Treatment of Pterygium on the Refractive Errors: A Systematic Review
Article information
Abstract
Purpose
Pterygium is a chronic, degenerative condition of unknown cause, and its development can lead to significant refractive errors due to localized flattening of the cornea near the central area of the leading edge. However, to date, the impact of pterygium and its surgical removal on refractive errors has not been thoroughly compiled in a comprehensive study. This systematic review aims to evaluate the effect of pterygium surgery on refractive errors and to examine the relationship between the size of the pterygium and its effect on refractive errors both before and after pterygium surgery.
Methods
The Cochrane methodology was used to design and conduct the present systematic review. Relevant articles published up to December 2024 were searched and collected from four electronic databases: PubMed, Scopus, MEDLINE, and Web of Science. Additionally, a manual search was conducted to locate relevant studies. The keywords used in the search included “pterygium” combined with terms such as “refractive errors,” “myopia,” “hyperopia,” “astigmatism,” and “presbyopia.”
Results
In total, 23 studies including 1,663 eyes were included in this review. In the majority of studies, more than one technique was used, with conjunctival autograft being the most common technique for pterygium treatment. In most reviewed studies, a significant improvement in visual acuity, keratometry values—both horizontal keratometry (K1) and vertical keratometry (K2)—corneal astigmatism, corneal spherical power, surface regularity index, and surface asymmetry index, as well as a decrease in corneal astigmatism, spherical error, and wavefront aberration, were reported after pterygium excision.
Conclusions
Pterygium surgery can be effective in reducing refractive errors, including astigmatism, wavefront aberration, and spherical aberration, in various ways. However, this also depends on the size of the pterygium. The findings of this study suggest that early removal of pterygia reduces the likelihood of significant residual aberrations. Pterygia between 3 and 4 mm in size pose a notable risk for residual aberrations
Pterygium is a chronic, degenerative condition of unknown cause, frequently found in individuals residing in hot, arid regions. It occurs more frequently in older adults and men than in women, primarily because of extended periods spent outdoors [1–3]. Pterygium commonly appears on the nasal side of the bulbar conjunctiva between the interpalpebral fissures but can also develop on the temporal side, often accompanying nasal pterygium. It can be either unilateral or bilateral, though it is not symmetrical [4–6].
The primary symptoms include a feeling of having a foreign object in the eye, irritation, cosmetic concerns, and impaired vision as it grows onto the cornea, causing astigmatism. Pterygium can advance, potentially reaching or covering the pupillary margin, thereby blocking the visual axis [7–9]. Pterygium can be categorized into two types based on its progression [10]: “progressive,” which is thick, fleshy, and highly vascular, often featuring Fuchs spot; and “regressive or atrophic,” which is thin, atrophic, and minimally vascular, often displaying Stocker line, and never completely disappears.
Pterygium is characterized by the expansion of fibrovascular tissue from the bulbar conjunctiva onto the cornea. This condition can result in substantial visual impairment by impacting the visual axis or causing significant regular and irregular astigmatism. The high astigmatism associated with pterygium usually diminishes after it is removed [2].
The development of a pterygium can lead to significant astigmatism, often described as with-the-rule (WTR) astigmatism, resulting from localized flattening of the cornea near the central area of the leading edge. Typically, a pterygium causes localized flattening at its central apex. Because this flattening occurs along the horizontal meridian, it usually results in WTR corneal astigmatism [10,11]. In 1998, Fong et al. [12] were the first to observe that the excision of a pterygium generally reverses the corneal flattening induced by the pterygium.
Since then, numerous studies have demonstrated significant improvements in astigmatism caused by pterygium following surgery. These studies have indicated that larger pterygia induce greater amounts of astigmatism and that removing larger pterygia results in more significant changes in corneal astigmatism, which is correlated with the size of the pterygium. Additionally, some studies have assessed postoperative changes in astigmatism using eye refraction, corneal topography, or both. Corneal topography measures the front surface of the cornea to calculate astigmatism, but does not directly measure the back corneal astigmatism, potentially leading to significant errors in evaluating total corneal astigmatism [13,14]. Therefore, to accurately assess the effects of pterygium surgery on corneal astigmatism, it is crucial to evaluate both the front and back corneal surfaces [15].
