Topographic corneal changes in astigmatism due to
pterygium’s limbal-conjunctival autograft surgery
Pere Pujol Vives, MD1; Amélia Maria de Carvalho Mendes Castanheira, MD1;
Gemma Julio Morá, BS, PhD2; Sara Lluch Margarit, BS, PhD2; Dolores Merindano Encina, BS, PhD2;
Imma Sola Garcia, OD1.
PURPOSE: To evaluate the effect of pterygium size and excision with limbal-conjunctival autograft on corneal astigmatism before, and one month and three months after surgery.
SETTING: Consorci Sanitari de Terrassa. Terrassa, Barcelona, Spain.
METHODS: This is a descriptive, longitudinal, prospective, non-randomised study of 32 eyes in 32 patients with pterygium, and operated using the limbal-conjunctival autograft technique in our hospital in the year 2011. Standardised photographs were taken and corneal topography was performed preoperatively, one month, and 3 months after the intervention. The variables studied were length of pterygium invasion of the cornea, central corneal astigmatism and axis.
RESULTS: Mean pterygium length was 2 ± 0.6 mm. Mean preoperative astigmatism was 1.8 ± 1.35 dioptres, 1.15 ± 0.9 dioptres at one month and 1 ± 0.46 dioptre three months after the intervention. A statistically significant correlation (p < 0.05) was obtained between pterygium length and preoperative astigmatism, but no correlation was observed between length and astigmatism at one month and at 3 months post-intervention. A statistically significant reduction was found between pre-surgical astigmatism and astigmatism at one month and at three months, although no differences were observed between one month and 3 months. No statistically significant differences were found when comparing the pre-surgical astigmatism axis, powered by Editorial Manager® and Preprint Manager® from Aries Systems Corporation (93.5 ± 27) with the axis at one month (85.9 ± 35) and three months (84 ± 33 degrees) post-intervention.
CONCLUSIONS: Pterygium surgery with limbal-conjunctival autograft moderately reduces corneal astigmatism and preoperative astigmatism is associated with the size of the pterygium.
J Emmetropia 2013; 4: 13-18
Pterygium, from the Greek pterygos meaning “wing”, is a common ocular surface lesion characterised by elastotic degeneration of collagen and fibrovascular proliferation, with an overlying covering of epithelium. It originates on the bulbar conjunctiva within the palpebral fissure, and it can grow across the limbus onto the cornea. Because early pterygia are usually asymptomatic, many ophthalmologists commonly consider them an insignificant problem until they reach the visual axis and induce corneal astigmatism, resulting in loss of vision. Previous reports have demonstrated that even before entering the optical zone, an advancing pterygium can cause visual impairment by locally flattening the cornea and inducing with-the-rule astigmatism1–5 and that the topographic changes in
the cornea and visual impairment induced by pterygia
Submitted: 12/07/2012 Accepted: 01/01/2013
1 Consorci Sanitari de Terrassa, Spain
2Facultad de Óptica y Optometría de Terrassa, Universitat
Politècnica de Catalunya, Spain.
Financial disclosure: The authors report no financial or other conflict of interest relevant to the subject of this article.
Acknowledgements: SECOIR has a program to promote the publication of research in Ophthalmology. The authors were awarded a grant from the Society to benefit from editorial support for the publication of this study.
Corresponding Author: Pere Pujol Vives, MD
Consorci Sanitari de Terrassa, Departamento de Oftalmología. Carretera Torrebonica, s/n. 08227 Terrassa, Barcelona. Spain
of surgical procedures have been described in the treatment of pterygium, such as conjunctival autograft described by Kenyon and collaborators7, others using
mitomycin C8, and the newest technique using
limbal-conjunctival autograft. This latter technique has been proved to be as safe as the conjunctival autograft transplant but more effective in preventing recurrence after excision of recurrent pterygium9 and also in
primary pterigium10. However, no investigators have
reported the effect of pterygium surgery using limbal-conjunctival autograft on corneal astigmatism and its correlation with pterygia size. Hence, we performed this study in order to investigate the effect of pterygium size and excision with limbal-conjunctival autograft on corneal astigmatism before, and one month and three months after surgery.
with 2% lidocaine (Braun Melsungen AG; Melsungen, Germany) was administered, then the pterygium was removed starting with a conjunctival incision on the body of the pterygium using Westcott scissors (Miltex; York, PA, U.S.A.) and Tenon’s capsule tissue under the body of the pterygium was also removed. The head above the cornea was scraped off with a crescent angled bevel-up (Surgidis® Croma GmbH; Leobendorf, Austria). After the pterygium mass was removed, regular tip microsponges (Alcon Cusi, S.L.; El Masnou – Barcelona, Spain) soaked with 0.025% mitomycin C solution were placed on the exposed sclera surface for 5 minutes, and then they were removed. Subsequently, the exposed sclera was irrigated with 40 ml of balanced salt solution. Afterwards, a limbal-conjunctival autograft was obtained from the upper conjunctiva; the graft dissection was extended approximately 0.5 mm into clear cornea to include the Vogt palisades and limbal stem cells. This graft was moved to cover the defective area and was secured with 10-0 nylon sutures. The limbal end of the autograft was placed directly over the limbal area of the surgical bed. The removed tissue was sent for histopathological analysis. After surgery, a therapeutic contact lens was applied until corneal reepithelialization was completed. The sutures were removed after conjunctival epithelialisation occurred, in the third postoperative week.
