The Pivotal Role of Conjunctival Microvilli in Ocular Surface Health and Disease and the Transformative Impact of Scanning Electron Microscopy

Conjunctival Microvilli: A Biomarker of Cellular Vitality

Microvilli are small extensions of cells that perform major functions on the ocular surface. These structures enhance the surface area of epithelial cells. This ensures that the tear film adheres and spreads well, keeping the epithelium moist. The glycocalyx is a mucin-rich matrix that, outside the cell, attaches to the microvilli. It helps in stabilizing the tear film and protects against germs [4]. Changes in the shape and number of conjunctival microvilli are often the first signs of stress or injury to epithelial cells. These changes may result from environmental damage, systemic diseases, or conditions that inflame the surface of the eye. For example, fewer microvilli, odd shapes, or complete loss have been observed in conditions such as dry eye syndrome, Sjögren’s syndrome, and scarring pemphigoid. These changes impair the integrity of the tear film, causing eye discomfort, inflammation, and chronic epithelial damage [4, 5]. Elucidation of such fine changes is crucial for the diagnosis and treatment of eye surface disorders. The observation of microvilli used to be possible only with invasive biopsies until recently. However, with new strides in impression cytology and its combination with SEM, there has been a revolution in assessing microvilli without invasion. This forms a big leap forward not only in clinical care but also in research [6].

Scanning Electron Microscopy: Transforming Diagnostics

SEM has been a very effective imaging technique in research for the examination of ultrastructural changes in epithelial tissues. Traditionally, this was confined to invasive biopsy samples. Much information regarding cellular morphology and early signs of ocular surface pathology has been provided by it. Today, SEM combined with impression cytology enables clinicians and researchers to get high- resolution images of the ocular surface non-invasively [7]. In IC-SEM, the epithelial cells are sampled by applying a strip of bibulous paper to the conjunctiva. The non-invasive approach maintains cellular integrity and allows SEM analysis of microvilli density, morphology, and distribution. High-resolution, three-dimensional images obtained with SEM delineate ultrastructural details that are usually beyond conventional imaging modalities, such as light microscopy [6]. Troisi, et al. highlighted the primary role played by SEM in defining early ultrastructural changes to the conjunctiva.

It can show slight microvillar abnormalities in patients with a light form of dry eye syndrome who do not present with clinically evident diseases, as indicated either by Schirmer’s test or by tear break-up time. Thus, early diagnosis will be possible to perform an early intervention and prevent disease propagation [8].

Clinical Applications of SEM in Ocular Surface Health

Besides, SEM enables the visualization of microvilli and hence is very useful in the diagnosis of tear film instability- related diseases like dry eye syndrome. It has also been quite useful in assessing ocular surface impairment in systemic diseases such as Sjögren’s syndrome, in which a reduction in density and alteration in morphology of microvilli are among the early signs of epithelial distress [5].

In cases of chronic conjunctival inflammation or resistant keratoconjunctivitis, SEM has been used to detect microbial pathogens, including Acanthamoeba and Chlamydia, which may not be possible with routine culture. Its ability to visualize inflammatory infiltrates, cellular damage, and pathogen presence makes SEM a critical tool in diagnosing infectious and inflammatory ocular surface diseases [9, 10, 11].

Evaluating Therapeutic Interventions and Development of New Therapies

SEM can also provide information about the efficacy of therapeutic agents such as artificial tears and anti- inflammatory drugs. In this way, it will be possible to follow the changes in microvillar morphology. Troisi et al. describe the application of SEM in studying the effect of an artificial tear formulation based on cross-linked hyaluronic acid, trehalose, and cationic liposomes. This investigation showed clearly the increase of microvillar density and morphology, directly confirming that this product may restore health to the epithelium [8].

This application extends into the evaluation of toxicological effects of ophthalmic drugs, especially those containing preservatives such as benzalkonium chloride. The SEM will thus objectively document drug-induced epithelial damage and can be helpful in developing non-cytotoxic formulations [12].

Additionally, SEM has been used in preclinical trials to evaluate novel therapeutic agents, offering a detailed understanding of their effects on conjunctival microvilli and overall epithelial health [3].

Complementary Techniques: Building a Holistic Approach

While SEM alone offers unparalleled resolution and structural detail, the integration of this technique with other complementary diagnostic modalities extends its clinical utility. For example, Raman spectroscopy can provide molecular-level insights into tear film composition, while in vivo confocal microscopy enables real-time visualization of dynamic changes within both the conjunctiva and the cornea. Each modality together provides a complete view of ocular surface health from the structural, cellular, and molecular perspectives. Additionally, biomarkers such as mucin expression, goblet cell density, and inflammatory cytokines (e.g., IL-6, TNF-α) can complement SEM findings. These parameters offer functional insights that, when paired with SEM’s structural data, enable a multidimensional approach to diagnosing and managing ocular surface diseases [3].