However, to date, the impact of pterygium and its surgical removal on refractive errors has not been thoroughly compiled in a comprehensive study. This systematic review aims to evaluate the effect of pterygium surgery on refractive errors and examine the relationship between the size of the pterygium and its effect on refractive errors both before and after pterygium surgery.
Materials and Methods
This systematic review was conducted using the Cochrane methodology and focused on studies evaluating the impact of pterygium treatment on refractive errors. The following seven steps of the Cochrane approach were used [16]: formulating a question, setting eligibility criteria, conducting a search, eliminating irrelevant studies based on eligibility criteria, assessing quality, extracting data, and engaging in discussion.
Inclusion and exclusion criteria
The selection of papers for the review was guided by the PICO (participants, intervention, comparison, outcome) criteria. The inclusion criteria required a clear description of the methodological technique, a focus on the treatment of pterygium and its effects on refractive errors, human subject research, and publication in English. Articles addressing other complications of pterygium treatment, those with insufficient data, studies involving animal samples, in vitro research, narrative studies, reviews, qualitative studies, and books were excluded from the study. This review exclusively considered prospective intervention studies, while all other types, including retrospective studies, non-interventional studies, case reports, and case series, were excluded. Moreover, studies focused on childhood pterygium and articles with a low sample size (fewer than 45 eyes) were excluded from the present review.
Literature search
During the search process, electronic databases such as PubMed, Scopus, MEDLINE, and Web of Science were examined up to December 2024. Additionally, a manual search was conducted to locate relevant studies. The keywords used in the search included “pterygium” combined with terms like “refractive errors,” “myopia,” “hyperopia,” “astigmatism,” and “presbyopia.”
Study design and data extraction
In this current review, we incorporated all studies evaluating the treatment of pterygium on refractive errors such as myopia, hyperopia, astigmatism, and presbyopia. The search process was conducted by two trained investigators, who analyzed all published articles based on the specified study goals. We searched four databases: PubMed, Scopus, MEDLINE, and Web of Science up to 2024 using the keywords mentioned earlier. The search spanned 1 month (from November 1 to December 1, 2024). The investigators also searched additional databases, including Google Scholar, to locate further relevant studies and ensure no data were missed. Initially, the titles and abstracts of the papers were reviewed by the researchers, and irrelevant articles were excluded based on eligibility criteria. For articles where relevance could not be determined from the titles and abstracts alone, full texts were retrieved for further evaluation. The two researchers consulted each other during the process of including or excluding studies to reach a consensus. Once the articles were selected, the full-text versions were thoroughly reviewed. For unavailable studies, the researchers attempted to obtain the information by contacting the corresponding author via email. During data extraction, the two researchers maintained constant communication. Data were extracted from the selected papers according to the study objectives and recorded in a checklist. The extracted data included information such as sample size, age, sex ratio, type of treatment, and refractive errors including myopia, hyperopia, astigmatism, and presbyopia.
Quality assessment
The evaluation of the quality of the chosen articles was examined across seven areas of bias [17]: sequence creation, allocation masking, blinding, missing outcome data, selective reporting, and other bias sources. Low, high, and unclear risks of bias in these domains were documented as “yes,” “no,” and “unclear,” respectively.
