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ORIGINAL ARTICLE
Year : 2017  |  Volume : 4  |  Issue : 4  |  Page : 109-113

The effect of pterygium on corneal thickness, corneal curvature, tear volume, and intraocular pressure in a Sudanese Population


Department of Optometry and Low Vision Aids, Faculty of Optometry and Visual Sciences, Al-Neelain University, Khartoum, Sudan

Date of Web Publication7-Jun-2019

Correspondence Address:
Dr. Rawia Tagelsir Eias Ali
Department of Optometry, Faculty of Optometry and Visual Sciences, Al-Neelain University, Khartoum
Sudan
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DOI: 10.4103/bijo.bijo_15_18

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  Abstract 


Background: Pterygium is a triangular fold of bulbar conjunctiva usually found in the nasal side of the interpalpebral fissure. It consists from apex and base. Its apex advancing progressively toward the cornea. The exact cause of pterygium is not well understood, but long-term exposure to sunlight, especially ultraviolet rays, wind, and chronic eye irritation from dry and dusty conditions seems to play an important causal role. It looks like scar, but it is not. The growth might spread slowly during a life or stop after a certain point. In extreme cases, pterygium can cover pupil and cause vision problems.
Aim: The aim of this study is to reveal the effect of pterygium on corneal thickness, corneal curvature, tear volume, and intraocular pressure (IOP).
Materials and Methods: A total of 100 patients have primary pterygium in one eye (unilateral) compared to their healthy (control) eye. The study was conducted in Makkah Eye Complex in Alkalakla branch between April 2016 and November 2017. The criteria of admission included individuals who have no history of systemic/chronic or other eye diseases. The patients whose pterygium enters the cornea within 2.0–3.0 mm and visual acuity at least 0.50 decimal (6/12) were selected. The data included age and gender, while the clinical procedures included testing vision and visual acuity (Snellen's type), autorefraction and autokeratometry, ultrasound pachymetry, applanation tonometry, and break-up time tear assessment. Frequency distribution tables and t-test were used to present the data.
Results: The results showed that the pterygium was more apparent among male (53%) than female (47%). Significant decrease on visual acuity (77%) and tear volume (86%) of the pterygium eye (P < 0.0001) was observed as compared to healthy eye (HE). The primary pterygium caused meridional steepness in corneal curvature (98%). With-the-rule corneal astigmatism was dominant (61%) among other types. Statistically, there were little decrease on central corneal thickness and nonsignificant effect in IOP between the two eyes.
Conclusions: Pterygium can cause significant change in ocular functions compared to HEs according to study parameters. Ocular dryness complications and vision impairment due to corneal astigmatism should be considered to make correct diagnoses for eye symptomatology.

Keywords: Autokeratometry, break-up time, central corneal thickness, corneal curvature, intraocular pressure, pterygium, ultrasound pachymetry


How to cite this article:
Eias Ali RT, Mohamed Ali AB. The effect of pterygium on corneal thickness, corneal curvature, tear volume, and intraocular pressure in a Sudanese Population. Albasar Int J Ophthalmol 2017;4:109-13

How to cite this URL:
Eias Ali RT, Mohamed Ali AB. The effect of pterygium on corneal thickness, corneal curvature, tear volume, and intraocular pressure in a Sudanese Population. Albasar Int J Ophthalmol [serial online] 2017 [cited 2019 Oct 14];4:109-13. Available from: http://www.bijojournal.org/text.asp?2017/4/4/109/259771




  Introduction Top


Pterygium was defined as a raised fleshy triangular fibrovascular tissue growth of the conjunctiva encroaching onto a clear cornea.[1] It is a wing-shaped and located nasally with the apex toward the cornea, onto which they extend progressively. Histologically, the collagen structure is altered due to excessive exposure to the reflected or direct ultraviolet (UV) component of sunlight.[2] The prevalence of pterygium was found to be 10.2% in the world.[3] Pterygia are reported to occur in males twice as in females. The prevalence of pterygium in Sudan population is high, low because of the tropical climate and rainfall.[4]

