Our Director of Laboratory Animals Research, Vytautas Baranauskas, authored an article discussing Rabbit models of dry eye disease in the context of preclinical studies. At Cureline Baltic, we offer our expertise and support to assist you in the integration of these techniques into your research. Read the article to know what Rabbit models are best for dry eye disease.
Rabbit Models of Dry Eye Disease: Comparative Analysis
AIM: To report ocular changes in rabbits after the implementation of three different induction methods to create dry eye (DE) conditions and provides evidence of DErelated disease evolution.
- METHODS: Experimental methods were divided into 3 models. The first model used involved triple injection of complete Freund’s adjuvant, 50 µL each, also called the meibomian gland dysfunction (MGD) model. In the second model, DE conditions were created by the resection of nictitating membranes (NM), Harderian glands (HG), and main lacrimal glands (LG), also called the LGR model. The third model involved the topical administration of benzalkonium chloride (BAK) 0.1% solution. The Schirmer test, ocular surface staining with fluorescein, and tear breakup time tests were implemented before and after excision. After euthanasia, the ocular tissues were dissected. Cornea, conjunctiva, and meibomian glands were treated with periodic acid–Schiff (PAS) staining and haematoxylin–eosin staining.
- RESULTS: The MGD model triggered inflammation of meibomian glands. It detected changes in the lipid layer of the tear film. The bilateral resection of NM, HG, and LG reduced the watering layer of the tear film. The topical administration of BAK of 0.1% solution impacted the mucosal layer of the tear film.
- CONCLUSION: Different changes are observed with different DE syndrome models. The composition of the tear film differ depending on which part of the eye is targeted. More studies need to be done to confirm whether an increased thickness of the cornea has any impact on the DE disease.
KEYWORDS: ocular surface; lid inflammation; keratitis; tear deficiency; rabbits; dry eye disease
Lacrimal Gland Resection Model Bilateral resection of the NM, HG, and main LG proved that it can create symptoms of DED. This is because the LG is responsible for producing a significant portion of the aqueous component of the tear film, and removing it can lead to a decrease in tear production and more severe dry eye symptoms. Therefore, after LGR, the reduced tear production leads to a decreased volume of tears, and a shorter TBUT. The experiment showed a reduction in tear volume was around 50%, which comfirms in a significant reduction in tear production. TBUT was significantly shorter than at the baseline of the measurements too Fluorescein staining confirmed damage on the corneal surface. These findings are similar to dry eye symptoms, such as discomfort, irritation, and even corneal damage. Ali et al carried out assessments on the effect of DED on the central corneal thickness (CCT) of the eyes of individuals affected with DED in comparison to the eyes of age-matched healthy individuals (70 patients with DED and 70 controls). Patients that were diagnosed with DED showed a lower CCT (mean: 536.5) compared to the control group (mean: 561.3) at P<0.01. . Reduced corneal thickness can be attributed to chronic dehydration due to high levels of inflammatory mediators. A study by Fujimoto et al sought to determine if there existed differences in corneal thickness between patients with DED and normal individuals using a rotating camera and anterior segment optical coherence tomography. The outcome of the study revealed that there existed a strong correlation between the measurement of CCT and thinnest corneal thickness in patients with DED. The difference in central (nonDED: 11.8 and severe DED 19.6) and thinnest corneal (nonDED: 13.1 and DED 20.7) thickness was significant. As such, clinicians should consider the morphological assessment of the cornea for the diagnosis of DED. Another physiological feature that might be of importance in the detection of DED is the ocular surface thickness. In a study by Liang et al that sought to examine and compare the ocular surface thickness including central corneal limit and bulbar conjunctival epithelium thickness using optical coherence tomography, the limbal epithelium in DED patients was found to be thinner and the bulbar conjunctival epithelium was found to be thicker compared with normal controls. The degree of changes in the central corneal limit and the bulbar conjunctival epithelium thickness was directly correlated to alterations in the tear film, and this was associated with the varying symptoms of DED in the patients. A study by Abou Shousha et al sought to evaluate the importance of using corneal epithelial profile maps for the diagnosis and management of DED. The prospective casecontrol study used ultrahigh-resolution optical coherence tomography (UHR-OCT) for assessing corneal epithelial thickness. The study included 71 subjects, out of which 52 had DED. The symptoms of DED were assessed, and it was reported that patients with DED had a highly irregular corneal thickness compared with the corneal thickness of control subjects. Unfortunately, with our experiment, we were not able to confirm if the increased thickness of the cornea has any impact on DED.
