Table 2. .

Summary of the Neurophysiology of Sensations That May Be Responsible for CLD

Factors	Stimulus Modality	Transduction Channels	Sensory Neurons	CNS Second-Order Neurons	Sensations
CL-associated factors
Fit, movement, edge	Mechanical	SA, TRPV1, TRPA1, ASICs 1, 3	Polymodal nociceptor, LT and HT mechanoreceptor	WDR, HT mechanoreceptor	Irritation, foreign body, grittiness
Drying (evaporation of tears)	Osmolarity	TRPV1–4, TRPA1, TRPC5 TRPM3, ASIC3	Polymodal nociceptor	LT mechanoreceptor	Dryness, irritation, stinging, burning
	Cooling	TRPM8, TRPA1, K2P	Cold thermoreceptor	WDR	Coolness
	Shrinking (mechanical)	SA, TRPV1, TRPA1, ASIC1–3	Polymodal nociceptor	HT mechanoreceptor	Irritation, grittiness
Eyelid over CL surface	Mechanical	SA, TRPA1, TRPV1 ASICs 1, 3	Polymodal nociceptor, LT and HT mechanoreceptor	WDR, HT mechanoreceptor	Irritation, foreign body, grittiness
Solution-associated factors	Chemical	TRPV1, TRPA1, ASICs	Polymodal nociceptor	WDR, HT mechanoreceptor	Irritation, burning
Inflammation	Chemical	TRPV1, TRPA1, ASIC3, P2X, K+	Polymodal nociceptor MIA	WDR, HT mechanoreceptor	Irritation, burning, stinging,
		TRPM8, GPCR	Cold thermoreceptor MIA	WDR, HT mechanoreceptor	Coolness, cold pain, itch

CL, contact lens; GPCR, G protein–coupled receptor; HT, high threshold; K2P, two-pore potassium channels; LT, low threshold; MIA, mechanically insensitive afferent; P2X, purinergic channels; SA, stretch-activated channels; TRP, transient receptor potential; WDR, wide dynamic range.