A Role of Corneal Mechanical Adaptation in Contact Lens–Related Dry Eye Symptoms

Abstract

PURPOSE.To compare corneal mechanical adaptation measured psychophysically in contact lens wearers with or without dry eye symptoms. METHODS. Two groups of contact lens wearers were recruited. One group (symptomatic) consisted of subjects with dry eye symptoms (according to the subjective evaluation of symptom of dryness [SeSoD] questionnaire). The second control group (asymptomatic) consisted of subjects reporting no symptoms. There were 32 (aged 20 to 42 years, 6 males and 26 females) and 29 subjects (aged 21 to 36 years, 9 males and 20 females) in the symptomatic and asymptomatic groups, respectively. Mechanical stimulus thresholds of the cornea were determined using a Belmonte pneumatic esthesiometer and the ascending method of limits. Then three stimulus intensity groups (subthreshold, threshold, and suprathreshold) were applied to the eye in random order, each 20 times. Subjects rated the intensity of the stimuli using a scale of zero to four. The rating data from the two groups were compared by Friedman nonparametric ANOVA. Adaptation was defined as the reduction in subsequent ratings compared with earlier ones. RESULTS. No significant difference was seen in subjects' thresholds in both groups (P ϭ 0.22). The symptomatic group rated their sensations to suprathreshold stimuli higher than the asymptomatic group. More importantly, there was significant adaptation with suprathreshold mechanical stimulation in the asymptomatic group (P ϭ 0.006) but not in the symptomatic group (P ϭ 0.08). There was no adaptation during threshold and subthreshold stimulus sessions in either group. CONCLUSIONS. Adaptation was found to suprathreshold mechanical stimuli in the asymptomatic group but not in the symptomatic group. (Invest Ophthalmol Vis Sci. 2011;52: 1200 -1205) DOI:10.1167/iovs.10-5349 C ontact lens-related dry eye symptoms have received attention from both clinicians and researchers. It was reported in an examination of optometric practices that half of contact lens wearers (50.1%) had dry eye symptoms, whereas much fewer than half of the number of non-lens wearers reported symptoms (21.7%).1 Dry eye symptoms have been reported to be a major reason for the discontinuation of contact lens wear.2,3 Because of the distinct pattern of contact lens-related dry eye, as well as the different sex and age prevalence in non-lens wearers, 4 the mechanisms of contact lens-related dry eye could be different from that of non-contact lens-related dry eye. 5,6Factors related to lens wear comfort may include the geometry of the lens (particularly thickness and edge design), environmental conditions (temperature and humidity), tear film structure, corneal physiology, and factors affecting ocular surface neural activity.7 Recently adopted daily disposable lenses have decreased the effect of deposits on the lenses, and so chronic lens deposition itself is perhaps of less etiologic importance in contact lens-related discomfort.8 Hypoxia is a factor that has been suggested to be closely related to contact lens comfort, 9 -11 and numer...

The role of corneal afferent neurons in regulating tears under normal and dry eye conditions

“…These results also run counter to the cornea and lacrimal gland feedback model proposed by Mathers (Mathers, 2000), in which it was hypothesized that dry eye produces a decrease in the sensitivity of corneal primary afferent neurons. The effect of dry eye on the properties of mechanoreceptive and polymodal neurons has not been examined, yet sensitization of these neurons would be consistent with studies that have reported significant hyperesthesia in individuals symptomatic for ocular dryness (Chen and Simpson, 2011; De Paiva and Pflugfelder, 2004; Situ et al, 2008a; Situ et al, 2008b; Tuisku et al, 2008)(but see (Benitez-Del-Castillo et al, 2007; Bourcier et al, 2005; Stapleton et al, 2006)).…”

Lid Margin Sensitivity and Staining in Contact Lens Wear Versus No Lens Wear

“…43 A more recent investigation found corneal adaptation to suprathreshold stimuli in asymptomatic SCL wearers but not in symptomatic wearers, although there was no difference in thresholds between the 2 groups. 44 All these findings show that the understanding of the relationship between CLD and sensitivity of the ocular surface is still limited.…”

Hypersensitivity to Cold Stimuli in Symptomatic Contact Lens Wearers

“…Consistent with previous results, 11,12 sensitivity in the asymptomatic group tended to be reduced compared to controls suggesting neural adaptation. 19 In contrast, the symptomatic group was the most sensitive.…”

“…39 These suggest the development of sensitization and the alteration of neural control of the functional unit in symptomatic wearers, 40 although maybe additional adaptation mechanisms could also affect the sensory processing in symptomatic wearers. 19 …”

“…However, it is unclear how these changes in sensory processing with contact lens wear could contribute to CLD, although recently it has been suggested that differences in sensory adaptation in symptomatic and asymptomatic lens wearers may play a role. 19 Little is known about the relationship between the presence of CLD symptoms and corneal sensitivity as well as subjective experiences of the cooling stimulation, although recent evidence has suggested that cold receptors may contribute to ocular dryness and discomfort. 20 In order to investigate these questions, the current study was designed to examine the differences in pneumatic cool thresholds and sensation magnitude at threshold in symptomatic and asymptomatic contact lens wearers and non-lens wearing normal controls.…”