Abstract
PURPOSE:
To assess the severity of dry eye in individuals with pterygium in a tertiary care hospital.
METHODS:
This cross-sectional study was done on 70 individuals with pterygium who were attending the outpatient department of ophthalmology. Objective dry eye tests were done, including Schirmer’s tests 1 and 2, tear film breakup time, and tear meniscus height (TMH). In this study, patients with one or more positive clinical tests were diagnosed to have dry eyes. Dry eye was graded as mild, moderate, severe, or severe disabling.
RESULTS:
Among 140 eyes, 79 eyes had pterygium. According to Schirmer’s test 1 in eyes with pterygium, 29.1% of the eyes had mild dry eyes, and 26.6% had moderate dry eyes. According to Schirmer’s test 2 in eyes with pterygium, 25.3% of the eyes had mild dry eyes, and 26.6% had moderate dry eyes. Tear film breakup time in eyes with pterygium showed a mild dry eye in 25.3% and moderate dry eye in 17.7%. TMH in eyes with pterygium was low at 7.6%.
CONCLUSION:
The majority of eyes with pterygium have mild or moderate dry eye according to Schirmer’s test 1, Schirmer’s test 2, and tear film breakup time. No eyes with pterygium have severe dry eyes. TMH was also low in a small proportion of eyes with pterygium. Dry eye evaluation by Schirmer’s test and tear breakup time is, therefore, a crucial clinical tool for early detection and prompt management of dry eye syndrome in pterygium patients.
Keywords: Dry eye, pterygium, severity
Introduction
Dry eye is a multifactorial disease of ocular surface and tears that cause tear film instability and damage to the ocular surface.[1] Tear film abnormalities result in local drying of conjunctiva and cornea, which predisposes to ocular surface disorders like pterygium.[2]
A significant percentage of the population is affected by dry eye disorder.
Pterygium is an independent factor associated with dry eye.[3]
“Pterygium is a degenerative condition of the subconjunctival tissues which proliferate as vascularized granulation tissue to invade the cornea, destroying the superficial layers of the stroma and Bowman’s membrane.”[4]
Usually, it is asymptomatic, but it can cause foreign body sensation, redness, and distortion of tear film. Once it encroaches on the pupillary area, it can result in a significant impact on vision.
Dry eye syndrome can damage the ocular surface and is associated with tear film instability.
Much research has been done to find the relation between dry eye and pterygium. Some studies found that pterygium causes a local elevation in the conjunctiva and an irregular distribution of tears, leading to dry eye abnormalities in tear dynamics.[5,6]
Chronic ocular surface inflammation and altered tear film dynamics result in tear film instability in pterygium.[7]
The inflammatory basis of dry eye syndrome implies that inflammatory mediators in the pterygium may have an indirect influence.
Pterygium prevalence varies considerably depending on age group and geographical location. Pterygium is more prevalent in equatorial countries. Lifetime sun exposure and other risk factors, such as increasing age, male gender, and living in a rural area, are positively correlated with the incidence of pterygium.
Pterygium is more common in the male population as they are more involved in outdoor activities and thus exposed to ultraviolet rays in sunlight.
Schirmer’s test value was decreased in patients with pterygium.[8]
Patients with pterygium are more likely to have symptoms of dry eye.
There is no single highly sensitive and specific test for diagnosis of dry eye. It depends on a combination of history, examination, and various diagnostic tests.
This study uses Schirmer’s tests 1 and 2, tear film breakup time (TBUT), and tear meniscus height (TMH) to diagnose and grade dry eye.
Although dry eye and pterygium are often associated, dry eye may be missed, so this study is trying to find out the severity of dry eye in individuals with pterygium.
Dry eye is a major problem even in individuals with early pterygium.
Methods
Study design and study setting
In this tertiary hospital-based cross-sectional study, all individuals (70 patients) with pterygium in at least one eye attending the outpatient department of ophthalmology, during a period of 2 years from December 2020 to May 2022, were included after obtaining institutional ethical committee clearance.
The study adheres to the tenets of the Declaration of Helsinki.
Exclusion criteria
Recurrent pterygium
Medications-lubricant eye drops and drugs that are likely to increase the severity of dry eye
Systemic disease associated with dry eye (for example, Sjogren’s syndrome)
Contact lens users
Adnexal disease which alters tear secretion and stability
History of ocular surgeries in the past.
Sampling technique
Every consecutive patient who came to the ophthalmology outpatient department and fulfilled the inclusion criteria were included in the study.