Meibomian Gland Dysfunction Model Among the various causative factors of DED, MGD is the most frequently observed cause. Also known as meibomitis, MGD appears as a heterogeneous condition that involves inflammation and hyperemia in the conjunctiva and eyelids, damage and staining to the cornea, and dry eyes due to the instability of the tear film, increased tear evaporation rate and decreased tear volume. Structural changes of these glands and inflammation are two simultaneous events that cause MGD. The triple injection with CFA (each 50 µL) triggered inflammation of meibomian glands (meibomitis is a subtype of obstructive MGD) in New Zealand rabbits. In our rabbit model of MGD experiment, tear production was slightly increased despite the presence of MGD-related symptoms. This could be due to a compensatory response by the LG in an attempt to maintain adequate tear film stability. However, the tear film quality was compromised as shown by the decreased TBUT and widespread corneal fluorescein staining, which indicates increased ocular surface damage. The clear inflammation of the eyelid detected in the histopathological HE slides is consistent with the known inflammatory component of MGD. The inflammatory process can damage the meibomian glands and lead to the production of altered meibum that contributes to tear film instability and ocular surface damage. Therefore, the combination of increased tear production with reduced tear film stability and increased ocular surface damage in the rabbit model of MGD suggests a complex interplay between different factors involved in the pathophysiology of this disease. Aragona et al and Liu et al focused on MDG as a pathological event in DED. They reported that instability of the tear film causes inflammation and hyperosmolarity, both of which lead to DE syndrome. A study on aqueousdeficient DE patients with punctal plugs insertion performed by Liu et al showed improvement in DE parameters and meibomian gland function for at least 6mo in both groups, except for meiboscore.
Benzalkonium Chloride Model When administered topically to the eyes of rabbits, BAK at a concentration of 0.1% has been shown to increase tear production, possibly as a result of irritation to the ocular surface. However, the decreased tear film stability (as indicated by the decreased TBUT) and increased fluorescein staining observed in the cornea suggest that the increased tear production may not be sufficient to maintain the normal ocular surface function. The reduction of goblet cells and thinning of corneal epithelium seen in the histopathological HE slides may be due to the direct toxicity of BAK on these tissues. It is important to note that while inflammation was not observed in the eyelids, it is possible that other inflammatory markers or cytokines were present, but not detected by the HE staining. The results differed depending on the DE syndrome model, which explains that the composition of tear film can differ depending on which part of the eye was targeted by DE syndrome induction methods. In our first model, triple injection with CFA (each 50 µL) triggered inflammation of the meibomian glands (meibomitis is a subtype of obstructive MGD) in New Zealand rabbits. The MGD model changed the lipid layer of the tear film. The bilateral resection of the NM, HG, and main LG reduced the watering layer of the tear film by reducing its production. Topical administration of the prepared BAK 0.1% solution impacted the mucosal layer of the tear film by reducing goblet cells of the conjunctiva. Overall, the three rabbit models of DED have different underlying mechanisms and pathologies, leading to different manifestations of the disease. MGD and BAK-induced DED models primarily affect the meibomian glands and ocular surface, while the LG removal model is an aqueous-deficient DED model. The differences in tear production, TBUT, corneal staining, and histopathological findings reflect the different pathologies and mechanisms involved in each model. These models provide a valuable tool for studying the pathogenesis of DED and testing potential therapeutic agents. However, caution should be exercised when interpreting the results obtained from different DED models, as the pathologies and underlying mechanisms may differ significantly.
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