea. Small pterygia may measure less than a millimeter in diameter, large pterygia may extend over considerable parts of the ocular globe. Visual inspection may further reveal the respective tissue to be slightly elevated over the corneal surface, and to be highly vascularized. In most cases, pterygia develop in close proximity to the nasal limbus. The second most common site of pterygia is the temporal limbus of the eye, but they may cover any part of the cornea.
Most patients do report some discomfort, though. They may claim constant, involuntary blinking due to a foreign body sensation, a burning feeling and dryness. If pterygia induce corneal astigmatism, this may result in blurred vision. Large pterygia may also obstruct the visual axis and limit eye movements. Time passed between the initial observation of a pterygium and the onset of such symptoms varies largely. In general, pterygia grow slowly and visual impairment due to this benign mass is uncommon. However, surgical excision and recurrence may enhance its rate of growth , and this fact should be considered when making a decision regarding treatment.
Usually, no anomalies can be observed in the contralateral eye.
Visual inspection of an affected individual generally allows for a reliable diagnosis of pterygium. However, additional diagnostic measures may be indicated to assess corneal damage and visual impairment that may be inflicted by the fibrovascular mass extending over the cornea. Automated and manual keratometry, corneal topography and Scheimpflug imaging may be employed to measure corneal astigmatism; repeated measurements should be carried out applying the same technique . Standard ophthalmological approaches are to be used to evaluate visual acuity, field of vision and related parameters. Based on the results of those tests, each pterygium may be classified according to the comprehensive system for pterygium classification developed by Johnston et al. :
Watchful waiting is the therapeutic approach of choice for asymptomatic patients who don't request surgery for cosmetic reasons. Medical indications of surgical excision of pterygia include chronic or recurrent inflammation, epiphora, corneal astigmatism and visual impairment due to the pterygium covering the visual axis . It should be noted, though, that treatment of pterygia is associated with a high rate of recurrence; furthermore, growth rates may be enhanced after excision of the primary lesion. Also, the risk of complications arising during and after surgery should be considered when defining the endpoint of observation.
Surgical removal of pterygia is the only effective treatment. Either a conjunctival autograft or an amniotic membrane graft may be used to cover the site of excision, but the rate of recurrence has been shown to be higher in patients who underwent amniotic membrane transplantation . Similarly, amniotic membrane grafts seem to favor conjunctival inflammation . Transplants are to be sutured onto adjacent conjunctiva, sclera or underlying layers of the cornea. Tissue glue has been used successfully instead of sutures. In order to avoid recurrence, topical chemotherapeutic agents mitomycin C or 5-fluorouracil may be applied intraoperatively . Antibiotic and anti-inflammatory treatment is required after surgery.
Recently, pterygium extended removal followed by extended conjunctival transplant has been reported to be a valuable alternative approach due to very low rates of recurrence . Here, response to therapy has furthermore been shown to be independent of the application of the abovementioned chemotherapeutics.
In most cases, reduced visual acuity and field of vision may be cured. Furthermore, the cosmetic results of surgical removal of a pterygium are satisfactory. Treatment is generally well tolerated and relieves symptoms for prolonged periods of time. However, recurrence is likely, and renewed surgery may be required. Because complications may arise - e.g., infection, inflammation, and even central retinal artery occlusion - surgery is not generally recommended to asymptomatic patients. The probability of them developing visual impairment due to pterygium growth is low.
The etiology of pterygium development is only poorly understood. Exposure to ultraviolet light has repeatedly been suggested as a major risk factor, and epidemiological data are in agreement with that hypothesis: Pterygia have mainly been described in habitants of subtropical and tropical climates . However, this correlation could not be confirmed in all studies conducted to this end . In any case, ultraviolet light is known to provoke the generation of reactive oxygen species that may damage nucleic acids. Furthermore, ultraviolet light may not only cause DNA double-strand breaks, but has also been shown to induce the release of growth factors and pro-inflammatory cytokines. Besides inflammation, the patient's genotype has been assumed to predispose for the disease. On the one hand, CYP1A1 polymorphisms have been related to pterygia, and this gene encodes for an enzyme of the cytochrome P450 superfamily that may be required to prevent the formation of DNA adducts and cell cycle anomalies . Also, familial accumulation of pterygia has been observed. Little is known about the genotype of members of affected families, but there are studies relating pterygia with reduced capacities of DNA repair . Thus, there is a certain consensus in that DNA damage triggers pterygium development.
