The purpose of this study was to assess spontaneous eyeblink activity in the primary eye position, and its relationship to the exposed ocular surface area in elderly individuals without significant ocular surface disease. Spontaneous eyeblink frequency (SEBF) was assessed for a group of Caucasians aged 61 to 81 years, by videography in silence over a 5 min period; inter-blink interval (IBI), the maximum inter-blink interval (mIBI) and the modal eyeblink frequency (mEBF) were derived from video recordings. The ocular surface area was calculated from video-planimetry using different formulae. The average palpebral aperture was 8.3 +/- 2.3 mm (n = 45, +/- S.D.), resulting in an average exposed area of 1.13-2.13 cm2 depending on the formula used; the preferred estimate was 1.25 cm2. A highly significant relationship (P < 0.001, r2 = 0.835) was found between time-averaged palpebral aperture (p) and exposed ocular surface (A = 0.244p-0.763). An average SEBF of 11.9 blinks min-1 was measured (range 0.8-43.6). No correlation (P > 0.35, r2 < or = 0.01) was found between SEBF, IBI, mIBI, or mEBF and the palpebral aperture or the exposed surface area, regardless of the formulae used. The exposed ocular surface area per se does not appear to be an important determinant of spontaneous eyeblink activity in elderly Caucasians.