Srividya Lonkala1*, Prasada swamy Thirunahari2
1University College of Pharmaceutical Sciences, Satavahana University, Karimnagar, India
2Goverment Medical College, Karimnagar, India
*Corresponding Author: Srividya Lonkala, Head of Department, Department of Pharmaceutical Analysis, University College of Pharmaceutical Sciences, Satavahana University,Karimnagar, India, Email: svps11288@gmail.com
Received date: 05 Jan, 2026; Accepted date: 22 Jan, 2026; Published date: 28 Jan, 2026
Citation: Srividya Lonkala, and Prasada swamy Thirunahari. “Development and Evaluation of Oxytocin-Loaded Chitosan Transdermal Patches for Ocular Surface Enhancement in Dogs Using Schirmer Tear Test”. J Pharmacol Drug Deliv (2026): DOI: 10.59462/JPDD.4.1.107
Copyright: © 2026 Srividya Lonkala. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Abstract
The present study investigates the development and evaluation of Oxytocin-loaded chitosan transdermal patches for ocular surface enhancement and tear secretion improvement in dogs. Oxytocin, a neuropeptide hormone with uterotonic, neuromodulatory, and cytoprotective functions, was explored for its activity to enhance ocular surface health through cyclic adenosine monophosphate (cAMP)-mediated signalling. The patches were prepared using the solvent casting technique and applied near the periocular muscles to facilitate local absorption. Evaluation was carried out through Schirmer Tear Test (STT), corneal clarity scoring, blink reflex monitoring, and behavioural assessments for 7 days using adult male healthy Beagle dogs of 2 to 4 years old, 8–12 kg. Results demonstrated a significant increase in tear production, improved corneal transparency, and enhanced ocular comfort. The findings support the potential of Oxytocin-loaded chitosan patches as a novel therapeutic approach for tear film stabilization and ocular health management. This study provides new insights into periocular Oxytocin delivery can improve accommodative response and ocular muscle activity, indicating potential therapeutic applications in early presbyopia management.
Keywords: Oxytocin, Chitosan transdermal patch, Ocular pharmacology, Tear secretion, Canine dry eye, Sustained release.
Introduction
Current study was performed in dogs, the tear-stimulatory and ocular-surface-protective effects of Oxytocin observed in this experiment demonstrate strong translational potential for human ophthalmology. In humans, Oxytocin receptors are expressed in the lacrimal gland, conjunctival epithelium, and ocular adnexa, where they mediate cyclic AMP (cAMP) and PKA-driven fluid secretion similar to the mechanism demonstrated in canines. Clinical studies have shown that Oxytocin can increase human lacrimal gland output by 30 to 40%, enhance epithelial regeneration by 25 to 35%, and reduce ocular surface inflammatory markers by up to 50%. [1-4] These findings support the possibility that a sustained-release periocular or transdermal Oxytocin delivery system may improve sight in humans by stabilizing the tear film, reducing corneal surface irregularity, and improving optical clarity.
Human dry eye disease affects nearly 344 million people worldwide, with a tear-deficiency prevalent in 30% in adults, the development of an Oxytocin transdermal system can make a new model for long-acting tear stimulation without repeated instillation of eye drops. [5,6] Increased tear secretion has been correlated with measurable improvement in visual acuity fluctuations and contrast sensitivity, therefore better contributes to functional sight in day to day life.
Research on Neuromodulation clears that periocular Oxytocin may influence extraocular muscle tone and ciliary body responsiveness, leading to improvements in near-focus ability. Early pilot observations have indicated up to 1.0 diopter accommodation enhancement following periocular peptide stimulation in human subjects. [7] Further clinical trials are needed, but preliminary data support the potential use of Oxytocin-based patches for presbyopia management.
The cytoprotective, anti-apoptotic, and epithelial healing effects in human corneal cell lines have contributed to periocular surface clearance, improved corneal clarity with significant reduction in oxidative stress, and restoration of corneal transparency metrics in injured models. [3,8] The biological effects directly representing the eye sight improvement in Humans, since, corneal smoothness and tear-film uniformity accounts to 70% of the eye’s total optical power.
Oxytocin acts through G-protein-coupled receptors, activating adenylate cyclase and stimulating intracellular cyclic adenosine monophosphate (cAMP) formation. This, in turn, activates protein kinase A (PKA) pathways that mediate smooth muscle contraction and glandular secretion. The lacrimal glands and periocular tissues contain oxytocin receptors, and their stimulation can enhance tear secretion. [9,10] Reduced tear production leads to ocular surface disorders such as keratoconjunctivitis sicca (KCS), commonly observed in aged dogs. Conventional therapies involve lubricating drops or systemic medications that provide only temporary relief. [11-14] Hence, a sustained, site-specific delivery approach such as a chitosan-based transdermal patch can enhance local drug bioavailability, improve comfort, and minimize dosing frequency.
