Wearing contact lenses (CL) is one factor that can disturb tear dynamics, potentially resulting in ocular discomfort, dryness, and ocular surface disease.
1–4 CL-related comfort issues might involve a wide range of factors, which are particularly active under certain environmental conditions.
5 More than half of CL wearers self-report dry eye symptoms.
1 Some of these wearers reduce their lens wear time and some eventually abandon lens wear. Over 15% of lens wear dropout is attributed to dryness, and nearly 30% to ocular discomfort.
6,7
Regarding rigid gas permeable lenses (RGP), it is commonly accepted that initial comfort will be low, increasing during the first few days until regular use during the whole day.
8 A unique case within the RGP field is overnight orthokeratology for corneal reshaping or corneal refractive therapy (CRT). Clinicians are aware that the eyelids play a major role in RGP, CL-related discomfort during blinking, and this is common at first and within the adaptation period of all RGP lenses. This inconvenience is minimized in CRT
9 because the lenses are worn overnight with no blinking interactions.
The Dry Eye Workshop proposed to diagnose dry eye by combining different tests to identify signs and symptoms.
10 However, it is necessary to be aware that the diagnosis of dry eye is difficult due to the poor correlation between dry eye signs and symptoms.
11 Analytical techniques are providing valuable information about new components in tears that may have important biochemical and physiological functions.
12 Among these tear components, diadenosine polyphosphates emerge as interesting compounds. They are released in the tear film by corneal shear stress during blinking, inducing an increase of dinucleotide concentration,
13 and have important intracellular and extracellular physiological actions. It is known that Ap
4A and Ap
5A concentrations increase in patients with dry eye symptoms and Sjögren syndrome, suggesting the possibility of these compounds being used as objective markers to diagnose and classify dry eye.
13,14 Moreover, a single-dose topical application of the dinucleotide Ap
4A in rabbits has demonstrated to stimulate tear secretion, which confers to these compounds a secretagogue action.
15 Ap
4A also has the ability to accelerate corneal wound healing in New Zealand white rabbits.
16
Due to the involvement of diadenosine polyphosphates in the ocular surface physiopathology and its release mechanism related with blinking, it is a matter of interest to investigate a possible relationship between the concentrations of these substances and the development of dry eye in CL wearers—in this case, RGP lenses with different wearing schedules. With the aim of examining this relationship, the present work described variations in the levels of diadenosine polyphosphates (Ap4A and Ap5A) during 1 month with alignment-fit aspheric RGP lenses worn on a daily basis, followed by a washout period of 2 weeks, and finally another month with reverse geometry for CRT worn overnight. Furthermore, study authors examined tear volume and stability, corneal staining, and discomfort and dryness symptoms, which may be present during dry eye.