Results
In the initial search of the four databases, a total of 894 papers were identified. Out of these, 716 articles were excluded due to their irrelevance and focus on other diseases, such as cataract. Subsequently, 62 duplicate articles were also removed. From the remaining 93 articles, 5 published in languages other than English and 2 with inaccessible full-text versions (unavailable articles) were eliminated. Additionally, 16 qualitative and narrative reviews, 3 in vitro studies, and 5 books were excluded, along with 34 retrospective and noninterventional studies, 9 case reports and case series, 1 study on childhood pterygium, and 18 articles with sample sizes fewer than 45 eyes. Ultimately, 23 studies were included in the review process (Fig. 1 and Table 1–3) [7,10,12,14,15,18–35].
PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) flowchart of the article selection process.
Characteristics of the included studies
Visual and refractive outcomes of the included studies
Clinical outcomes and interpretation of the included studies
In this review, all studies included were prospective, nonrandomized interventions. A total of 1,663 eyes were evaluated for various aspects of refractive errors among patients who underwent different types of pterygium surgery. The mean age of patients ranged from 32.54 to 64.6 years, with an overall age range of 18 to 86 years. One study did not determine the frequency of sex [7]. In the remaining studies, there were 927 men and 648 women, resulting in a male to female ratio of 1.43:1. The degree of pterygium was not determined in only one study [31]. Fourteen studies focused solely on primary pterygium [10, 12,14,15,18,20,21,23,27,28,30,32,33,35]. In three studies, both primary and recurrent pterygium were assessed [21,25,29], while five studies evaluated patients with various degrees of pterygium [7,19,24–26].
The majority of the reviewed studies (20 of 23, 86.9%) were conducted in Asia, due to the high prevalence of pterygium in various regions of Asia, especially in South Asia. Among the 20 studies conducted in Asia, 10 were performed in South Asia (nine in India [7,18,21,24–27,30,32], one in Nepal [20]), 2 studies in Southeast Asia (one in Thailand [34], one in Singapore [12]), 5 studies in West Asia (three in Turkiye [21,29,31], one in Iran [15], and one in Israel [23]), and 3 studies in the Far East (one in China [3], one in South Korea [28], one in Japan [14]). One study each was conducted in Europe (Spain) [33], Australia [19], and Africa (Nigeria) [10].
In the majority of studies, more than one technique was used for pterygium treatment [10,12,14,15,18–21,23,27,29–35]. Conjunctival autograft was the most common technique, used in 16 studies [7,14,15,18,19,21,22,25–29,31–33,35]. In six of these studies, limbal-conjunctival autograft (LCA) was employed [25–27,31–33], and in one of them, LCA was compared with and without mitomycin C (MC) [31]. The bare sclera technique was used for pterygium excision in six studies [10,12,15,23,27,31], with three of these incorporating MC. Amniotic membrane graft (AMG) was utilized in three studies [14,15,27]. Autologous stem cell grafting and autologous blood techniques were each applied in one study. In two studies, pterygium excision was performed using the traditional method [18,21]. Other techniques used for pterygium treatment included adjunctive triamcinolone, fibrin glue technique, and bridge technique. The duration of refractive error assessment after pterygium treatment ranged from 3 weeks to 12 months.
Visual acuity, uncorrected distant visual acuity (UCDVA), corrected distant visual acuity (CDVA), and best-corrected visual acuity (BCVA) were assessed in 12 studies [10,18,20–27]. Some studies confirmed the improvement of visual acuity after pterygium excision [18,19], while one study rejected this finding [20]. According to the results of one study, CDVA improved after pterygium excision and limbal stem cell autograft transplantation [21], whereas another study showed no significant difference in CDVA after pterygium excision with conjunctival autograft transplantation [22]. Three studies confirmed the effect of pterygium excision with the bare sclera technique with MC and autologous graft surgery on the improvement of BCVA [10,23,24]. Additionally, three studies confirmed the effect of pterygium excision along with LCA, bare sclera technique, and AMG on the improvement of uncorrected visual acuity (UCVA) [25–27]. However, one study rejected this finding after pterygium excision with conjunctival autograft transplantation [22].