Preparation of Oxytocin Transdermal Patches
The Oxytocin transdermal patches were prepared using the solvent casting method, a simple and widely adopted technique for producing uniform polymeric films. Chitosan (2% w/v) was dissolved in 1% v/v acetic acid under continuous magnetic stirring for 4–5 hours to obtain a clear, homogeneous polymer solution. [15] Accurately weighed Oxytocin was incorporated into the polymeric solution with gentle stirring to ensure uniform drug distribution. Glycerol (0.5–1.0 mL) or polyethylene glycol 400 (PEG 400) was added as a plasticizer to impart flexibility and enhance mechanical strength [16].
The viscous mixture was degassed to remove air bubbles and cast onto a levelled, sterilized Petri dish lined with Teflon sheets to prevent adhesion. The films were dried at ambient temperature (25–30 °C) for 24 hours in a dust-free environment. After complete drying, the patches were peeled off, inspected for physical integrity, and stored in a desiccator until further evaluation.
Physical Characteristics of Oxytocin Transdermal Patches
The prepared Oxytocin patches were evaluated for physical characteristics to ensure uniformity, mechanical strength, and suitability for ocular application. Each patch was visually examined for surface uniformity, transparency, and absence of air bubbles or cracks.
Patch thickness was measured using a digital micro meter screw gauge at five random points, and the mean value (±SD) was calculated [17]. Weight uniformity was determined by individually weighing 2 × 2 cm patch samples on an analytical balance [16].
Moisture content was evaluated by drying patches in a desiccator over silica gel until a constant weight was achieved. Moisture absorption was determined by exposing patches to 75% relative humidity for 24 hours and calculating the percentage increase in weight [18].
Folding endurance was measured by repeatedly folding a patch at the same place until it broke, and the number of folds was recorded [19].
All patches showed smooth, uniform surfaces, thickness between 0.20–0.26 mm, minimal weight variation, and folding endurance above 300, confirming flexibility and mechanical robustness.
| Parameter | Observation (Mean ± SD) |
|---|---|
| Appearance | Transparent films, smooth texture |
| Thickness (mm) | 0.22 ± 0.03 |
| Weight Uniformity (mg) | 108.5 ± 2.8 |
| Moisture Content (%) | 3.42 ± 0.15 |
| Moisture Absorption (%) | 4.18 ± 0.23 |
| Folding Endurance (No. folds) | >300 |
| Surface pH | 6.6 ± 0.2 |
| Drug Content Uniformity % | 98.4 ± 1.1 |
| Tensile Strength (kg/mm²) | 1.85 ± 0.07 |
Table 1: Properties of Oxytocin Transdermal Patches
INVIVO Tests
Schirmer Tear Test (STT)
Tear production was evaluated using standardized Schirmer strips (Whatman filter paper, 5 × 35 mm). The strip was gently placed in the lower conjunctival sac at the temporal canthus, ensuring minimal irritation during insertion. After 5 minutes, the length of the moistened area was recorded in millimeters.
This test is widely used to quantify aqueous tear secretion and detect tear-deficiency disorders such as keratoconjunctivitis sicca. An increase in STT values following patch application reflects enhanced lacrimal gland stimulation and improved tear-film stability [20,21].
Step by step procedure:
• Ensure the animal is calm and gently restrained to avoid excessive blinking or movement.
• Wash hands and wear clean gloves.
• Remove one Schirmer strip from the sterile pack and fold it at the notched end, approximately 5 mm from the tip.
• Hold the strip by the upper end, avoiding contact with the lower end that will enter the conjunctival sac.
• With the other hand, gently elevate the lower eyelid of the dog at the temporal canthus (outer corner of the eye).
• Insert the bent end of the strip into the lower conjunctival sac, making sure it rests comfortably without touching the cornea.
• Allow the strip to remain in place for 5 minutes.
• Ensure the dog’s eyes remain open but calm during this period. Avoid excessive stimulation
• After 5 minutes, gently remove the strip in one smooth motion.
• Immediately measure the length of the moistened (blue-dyed) area in millimeters using the marked scale on the strip.
• Record the value as mm/min tear production.
Interpretation
Normal tear production ≥15 mm/min
Mild to moderate tear deficiency 10–14 mm/min
Significant tear deficiency (KCS) <10 mm/min
Corneal Clarity Index
Corneal transparency was assessed through direct visual inspection and confirmed using slit-lamp biomicroscopy.
Procedure
Perform hand hygiene and don gloves.
Ensure the examination room has a calm, dimmable ambient light to allow slit-lamp contrast.
Restrain the animal gently (assistant) to minimize head movement and stress.
If ocular discharge is present, gently clean eyelid margins with sterile saline and gauze; avoid touching the cornea.
Visual Inspection
Position the animal so both eyes are easily visible.
Use diffuse room light or a handheld penlight to inspect the cornea from several angles.
Look for gross abnormalities: haze, opacity, neovascularization, ulceration, stromal scars, or pigmentation.
Note eyelid position, conjunctival hyperemia, and tear pooling.
Make an initial provisional score (0–3) based on visible haze/opacity.
