Allergies is the most common and probably the most complex cause for red eye symptoms. In general allergies are poorly understood, for example we can not fully explain or cure many allergy induced disorders such as asthma, rosacea or chronic urticaria.

We can be allergic to almost anything, for example some researchers believe Rosacea is caused by an allergy to microscopic mite (Demodex folliculorum) that lives in the hair follicle. Knowing that eyes also provide a broad surface area for the collection of any airborne allergens it would not be surprising that some hidden allergy may be responsible for the adverse reaction, as people may experience allergic reactions limited solely to ocular tissues.

Perennial allergic conjunctivitis may last throughout the year and although itching is the key symptom for diagnosing ocular allergy disorders it is often absent in allergic conjunctivitis. Some types of allergies, for example hay fever, make the eyes itchy, while others may merely produce a chronic redness. It’s not only invisible microscopic particles that are all around us and abnormal immune system that may cause red eye symptoms, hidden food allergies may also create an allergic reaction of the eyes with usual symptoms such as itchy or red eyes.

The first line treatment is identifying allergens and avoiding them. The most popular medicines used in ocular allergy treatment are artificial tear drops (such as systane, theratears or refresh endura) and Patanol which is a combination of anti histamine and mast cell stabiliser. People who do not respond well to first line treatment may be prescribed with Alrex, which is a corticosteroid approved by FDA for the treatment of allergic conjunctivitis. Long term use of corticosteroids have serious side effects such as elevated eye pressure or a possible development of cataract, therefore some specialists use Restasis (cyclosporin) for long term anti inflammatory effect, especially when dry eye symptoms are observed. A new possible trend in allergic eye inflammation treatment may be anti - immunoglobulin E medicine (such as Xolair), which is currently only approved for asthma.

Stem Cell Factor (SCF)- The c-kit ligand

Hematopoiesis is governed by a number of cytokines that promote the survival, proliferation, and differentiation of hematopoietic stem cells and progenitor cells. Stem cell factor (SCF; also known as kit ligand, mast cell growth factor, or steel factor) is a hematopoietic cytokine that triggers its biologic effects by binding to its receptor, c-kit.It is a glycoprotein that plays a key role in hematopoiesis acting both as a positive and negative regulator, often in synergy with other cytokines. The concentration of SCF in normal human serum is, on average, 3.3 ng/mL.SCF is a member of the helical cytokine structural superfamily characterized by a double-crossover four-helix bundle topology. It is normally found in both soluble and transmembrane forms. Soluble SCF exists as a non-covalently associated homodimer is glycosylated, and has considerable secondary structure, including regions of alpha helices and beta sheets. Each SCF monomer contains two intra-chain disulfide bridges, Cys4–Cys89 and Cys43–Cys138. The N-terminal 141 residues of SCF have been identified as a functional core, SCF1–141, which includes the dimer interface and portions that bind and activate the receptor Kit. The human SCF gene has been mapped to chromosome 12q22-12q24. SCF is produced by various fibroblast-type cells including bone marrow stromal cells.SCF transduces signals by ligand mediated dimerization of its receptor, Kit, which is a type III receptor protein-tyrosine kinase related to the receptors for platelet-derived growth factor (PDGF), macrophage colony-stimulating factor, Flt-3 ligand and vascular endothelial growth factor (VEGF). The class III receptors are characterized by the presence of five immunoglobulin-like domains in their extracellular portion. SCF binds to the second and third immunoglobulin domains while the fourth domain plays a role in receptor dimerization. Binding of SCF to Kit leads to receptor dimerization and activation of protein kinase activity. The receptor becomes autophosphorylated at tyrosine residues during activation; the resulting phosphotyrosine residues serve as docking sites for signal transduction molecules containing SH2 and phosphotyrosine-binding (PTB) domains. Activated Kit also catalyzes the phosphorylation of substrate proteins.SCF is of particular importance in the mast cell and erythroid lineages, but also acts on multipotential stem and progenitor cells, megakaryocytes, and a subset of lymphoid progenitors. It also plays a key role in mast cell development, gametogenesis, and melanogenesis. The role of SCF also includes to change the BFU-E(burst-forming unit-erythroid) cells, which are the earliest erythrocyte precursors in the erythrocytic series, into the CFU-E (colony-forming unit-erythroid). SCF, along with bFGF (basic fibroblast growth factor) and LIF (lymphocyte inhibitory factor), prevents spontaneous differentiation of primitive embryonic stem cells in cell culture.