Tissue graft surgery to treat a wing-shaped growth (pterygium) in the eye

Review question
We reviewed the evidence to see which surgery used to treat pterygium (a growth in the eye) is better and safer? We wanted to known which surgery was better at preventing the pterygium from growing back.

Background
A pterygium is a wing-shaped growth in the outer layer of an eye from the corner of the eye and crosses the border between the white of the eye and the iris (the colored part of the eye). Its cause is believed to be exposure to ultraviolet light from the sun. The growth is more common in men and older people. If the pterygium is large enough, seeing can be difficult. It also can make the patient feel that their eye is irritated, dry, or has something in it. It also can cause cosmetic concerns. In some people, the pterygium grows to cover the entire front of the eye and makes it hard to see.

Surgery is required to treat this growth. Even after surgery, it can grow back. When the doctor removes only the growth and leaves the spot underneath exposed, the growth returns in about 80% of patients. A new surgery technique removes the growth and then covers the spot with tissue. This surgery is called a tissue graft. When a tissue graft is used to cover the bare spot, the pterygium does not regrow in as many eyes as when the spot is left bare.

There are two types of tissue graft surgery: conjunctival autograft surgery (CAG) and amniotic membrane transplant (AMT). The purpose of this review was to compare recurrence of pterygium after these two types of tissue graft.

In CAG, tissue from another part of the patient’s eye is removed and then placed over the bare spot that was left where the pterygium was removed. In AMT, tissue from a baby’s placenta after childbirth is used to cover this bare spot. The surgeon gets this tissue from a tissue bank.

Study characteristics
We considered the type of pterygium surgery to be better if it the pterygium returned in a smaller proportion of people at three and six months after the surgery. We searched online databases of published medical articles to find studies that had assigned participants to one of the two surgeries. We included in our review only the studies in which the participants were assigned randomly to their surgery, so that they had an equal chance of being assigned to either one. Study participants could have this growth for the first time (primary pterygium) or could need another surgery because their growth had returned previous surgery. The evidence is current to November 2015.

Key results
We found 20 studies that compared the two surgeries in a total of 1947 eyes. We combined information from the studies to determine which surgery was better. Six months after surgery, the pterygium returned only one third to over half as often in people who had CAG surgery than in people who had AMT surgery. This difference could not be explained by chance alone.

The studies we found did not answer all of our questions. We still want to know the effects of the surgeries on clarity of vision, quality of vision, quality of life and costs. More research studies are needed that answer these questions.

Quality of the evidence
The overall quality of the evidence in favor of CAG is low to moderate because of issues in the conduct of the studies and results were sometimes not similar across studies. Future published research may have an impact on the conclusions provided in this review.

Authors' conclusions: 

In association with pterygium excision, conjunctival autograft is associated with a lower risk of recurrence at six months' after surgery than amniotic membrane transplant. Participants with recurrent pterygia in particular have a lower risk of recurrence when they receive conjunctival autograft surgery compared with amniotic membrane transplant. There are few studies comparing the two techniques with respect to visual acuity outcomes, and we identified no studies that reported on vision-related quality of life or direct or indirect costs. Comparison of these two procedures in such outcome measures bears further investigation. There were an insufficient number of studies that used adjunctive mitomycin C to estimate the effects on pterygium recurrence following conjunctival autograft or amniotic membrane transplant.

Read the full abstract...
Background: 

A pterygium is a fleshy, wing-shaped growth from the conjunctiva, crossing over the limbus onto the cornea. Prevalence ranges widely around the world. Evidence suggests that ultraviolet light is a major contributor in the formation of pterygia. Pterygia impair vision, limit eye movements, and can cause eye irritation, foreign body sensation, and dryness. In some susceptible patients, the pterygium can grow over the entire corneal surface, blocking the visual axis.

