Fig. 1 (click to enlarge) Fig. 2 (click to enlarge)

• The ocular (eye) surface includes two major territories, i.e., the cornea and the conjunctiva, bordered by upper and lower lids.
  
• Unlike the skin covering the rest of the body, the ocular surface is covered by a thin layer of tear film. A stable tear film present when the eye is open is the key mechanism to maintain the ocular surface health.
  
• The ocular surface health controls our clear vision, comfort and guards against infection.
  
• A stable tear film is governed by compositional and hydrodynamic factors inherently built in tissues and glands around the eye surface (see Fig. 1)
  
• Both compositional and hydrodynamic factors, listed in Fig. 1, work in concert through neuroanatomic integration by two neural reflexes mediated by the sensory input of the first branch of the trigeminal nerve (V1) and the parasympathetic branch and the motor branch of the facial nerve, respectively (see Fig. 2).

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• Patients with ocular surface diseases suffer from loss of vision, discomfort, infection, erosion, ulceration, and destruction with scarring of the eye surface
  
• One common cause of the ocular surface diseases is the dysfunction of neuroanatomic integration of compositional and hydrodynamic factors, leading to "dry eye" or "unstable tear film"
  
• Besides dry eye, dysfunction of neuroanatomic integration also results in Neurotrophic Keratopathy, Delayed Tear Clearance (see also Non-preserved Steroid Treatment) and Blink-related Microtrauma.
  
• Effective treatments of dry eye rely on thorough analyses of each component described in neuroanatomic integration using a variety of Diagnostic Tests and initiation of Medical Treatments and Surgeries to restore each specific dysfunctional elements.

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Fig. 3 (click to enlarge)

• Based on the altered ocular surface epithelial phenotype, there are two major types of ocular surface failure.
  
• The first is "Limbal Stem Cell Deficiency", in which the corneal epithelium is replaced by conjunctival epithelium (Fig. 3, upper panel).
  
• The second is "Squamous Metaplasia", in which the corneal or conjunctival epithelium exhibits "Skin-like" changes with keratinization and loss of mucosal epithelial characteristics including the expression of goblet cells (Fig. 3, lower panel)
• These two types of ocular surface failure are best detected by Impression Cytology.

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Fig. 4 (click to enlarge)

• The hallmark of limbal stem cell deficiency (LSCD) is "conjunctivalization", which is best detected by Impression Cytology
  
• Patients suffering LSCD complains of annoying photophobia (light sensitivity) and severe loss of vision.
  
• Corneal transplantation is contraindicated and cannot be used to correct LSCD because it does not transplant the "missing" limbal stem cells.
  
• Ocular surface diseases manifesting LSCD can be found in Fig. 4.

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