The majority of studies (22 of 23, 95.6%) showed that astigmatism decreased after pterygium excision with different treatment methods. Most studies assessing the keratometry values (horizontal keratometry [K1] and vertical keratometry [K2]; 7 of 23, 30.4%) reported that these values improved after pterygium excision [7,15,18,24,28–30].
Most studies assessing the keratometry values (K1 and K2) reported that these values improved after pterygium excision. Pterygium leads to the flattening of the horizontal meridian, and evidence showed that after its removal, this flattening process stops and reverses.
Three studies confirmed the effect of pterygium excision with conjunctival autograft and bare sclera technique on spherical error (SE) [7,22,31]. The effectiveness of pterygium excision on corneal spherical power (SP) was confirmed in two studies after treatment with the bare sclera technique with MC, LCA [31], and AMG [14].
The effectiveness of pterygium excision (100%) on surface regularity index (SRI) and surface asymmetry index (SAI) was confirmed by three studies [14,23,29]. Two studies confirmed the improvement of wavefront aberration after pterygium excision [19,22]. The majority of studies confirmed the correlation between pterygium size, especially when extending more than 3.50 mm, and refractive errors, including astigmatism, SE, corneal wavefront aberrations, and root mean square (RMS) wavefront aberration, as well as visual factors such as visual acuity, SP, and keratometric value.
The recurrence rate of pterygium following surgery ranged from 0% to 10%, as reported by six studies [14,23,26,30,32,33]. Only one study, conducted by Ozgurhan et al. [22], assessed the impact of pterygium treatment on patients with and without recurrence. This study revealed that pterygium surgery can significantly decrease corneal wavefront aberrations, such as total wavefront errors (WFE), higher order aberrations (HOA), trefoil, and coma, in eyes affected by primary or recurrent pterygium. However, postoperative corneal aberrations were higher in the recurrent group compared to the primary group.
Quality assessment
This review exclusively comprised prospective interventional studies. The risk of bias for these three articles was evaluated across six domains following the Cochrane guidelines. The findings revealed a high risk of bias associated with participant selection in these studies. However, regarding other aspects such as bias due to confounders, bias due to the measurement of variables, bias due to missing data, incomplete outcome data, freedom from selective reporting, and other sources of bias, we observed a low risk of bias. The quality assessment results are presented in Fig. 2 and Table 4 [7,10,12,14,15,18–35].
Quality assessment of included articles in review process.
Quality assessment of entered studies in the review
Discussion
The effect of pterygium excision on astigmatism
The overgrowth of connective tissue in pterygium frequently results in changes to corneal topography. Although the exact cause of these alterations is uncertain, several theories suggest that disruption of the tear film and traction from the pterygium tissue contribute to corneal distortion [36]. Pterygium leads to the flattening of the horizontal meridian, and evidence shows that after its removal, this flattening process stops and reverses.
The majority of studies evaluating keratometry values— both K1 and K2—demonstrated that these values improved following pterygium excision [7,15,18,24,28–30].
The pulling force exerted by the contractile components of the pterygium causes mechanical distortion and flattening of the cornea along the horizontal meridian, resulting in hypermetropic WTR astigmatism. As a pterygium grows larger, it causes the horizontal meridian to become flatter, which increases K1. This, in turn, increases the difference between keratometry readings (K2 – K1), resulting in a greater astigmatic refractive error. Primary pterygium frequently results in increased steepness of the vertical meridian instead of the horizontal meridian. This happens because pterygium typically invades the cornea from the nasal side in a horizontal manner, causing the horizontal meridian to flatten. The study by Vadodaria et al. [7] concluded that pterygium results in simple myopic WTR astigmatism, as well as compound hypermetropic and myopic astigmatism refractive errors. After pterygium removal, K1 decreases significantly, while K2 increases compared to presurgical values. This means that the flatter meridian (K1) becomes less curved, and the steeper meridian (K2) becomes more curved after the surgery.
