Postlens Tear Film Research Articles

Osmotic determinants of postlens tear film morphology and hydrogel lens movement

The determinants of postlens tear film (PTF) composition in hydrogel lens wear are poorly understood, although this layer has important roles in lens movement and corneal integrity. We investigated the hypothesis that the PTF could be depleted by instillation of hypotonic saline, using a randomized, double masked, placebo controlled study design. Solutions of 0.90, 0.60 and 0.45% NaCl were instilled into the eyes of 12 subjects wearing ionic and nonionic high water content hydrogel lenses. Postlens tear film appearances in specular reflection were categorized as amorphous, faint coloured or coloured, where the coloured patterns represent a progressive thinning of the PTF. With instillation of the hypotonic solutions (0.60 and 0.45% NaCl), the appearance of the PTF in specular reflection changed to a faint coloured or coloured pattern in at least 67% of subjects for each lens type (Friedman ANOVA, P < 0.002). For the 0.45% NaCl solution, median lens movement decreased from 0.50 to 0.10mm (Friedman ANOVA, P = 0.02); however, there were no significant changes in measured lens parameters and no difference between lens types. Postlens tear film depletion due to a hypotonic shift in tear osmolality, as demonstrated here, may explain the clinically observed phenomenon of lens binding.

Osmotic determinants of postlens tear film morphology and hydrogel lens movement

SummaryThe determinants of postlens tear film (PTF) composition in hydrogel lens wear are poorly understood, although this layer has important roles in lens movement and corneal integrity. We investigated the hypothesis that the PTF could be depleted by instillation of hypotonic saline, using a randomized, double masked, placebo controlled study design. Solutions of 0.90, 0.60 and 0.45% NaCl were instilled into the eyes of 12 subjects wearing ionic and non‐ionic high water content hydrogel lenses. Postlens tear film appearances in specular reflection were categorized as amorphous, faint coloured or coloured, where the coloured patterns represent a progressive thinning of the PTF. With instillation of the hypotonic solutions (0.60 and 0.45% NaCl), the appearance of the PTF in specular reflection changed to a faint coloured or coloured pattern in at least 67% of subjects for each lens type (Friedman ANOVA, P &lt; 0.002). For the 0.45% NaCl solution, median lens movement decreased from 0.50 to 0.10mm (Friedman ANOVA, P = 0.02); however, there were no significant changes in measured lens parameters and no difference between lens types. Postlens tear film depletion due to a hypotonic shift in tear osmolality, as demonstrated here, may explain the clinically observed phenomenon of lens binding.

Hydrogel (Acuvue) lens movement is influenced by the postlens tear film.

The determinants of hydrogel lens movement with thin mid-water content lenses may be better understood by taking into account the lubrication properties of the tear film. We assessed lens movement, postlens tear film (PTF) status, and tear meniscus height with 58% water content (Acuvue) lenses worn over 6 h on each of 2 consecutive days. Median lens movement was near zero initially and increased within the first hour to 0.34 and 0.30 mm on days 1 and 2, respectively (Friedman analysis of variance by ranks, days 1 and 2, p < 0.001). The small lens movement at 15 min was related to the increased PTF depletion (Kruskal-Wallis analysis of variance; day 1, p = 0.02; day 2, p = 0.007). In some subjects, lens movement and PTF status co-varied throughout the lens wearing periods. These findings suggest the PTF is a determinant of hydrogel lens movement.

Postlens tear film morphology, lens movement and symptoms in hydrogel lens wearers.

Postlens tear film morphology, lens movement and symptoms were assessed in 100 subjects wearing hydrogel contact lenses on a daily wear schedule. Postlens tear film appearance in specular reflection was categorized as amorphous, coloured, striated or dynamic (variable with blinking), and subjects' symptoms were assessed using a questionnaire. Non-amorphous appearances were present in 25% of subjects and occurred approximately equally with HEMA, Acuvue, Igel 55 and other lens types. Patterned appearances were found to be associated with reduced lens movement (Kruskal-Wallis ANOVA, P < 0.001). The most common symptom (dryness) was not significantly related to postlens tear film appearance. Postlens tear film morphology was shown to be a determinant of lens movement, but may be unrelated to common symptoms.

Analysis of blink-induced vertical motion of contact lenses.

This report discusses blink-induced vertical motion of contact lenses as measured with a slit lamp. The motion seen this way represents the displacement of the lens from its position just before a blink to its position immediately after the blink. Motion amplitudes reported in the literature will be discussed in the context of a hypothesis which seeks to account for lens motion by taking into consideration the post-lens tear film characteristics, the diameter of the lens, and the geometry of the anterior segment of the eye.