Pterygium symptoms include redness, blurred vision, and eye irritation. If pterygium grows large enough to cover the cornea, it can interfere with vision. Thick or large pterygium can also cause the feeling of the presence having a foreign object on the eye. A patient might not be able to continue wearing contact lenses in the presence of pterygium due to discomfort. Rarely, pterygium can lead to severe cornea scarring that affects vision. Treatment usually involves UV blocking spectacle glasses, eye drops, or ointment to treat inflammation and eventually surgery either excision or a corneal transplant in extensive scarring.[4]


  Materials and Methods Top


One hundred (n = 100) Sudanese males and females aged between 18 and 45 years having pterygium in one eye and another eye being normal were recruited and examined at Makkah Eye Complex, Alkalakla branch, Khartoum, Sudan between April 2016 and November 2017. After well informed consent, ophthalmic medical history and demographic data (age and gender) of all participants were reported in the predesigned “Data Collection Forms” at the time of examination. The inclusion criteria included the visual acuity of the eye with pterygium not <0.5 (6/12), spherical refractive error should not exceed (±0.50 Diopter [D] sphere), and participants were free of any systemic, chronic, or local diseases apart from pterygium in one eye that extended to on the corneal surface not <2 mm and not exceeding 3 mm.

Best corrected visual acuity (BCVA) before and after correction was assessed for each eye separately using projected Snellen's Chart by Chart Projector (CP; Chart Projector, CP-770; Nidek Co., Ltd., 34-14 Maehama, Hiroishi-cho, Gamagori, Aichi 443-0038, Japan; www.nidek.com). Refraction was done by autorefractometer (AR 510 A, Nidek). Autokeratometry to measure the corneal curvatures was done by a portable hand-held keratometer (KM-500, Nidek) and then pachymetry to measure the corneal thickness was done by ultrasound pachymetry (US-4000 Echoscan, Nidek). Intraocular pressure (IOP) measurement was done by Goldman Applanation Tonometer (Haag-Streit Diagnostics-Applanation tonometer AT900®/870 18. Edition/2014-11; Haag-Streit AG Gartenstadtstrasse 10 3098 Koeniz, Switzerland, www.haag-streit.com). Tear assessment was performed by break-up time (BUT) and the assessment when <10 s indicates abnormal tear film.

Data were analyzed statistically by Statistical Program for the Social Sciences (SPSS) version 20 (Manufactured by IBM SPSS Inc., PASW Statistics for Windows, Version 20.0; 2009. Chicago: SPSS Inc., IL, USA). The t-test was used to compare variables, and a P < 0.05 was considered clinically significant. Ethical approvals were obtained from Al Neelain University, Khartoum Sudan Ethical Committee, and Makkah Research Center.


  Results Top


The mean age of the participants was 30.15 ± 7.30 years. Males were 53 (n = 53; 53%) and females were 47 (n = 47; 47%) giving a distribution ratio between males and female, almost equal to each other's (1.13:1) [Figure 1]. The overall results showed that the pterygium was more apparent among male (53%) than female (47%). Significant decrease on visual acuity (77%) and tear volume (86%) of the pterygium eye (PE) (P < 0.0001) was observed as compared to healthy eye (HE). The primary pterygium caused meridional steepness in the corneal curvature (98%) [Table 1]. With-the-rule corneal astigmatism was dominant (61%) among other types [Table 2]. Statistically, there were little decrease on central corneal thickness (CCT) and nonsignificant effect in IOP between the two eyes [Table 1].
Figure 1: Sex distribution

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Table 1: Comparison in descriptive statistics between healthy and pterygium eyes

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Table 2: Comparison of astigmatism types between healthy and pterygium eyes