The reduction of K2 – K1 following pterygium excision surgery with conjunctival autograft results in a decrease in mean SE and astigmatic error (AE) [13]. Research by Barman et al. [18] indicated that pterygium significantly affects both K1 and K2 readings. According to the study by Jain and Pandey [24], the preoperative K1 and K2 showed that the vertical meridian is comparatively steeper. The estimated mean keratometry closely matched the actual postoperative mean keratometry. Their findings indicate that pterygia shorter than 2.0 mm rarely cause postoperative changes, allowing for combined surgery using the preoperative mean keratometry. The study used automated keratometry rather than corneal topography, enabling a more accurate prediction of the postoperative mean keratometry. Topographic measurements are often influenced by tear film stability and corneal opacity, leading to outliers in both preoperative and postoperative data, and resulting in high variability in mean keratometry predictions.
Fong et al. [12] noted that the removal of pterygium typically results in the reversal of corneal flattening caused by the pterygium. Moreover, the study by Chourasia et al. [32] confirmed that the removal of pterygium leads to a reversal of the corneal flattening associated with pterygium. According to the study by Kheirkhah et al. [15], before surgery, WTR and against-the-rule (ATR) decreased 1 month after surgery and remained stable afterward. It has been shown that in normal eyes, the corneal back surface is steeper in the vertical meridian (WTR astigmatism), despite having negative power. As primary pterygium enlarges, it induces significant WTR astigmatism, which increases as the lesion grows. Pterygium causes corneal distortion, leading to WTR astigmatism more frequently due to the flattening of the horizontal meridian. However, ATR astigmatism has also been observed in patients with pterygium. Pterygium excision results in a decrease in both WTR and ATR astigmatism.
Most of the studies reviewed (95.6%) indicated a reduction in astigmatism following pterygium excision using various treatment methods. According to Niruthisard et al. [34], 73.3% of patients exhibited stability in corneal astigmatism and keratometry after the excision of pterygium. An increase in corneal refractive power and a decrease in astigmatism after pterygium surgery have been reported in various studies [14,26,30]. Bahar et al. [23] noted that corneal astigmatism at the 3-mm mark dropped from 3.12 to 2.5 diopters (D) after surgery, with the axis staying the same. In other words, while the surgery may have altered the magnitude or severity of the astigmatism, it did not change the specific angle or meridian along which the astigmatism was oriented. Nevertheless, in some cases, up to 2 D of astigmatism remained. It is uncertain whether this persistence is attributable to the inherent characteristics of the cornea and pterygium or the surgical method used.
In this regard, Vadodaria et al. [7] found that 56% of subjects had no refractive error after surgery, with 26% having simple myopic astigmatism. After surgery, ATR astigmatism decreased to 14%, while simple myopic astigmatism (32%) and hypermetropic astigmatism (28%) became more common. Overall, the study indicated that in patients with grade 1 pterygium, simple myopic AE remains almost unchanged after surgery. In contrast, for those with grade 2 and 3 pterygium, compound hypermetropic astigmatism is completely eliminated. Fong et al. [12] reported similar findings in their study.
The cornea’s refractive characteristics keep evolving for a prolonged period after surgery. Keratometric astigmatism, surgically induced corneal astigmatism, and the mean total corneal refractive power show significant decreases up to 3 months compared to 2 weeks postoperatively. Additionally, the RMS values of HOA also notably decrease over time [19,37]. The research conducted by Kheirkhah et al. [15] demonstrated that following pterygium surgery, there were notable decreases in refractive and corneal astigmatism, linked to significant alterations on the anterior corneal surface. While the overall level of astigmatism at the posterior corneal surface remained unchanged, its axis shifted after surgery. The induced astigmatism stabilized 1 month after the operation, and no significant changes were observed during the subsequent 6 months of follow-up, aligning with findings from previous research [12,38]. Similar findings of stability after the first month were reported in other studies using refraction or corneal topography over the same 6-month follow-up duration [12,14]. Thus, it appears that the cornea stabilizes one month after surgery. However, there is a lack of data regarding corneal changes beyond 6 months after surgery. Consequently, it is uncertain if additional changes occur later, especially in cases involving advanced pterygium that necessitate extensive surgical intervention. Moreover, in the study by Kheirkhah et al. [15], discrepancies between the refractive astigmatism and the anterior corneal or equivalent keratometric readings became negligible after the surgery, which may be due to the asymmetrical nature of pterygium-induced astigmatism, where the more normal part of the cornea (typically temporal) mitigates the refractive impact of the nasal cornea [39].