Data collection methods
Informed consent was taken. They underwent slit-lamp examination to evaluate the anterior segment of the eye and to measure the size and transparency of the pterygium.
Using the Haag-Streit slit lamp graticule the length of the horizontally positioned slit beam was adjusted to determine the pterygium's size from limbus to apex.
Severity grading of pterygium based on the size;[9]
(1) Grade 1: 0–2 mm, (2) Grade 2: 2–4 mm, (3) Grade 3: >4 mm.
Severity grading of pterygium based on its transparency under slit lamp;[9]
(1) Grade 1: Atrophic-clearly visible episcleral vessels under the body of pterygium, (2) Grade 2: Intermediate-partially visible episcleral vessels under the body of pterygium, (3) Grade 3: Fleshy-totally obscured episcleral vessels under the body of pterygium.
An objective examination of the dry eye includes the following:
TBUT measurement was performed by placing a fluorescein strip into the inferior tarsal conjunctiva. The patient was instructed to blink once or twice and then stare straight ahead without blinking. TBUT was measured as the interval between the last blink and the occurrence of the first corneal dark spot using a blue cobalt filter. TBUT value <10 s is normal, 5–10 s is mild to moderate, and <5 s is severe. If the value was immediate, it was very severe
Schirmer’s test: By placing the Whatman 41 filter paper strip, which was folded 5 mm from one end and inserted into the inferior fornix at the junction of the medial 2/3rd and lateral 1/3rd of the lower eyelid. The patient was asked to keep their eyes open. After 5 min, filter paper was removed, and the amount of wetting from the fold was measured. Schirmer’s test 1 (without a topical anesthetic agent): This test measures baseline and reflex tear secretion. A reading <10 mm is abnormal. Schirmer’s test 2 (with a topical anesthetic agent): Measures baseline secretion of tears. A reading <5 mm is abnormal
TMH: Under the thin beam of slit-lamp biomicroscope, an inspection of the tear meniscus between the globe and the lower eyelid (normally 1 mm in height and convex). A reading <0.25 mm is abnormal.
In this study, patients with one or more positive clinical tests (TBUT ≤10 s, SCH1 ≤10 mm, SCH2 ≤5 mm, and TMH <0.25 mm) were diagnosed with dry eye. According to the DEWS workshop,[10] dry eye syndrome was graded as mild, moderate, severe, or severely disabling, as shown in Table 1.
Table 1.
Grading of dry eye
| Dry eye severity level | Mild | Moderate | Severe | Severe disabling | ||||
|---|---|---|---|---|---|---|---|---|
| Tear film breakup time (s) | Variable | ≤10 | ≤5 | Immediate | ||||
| Schirmer’s score (mm) | Variable | ≤10 | ≤5 | <2 |
In this study, artificial tear substitutes are used in the management of patients diagnosed with dry eye disease.
Operational definition
According to the NEI workshop grading system,[11] dry eye is diagnosed as one having one or more symptoms along with one or more positive clinical findings (dryness, grittiness, scratchiness, soreness, irritation, burning or watering, and eye fatigue) and one or more positive clinical tests (Schirmer’s test I, II, TBUT, and TMH).
For the diagnosis of dry eye, this study used only objective tests.
“Pterygium (meaning “a wing”) is a triangular encroachment of the vascularized granulation tissue covered by conjunctiva in the interpalpebral area.”[12]
This study only evaluates the severity of dry eye in patients with pterygium. To assess various diagnostic modalities of dry eye, another study is needed.
Data analysis
Categorical and quantitative variables were expressed as frequency (percentage) and mean ± standard deviation, respectively. The Chi-square test was used to find the association between categorical variables. For all statistical interpretations, P < 0.05 was considered the threshold for statistical significance. Statistical analyses were performed using a statistical software package IBM SPSS Armonk, NY Statistics for windows, version20.0.
Ethical considerations
Institutional ethical committee clearance was obtained before the commencement of the study. Written informed consent was taken from all study participants. Privacy and confidentiality were maintained during all stages of the study.
Results
Of the 140 eyes of the 70 patients, 79 had pterygium.
Among the study subjects, the relationship of dry eye with demographic factors such as age, gender, and occupation was studied. In people older than 50, 63.6% had dry eyes. Age was found to have significant association with dry eye (P < 0.01). Females had a higher prevalence of dry eye than males with 55.2% and 45.1%, respectively, as shown in Table 2 and Figure 1.
Table 2.