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Generally, [Table 1] demonstrates the comparison in descriptive statistics between those with no pterygium or HEs and those with pterygia (PEs) regarding minimum and maximum vision and IOP which were almost the same between the two categories; HE and PE. CCT was slightly higher in HEs than in PEs. The minimum dioptric values of ocular astigmatism were exactly equal in both HE and RE groups (0.25 DC), while the maximum values were far higher in PEs than in HEs (5.0 DC compared to 1.5 DC). The minimum K1 (D) was more in HEs and equal in both regarding the maximum K1 (46.00 D). The minimum K2 (D) was also equal in HE and PE, while the maximum K2 was a pit different, higher in PEs [Table 1]. PEs demonstrated higher percentage of astigmatism with rule than HEs (61%–18%), the same case as in oblige astigmatism. Spherical error was far higher in HEs [Table 2]. [Table 3] shows the Pearson's correlation of variables between HEs and PEs; all were statistically significant (P < 0.0001) except in the axis of corneal astigmatism and the cylindric values [Table 3]. In the comparison of t-test of variables between HEs and PEs were statistically significant in vision, tear BUT, axis of corneal astigmatism, the cylindric value (P < 0.0001) and CCT (P = 0.014 which was less the required target of P < 0.05) [Table 4]. Correlation and t-test for K-readings (K1– K2) HEs and PEs were almost all were clinically significant except HE K1 to HE K2[Table 5].
Table 3: Correlation of variables between healthy and pterygium eyes

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Table 4: Comparison of t-test of variables between healthy and pterygium eyes

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Table 5: Correlation and t-test for K-readings between healthy and pterygium eyes

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  Discussion Top


Overview

Pterygium is a common ocular surface disorder which leads to invasion of the bulbar conjunctiva onto the cornea. Although its exact etiology is unknown, environmental factor may be the main risk elements. Besides age, hereditary, and ethnicity,[1] sunlight, chronic inflammation, microtrauma, and dry eye are other possible contributing factors.[5] A pterygium-induced refractive change often leads to visual impairment due to considerable effect on corneal topographic features.[6],[7] Abnormal tear film function is usually associated with pterygium. BUT values improved significantly after primary pterygium excision; dry eye may cause the recurrence of pterygium.[5]

Some studies such as the Blue Mountains Pterygium and Pinguecula Eye Study[8] reported significant associations between pterygium and increased pigmentation (skin and hair color), decreased skin sun sensitivity, and sun-related skin damage. The age- and sex-specific pterygium prevalence rates in the present study are similar to rates found in non-Aboriginals examined in the 1980 Australian Trachoma Program and The Blue Mountains Pterygium and Pinguecula Eye Study.[8] The above assumption of increased rate of pterygium in colored individuals, such as Sudanese people, may partially explain the high rate of the pterygium, especially males.

The current study reported higher percentage of pterygium among males as compared to females. In Sudan, most of the male individuals, especially in rural and low socioeconomic situations, spend most of the day hours outside to work directly under the hot “poor Sudan Savanna climate”[9] sunlight and its UV light component. Thus, exposure to UV light damages the conjunctival tissue and this damage causes the pterygium to form and grow. McCarty et al. in their study of epidemiology of pterygium in Victoria, Australia, examined in more detail the relation of UV-B and sunlight with pterygium to concluded that attributable risk of sunlight and ocular UV-B to pterygium was as high as 43.6% (95% confidence level = 42.7, 44.6).[10]

This result agreed with the study of Fotouhi and Hashemi et al. in Iran, 2009;[4] in their study, a sample of 4564 individuals showed the prevalence of pterygium 1.4% and 1.1% in men and women, respectively. Furthermore, similar result was obtained by Dereje Hayilu et al. in Gondar city, 2017;[5] in their study, a sample of 390 individuals showed the prevalence of pterygium 2.2: 1.28 male to female. The domination of male to female in acquiring pterygium was well highlighted in the Blue Mountains Eye Study in Australia, where significantly more men (11%) than women (4.5%) had pterygium.[8]

Some studies such as the Blue Mountains Pterygium and Pinguecula Eye Study[8] reported significant associations between pterygium and increased pigmentation of the skin. The above assumption of increased rate of pterygium in colored individuals, such as Sudanese people, may partially explain the high rate of the pterygium, especially Sudanese males.

BCVA in this study reported a significant decreased (P < 0.0001) in BCVA of PEs as compared to HEs with moderate and positive correlation. This was due to pterygium-induced corneal refractive changes; the result was in line with Maheshwari, who reported that pterygium leads to a considerable effect on corneal refractive status.[6] Fong et al. proved these postulations by reporting considerable improvements in BCVA after pterygium excision surgery. Still, Oh and Wee in Seoul National University Hospital, Seoul, Korea, proved that pterygium surgery can improve vision and contrast sensitivity and corneal topographic changes.[11]

