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Impact of Pterygium on Dry Eye and Meibomian Gland Parameters: A Case- Control Study

This case-control study conducted in Nepal demonstrates that pterygium is significantly associated with impaired aqueous tear production, reduced tear film stability, compromised lipid layer integrity, and increased meibomian gland loss, suggesting a direct mechanical relationship between the condition and evaporative dry eye disease.

Original authors: Sushant Gyawali, Ghana Shyam Mahato, Gopal Bhandari, Anju Shrestha, Pushpa Giri Shrestha, Suyel Gyawali, Prativa Acharya

Published 2026-07-30

📖 6 min read🧠 Deep dive

CC BY 4.0

Original authors: Sushant Gyawali, Ghana Shyam Mahato, Gopal Bhandari, Anju Shrestha, Pushpa Giri Shrestha, Suyel Gyawali, Prativa Acharya

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Eye's Delicate Raincoat and the Unwanted Invader

Imagine your eye as a tiny, high-tech camera that never sleeps. To keep its lens crystal clear, it relies on a constant, gentle rain. This isn't just water; it's a sophisticated three-layered "raincoat" that protects the eye from drying out and keeps vision sharp. The bottom layer is the water itself, the middle layer is a slippery mucus that helps the water stick, and the top layer is a special oily film. Think of this top layer like the wax on a car or the oil on a salad; without it, the water underneath would evaporate instantly, leaving the eye parched and irritated. This top layer is produced by tiny, hidden factories inside your eyelids called Meibomian glands.

Sometimes, an unwanted invader shows up on the surface of the eye. It's called a pterygium (pronounced teh-ri-gee-um). Picture it as a piece of fleshy, fibrous tissue that starts on the white part of the eye and slowly creeps across the clear window (the cornea) like a vine growing over a garden gate. While it's often caused by too much sun exposure, the big question scientists have been asking is: Does this invader just sit there and block your view, or does it actually mess with the eye's delicate raincoat system? Does it break the factories that make the oil, or does it just make the eye feel dry because it's there? Understanding this is crucial because if the raincoat is broken, the eye stays uncomfortable even after the vine is removed.

The Investigation: A Tale of Two Groups

In a hospital in Nepal, a team of researchers decided to play detective. They gathered two groups of people: 32 individuals who had this "vine" (pterygium) growing on their eyes, and 32 healthy people of the same age and gender who didn't have it. They wanted to see if the eye with the pterygium was secretly suffering from a broken raincoat system compared to the healthy eye.

They didn't just ask, "Does your eye feel dry?" because sometimes our brains are tricky and don't notice the problem until it's huge. Instead, they used a toolbox of high-tech gadgets to measure the eye's health like a mechanic checking a car engine. They measured:

How much water the eye makes: Using a special test where a tiny strip of paper touches the eye to see how wet it gets.
How long the tear film lasts: Watching how quickly the tear film breaks apart (like a soap bubble popping).
The thickness of the oily top layer: Using infrared cameras to see how thick the "wax" layer is.
The health of the oil factories: Taking pictures of the eyelids to see if the Meibomian glands were still there or if they had disappeared.

What They Found: The Raincoat is Broken

The results were a mix of "surprisingly quiet" and "loudly broken."

First, the researchers asked the patients how much their eyes bothered them. Surprisingly, the people with the pterygium didn't complain much more than the healthy people. Their "dry eye score" was slightly higher, but not enough to be statistically different. It's as if the patients had gotten used to the feeling, or perhaps their brains just tuned it out.