Postoperatively, patients were treated with topical tobramycin 3 mg/ml and dexamethasone 1mg/ml (Tobradex®; Alcon Cusi, S.A.; El Masnou - Barcelona, Spain) three times a day, for four weeks.
Topographic analysis
Corneal topography was obtained with computerized videokeratography (ATLAS TM Corneal topography System 2009, Carl Zeiss Meditec, Inc.; Jena, Germany) before surgery, and one month and three months after surgery. The parameters studied were dioptres of astigmatism and astigmatism axis.
Statistical analysis
Statistical analysis was performed using SPSS version 19. After an exploratory analysis, the normal distribution of the variables was confirmed using the Kolmogorov–Smirnov test. The relationship between preoperative size of the pterigyum and pre- and postoperative astigmatism was performed using the Pearson correlation and the comparison between pre- and postoperative astigmatism was made using a paired two-tailed t-test.
The comparison between the pre- and postoperative astigmatism axis was performed using the Wilcoxon test for non-normal axis data distribution. Statistical significance was considered at p < 0.05.
PATIENTS AND METHODS
Thirty two eyes from 32 patients with symptomatic primary pterygia were enrolled in the study. This patient group included 18 men and 14 women, with an age range of 27 to 56 years (mean 36.7 ± 7.4). The pterygia included in the study were symptomatic and generated with-the-rule astigmatism. Patients with a history of ocular surgery, ocular trauma, contact lens wear, corneal scarring, pseudopterygia or anterior segment diseases other than pterygium, were excluded from the study. The study was conducted in accordance with ethical standards in research, including the use of a consent form by the participants. Our institution followed the Helsinki Declaration and the study was carried out with the approval of the ethics committee of Consorci Sanitari de Terrassa.
Pterygium size
In our study, a standardised photograph was taken of the patient’s affected eye at different times during the curative process: before surgery, at one month and at 3 months. The length of pterygium was calculated from the photographs using the ImageJ open-source computer software (W Rasband, National Institutes of Health, Bethesda, MD; http://rsb.info.nih.gov/ij/). The length of the pterygium was taken as the imaginary straight line between the vertex of the head of the pterygium and the sclerocorneal limbus.
Surgical technique
All surgeries were performed by a single surgeon (P.P.) using the same technique (limbal-conjunctival autograft). First, topical anaesthesia was applied to the eye with Colicursi® 0.5% (Alcon Cusi, S.L.; El Masnou
RESULTS
The data from the 32 patients, 18 men (57.6%) and 14 women (42.4%), were analysed. Ages ranged from 27 to 56 years (mean: 36.7 ± 7.4 years). Table 1 shows the descriptive statistics of the study variables.
Of the 32 patients operated, 9 had greater astigmatism after surgery and 23 presented less astigmatism after surgery.
When the study variables were examined, it was confirmed that both pterygium length and astigmatism in dioptres showed a normal distribution.
Figure 1. Correlation between pre-surgical astigmatism and pterygium length. This figure shows on the x-axis the pre-surgical astigmatism in dioptres of the 32 cases under study and on the y-axis, the length of the intracorneal portion of the pterygium in mil-limetres. The result is a cloud of 32 points which show a Pearson correlation (r = 0.62) with high statistical significance (p < 0.01).
Figure 2. Comparison between the means of the astigmatism axis, pre-surgery and at one and three months post-surgery. This figure shows the mean astigmatism axis before surgery, and one month and three months after surgery in the 32 cases under study. Although a change can be observed in the figure, it is not significantly signifi-cant (p > 0.05).
The correlation between the preoperative length and preoperative astigmatism was analysed using the Pearson correlation coefficient (r=0.62) and a statistically significant correlation was determined (p<0.01) (Figure 1). However, no statistically significant correlation was observed between the length of the pterygium and post-surgical astigmatism at one month (p=0.11) and at 3 months (p=0.09).
