On being told that they have dry eye disease, many a patient jokes that they will need to cry more. Management, however, typically involves topical supplementation and sometimes reducing drainage by plugging to increase the tear volume.
The neural control of tear production involves the trigeminal (fifth) cranial nerve. External stimuli on the ocular surface, such as lid activity and atmospheric influence, trigger impulses in afferent fibres in the ophthalmic branch (V1) of the trigeminal.
These pass to the pons in the midbrain where processing occurs to then send signals via both sympathetic and parasympathetic fibres to the sphenopalatine ganglion and then via ophthalmic nerve branches to the lacrimal gland, meibomian glands and goblet cells to produce tears.
What is less known is that sensory signals from the nasal mucosa, via the maxillary branch (V2) also contribute to tear production. In fact, the nasolacrimal reflex is important to normal tear production, and normal breathing through the nose is thought to contribute to more than 30 per cent of basal tear production. This is distinct from the noxious reflex that makes our eyes water when, for example, pulling a nose hair.
If the afferent nerves from the nasal mucosa could be stimulated, this might be expected to increase tear production and therefore combat any deficiency caused by dry eye disease. This is the theory behind a novel device being introduced to optometrists by Allergan – the TrueTear (figure 1).
The TrueTear
The TrueTear is described as an intranasal tear stimulator and is a small, handheld device capable of producing small electrical impulses from a battery-operated base unit. A button on the unit allows the user to select one of five levels of stimulation in the form of electrical micropulses as advised by their practitioner.
The impulse is passed to the nasal mucosa via a disposable tip comprising two long prongs which are inserted deep into the nostrils until they touch the mucosa. Daily replacement off the tips ensures that there is no risk of infection from repeated use.
Clinical trials
Since the unit received FDA approval in the US, a number of studies have been produced suggesting the unit is safe and effective. In one study of 48 adults diagnosed with dry eye disease (as defined by a Schirmer’s score of less than 10mm in five minutes and an OSDI score of at least 13), the TrueTear device produced a significant increase to aqueous tearing compared to an intranasal device sham control.
An average Schirmer score of 25.3mm ±10.7 was observed during active neurostimulation, compared with only 9.2mm ±7.3 for the sham control application. The mean difference between Schirmer score with active stimulation versus sham was 16.1mm.
A second study of 97 patients assessed as having aqueous deficient dry eye (baseline OSDI score of at least 23, a baseline Schirmer test with anaesthetic of ≤ 10mm in five minutes, and corneal fluorescein staining in the same eye) showed that use of the device on one eye between two and 10 times a day resulted in an improved Schirmer score compared with the fellow ‘control’ eye.
The increased response was seen to plateau after around one month (see figure 2). Adverse responses during any of the reported studies were of little significance, with a few reporting a ‘tingling’ sensation but little else.
Figure 2
Use
Allergan suggest initial use of two three-minute stimulation sessions per day at the level two setting. This can then be varied on practitioner advice as required. The unit is proving popular in the US, despite being costed at several hundred dollars along with the ongoing cost of replacement tips. If we see the unit in Europe soon, I believe it will prove to be an important addition to our armoury in the management of dry eye disease.
For further information see www.truetear.com