The cornea was evaluated under uniform illumination, and clarity was graded on a four-point opacity scale:
0 = Transparent, normal clarity
1 = Mild haze, slight loss of transparency
2 = Moderate haze, noticeable opacity
3 = Opaque, severe loss of transparency
This test evaluates surface integrity and stromal health. Improvement in corneal clarity indicates adequate lubrication, reduced epithelial damage, and restored optical quality following treatment [22].
Blink Reflex Frequency
Blink rate was measured using high-speed digital video recording (60 frames per second). Dogs were placed in a quiet environment to avoid reflexive blinks caused by noise or movement. Recordings of 2–3 minutes were analyzed, and spontaneous blinks per minute were counted.
A stable or reduced blink frequency is associated with improved ocular comfort and adequate tear-film volume, while increased blinking indicates dryness or irritation. Therefore, changes in blink rate provide a non-invasive biomarker of ocular surface comfort and tear stability [23].
Behavioral Indicators
General ocular comfort was assessed through behavioural observations made throughout the study. Parameters included:
Photophobia (sensitivity to light)
Grooming behaviour, especially pawing or rubbing of the eyes
Signs of discomfort, such as squinting or excessive tearing
A standardized 0–3 scoring scale was used to quantify discomfort. Reduced rubbing, normalized grooming, and improved tolerance to ambient light indicated better ocular surface health after treatment. Behavioural assessments complement physiological tests and provide insight into the animal’s subjective comfort [24].
| Parameter | Baseline before treatment | After Treatment | % Improvement | Interpretation |
|---|---|---|---|---|
| Schirmer Tear Test (mm/min) | 10.21 ± 1.05 | 18.04 ± 1.08 | ↑ 60.17 % | Significant increase in tear production indicating enhanced lacrimal secretion |
| Corneal Clarity Index (0–3 scale) | 1.6 ± 0.4 | 0.62 ± 0.12 | ↓ 66.37 % | Improved transparency and reduced epithelial dryness |
| Blink Reflex Frequency (blinks/min) | 14.6 ± 2.1 | 12.8 ± 1.9 | ↓ 12.21 % | Stabilized blink rate indicating ocular comfort |
| Behavioral Discomfort Score (0–3 scale) | 2.2 ± 0.3 | 0.8 ± 0.2 | ↓ 63.60 % | Reduced photophobia and rubbing; improved grooming behavior |
Table 2: Evaluation of Ocular Parameters after Oxytocin Patch Application in Dogs
Results
Physicochemical Evaluation of prepared Oxytocin loaded chitosan patches were flexible and stable structurally. The thickness and weight variation remained within narrow limits, indicating robust formulation reproducibility. Moisture content (<4%) and absorption (<5%) shows stability of prepared films under ambient conditions. High folding endurance (>300) demonstrated good mechanical strength necessary for transdermal application. Drug content uniformity (>98%) validated effective drug incorporation.
In-Vivo tests reveal Oxytocin patches were found to have significant improvement in ocular parameters. The tear production in dog increased by 60.7%, demonstrating strong lacrimal gland stimulation, corneal clarity improved by 66.7% with enhanced epithelial hydration and reduced dryness. Blink reflex intensity decreased by 12.3%, inferring ocular comfort and stable film across ocular layer. Further to add in all Cases have not found irritation or allergic reaction.
Oxytocin-loaded chitosan transdermal patches provide a sustained and biologically effective method for enhancing tear production and improving ocular surface health. The significant rise in Schirmer Tear Test values correlates with activation of the oxytocin receptor–adenylate cyclase–cAMP–PKA signalling pathway, previously shown to stimulate lacrimal gland myoepithelial cells. This mechanistic pathway explains the increased aqueous tear secretion seen in treated dogs.
Scope of the Study
The positive outcomes in dogs—an accepted model for tear physiology—support future clinical evaluation in humans. Chitosan's biocompatibility and permeability-enhancing properties likely contributed to the efficient dermal penetration and sustained release of Oxytocin. This delivery method avoids the limitations of eye drops, which often require frequent application and have poor retention on the ocular surface.
In the current study, periocular application of oxytocin-loaded chitosan transdermal patches resulted in a marked increase in tear secretion, with Schirmer Tear Test values rising from 10.21 ± 1.05 mm/min at baseline to 18.04 ± 1.08 mm/min after treatment, representing an improvement of approximately 60%. Corneal clarity scores improved by 66.37%, while blink reflex frequency decreased by 12.21%, indicating enhanced ocular comfort and tear-film stability. These outcomes are consistent with activation of oxytocin receptor–mediated cAMP–PKA signalling pathways known to stimulate lacrimal gland secretion and epithelial hydration. However, direct extrapolation of these findings to human visual performance or presbyopia management should be approached with caution. The present results do not establish clinical efficacy in humans, but provide preliminary experimental evidence supporting the potential of sustained periocular oxytocin delivery as an adjunct strategy for tear-film stabilization and ocular surface support. Further controlled clinical studies in human subjects are required to confirm safety, optimal dosing, and functional visual outcomes.
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