The current work demonstrated an obvious higher percentage of astigmatism with rule in PEs than HEs (61%–18%), the same case as in oblige astigmatism (0.25–5.0 DC) in PEs (P < 0.0001). However, a low correlation found between astigmatic error of the HE and PE (r = 0.212), which may elicit that the growth of pterygium significantly onto the cornea could cause different forms of astigmatism. Anyhow, the higher results of astigmatism with rule and the oblige astigmatism in PEs than HEs can be supported by many similar studies in the literature. This result agreed with the study conducted by Popat et al.[12] of 95 patients had unilateral primary pterygium that revealed a mean astigmatism of (6.20 ± 3.58 D) which hampered the vision of patients and improved after pterygium excision surgery. Mohite et al. in India, 2017 proved effectiveness of pterygium surgery on pterygium-induced corneal astigmatism which was monitored by keratometry readings, an observation that can support the presence of corneal astigmatism with pterygium.[12],[13]

In the current work, the CCT results showed decrease of CCT measurements in the PE than HE (P = 0.0140) with strong correlation (r = 0.908) This result was in contrary to other results by Gros-Otero et al.[14] and Rasit et al.,[15] which showed that primary active pterygium (Grades 1 or 2) had no significant changes in the corneal central thickness.

Although minimum and maximum IOP scores found to be almost the same between the HE and PE [Table 1], some shows little decrease on PE measurements but not significant P < 0.279. This result was similar to the findings of Oner et al.,[16] which showed that there was no significant difference between the eye with pterygium and healthy fellow eye (P ≤ 0.948). There was strong correlation between the IOP of pterygium and that of HE (r = 0.874), which indicates that the two eyes are going parallel without significant difference. Early IOP elevation was reported after pterygium surgery, but it quite possible it is due to early postoperative steroid medications.[17],[18]

The keratometric readings of PE showed a noticeable difference between (K1 and K2) compared to corresponding values for HE (K1 and K2), this condition occurs as a result of unequal curvature along the two principal meridians due to irregular contour or shape of anterior corneal surface that been distorted by the pterygium. This agreed with the result of Popat et al.[12] in their study of 100 eyes who had primary pterygium. They found that mean astigmatism was 6.20 D. In conclusion, pterygium causes significant corneal astigmatism.

All types of astigmatic axis were found in this study; however, with-the-rule astigmatism was more dominant among the PEs. Low correlation (r = 0.202) between the axis of HE s and that of PEs indicates differences in the types. This result reveals that primary pterygium often leads to steepness in vertical meridian rather than horizontal meridian. This condition occurs because pterygia generally invade the cornea from the nasal side in a horizontal direction and this causes the horizontal meridian to flatten. Similar result was found by Avisar et al.[19] They concluded that when primary pterygium more than 1.0 mm in size from the limbus, it induced with-the-rule significant astigmatism (≥1.0 D). In case of huge pterygia, they induce visually significant central with-the-rule astigmatic changes that may not be apparent by subjective refraction[19] as there is correlation between pterygium size and induced corneal astigmatism.[20] This odd condition can be improved by early successful removal of the pterygium.[21]


  Conclusions Top


According to this study, primary nasal pterygium causes significant corneal astigmatism and dryness of the eye which leads to a prominent defect of vision and eye irritation. However, there is no evidence that pterygium affects IOP. However, according to this study, the PEs showed a little thinning in the CCT. In Sudan, the use of protective glasses and avoiding dryness of eyes are important measures for preventing pterygium.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Zhong H, Chen Q, Li J, Shen W, Sheng X, Niu Z, et al. Ethnic variations in pterygium in a rural population in Southwestern China: The Yunnan minority eye studies. Ophthalmic Epidemiol 2016;23:116-21.  Back to cited text no. 1
    
2.
James B, Bron A, Parulekar MV. Lecture Notes Ophthalmology. 12th ed. The Atrium, Southern Gate, Chichester, West Sussex, UK: Wiley Blackwell Publication: A John Wiley & Sons, Inc.; 2016. p. 117-8.  Back to cited text no. 2
    
3.
Liu L, Wu J, Geng J, Yuan Z, Huang D. Geographical prevalence and risk factors for pterygium: A systematic review and meta-analysis. BMJ Open 2013;3:e003787.  Back to cited text no. 3
    