Pterygia are common, although the prevalence of pterygium has been reported to vary with geographical location. As mentioned above, it is generally assumed that pterygium prevalence decreases with geographical latitude, i.e., that most patients are living in subtropical and tropical climates. According to a recently published meta-analysis, prevalence in latitudes above 40° is less than 5%, while up to 15% of people living between 0 and 10° are affected by pterygium . Interestingly, rural populations have been found more prone to pterygium than urban populations. Both racial and gender predilections have been reported. Darker skin has been proposed to confer a certain degree of protection from pterygium and men may be affected significantly more often than women . Of note, other studies reported almost identical prevalence rates in both genders . Furthermore, pterygium prevalence increases with age. According to the aforecited meta-analysis, pterygia have been observed twice as often in persons aged 60 years and older than in those individuals younger than 50 years (prevalence of 20.1% and 11%, respectively). Pterygia in pediatric patients are rare, but have occasionally been described .
The pathogenesis of pterygium development is only poorly understood. The aforedescribed observations regarding the disease' etiology as well as the fact that recurrence rates may be lowered by intraoperative application of antineoplastic agents like mitomycin C or 5-fluorouracil suggest an uncontrolled proliferation of limbal basal epithelial stem cells due to DNA damage and impairment of repair processes. On the other hand, pterygium may be considered a degenerative disorder: Ultraviolet light has been shown to provoke structural and functional alterations of connective tissue fibers. In this context, elastodysplasia and elastodystrophy have long since been shown to be related to the onset of pingeuculas, which correspond to stage 0 pterygia  . Furthermore, the release of pro-inflammatory cytokines and growth factors mediated by ultraviolet radiation stimulates fibroblast proliferation and angioneogenesis. Those processes occur simultaneously and give rise to the migration of altered stem cells onto the cornea and the development of fibrovascular tissue forming the wing-shaped pterygium. Bowman's membrane is increasingly degraded during pterygium development, possibly by matrix metalloproteinases released from infiltrating immune cells .
Because exposure to ultraviolet radiation is assumed to be a major risk factor, minimization of ultraviolet light reaching the eyes may decrease the individual risk of developing a pterygium. Accordingly, it is recommended to wear sunglasses conferring protection from ultraviolet radiation. Wearing a cap may be very helpful, too. First and foremost, patients with a family history of pterygia, those individuals living in geographical areas of high solar radiation and persons who engage in outdoor activities are to be advised of these measures.
Pterygium is the chosen designation for the benign growth of conjunctival tissue onto the cornea. It usually develops in close proximity to the nasal limbus, but may also originate from the temporal limbus. Unilateral pterygia are more common than the bilateral form of the disease. Affected individuals frequently claim the sensation of a foreign body in their eye, ocular irritation and dryness. As the pterygium grows, it may increasingly interfere with eye movements and vision. Surgical removal of excess tissue is the only treatment option available, but recurrence rates exceed 80% . Recently, tissue graft surgery, namely coverage of the affected cornea with a conjunctival autograft or an amniotic membrane graft, has gained interest due to lower rates of recurrence. Fortunately, pterygia grow slowly, especially during initial manifestation. Thus, watchful waiting may be the approach of choice in asymptomatic patients who don't request the excision of pterygia for cosmetic reasons.
Of note, pterygium colli or webbed neck refers to the presence of bilateral skin folds extending from the mastoid to the acromion. It may be encountered in patients suffering from Turner syndrome or multiple pterygium syndrome.
The medical term pterygium refers to the benign growth of corneal stem cells and the development of a wing-shaped, whitish-colored and well-vascularized mass that extends onto the visual surface of the eye. This mass is generally slightly elevated and most commonly develops in close proximity to the nasal limbus, i.e., on the inner side of the eye. The lesion is painless, but may cause foreign body sensation, a burning feeling and dryness that trigger constant and uncontrolled blinking. In severe cases, pterygia may obstruct the visual axis and thus cause a reduction of the patient's field of vision; they may also alter the cornea's curvature and provoke astigmatism and blurred vision. However, some patients suffering from pterygium may not experience any of those symptoms, but seek medical attention only for cosmetic concerns.
Both visual and cosmetic prognoses are generally good. The only effective treatment for pterygia is surgical removal of excess tissue, and this procedure is usually well tolerated by patients. The site of excision is subsequently covered with a conjunctival autograft or an amniotic membrane graft. Furthermore, chemotherapeutic agents may be applied to reduce the rate of recurrence, which is the main cause of unsuccessful treatment. In fact, recurrence rates have been reported to be as high as 80%. Re-treatment is possible, though. But because every surgical intervention is associated with minor risks of infection, inflammation and possibly permanent damage, watchful waiting may be recommended to asymptomatic patients instead.
The triggers of pterygium development are only poorly understood. DNA damage induced by exposure to ultraviolet light and genetic factors have been proposed to be involved in the disease' etiology, and consequently, the use of sunglasses conferring protection from ultraviolet radiation, wearing a cap and reducing sun exposure and general may aid to reduce the individual risk of pterygia and recurrence.