Surgery is the only effective treatment for pterygium, though recurrences are common. With simple excision techniques (that is, excising the pterygium and leaving bare sclera), the risk of recurrence has been reported to be upwards of 80%. Pterygium excision combined with a tissue graft has a lower risk of recurrence. In conjunctival autograft surgery, conjunctival tissue from another part of the person's eye along with limbal tissue is resected in one piece and used to cover the area from which the pterygium was excised. Another type of tissue graft surgery for pterygium is amniotic membrane graft, whereby a piece of donor amniotic membrane is fixed to the remaining limbus and bare sclera area after the pterygium has been excised.

Objectives: 

The objective of this review was to assess the safety and effectiveness of conjunctival autograft (with or without adjunctive therapy) compared with amniotic membrane graft (with or without adjunctive therapy) for pterygium. We also planned to determine whether use of MMC yielded better surgical results and to assess the direct and indirect comparative costs of these procedures.

Search strategy: 

We searched CENTRAL (which contains the Cochrane Eyes and Vision Trials Register) (Issue 10, 2015), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to November 2015), EMBASE (January 1980 to November 2015), PubMed (1948 to November 2015), Latin American and Caribbean Health Sciences Literature Database (LILACS) (1982 to November 2015), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com) (last searched 21 November 2014), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic search for trials. We last searched the electronic databases on 23 November 2015.

Selection criteria: 

We included in this review randomized controlled trials that had compared conjunctival autograft surgery (with or without adjunctive therapy) with amniotic membrane graft surgery (with or without adjunctive therapy) in people with primary or recurrent pterygium.

Data collection and analysis: 

Two review authors independently screened search results and assessed full-text reports from among the potentially eligible trials. Two review authors independently extracted data from the included trials and assessed the trial characteristics and risk of bias. The primary outcome was the risk of recurrence of pterygium at 3 months and 6 months after surgery. We combined results from individual studies in meta-analyses using random-effects models. Risk of recurrence of pterygium was reported using risk ratios to compare conjunctival autograft with amniotic membrane transplant.

Main results: 

We identified 20 studies that had analyzed a total of 1947 eyes of 1866 participants (individual studies ranged from 8 to 346 participants who were randomized). The studies were conducted in eight different countries: one in Brazil, three in China, three in Cuba, one in Egypt, two in Iran, two in Thailand, seven in Turkey, and one in Venezuela. Overall risk of bias was unclear, as many studies did not provide information on randomization methods or masking to prevent performance and detection bias.

The risk ratio for recurrence of pterygium using conjunctival autograft versus amniotic membrane transplant was 0.87 (95% confidence interval (CI) 0.43 to 1.77) and 0.53 (95% CI 0.33 to 0.85) at 3 months and 6 months, respectively. These estimates include participants with primary and recurrent pterygia. We performed a subgroup analysis to compare participants with primary pterygia with participants with recurrent pterygia. For participants with primary pterygia, the risk ratio was 0.92 (95% CI 0.37 to 2.30) and 0.58 (95% CI 0.27 to 1.27) at 3 months and 6 months, respectively. We were only able to estimate the recurrence of pterygia at 6 months for participants with recurrent pterygia, and the risk ratio comparing conjunctival autograft with amniotic membrane transplant was 0.45 (95% CI 0.21 to 0.99). One included study was a doctoral thesis and did not use allocation concealment. When this study was excluded in a sensitivity analysis, the risk ratio for pterygium recurrence at 6 months' follow-up was 0.43 (95% CI 0.30 to 0.62) for participants with primary and recurrent pterygium. One of the secondary outcomes, the proportion of participants with clinical improvement, was analyzed in only one study. This study reported clinical outcome as the risk of non-recurrence, which was seen in 93.8% of participants in the conjunctival limbal autograft group and 93.3% in the amniotic membrane transplant group at 3 months after surgery.

We did not analyze data on the need for repeat surgery, vision-related quality of life, and direct and indirect costs of surgery due to an insufficient number of studies reporting these outcomes.

Thirteen studies reported adverse events associated with conjunctival autograft surgery and amniotic membrane transplant surgery. Adverse events that occurred in more than one study were granuloma and pyogenic granuloma and increased intraocular pressure. None of the included studies reported that participants had developed induced astigmatism.

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