Comparison of sociodemographic factors associated with dry eye
| Dry eye, count (%) |
χ 2 | P | ||||||
|---|---|---|---|---|---|---|---|---|
| No | Yes | |||||||
| Age | ||||||||
| ≤50 | 47 (63.5) | 27 (36.5) | 10.29** | 0.001 | ||||
| >50 | 24 (36.4) | 42 (63.6) | ||||||
| Gender | ||||||||
| Male | 45 (54.9) | 37 (45.1) | 1.37 | 0.241 | ||||
| Female | 26 (44.8) | 32 (55.2) | ||||||
**Significant at 0.01 level. χ2: Chi-square test
Figure 1.
Comparison of sociodemographic factors associated with dry eye
Based on occupation, all fishermen have dry eye. Farmers and unemployed study subjects had more prevalence of dry eye of 59.4% and 56.7%, respectively, as shown in Table 3 and Figure 2.
Table 3.
Distribution of occupation based on dry eye
| Occupation | Dry eye, count (%) |
|||
|---|---|---|---|---|
| No | Yes | |||
| Unemployed | 26 (43.3) | 34 (56.7) | ||
| Fisher man | 0 | 4 (100.0) | ||
| Farmers/laborers | 13 (40.6) | 19 (59.4) | ||
| Office worker | 12 (85.7) | 2 (14.3) | ||
| Shop keeper | 14 (63.6) | 8 (36.4) | ||
| Driver | 6 (75.0) | 2 (25.0) | ||
Figure 2.
Distribution of occupation based on dry eye
However, gender and occupation were not found to have a statistically significant association with dry eye.
Table 4 and Figure 3 shows the distribution of values obtained for Schirmer’s Test 1, Schirmer’s Test 2, and tear breakup time in eyes with pterygium and eyes without pterygium.
Table 4.
Association between severity of dry eye disease and eye with pterygium based on Schirmer’s test 1, Schirmer’s test 2, and tear film breakup time
| Eye with pterygium, count (%) |
Z # | P | ||||||
|---|---|---|---|---|---|---|---|---|
| No | Yes | |||||||
| SCH 1 | ||||||||
| Normal | 47 (77.0) | 35 (44.3) | 4.46 | <0.01 | ||||
| Mild | 14 (23.0) | 23 (29.1) | ||||||
| Moderate | 0 | 21 (26.6) | ||||||
| SCH 2 | ||||||||
| Normal | 50 (82.0) | 38 (48.1) | 4.56 | <0.01 | ||||
| Mild | 11 (18.0) | 20 (25.3) | ||||||
| Moderate | 0 | 21 (26.6) | ||||||
| TBUT | ||||||||
| Normal | 49 (80.3) | 45 (57.0) | 3.29** | 0.001 | ||||
| Mild | 12 (19.7) | 20 (25.3) | ||||||
| Moderate | 0 | 14 (17.7) | ||||||
**Significant at 0.01 level, #Mann–Whitney U-test. SCH 1: Schirmer’s test 1, SCH 2: Schirmer’s test 2, TBUT: Tear film breakup time
Figure 3.
The association between the severity of dry eye disease and eye with pterygium is based on Schirmer’s test 1, Schirmer’s test 2, and tear film breakup time
When Schirmer’s test 1 was performed on eyes with pterygium, 29.1% of the eyes had mild dry eyes, 26.6% had moderate dry eyes, and 44.3% had normal values.
Using Schirmer’s test 2 performed on eyes with pterygium, 25.3% of the eyes had mild dry eyes, 26.6% had moderate dry eyes, and 48.1% had normal values.
TBUT was done in the eyes with pterygium. There was a mild dry eye in 25.3%, moderate dry eye in 17.7%, and normal value eye in 57%.
TMH was done in eyes with pterygium, which was low in 7.6% and normal in 92.4%.
Table 5 and Figure 4 shows the distribution of values obtained for TMH in eyes with pterygium and eyes without pterygium.
Table 5.
Association between severity of dry eye disease in eye with pterygium based on tear meniscus height
| TMH | Eye with pterygium, count (%) |
χ 2 | P | |||||
|---|---|---|---|---|---|---|---|---|
| No | Yes | |||||||
| Normal | 61 (100.0) | 73 (92.4) | 4.84* | 0.028 | ||||
| Low | 0 | 6 (7.6) | ||||||
*Significant at 0.05 level. χ2: Chi-square test. TMH: Tear meniscus height
Figure 4.
