There are several accepted methods for delivering fluorescein sodium solution onto the ocular surface when performing fluorescein staining. In the current study, we compared standard fluorescein strips and a 1 mL syringe method with an innovative newly developed fluorescein pen. The standard fluorescein strip method cannot administer exact concentrations and quantities. In contrast, the 1 mL syringe method can fix concentrations but it is difficult to accurately control the infusion amount. Additionally, the above two methods are either single-use or their viable single-use period is short. These shortcomings may reduce the use of corneal fluorescence staining in clinical practice, resulting in missed diagnoses or misdiagnoses. To the best of our knowledge, we have conducted the first study evaluating the use of a fluorescein pen, a novel methodology newly developed by our research group for use in ophthalmic evaluations.
In the current study, images were taken immediately following three blinks after the fluorescein was dripped into the conjunctival sac. This difference is likely one reason that the image quality in the fluorescein pen group was best as compared with the other two tools. Because the amount of fluorescein dripped into the conjunctiva sac (controlled by the pen plunger) can be subtle enough to not cause changes in the volume of the tear film, the fluorescein immediately forms an evenly distributed thin green film, allowing the fine corneal lesion to be easily detected. Both the fluorescein strip and 1 mL syringe methods may lead to overdosing. However, our data indicate that prolonged observation under slit lamps as well as rinsing fluorescein from the ocular surface within the latter two tools can lead to an equally good images as compared with the pen tool, though necessitating more time and the performance of a more complex procedure to derive results of similar quality (data not shown).
The reported concentrations of fluorescein used in ocular surface staining differ, ranging from 0.1–1%[5–7]. We applied a concentration of 0.5% in our study, because this was the optimal concentration identified in our pilot study and because we use this concentration for corneal staining in our practice (data not shown). A higher concentration might lead to a darker background, with an image that is undiscernible immediately after staining; a prolonged observation period is needed under this scenario.
An ease-of-use evaluation by 15 ophthalmologists illustrated the superiority of the fluorescein pen as compared with the other two tools. This result is likely due to the portable pen style, which can be kept in the physician’s pocket for ready administration. In addition, the fluorescein pen is safe for multiple uses, and can be used for as long as three months as observed in our study.
The patients’ subjective assessments of the three methods illustrated that the pen tool causes less discomfort as compared with the other two tools. It is important that staining methods induce little irritation and prevent reflex tearing, as this dilutes the solution and causes epiphora. Good compliance and cooperation from patients are vital to achieving stable and repeatable results within ocular surface check-ups.
Although fluorescein quenching is a common phenomenon, prolonged usage of the pen (up to a maximum of four months) did not result in colour fading or in debilitating the staining effect. Prolonged and multiple usage is the major advantage of the pen tool and chemical stability is a precondition. No side effects were detected during the application. In contrast, the latter two tools (as well as other tools not evaluated in the current study) are single-use or their viable single-use period is short.
The generation of a fluorescein pen was inspired by the fact that an insulin pen can be used multiple times (i.e., for prolonged use) and that the insulin solution can only be discharged without suction, thus preventing microbial contamination. In addition to the substantial strengths of this study, including its novelty and innovation, limitations of this investigation include the fact that the needle attached to the pen is sharp and carries the potential risk of puncturing the eyeball upon incautious performance. However, we note that we did not cause any damage to the eyeball in this study. Innovating the device with a silicone needle in order to avoid damaging the eye as well as with a slimmer cartridge (i.e., with one dial for delivering a suitable quantitative volume of fluorescein) would greatly enhance the advantages of the fluorescein staining procedure in the future.