Total corneal astigmatism is influenced by both the anterior and posterior corneal surfaces. Studies have shown that posterior corneal astigmatism compensates for 12.9% to 31% of anterior corneal astigmatism. Consequently, ignoring direct measurements of the posterior corneal surface can significantly impact the assessment of surgical effects on corneal topographic astigmatism [40–42]. Previous studies have shown that in healthy eyes, the posterior corneal surface is steeper along the vertical meridian (WTR astigmatism), despite having negative power. Consequently, pterygium seems to induce an axis shift in posterior corneal astigmatism towards a steeper meridian at oblique or horizontal axes, which reverses after surgery [43]. However, longitudinal research is necessary to precisely determine the changes in the posterior corneal surface before and after pterygium development.
The effect of pterygium excision on the visual acuity
The majority of review studies confirmed an improvement in visual acuity (UCDVA, CDVA, BCVA) after pterygium excision [10,18,19,21,23–25]; while it was contradicted by other studies [20,22].
According to the research conducted by Barman et al. [18], pterygium significantly affects visual clarity and both horizontal and vertical keratometry readings. While no noticeable changes were observed in the required spherical corrective lenses, alterations in cylindrical corrective lenses were noted. In the study by Verma et al. [26], visual improvement was observed in 33 eyes (66%) after pterygium surgery, primarily due to a reduction in corneal astigmatism and the removal of the pterygium from the visual axis, particularly in patients with pterygia larger than 2 mm. However, visual acuity remained unchanged after surgery in cases where the horizontal extent of the pterygium was 2 mm or less from the limbus.
Jain and Pandey [24] found that BCVA significantly improved across all pterygium grades following surgical excision at the 4-month mark. However, other studies have reported BCVA improvement in only 50% to 60% of cases [44,45]. Kazanci et al. [29] observed that the diamond burr group experienced quicker UCVA recovery compared to the manual group within 1 week. This may be attributed to a smoother corneal bed with reduced surgical trauma, resulting in decreased light scattering and improved unaided vision. The surgical removal of pterygia has been demonstrated to significantly impact the corneal refractive state, resulting in improvements in SP, astigmatism, and corneal surface irregularities. These changes collectively contribute to a notable enhancement in visual acuity [10,33].
The effect of pterygium excision on SE
All studies that assessed the impact of pterygium excision on spherical error confirmed its effectiveness in improving SE [7,22,31]. Vadodaria et al. [7] found that pterygium removal surgery with conjunctival autograf t, regardless of whether sutures are used, significantly decreases mean SE and AE. The measurements of SE and AE taken before surgery, on the first day after surgery, and during subsequent follow-ups, all showed statistically significant reductions. These results, demonstrating the decrease in both SE and AE after surgery, have been supported by other studies [31,46,47].
Ozgurhan et al. [22] highlighted that corneal stability is not achieved in the early postoperative period (3 months), and significant changes in HOA continue to occur even a year after pterygium surgery. All corneal wavefront aberrations, except for spherical aberration, were notably higher in the recurrent group compared to the primary group at both 3 and 12 months postoperatively. However, the RMS of spherical aberration was not linked to the size of the pterygium.
The reason for these contradictory results is unclear. It may be due to differences in the pterygium grades used in the studies or the variations in the instruments used for pterygium surgery. Further research is recommended to clarify these discrepancies.
