Women (12%-22%) and individuals who spend prolonged periods of time working on computers, smartphones, or other digital screens (70%) have a high risk of DED. The increased risk in women may be due to hormonal effects on the lacrimal and Meibomian glands (MG) and ocular surface.³ 

Categorisation and symptoms of DED 

DED is categorised into three types: Aqueous deficient, evaporative, and mixed. One of the primary causes of evaporative DED is MG dysfunction (MGD), which is marked by alterations in the tear film's lipid layer. MGD is responsible for ~70% of cases.^1,2 

The symptoms of DED range from mild to severe. In mild cases, patients may experience stinging, burning, or a feeling of pressure in the eyes. They may also have a sensation of sandiness, grittiness, or a foreign body in the eye. Blurry vision, particularly intermittent blurry vision, is common and can be accompanied by glare or halos around lights at night. Vision fluctuations and difficulties in reading are also typical.³  

Patients may also feel a sensation of heavy eyelids or have difficulty opening their eyes, and they may blink excessively or experience eyelid twitching. Contact lens wearers often report dryness and irritation, making lenses uncomfortable or even impossible to wear. Furthermore, tired eyes are common, with relief sometimes found by closing the eyes.³ 

In more moderate cases, patients may experience epiphora or excessive tearing. This symptom can seem counterintuitive as dryness leads to pain or irritation, resulting in intermittent excess tearing.³  

Redness of the eyes is another moderate symptom, often worsened by the rebound effect of vasoconstrictors found in many over-the-counter eye drops designed to reduce redness. These drops may temporarily decrease redness by constricting episcleral vessels but can lead to increased redness after the effect wears off.³ 

Severe symptoms include pain, which can be either sharp or dull and may be localised to a specific part of the eye, behind the eye, or around the orbit. In the most severe cases, patients may experience an inability to cry due to symptom severity.³ 

Replacing or supplementing natural tear film 

The primary goal of treating DED is to restore the homeostasis of the ocular surface and tear film. Current treatments for DED include artificial tears or ocular lubricants, nutraceuticals, anti-inflammatory agents, tear stimulants, autologous serum, antibiotics, and other therapies such as warm compresses, herbal products, punctal occlusion, and surgical approaches.⁴ 

Artificial tears, which substitute or supplement the natural tear film, are usually recommended as first-line treatment for managing DED. They help alleviate symptoms such as burning, irritation, and discomfort, providing temporary relief from dryness. The ideal formulation should spread uniformly and evenly across the eye, minimise friction during blinks, and have minimal side effects.^4,5 

Most artificial tears target either the lipid or aqueous layer of the tear film. Propylene glycol and hydroxypropyl guar (PG-HPG) nano-emulsion is an advanced eye drop designed for DED due to lipid or aqueous deficiency but can also be used for mixed DED. It uses PG as the active ingredient and an enhanced HPG gelling technology. The nano-emulsion contains smaller lipid droplets for better coverage and a more translucent appearance.¹ 

When applied, the HPG/borate meshwork forms a protective barrier on the eye's surface, which cross-links to release lipids slowly into the tear film. The anionic phospholipid dimyristoylphosphatidyl glycerol in the formulation supplements and stabilises the tear film's lipid layer, addressing gaps caused by MGD. This formulation helps restore the tear structure, preventing dry eye exacerbations and maintaining a healthier ocular surface.¹  

Efficacy and safety of PG-HPG nano-emulsion artificial tears in different patient subgroups 

A review by Srinivasan and Williams (2020) showed that PG-HPG not only improves symptoms, but also enhances tear film stability, and lipid layer thickness, supporting eye surface health in patients living with DED, regardless of subtypes.⁴  

Silverstein et al (2020) conducted a phase IV, multi-centre, open-label, interventional study to evaluate the effectiveness and tolerability of PG-HPG nano-emulsion in adult patients (n=134) living with DED of aqueous-deficient, evaporative, and mixed subtypes.¹  

The median changes from baseline in dry eye symptom scores were -1.0 at zero hours, -2.0 at four hours, and -2.0 at eight hours. Subgroup analysis showed a median change of -2 for aqueous-deficient and evaporative subtypes, and -1 for mixed subtype at eight hours. Median soothing sensation scores were three at zero and four hours, and 3.5 at eight hours, with a range of 0–10.¹ 

Tolerability scores for burning, stinging, and blurring sensations had a median of 0 (range: 0–8), and foreign body sensation had a median of 0 (range: 0–10). Most patients reported tolerability scores in the range of 0–5 across all DED subtypes.¹ 

