Eye drops are one of the most commonly used health care products. Your local drugstore has a wide variety of brands and formulations, both over the counter and prescription. Many contain drugs for specific conditions. Others are called “artificial tears”, intended for a general deficiency of natural tears.
Dry eye is highly uncomfortable because tears are essential for eye health. When the quantity or quality of tears is substandard, the eyes feel scratchy or sandy. Other symptoms may include stinging or burning, episodes of dryness followed by excess tearing, pain, redness of the eye, heaviness of the eyelids, and even visual impairment.
Tears do more than lubricate the eyes. They provide essential proteins and nutrients to prevent eye infection and promote wound healing. The cornea has no blood supply, since it must be clear to allow light to pass through. It is nourished by the aqueous humor in the interior of the eye, and by tears on the eye surface.
Commercial eye drops do not provide the protein and vitamin components of natural tears. For severe cases of dry eye and for injuries to the eye surface, doctors can make custom eye drops from the patient's blood serum.
Reference 2 offers a comparison of tears and serum in terms of the molecular factors that are believed to be important for corneal health:
1. Epithelial growth factor (ng/ml): tears 0.2 to 3.0, serum 0.5
2. Transforming growth factor beta (ng/ml): tears 2 to 10, serum 6 to 33
3. Lysozyme (mg/ml): tears 1.4, serum 6
4. Immunoglobulin A (micrograms/ml): tears 1190, serum 2
5. Fibronectin (micrograms/ml): tears 21, serum 205
6. Vitamin A (mg/ml): tears 21, serum 205.
In addition, tears and serum have the same pH and electrolyte strength. Serum may be diluted to 20% or 50% with saline solution, or used 100% without dilution, depending on the eye condition being treated. The serum is stored in the refrigerator for one day to one week, or in the freezer for up to one month. The patient is given multiple bottles with instructions for storage. Careful handling is necessary to prevent eye infection from bacterial contamination.
Autologous serum eye drops are used for: