• Ocular surface disease
• allogeneic serum drops
• immunology
• tears
• ocular surface

Serum eye drops contain growth and neurotrophic factors, fibronectin and vitamin A that promote corneal epithelialisation and nerve healing and are a well-established treatment for ocular surface disorders.1 Though normally derived from autologous blood, not all patients can be donors for reasons such as infancy, poor venous access and comorbidities. Also, autologous serum from some patients could potentially contain concentrations of drugs,2 or possibly, inflammatory mediators, harmful to the eye. Allogeneic drops are an alternative in such circumstances.

Complex mechanisms make the eye an immunologically privileged site.3 Cornea and conjunctiva bear ABO antigens and some HLA.4 Serum contains antibodies and complement. Nevertheless, successful treatment with ABO-unselected allogeneic serum is reported.5 ,6 Furthermore, ABO-matching is unnecessary for corneal or conjunctival transplants and, other than haemolysis, minor ABO-mismatched, plasma-containing, platelet transfusions pose little risk of type II hypersensitivity reactions. There are no reports of adverse effects, analogous to transfusion-related acute lung injury, from antibodies such as anti-HLA in allogeneic serum eye drops. Alloimmunisation to RBC, leucocyte or platelet antigens is unlikely as serum is cell-free. However, we are unsure about alloimmunisation to proteins in serum eye drops, especially in those with eyes with other risk factors. Haemovigilance, and other appropriate follow-up, is necessary.

In 2007, a regulatory body-approved allogeneic serum eye drop service was developed in New Zealand for patients unable to be autologous donors. Allogeneic drops are produced like autologous drops except that Group AB donors who lack anti-A/B are used. Currently, demand does not exceed supply from this source. Donor health is assessed and donated blood is tested for transfusion-transmissible infections. Sixty-seven per cent of donors to date have been female, an important point in relation to the discussion on HLA antibodies above. Briefly, blood is allowed to clot and, by centrifugation, serum is obtained. Under sterile conditions, 50 ml of serum and 150 ml of balanced salt solution are mixed and thirty five ml sterile eye drop phials are filled through a 0.22 μm filter. Bottles are stored at −35.0°C. Each batch is tested on an automated microbial detection system.

Allogeneic serum eye drops are produced centrally and sent to blood banks around New Zealand on dry ice. Patients store the drops in the freezer compartment of home refrigerators for up to 6 months thawing bottles as required. Thawed drops are kept refrigerated and discarded if unused after a week. Autologous or allogeneic, production costs are US$232 for 30 phials. Costs could be less if more than one batch were made from a donation. This may be easier with allogeneic, than with autologous, donors.

Since 2007, 39% of all serum eye drops issued in New Zealand have been allogeneic.

Twenty ophthalmologists have used allogeneic drops to treat 73 patients. Treatment duration has varied from 1 to 23 months with 43% of patients on the allogeneic drops for ≥6 months. Sjogren's syndrome (24%), neurotrophic cornea (21%) and limbal stem cell deficiency (4%) were the commonest diagnoses. Comorbidities (32%), difficult venepuncture (20%), logistical difficulties in collecting autologous blood (13%) and concomitant treatments (8%) were the top reasons for choosing allogeneic drops. As far as we know, allogeneic drops have been at least as effective as autologous drops. No adverse reactions have been reported.

In summary, we have developed an approved, effective and safe allogeneic serum eye drop service. They are more convenient and, maybe, safer for some patients, and more cost-effective than autologous drops. We believe it is now appropriate to move to an exclusively allogeneic serum eye drop service.