Association between severity of dry eye disease with pterygium based on tear meniscus height
In eyes with pterygium, there is a strong correlation between dry eye as measured by Schirmer’s tests 1 and 2, TBUT, and TMH with a statistically significant difference (P < 0.05), as shown in Tables 4 and 5.
A correlation analysis was performed between the severity of dry eye tests (SCH1, SCH2, TBUT, and TMH) and grading of pterygium based on size shown in Table 6 and Figure 5. 75% of patients with pterygium size >4 mm had moderate dry eye according to SCH 1, SCH 2, and TBUT. Mild dry eye was commonly seen in eyes with 0–2 mm sized pterygium. TMH was low in pterygium with size 2–4 mm and >4 mm. A strong and statistically significant positive correlation was discovered (P < 0.01).
Table 6.
Relationship between severity of dry eye disease and pterygium size grading
| Absent (%) | 0–2 mm (%) | 2–4 mm (%) | >4 mm (%) | χ 2 | P | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| SCH 1 | ||||||||||||
| Normal | 77 | 66.7 | 13 | 0 | 76.02 | <0.01 | ||||||
| Mild | 23 | 29.2 | 30.4 | 25 | ||||||||
| Moderate | 0 | 4.2 | 56.5 | 75 | ||||||||
| SCH 2 | ||||||||||||
| Normal | 82 | 68.8 | 21.7 | 0 | 74.59 | <0.01 | ||||||
| Mild | 18 | 27.1 | 21.7 | 25 | ||||||||
| Moderate | 0 | 4.2 | 56.5 | 75 | ||||||||
| TBUT | ||||||||||||
| Normal | 80.3 | 77.1 | 34.8 | 0 | 65.56 | <0.01 | ||||||
| Mild | 19.7 | 20.8 | 34.8 | 25 | ||||||||
| Moderate | 0 | 2.1 | 30.4 | 75 | ||||||||
| TMH | ||||||||||||
| Normal | 100 | 100 | 91.3 | 50 | 46.73 | <0.01 | ||||||
| Low | 0 | 0 | 8.7 | 50 |
χ2: Chi-square test. SCH 1: Schirmer’s test 1, SCH 2: Schirmer’s test 2, TBUT: Tear film breakup time, TMH: Tear meniscus height
Figure 5.
The relationship between the severity of dry eye disease and pterygium size grading
A correlation analysis was performed between the severity of dry eye tests (SCH 1, SCH 2, TBUT, and TMH) and the grading of pterygium (based on transparency) shown in Table 7 and Figure 6. 85.7% of patients with fleshy pterygium had moderate dry eye according to Schirmer’s 1 (SCH 1) and Schirmer’s 2 (SCH 2), and 78.6% of patients with fleshy pterygium had moderate dry eye according to TBUT. According to TBUT, as pterygium severity increased, more individuals were found to have moderate dry eye. The majority of the patients had a mild dry eye in atrophic pterygium.
Table 7.
Relationship between severity of dry eye disease and grading of pterygium based on transparency
| Absent (%) | Atrophic (%) | Intermediate (%) | Fleshy (%) | χ 2 | P | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| SCH 1 | ||||||||||||
| Normal | 77 | 61.5 | 42.3 | 0 | 79.53 | <0.01 | ||||||
| Mild | 23 | 35.9 | 26.9 | 14.3 | ||||||||
| Moderate | 0 | 2.6 | 30.8 | 85.7 | ||||||||
| SCH 2 | ||||||||||||
| Normal | 82 | 64.1 | 50 | 0 | 80.35 | <0.01 | ||||||
| Mild | 18 | 33.3 | 19.2 | 14.3 | ||||||||
| Moderate | 0 | 2.6 | 30.8 | 85.7 | ||||||||
| TBUT | ||||||||||||
| Normal | 80.3 | 76.9 | 57.7 | 0 | 88.77 | <0.01 | ||||||
| Mild | 19.7 | 23.1 | 30.8 | 21.4 | ||||||||
| Moderate | 0 | 0 | 11.5 | 78.6 | ||||||||
| TMH | ||||||||||||
| Normal | 100 | 100 | 92.3 | 71.4 | 25.34 | <0.01 | ||||||
| Low | 0 | 0 | 7.7 | 28.6 |
χ2: Chi-square test. SCH 1: Schirmer’s test 1, SCH 2: Schirmer’s test 2, TBUT: Tear film breakup time, TMH: Tear meniscus height
Figure 6.