The study concluded that PG-HPG nano-emulsion provided immediate and sustained symptom relief for up to eight hours after a single application and was well tolerated by patients living with DED, as demonstrated by the assessment scales.¹ 

Awisi-Gyau et al presented their findings from a post-marketing, prospective, single-arm study conducted at four clinical sites in the United States, at the 2023 Association for Research in Vision and Ophthalmology Annual Meeting. The study included participants diagnosed with a tear break-up time of 10 seconds or less for both eyes, symptoms of sore eyes as measured by the Impact of Dry Eye on Everyday Living – Symptom Bother (IDEEL-SB) Questionnaire, a score of 16 to 65 on the IDEEL-SB, and those using cyclosporine or other topical dry eye medications for at least 60 days before enrollment.⁶ 

Participants received their first dose of PG-HPG nano-emulsion lubricant eye drops on day zero and then self-administered one drop (0.6%) four times daily for 28-days. Follow-up included a phone call on day 14 and an in-clinic visit on day 28.⁶ 

The primary endpoint was the change in sore eye symptoms from day zero to day 28, evaluated by the IDEEL-SB. Relief from sore eye symptoms was also assessed using a Likert questionnaire on day 28.⁶ 

The mean IDEEL-SB score for sore eye symptoms significantly decreased from 2.4 at baseline to 1.4 on day 28, with a mean change of -1.0. The proportion of participants reporting sore eye symptoms that bothered them 'moderately' or 'very much' decreased from 34.0% at baseline to 10.7% on day 14 and 8.0% on day 28. By day 28, 59.8% of subjects reported relief from sore eyes.⁶  

Furthermore, PG-HPG relieves ocular dryness and discomfort associated with daily contact lens wear. In two prospective clinical trials, PG-HPG nano-emulsion eye drops were evaluated for treating contact lens discomfort. The first trial showed significant improvement in symptom scores after two weeks of using PG-HPG nano-emulsion drops compared to baseline. Participants reported better comfort with the drops compared to those without treatment.⁴  

Another trial compared PG-HPG nano-emulsion to rewetting drops and no treatment. Both PG-HPG nano-emulsion and rewetting drops groups showed significant improvement in discomfort scores after two weeks, while the control group did not. Comfort at the end of the day was significantly better in both treatment groups compared to the control.⁴  

Additionally, a recent study assessed the efficacy of PG-HPG nano-emulsion in combination with saline for wearing mini-scleral contact lenses. The results demonstrated improved dryness, grittiness, burning, stinging, foreign body sensation, and fluctuating vision with PG-HPG nano-emulsion compared to saline alone, with faster improvement in dryness symptoms.⁴ 

Conclusion 

PG-HPG nano-emulsion eye drops have shown remarkable efficacy in alleviating symptoms of DED across various patient subgroups. Research indicates that these drops provide immediate and sustained relief for up to eight hours after a single application, significantly improving tear film stability and lipid layer thickness. Clinical trials demonstrate their effectiveness in treating contact lens discomfort, with participants reporting better comfort compared to those without treatment.  

References 

1. Silverstein S, Yeu E, Tauber J, et al. Symptom Relief Following a Single Dose of Propylene Glycol-Hydroxypropyl Guar Nano-emulsion in Patients with Dry Eye Disease: A Phase IV, Multicenter Trial. Clinical Ophthalmology, 2020. 
2. Chen H, McCann P, Lien T, et al. Prevalence of dry eye and Meibomian gland dysfunction in Central and South America: a systematic review and meta‑analysis. BMJ Ophthalmology, 2024. 
3. Golden MI, Meyer JJ, Zeppieri M, et al. Dry Eye Syndrome. [Updated 2024 Feb 29]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470411/  
4. Srinivasan S, William R. Propylene Glycol and Hydroxypropyl Guar Nanoemulsion - Safe and Effective Lubricant Eye Drops in the Management of Dry Eye Disease. Clinical Ophthalmology, 2022. 
5. Labetoulle M, Benitez-Del-Castillo JM, Barabino S, et al. Artificial Tears: Biological Role of Their Ingredients in the Management of Dry Eye Disease. Int J Mol Sci, 2022. 
6. Awisi-Gyau D, Miller JR, Bickle K, Tauber J. Effectiveness of propylene glycol-hydroxypropyl-guar nano-emulsion lubricant eye drops in relieving sore eyes symptom in subjects with dry eye disease: A prospective, multicenter study. ARVO Annual Meeting Abstract. June 2023. [Internet]. Available at: https://iovs.arvojournals.org/article.aspx?articleid=2788091