Mean pre-surgical astigmatism in oursample was 1.78 dioptres, mean astigmatism at one month was 1.16 and at 3 months it was 0.99 dioptres. Using the Student’s t-test for related variables, we compared pre-surgical
Table 1. Descriptive statistics
n = 32 Minimum Maximum Mean Standard Deviation
Pre-surgical astigmatism (dioptres) 0.6 6.6 1.781 1.3367
Pterygium length (mm) 0.79 3.67 2.002 0.6318
Post-surgical astigmatism at one month 0.43 5.52 1.168 0.9263 Post-surgical astigmatism at three months 0.09 2.10 0.999 0.4622 Pre-surgical astigmatism axis (degrees) 9 180 96.19 31.521 Post-surgical astigmatism axis at one month 8 166 85.97 34.732 Post-surgical astigmatism axis at three months 7 155 85.55 32.818 Table 2. Student t-test for related samples
Comparisons Mean t- value p- value
Pre-surgical astigmatism – Astigmatism at one month 0.612 2.822 0.008 Pre-surgical astigmatism – Astigmatism at three months 0.781 3.460 0.002 Astigmatism at one month – Astigmatism at three months 0.169 1.238 0.225 Table 3. Wilcoxon test for astigmatism axis
Comparisons Z p- value
Pre-surgical axis – Axis at one month –1.677 0.094 Pre-surgical axis – Axis at three months –1.854 0.064 Axis at one month – Axis at three months –0.025 0.980
and with astigmatism at 3 months (p=0.002), with statistically significant reductions being observed. However, the difference was not statistically significant when astigmatism at one month was compared with astigmatism at 3 months (p=0.225) (Table 2).
When the astigmatism axis was analysed, it was observed that it did not show a normal distribution, since in the Kolmogorov-Smirnov test, a p-value of 0.006 was obtained, so the pre- and post-surgery astigmatism axis was compared using the Wilcoxon test for non-normal distributions.
The average pre-operative astigmatism axis was 96.19 ± 32 degrees; one month after the intervention it was 85.97 ± 35 degrees and at 3 months post-surgery, it was 85.55 ± 33 degrees. No statistically significant differences were observed between the pre- and post-surgery axis at one month (p=0.094) or at 3 months (p=0.064), nor was astigmatism at one month statistically significantly different to astigmatism at 3 months (p=0.980) (Table 3).
statistically significant (p=0.002). Bahar et al. found a reduction of 3.12 to 2.5 dioptres after surgery, with no axis changes. Soriano et al.18 observed a significant reduction in central corneal astigmatism from 2.41 to 1.29 after pterygium surgery despite the small size of the sample (n = 23). The results of our study coincide with these authors, since we found a reduction in mean astigmatism from 1.8 to 1.15 dioptres at one month and 1 dioptre at 3 months. These changes were statistically significant. Our study also provides data on the time sequence of this refractive change, since we observe that this change occurs before the first month and stabilises at one month, as no significant differences were observed between astigmatism at one month and at three months.
Youn5 found that pterygium-induced with-the-rule
astigmatism changed to against-the-rule astigmatism after removal of the pterygium (p = 0.041), possibly because the flattening effect on the cornea disappears after surgery. Ozdemir et al.6 described how the
astigmatism axis returned to being with-the-rule after the third month post-surgery. In contrast, Bahar et al.2 did not find any significant correlation between
pre- and post-operative astigmatism and change in the pterygium-induced astigmatism axis. We agree with this author, as we did not find any significant change in the astigmatism axis, although we did observe a mild tendency towards horizontalising of the axis, from 96.2 ± 32 to 85.9 ± 35 at one month, but this change was not statistically significant.
Many studies demonstrate the efficacy of limbal-conjunctival autograft10 for the prevention of pterygium
relapse and our study contributes yet another reason for its use: it is a good refractive technique since it improves pterygium-induced corneal astigmatism and this refractive change is stable after one month.
Despite the limited number of patients in our study, we have been able to show that the limbal-conjunctival autograft surgical technique reduces pterygium-induced astigmatism, for which reason we believe that it would be interesting to carry out studies with larger patient numbers, in order to confirm the differences observed in our study and to determine if there is also a change in the astigmatism axis.
DISCUSSION
The results of our study show that the size of the pterygium is related with corneal astigmatism and that surgery using the limbal-conjunctival autograft technique reduces this astigmatism, but does not modify its axis.
It is currently accepted that the effect of the pterygium on corneal astigmatism is to increase with-the-rule astigmatism13. Alison et al.16 observed that
pterygia that extended over approximately 45% of the corneal radius or which occupied around 2.5 mm of the visual axis produced an increase in astigmatism. Avisar
et al.11 claimed that pterygia larger than 1 mm from
the corneal limbus induced with-the-rule astigmatism of more than 1 dioptre and that this astigmatism increased with the size of the lesion. In our sample, the mean length was 2 mm and the mean astigmatism was 1.8 dioptres. When the relationship between the degree of pre-surgical astigmatism and the length of the corneal portion of the pterygium is analysed, we find a statistically significant relationship between the two parameters, the larger pterygia being those with greater astigmatism. Accordingly, we conclude that the length of the pterygia is related with the induced astigmatism, and this data is in concordance with that of previous studies.
With regard to the effect of surgery on corneal astigmatism, it has been established that surgical excision corrects pterygium-induced astigmatism, although results from previous studies vary in this respect2-4-18.
In a sample of 27 patients, Cinal et al.4 showed that
astigmatism at 3 mm was 2.30 ± 2.08 D pre-surgery
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First author:
Pere Pujol Vives, MD
Consorci Sanitari de Terrassa, Departamento de Oftalmología. Carretera Torrebonica, s/n. 08227 Terrassa, Barcelona. Spain
