Allogeneic Serum Eye Drops: A Randomized Clinical Trial to Evaluate the Clinical Effectiveness of Two Drop Sizes

Allogeneic serum eye drops (SEDs), which are obtained from donor serum, are increasingly being used to treat patients with dry eye disease (DED). Until now, autologous SEDs have mostly been used, but have a number of hindrances with respect to collection, production, and standardization [1, 2]. From a clinical perspective, the definition of DED, as formulated by global DED experts is: “Dry eye disease is a multifactorial disease characterized by a persistently unstable and/or deficient tear film causing discomfort and/or visual impairment, accompanied by variable degrees of ocular surface epitheliopathy, inflammation, and neurosensory abnormalities” [3].

DED is caused by a disturbed tear film due to disfunction of Lacrimal glands, Meibomian glands, conjunctiva or eye lids, with secondary consequences for the cornea [4, 5]. Additionally, many systemic autoimmune diseases can cause moderate-to-severe DED [6].

Management of DED is complicated because of its multifactorial etiology associated with many mechanisms. In the Netherlands, management of DED follows a stepwise approach. The first step includes ocular lubricants of various types followed by treatment with immunosuppressive eye drops. The following step includes bandage contact lenses or even scleral contact lenses or punctum plugs. If these treatments are insufficient, SEDs are considered. SEDs offer a potential advantage over conventional therapies, as serum not only serves as a tear substitute to provide lubrication but also contains additional components to mimic natural tears more closely [7]. Although the data are heterogeneous, literature suggests that serum could be a viable treatment for DED [8‐10].

Allogeneic SEDs are explored as an alternative to autologous due to greater standardization and uniformity. Based on several clinical studies [2, 11‐18], allogeneic SEDs are now used as standard of care in countries such as Australia, Austria, Denmark, Germany, Poland, South Africa, the Netherlands, and United Kingdom.

Commonly, SED administration systems have a conventional drop size of about 50 µl, which is more than five times the volume of the tear film [19]. This amount potentially washes away most of the tear film, creating irritation and reflex tears. Application of a smaller eye drop would fit the eye, potentially leading to less damage of the tear film and creating less irritation and reflex tears. No prior data exist on the required drop size for SEDs, and it is unknown whether micro drops are as effective and user friendly as conventional drops for the treatment with serum of DED. We therefore hypothesized that a micro drop of approximately the volume of the tear film, which is 8 ± 3 µl [20], could be clinical effective.

We aimed to demonstrate the clinical effectiveness of SEDs in a large group of naïve patients with DED and that the effect is independent of the drop size, i.e., the effectiveness of micro-sized allogeneic SEDs of 7 µl and conventional-sized SEDs of 50 µl is not different.

In total, 53 patients were eligible, consented, and were randomized. Forty-nine patients completed the study (Supplementary Figure S3: flow diagram showing patients inclusion, treatment, and analysis). One patient that had withdrawn during the wash-out period (due to the beneficial effects of serum treatment) was not replaced. Enrolment started in December 2018 and the last patient finished the study in May 2021. Table 1 shows the baseline patient characteristics of included patients in the study; the majority were female with an average age of 60 years. The patient population consisted of those suffering from severe dry eye disease (45%), Sjögren’s disease (36%), and graft-versus-host disease (19%). In Supplementary Table S1, the baseline ocular medication is specified per patient group. Almost all patients used lubricants and only a very small proportion of patients used glaucoma eye drops, pressure and pain reducing eye drops. The baseline OSDI score averaged 55 (± 22) and ranged from 16 (mild symptoms) to 100 (severe dry eye symptoms all of the time) indicating the inclusion of patients with mild-to-severe dry eyes. Patients showed a short tear film break-up time (median TBT was 2 s (1–4) and 87% of the patients had a TBT ≤ 5 s), low tear production (median TP was 3 mm/5 min (0–12) and 58% of the patients had a TP ≤ 5 mm/5 min) and corneal punctate lesions were present.