The relationship between the severity of dry eye disease and grading of pterygium based on transparency
As the pterygium severity rises (intermediate and fleshy pterygium), a lower value of TMH is observed.
Discussion
Pterygium is a degenerative ocular surface disorder that has been attributed to environmental factors. The prevalence and severity of dry eye and pterygia vary in many regions of the world.[11]
140 eyes of 70 patients who have pterygium were examined, of which 79 eyes have pterygium. Considering the exclusion criteria and the study done during COVID-19 period, this study was restricted to a limited number of study subjects.
Their age varied from 31 to 80 years (mean age – 50.7 years). Most were among those aged between 51 and 60 years. There was a significant correlation of dry eye in age more than 50 years.
In the present study, the severity of SCH 1 and SCH 2 was found to be mild and moderate in eyes with pterygium, indicating inadequate tear film. None had a severe dry eye. This may be related to the severity of pterygium based on size and transparency, where Grade 3 severity of size more than 4 mm was only seen in 8 eyes with pterygium, and Grade 3 fleshy pterygium was only seen in 14 eyes with pterygium.
Roka et al. showed that Schirmer’s test values markedly decreased in those with pterygium.[11] Ishioka et al. observed that Schirmer’s test 2 was decreased in the eyes with pterygium and came to the conclusion that there is an association between pterygium development and tear film that is unstable.[12]
A low TBUT value is linked to unstable tear film.[13]
In this research, TBUT values were found to be low. Eyes with pterygium showed low TBUT value. On comparing TBUT severity in eyes with eyes without pterygium, eyes with pterygium have mild and moderate dry eye, whereas eyes without pterygium have only mild dry eye.
Pterygium itself can cause abnormal mucin in tear film.[14]
Restoration of normal tear film breakup time was noticed in patients who have undergone pterygium excision.[15]
Pterygia is characterized by inflammation and predominant vascular reaction.[16] This is associated with inflammatory damage to the meibomian gland and results in meibomian gland dysfunction.
Moreno et al. discovered that TBUT values markedly decreased in the eyes with pterygium.[17]
Pterygium can cause abnormal blinking and irregular surface epithelium, resulting in compromised surface tension of tear film and abnormal tear film stability.[1]
Wang et al. noticed that on comparing opposite healthy eyes with pterygium-affected eyes, there was a statistically significant variation in TBUT values.[18]
In this study, TMH was low in only 7.6% of eyes with pterygium. Higher TMH may be related to altered tear flow dynamics and reflex tearing due to chronic ocular surface inflammation.[19]
This may be related to the severity of pterygium based on size and transparency, where Grade 3 severity of size more than 4 mm was only seen in 8 eyes with pterygium, and Grade 3 fleshy pterygium was only seen in 14 eyes with pterygium.
In this study, evaluating the association between severity of dry eye (according to SCH1, SCH2, TBUT) and severity of pterygium based on size and transparency showed statistically significant results. As the severity of pterygium increases based on size and transparency, there was an increase in the number of patients with moderate severity of dry eye. Based on pterygium transparency, TMH was low in intermediate and fleshy pterygium. TMH was low in size 2–4 mm and >4 mm.
A study done by Gupta AK concluded that there was a positive correlation between the size of pterygium with Schirmer’s test and TBUT.[7]
Conclusion
The majority of eyes with pterygium have mild or moderate dry eye according to Schirmer’s test 1, Schirmer’s test 2, and tear film breakup time. No eyes with pterygium have severe dry eyes.
TMH was also low in a small proportion of eyes with pterygium.
Dry eye evaluation by Schirmer’s test and tear breakup time is, therefore, a crucial clinical tool for early detection and prompt management of dry eye syndrome in pterygium patients. Even in patients with early stage of pterygium, dry eye is a major problem. This needs to be addressed by starting tear substitutes.
This study only assesses the severity of dry eye using objective dry eye tests. To assess various diagnostic modalities of dry eye another study is needed.