4.
Fotouhi A, Hashemi H, Khabazkhoob M, Mohammad K. Prevalence and risk factors of pterygium and pinguecula: The Tehran Eye Study. Eye (Lond.) 2009; p. 1125. 10.1038/eye.2008.200.  Back to cited text no. 4
    
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Dereje H, Tsehay K, Biruktayit K, Atirsaw T. Prevalence and associated factors of pterygium among adults living in Gondar city, Northwest Ethiopia. PLoS ONE 2017; 12): e0174450. doi: 10.1371/journal.pone.0174450.  Back to cited text no. 5
    
6.
Maheshwari S. Pterygium-induced corneal refractive changes. Indian J Ophthalmol 2007;55:383-6.  Back to cited text no. 6
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7.
Fong KS, Balakrishnan V, Chee SP, Tan DT. Refractive change following pterygium surgery. CLAO J 1998;24:115-7.  Back to cited text no. 7
    
8.
Panchapakesan J, Hourihan F, Mitchell P. Prevalence of pterygium and pinguecula: The blue mountains eye study. Aust N Z J Ophthalmol 1998;26 Suppl 1:S2-5.  Back to cited text no. 8
    
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Callo-Concha D, Gaiser T, Webber H, Tischbein B, Müller F, Ewert M. Farming in the West African Sudan Savanna: Insights in the context of climate change. Afr J Agric Res 2013;8:4693-705.  Back to cited text no. 9
    
10.
McCarty CA, Fu CL, Taylor HR. Epidemiology of pterygium in Victoria, Australia. Br J Ophthalmol 2000;84:289-92.  Back to cited text no. 10
    
11.
Oh JY, Wee WR. The effect of pterygium surgery on contrast sensitivity and corneal topographic changes. Clin Ophthalmol 2010;4:315-9.  Back to cited text no. 11
    
12.
Popat KB, Sheth HK, Vyas VJ, Rangoonwala MM, Sheth RK, Shah JC. A study on changes in keratometry readings and astigmatism induced by pterygium before and after pterygium excision surgery. J Res Med Den Sci 2014;2:37-42.  Back to cited text no. 12
    
13.
Mohite US, Dole NB, Jadhav SS. Effectiveness of pterygium surgery on corneal astigmatism. Medpulse Int J Ophthalmol 2017;3:12-7. Available from: https://www.medpulse.in/Ophthlmology/. [Last accessed on 2016 Jan].  Back to cited text no. 13
    
14.
Gros-Otero J, Pérez-Rico C, Montes-Mollón MA, Gutiérrez-Ortiz C, Benítez-Herreros J, Teus MA, et al. Effects of pterygium on the biomechanical properties of the cornea: A pilot study. Arch Soc Esp Oftalmol 2013;88:134-8.  Back to cited text no. 14
    
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Rasit K, Sebile U, Alperen A, Ahmet O. The effect of pterygium existence on central corneal thickness. Duzce Univ Tip Fakul Derg 2015;17:13-5.  Back to cited text no. 15
    
16.
Oner V, Tas M, Ozkaya E, Bulut A. Influence of pterygium on corneal biomechanical properties. Curr Eye Res 2016;41:913-6. doi: 10.3109/02713683.2015.1080281.  Back to cited text no. 16
    
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Kuryan JT, Rosenberg J, Madu A. Risk factors for elevated intraocular pressure after pterygium excision. Invest Ophthalmol Visual Sci 2009;50:903.  Back to cited text no. 17
    
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Wu K, Lee HJ, Desai MA. Risk factors for early onset elevated intraocular pressure after pterygium surgery. Clin Ophthalmol 2018;12:1539-47.  Back to cited text no. 18
    
19.
Avisar R, Loya N, Yassur Y, Weinberger D. Pterygium-induced corneal astigmatism. Isr Med Assoc J 2000;2:14-5.  Back to cited text no. 19
    
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Lin A, Stern G. Correlation between pterygium size and induced corneal astigmatism. Cornea 1998;17:28-30.  Back to cited text no. 20
    
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Ozdemir M, Cinal A. Early and late effects of pterygium surgery on corneal topography. Ophthalmic Surg Lasers Imaging 2005;36:451-6.  Back to cited text no. 21
    


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