However, when the scientists looked at the actual numbers, the story changed completely. The eyes with pterygium were in trouble:

The Water Supply: The healthy eyes produced about 11.5 mm of wetness on the test strip, while the pterygium eyes only produced 7.03 mm. The pterygium eyes were making significantly less water.
The Bubble Pop: The tear film on healthy eyes lasted for about 9.69 seconds before breaking. On the pterygium eyes, it popped in just 5.09 seconds. The tear film was incredibly unstable.
The Missing Oil: The oily top layer, which is supposed to be thick and protective, was much thinner in the pterygium group. Healthy eyes had a layer about 68.2 nm thick, while the pterygium eyes had a layer only 45.0 nm thick. That's a massive drop in protection.
The Broken Factories: When they looked at the eyelids, the oil factories (Meibomian glands) were missing more often in the pterygium group. In the upper eyelids, about 35.2% of the gland area was lost in the pterygium group, compared to only 29.1% in the healthy group. The lower eyelids showed a similar pattern, with 29.6% loss versus 24.2%.

The Big Picture: A Mechanical Problem

The researchers concluded that having a pterygium isn't just about having a weird growth on the eye; it actively damages the eye's ability to stay moist. It seems the pterygium acts like a physical disruptor. As the "vine" grows, it might be physically pressing on the eyelids or the oil factories, causing them to shrink or stop working. It's like having a heavy rock sitting on a water hose; the water flow gets cut off, and the spray nozzle gets clogged.

The study suggests that the dryness isn't just a side effect; it's a direct result of the pterygium messing up the tear film's stability and the oil production. The fact that the oil layer is so thin and the tear film breaks so fast means the eye is suffering from "evaporative dry eye"—the tears are evaporating too fast because the oil shield is gone.

Interestingly, the study didn't find a strong link between how bad the pterygium looked and how much the patients felt it. This means a patient could have a severely damaged tear film and broken oil factories without realizing it, simply because they aren't complaining of pain.

What This Means for the Future

The takeaway from this study is clear: if a doctor sees a pterygium, they shouldn't just look at the growth. They need to check the eye's "raincoat" system, too. Because the pterygium seems to break the oil factories and thin out the protective layer, treating the eye might require more than just removing the growth. The doctors might need to fix the dry eye and the broken oil glands as well.

While this study was done on a specific group of people in Nepal and had a relatively small number of participants, the evidence points to a strong connection. The pterygium isn't just a cosmetic issue; it's a mechanical troublemaker that disrupts the delicate balance of the eye's moisture, leaving the eye vulnerable and dry.

Technical Summary: Impact of Pterygium on Dry Eye and Meibomian Gland Parameters

Problem Statement
Pterygium is a fibrovascular proliferative lesion originating from the bulbar conjunctiva, driven by factors such as chronic UV exposure and limbal stem cell failure. While its association with Dry Eye Disease (DED) is established, the specific mechanisms remain debated: whether impaired tear function is a primary risk factor for pterygium development or a secondary consequence of the lesion. Furthermore, while Meibomian Gland Dysfunction (MGD) is suspected in pterygium patients, comprehensive data quantifying the impact on lipid layer thickness (LLT), non-invasive tear break-up time (NIBUT), and specific meibomian gland morphology (via infrared meibography) in South Asian populations are limited. This study addresses the gap in understanding the multidimensional impact of pterygium on the ocular surface, specifically focusing on aqueous production, tear film stability, lipid integrity, and gland structure.

Methodology
This was a hospital-based, non-interventional case-control study conducted at Bharatpur Eye Hospital in Nepal. The study population consisted of 64 participants divided into two groups:

Group 1 (Case): 32 patients (32 eyes) diagnosed with pterygium, aged 18 and above, without systemic illness.
Group 2 (Control): 32 age- and sex-matched healthy volunteers with no history of pterygium.

Exclusion criteria included systemic medications affecting tear film, active ocular infections, prior ocular surgery, and contact lens use. The study adhered to the Declaration of Helsinki with IRB approval from the National Academy of Medical Sciences.

Assessment Parameters
The study employed a standardized sequence of tests to minimize inter-test interference:

Symptomatology: Ocular Surface Disease Index (OSDI) questionnaire.
Aqueous Production: Schirmer II test (with topical anesthesia) to measure basal tear secretion.
Tear Film Stability:
- Fluorescein Tear Film Break-up Time (TBUT).
- Non-invasive Tear Break-up Time (NIBUT) using interferometric imaging.
Lipid Layer Integrity: Lipid Layer Thickness (LLT) measured in nanometers via the IBRA SBM Sistemi device.
Meibomian Gland Morphology: Infrared meibography to assess gland loss percentage in upper and lower tarsal plates, graded using a standard meiboscale.