This study strongly recommends that clinical evaluation of dry eye must be considered an integral part of the ocular examination in pterygium patients to prevent complications that may lead to severe visual impairment affecting the quality of life of patients.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References
- 1.Manhas A, Gupta D, Gupta A, Kumar D, Manhas RS, Manhas GS. Clinical correlation between dry eye and pterygium: A study was done at the government medical college Jammu, Jammu and Kashmir, North India. Int J Res Med Sci. 2017;5:3087–94. [Google Scholar]
- 2.Paton D. Pterygium management based upon a theory of pathogenesis. Trans Am Acad Ophthalmol Otolaryngol. 1975;79:603–12. [Google Scholar]
- 3.Lee AJ, Lee J, Saw SM, Gazzard G, Koh D, Widjaja D, et al. Prevalence and risk factors associated with dry eye symptoms: A population based study in Indonesia. Br J Ophthalmol. 2002;86:1347–51. doi: 10.1136/bjo.86.12.1347. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Shihota R, Tandon R, editors, editors. Parson‟s Diseases of the eye. 21st. India: Elsevier; 2011. Diseases of the conjunctiva; p. 181. [Google Scholar]
- 5.Julio G, Lluch S, Pujol P, Alonso S, Merindano D. Tear osmolarity and ocular changes in pterygium. Cornea. 2012;31:1417–21. doi: 10.1097/ICO.0b013e318259c934. [DOI] [PubMed] [Google Scholar]
- 6.Pandey DJ, Mishra VK, Singh YP, Kumar A, Pandey DN. Quantitative and qualitative estimation of tear in pterygium. Indian J Ophthalmol. 1984;32:373–7. [PubMed] [Google Scholar]
- 7.Gupta AK, Nathwani Y. Correlation between pterygium and dry eye. Kerala J Ophthalmol. 2019;31:217–20. [Google Scholar]
- 8.Rajiv Mithal S, Sood AK. Pterygium and dry eye – A clinical correlation. Indian J Ophthalmol. 1991;39:15–6. [PubMed] [Google Scholar]
- 9.Tan DT, Chee SP, Dear KB, Lim AS. Effect of pterygium morphology on pterygium recurrence in a controlled trial comparing conjunctival autografting with bare sclera excision. Arch Ophthalmol. 1997;115:1235–40. doi: 10.1001/archopht.1997.01100160405001. [DOI] [PubMed] [Google Scholar]
- 10.Lemp MA, Baudouin C, Baum J, Dogru M, Foulks GN, Kinoshita S, et al. The definition and classification of dry eye disease: Report of the definition and classification subcommittee of the international Dry Eye WorkShop (2007) Ocular Surface. 2007;5:75–92. doi: 10.1016/s1542-0124(12)70081-2. [DOI] [PubMed] [Google Scholar]
- 11.Roka N, Shrestha SP, Joshi ND. Assessment of tear secretion and tear film instability in cases with pterygium and normal subjects. Nepal J Ophthalmol. 2013;5:16–23. doi: 10.3126/nepjoph.v5i1.7816. [DOI] [PubMed] [Google Scholar]
- 12.Ishioka M, Shimmura S, Yagi Y, Tsubota K. Pterygium and dry eye. Ophthalmologica. 2001;215:209–11. doi: 10.1159/000050860. [DOI] [PubMed] [Google Scholar]
- 13.Kiliç A, Gürler B. Effect of pterygium excision by limbal conjunctival auotografting on tear function tests. Ann Ophthalmol (Skokie) 2006;38:235–8.4. doi: 10.1007/s12009-006-0011-4. [DOI] [PubMed] [Google Scholar]
- 14.Rajab AY. Evaluation of tear film stability in pterygium and pingueculae. Ann Coll Med Mosul. 2013;39:132–5. [Google Scholar]
- 15.Asbell PA. New York: Thieme Medical Publishers, Inc; 2006. Dry Eye Disease: The Clinician‟s Guide to Diagnosis and Treatment; pp. 4–13. [Google Scholar]
- 16.Bandyopadhyay R, Nag D, Mondal SK, Gangopadhyay S, Bagchi K, Bhaduri G. Ocular surface disorder in pterygium: Role of conjunctival impression cytology. Indian J Pathol Microbiol. 2010;53:692–5. doi: 10.4103/0377-4929.72036. [DOI] [PubMed] [Google Scholar]
- 17.Moreno JC, Garcia VG, Garcia L. Evaluation of tear film in patients with pterygium. Eur J Ophthalmol. 2011 [Google Scholar]
- 18.Wang S, Jiang B, Gu Y. Changes of tear film function after pterygium operation. Ophthalmic Res. 2011;45:210–5. doi: 10.1159/000321531. [DOI] [PubMed] [Google Scholar]
- 19.Kampitak K, Tansiricharernkul W, Leelawongtawun W. A comparison of precorneal tear film pre and post pterygium surgery. J Med Assoc Thai. 2015;98(Suppl 2):S53–5. [PubMed] [Google Scholar]