The relationship between pterygium excision and SRI and SAI
The effectiveness of pterygium excision on the SRI and SAI has been confirmed by three studies [14,23,29]. Bahar et al. [23] employed computerized videokeratography to examine corneal topographic changes following bare sclera surgery for pterygium. This technique uses a solid-state light cone videokeratoscope with a short working distance. The TMS-2 device (Computed Anatomy Inc) calculates the SAI by summing the corneal power differences between corresponding points on the TMS-2 mires that are 180° apart. A normal corneal surface exhibits high symmetry in power distribution, making the SAI a valuable quantitative measure for monitoring corneal topographic changes. Normal corneas typically have SAI values below 0.5. The SRI is another quantitative descriptor, calculated based on the local regularity of the corneal surface within an average virtual pupil diameter of 4.5 mm. Similar to the SAI, normal corneal surfaces usually exhibit low SRI values, while higher SRI values indicate a surface of lower optical quality.
Similarly, the research by Tomidokoro et al. [14] demonstrated that the size of the pterygium was correlated with SP, astigmatism, SRI, and SAI prior to surgery. Following the surgical removal of the pterygium, there was a significant increase in the SP of the cornea, while astigmatism, SRI, and SAI significantly decreased. These findings suggest that the cornea’s refractive properties undergo substantial changes due to the surgery but stabilize within 1 month after operation. Therefore, it is advised that any refractive surgery be performed at least 1 month after pterygium surgery to ensure stabilization of the corneal refractive status.
The effect of pterygium excision on wavefront aberration
Two study confirmed that wavefront aberrations (WFE) improved after pterygium excision [19,22]. Pesudovs and Figueiredo [19] conducted the first documented investigation into the outcomes of wavefront aberrations following pterygium surgery. In this study, eyes with pterygium exhibited increased higher order wavefront aberrations across all Zernike orders and modes tested, with trefoil being the largest contributor to the WFE. Importantly, although surgical removal reduced most of these HOA, it did not completely eliminate them, and some cases still showed abnormal levels of HOA after surgery. The findings of this study suggest that early removal of pterygia reduces the likelihood of significant residual aberrations. Pterygia between 3 and 4 mm in size pose a notable risk for residual aberrations.
The study by Ozgurhan et al. [22] found that initial corneal wavefront aberrations were similar in both primary and recurrent pterygium cases, as well as comparable visual acuities and keratometry values. However, postsurgical corneal aberrations were more pronounced in the recurrent pterygium group than in the primary group. Total WFE and HOA decreased significantly in both groups at 3 and 12 months postoperatively compared to preoperative measurements, with the recurrent group showing higher aberrations than the primary group.
Before their study, no research had compared corneal wavefront aberrations between primary and recurrent pterygium cases. Nonetheless, Yagmur et al. [48] observed that visual acuity and topographic parameters did not differ significantly between primary and recurrent pterygium cases. Similarly, Gumus et al. [37] found that total coma and trefoil significantly reduced within the first 3 months after surgery. However, the RMS values for total quatrefoil, spherical, and total high astigmatism did not show a significant reduction by the third month after surgery. Nonetheless, by the 12-month postoperative mark, all RMS values except for total spherical aberration had decreased due to the pterygium surgery. It appears that corneal stability is not achieved within the first 3 months after surgery, and significant changes in HOAs continue to occur even beyond a year after the pterygium is removed.
It is recommended to remove pterygia before they exceed 4 mm and to discuss with patients the risk of residual wavefront aberrations as a possible consequence of not removing the pterygium when advising them on the risks and benefits of pterygium excision [49].
Size of pterygium and refractive errors
Many studies have confirmed the relationship between pterygium size, especially when it extends beyond 3.50 mm, and a variety of refractive errors including astigmatism, SP, corneal wavefront aberrations, and RMS wavefront aberration. They also identified a correlation with visual factors such as visual acuity, SP, and keratometric values.