Statistical analysis was performed using SPSS version 26, utilizing independent samples t-tests for continuous variables, with significance set at $p < 0.05$ .

Key Results
The study analyzed 32 eyes in each group, with a mean age of 44.7 years and a majority of participants (85.9%) from the Terai region (high UV exposure).

Symptoms: OSDI scores were numerically higher in the pterygium group ( $16.4 \pm 7.7$ ) compared to controls ( $13.0 \pm 7.5$ ), but this difference was not statistically significant ( $p = 0.08$ ).
Aqueous Tear Production: Schirmer II test values were significantly lower in the pterygium group ( $7.03 \pm 3.86$ mm) compared to controls ( $11.5 \pm 6.83$ mm; $p = 0.002$ ).
Tear Film Stability: Both NIBUT and TBUT were significantly reduced in the pterygium group.
- NIBUT: $6.38 \pm 3.30$ s (cases) vs. $9.38 \pm 4.43$ s (controls; $p = 0.003$ ).
- TBUT: $5.09 \pm 2.69$ s (cases) vs. $9.69 \pm 4.16$ s (controls; $p < 0.001$ ).
Lipid Layer Thickness: LLT was significantly lower in the pterygium group ( $45.0 \pm 13.7$ nm) compared to controls ( $68.2 \pm 18.0$ nm; $p < 0.001$ ).
Meibomian Gland Loss: Gland loss was significantly greater in the pterygium group for both the upper tarsal plate ( $35.2 \pm 10.2\%$ vs. $29.1 \pm 12.0\%$ ; $p = 0.034$ ) and the lower tarsal plate ( $29.6 \pm 10.3\%$ vs. $24.2 \pm 9.14\%$ ; $p = 0.029$ ).

Key Contributions and Claims
The paper claims to provide a comprehensive evaluation of pterygium's impact on the ocular surface in a Nepalese population, specifically integrating LLT and NIBUT with conventional tear film parameters and infrared meibography.

Evaporative Dominance: The study highlights a dissociation between subjective symptoms (OSDI) and objective signs. While symptoms were not significantly different, objective measures of tear film stability (TBUT, NIBUT) and lipid layer integrity (LLT) were severely compromised. This suggests that evaporative dry eye, mediated by lipid layer disruption, is the dominant subtype of tear film dysfunction in pterygium patients.
Structural and Functional Correlation: The significant reduction in LLT correlates with the observed meibomian gland loss, providing a mechanistic link between structural gland damage and functional tear film impairment.
Mechanism of Dysfunction: The authors propose that meibomian gland dysfunction in pterygium is likely driven by both mechanical and inflammatory factors. The spatial correspondence between the pterygium location (typically nasal) and gland abnormality suggests a direct mechanical relationship, where the fibrovascular mass may compress the tarsal plate during blinking, leading to atrophy.
Clinical Implication: The study asserts that pterygium management should not be isolated to the excision of the lesion. Given the high prevalence of concurrent MGD and evaporative dry eye, a comprehensive tear film assessment (including LLT and meibography) should be considered part of the standard of care for evaluating and managing pterygium patients to ensure optimal outcomes.

Limitations and Modesty
The authors explicitly note limitations, including a relatively small sample size ( $n=32$ per group) which may limit statistical power for subjective endpoints like OSDI. The study population was predominantly from the Terai region, which may restrict generalizability to other ethnic or geographic groups within Nepal. Additionally, the study did not grade pterygium by extension or invasiveness, preventing a dose-response analysis, nor did it assess the spatial asymmetry of gland loss relative to the pterygium location due to methodological constraints. The authors conclude that while their findings are significant, future prospective studies with larger samples and more granular grading are necessary to fully elucidate these relationships.