Serum Eye Drops

SERUM EYE DROPS

Emily Conway, BVMS, MS, MRCVS, DACVO

Has your pet ever been prescribed topical serum eye drops? This blood product has been widely used in both human and veterinary medicine.

The cornea (the clear layer at the front of the eye), has 4 layers: an outer epithelium, a thick stromal layer, a thin elastic layer called Descemet’s membrane, and a single layer of endothelial cells that line the inside of the cornea. An ulcer is wound or abrasion of the cornea – these can be superficial (involving only the epithelium), or can involve the stroma. The stroma is made up of different types of collagen (the same thing that makes up hair and nails).

Superficial, non-infected corneal ulcers often heal in a matter of days.  However, if an ulcer becomes infected, then enzymes (called collagenases) produced by bacteria or fungal organisms, or even from the cornea itself, can start to break down the collagen of the corneal stroma. Ulcers can become so deep that the stability of the cornea may become compromised! The enzymatic breakdown of the corneal collagen is referred to as corneal ‘melting’ or keratomalacia. 

In an effort to slow or stop corneal loss due to enzymatic destruction, substances that inactivate or bind to these collagenases can be used. While many anti-collagenase substances exist, blood products such as serum and plasma are used frequently for this purpose because they are relatively easily obtained, non-toxic, and generally non-irritating.  Serum is effective at blocking collagenases because it contains a specific protein (called alpha2-macroglobulin) that is a non-specific collagenase inhibitor (meaning that it binds collagenase no matter its source, and neutralizes it). Frequent application of serum can thus reduce collagenase activity and prevent further corneal breakdown. Serum is generally reserved for deep and/or melting ulcers.

Some things to know about using serum is that there is no preservative inside of it, and this means it can become contaminated by bacteria very easily.  New research also suggests that if serum is used too closely to topical antibiotics (less than 10 minutes apart), the serum may bind to and inactive the antibiotic!

In general, serum should be

·         Stored in the fridge for 1 week or less, but can be stored longer in the freezer

·         If left out of the fridge or potentially contaminated, it should be thrown away

·         Should be used at least 10—15 minutes apart from any topical antibiotics