When a primary pterygium extends more than 1.00 mm from the limbus, it results in significant WTR astigmatism of 1.00 D or more [13,46]. Evidence indicates that the timing of pterygium excision surgery is associated with the size of the pterygium. A pterygium measuring around 2.25 mm can induce approximately 2 D of astigmatism, suggesting that this size should be the threshold for surgical consideration [50]. Pterygia between 3 and 4 mm in size are at a high risk of causing residual aberrations. If the pterygium is removed at 3.00 mm, the chances of significant residual aberrations are low, but these chances increase when the pterygium reaches 4.00 mm [49].
According to Verma et al. [26], for patients with an atrophic and nonprogressive pterygium smaller than 2 mm, surgery can be performed right away without waiting for prior cataract surgery. However, if the pterygium exceeds 2 mm, it significantly affects the corneal refractive power, resulting in inaccurate intraocular lens power calculations and considerable residual refractive errors after surgery. Similarly, other studies advise that any refractive surgery, if planned, should be scheduled at least 1 month after pterygium surgery [14,15,43].
The study by Tomidokoro et al. [14] indicated that changes in SP and astigmatism were linked to the preoperative size of the pterygium. However, Fong et al. [12] discovered that the degree of astigmatism, as determined from manifest refraction, had a weak but statistically insignificant correlation with pterygium size. Other studies have confirmed that the reduction of astigmatism following pterygium excision is correlated with the grade of the pterygium [26,27,39,51].
Vadodaria et al. [7] found that lesions extending beyond 45% of the corneal radius or within 3.20 mm of the visual axis lead to increasingly higher levels of induced astigmatism. Additionally, other studies concluded that larger pterygium sizes correlate with increased corneal aberrations such as HOAs, total coma, trefoil, and tetrafoil, but not spherical aberration. The horizontal length of the pterygium significantly affects various aberrations, including higher order astigmatism [37,52]. Ozgurhan et al. [22] identified a significant positive correlation between the pterygium size and total WFE, HOA, coma, trefoil, and spherical aberration. However, there was only a weak correlation between the horizontal length of the pterygium and postoperative corneal wavefront aberrations, which may be influenced by factors like the total pterygium area and postoperative changes in the corneal surface and tear film stability. In the recurrent pterygium group, no significant correlation was found between the pterygium size and all corneal wavefront aberration values at baseline and at 3 and 12 months postoperatively.
Strengths and limitations
This systemic study offers valuable insights into the effects of pterygium treatment on refractive errors and examines the relationship between pterygium size and refractive errors posttreatment. Notably, the review did not include any randomized clinical trials due to ethical constraints in conducting such studies. Instead, only prospective studies with adequate sample sizes were included, while studies with small sample sizes and retrospective studies were excluded. As a result, the findings from these studies can be considered largely reliable. However, the absence of randomized clinical trials introduces a high risk of bias. Additionally, the central focus of most included studies limits the generalizability of the findings to other populations. Although all studies in this review assessed astigmatism, there were limitations in evaluating the impact of pterygium treatment on other refractive errors due to a lack of homogeneity among the articles. Finally, the heterogeneity of the studies made it impossible to perform a meta-analysis.
Conclusions
The majority of review studies have confirmed improvements in visual acuity (UCDVA, CDVA, BCVA) after pterygium excision. Most studies have reported an increase in corneal refractive power and a decrease in astigmatism following pterygium surgery, which is linked to the grade of the pterygium. Specifically, in patients with grade 2 and 3 pterygium, compound hypermetropic astigmatism is completely eliminated, while this improvement is not observed in patients with simple astigmatism. Additionally, keratometry values—both K1 and K2—showed improvement after pterygium excision, which could explain the effect of pterygium excision on the improvement of astigmatism. The positive impact of pterygium excision on SE, wavefront aberration, SRI, and SAI have also been confirmed.
Notes
Conflicts of Interest
None.
Acknowledgements
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Funding
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