In this study we found, irrespective of the volume of SEDs applied, a significant subjective improvement after administration of both drop sizes SEDs (improvement in mean OSDI score). More importantly, for the first time, we show a significant improvement in objective measures (reduction in percentage of corneal punctate lesions). Non-inferiority of the 7-µl micro-sized SEDs was established when compared to conventional 50-µl sized SEDs.

For the first time, the clinical efficacy of micro-sized drops for undiluted allogeneic serum eye drops was demonstrated. Aside from a significant improvement in OSDI score, the use of SEDs also resulted in a minor but significant improvement was observed for TBT for conventional-sized SEDs and a significant reduction in the percentage of affected surface after staining of the cornea in both treatment groups. No statistical difference was observed between the treatment groups. The results are in line with other studies performed with micro drop application systems for medicinal eye drops that showed comparable, and sometimes superior, efficacy to larger drop sizes [27‐30]. No prior data exist on the use of micro SEDs. During the study, patients were asked to record a diary on the ease of use of both eye drop application systems. The ease of use of the micro-sized system was significantly lower. No information was collected on where the inconvenience lies (for example in the packaging, in the activation of the system, in the administration). It is important to note that although patients’ perception of user-friendliness was inferior for the micro-sized system, the ease of use improved somewhat over time, but always was lower than for the conventional-sized drop system. Apparently, extended use, and possibly improved training could further reduce the difference in ease of use score between the two application systems. Side effects occurred in similar frequencies in both groups.

The study included patients who are normally eligible for treatment with SEDs according to current criteria, i.e., these are the ‘real-life’ patients. Post hoc analysis gives direction where future research is needed. Our study, as well as another study from our group [2], suggests that there are patients that respond, and those that do not respond to SEDs, and it is worthwhile to determine if there is an underlying common factor. For this, follow-up studies including specific patient groups are needed.

An additional benefit of single-use micro drop system is a somewhat lower risk for microbiological outgrowth as compared to the conventional system, which is allowed be stored in the refrigerator for 24 h after opening. Furthermore, the use of micro SEDs, when used less than six times per day, results in less spillage, lowering the cost, and allowing for more patients to be treated with the same amount of serum. This is of particular importance when taking into account the long-term daily treatment of patients suffering from DED with SEDs, and the scarce availability of male AB serum.

The present study has some limitations. For the patients enrolled in this study, diagnosis was based on objective and subjective complaints. Consequently, the patient population was very heterogeneous, for example with an OSDI score ranging from 16 to 100. Nonetheless, due to the cross-over design, the etiology was equally distributed. In follow-up studies, it would be of interest to differentiate patients based on the OSDI in order to determine the clinical effectiveness of SEDs in a more homogeneous patient population.

In the present study, no placebo group was included because it was concluded that it is not ethical to not treat this patient group. Furthermore, in a cross-over design, each patient generates data for both groups. By adding a washout period, patients served as their own control group. Increased patient numbers would allow for more statistical power, as well as increased understanding of the effect of SED on secondary outcomes (TBT, CP, and ST). Additionally, although only a minority of patients were using glaucoma eye drops (Table S1), this could potentially introduce a confounding factor. The patients in this study were naïve patients, e.g., never used SEDs as a treatment for their symptoms before. In a cross-over design type of study, the patients are not truly naïve in the second treatment period of the study, introducing a period effect. However, a statistical correction was performed to adjust for this. Furthermore, the present study suggests that patients with a relatively higher baseline OSDI score, such as patients suffering from graft-versus-host disease, may have a greater mean improvement in OSDI score. Given the heterogeneous patient cohort, more data should be generated to specifically identify and segregate those patient groups that do and do not benefit from SED treatment both in terms of OSDI score improvement, as well as in terms of TBT and CP.

We conducted the largest clinical evaluation of allogeneic SEDs in naïve patients with DED, and our study shows a large subjective improvement after administration of micro-sized and conventional-sized SEDs in OSDI. Notably, for the first time, also a significant improvement was found in the objective measures TBT and CP and a trend for improvement in TP. The clinical efficacy was considered similar for both drop sizes, as measured by the OSDI score. The upside of the micro drop system is that due to its smaller drop size, less serum is used, thereby saving valuable donor serum, which makes the system an attractive alternative.