April 2021
Volume 62, Issue 4
Open Access
Letters to the Editor  |   April 2021
Surface Area of the Exposed Eye
Author Affiliations
  • Thomas Millar
    Beyond 700 Pty Ltd, Dulwich Rd, Roseville, NSW, 2069, Australia. E-mail: tj.millar@outlook.com.
Investigative Ophthalmology & Visual Science April 2021, Vol.62, 18. doi:https://doi.org/10.1167/iovs.62.4.18
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      Thomas Millar; Surface Area of the Exposed Eye. Invest. Ophthalmol. Vis. Sci. 2021;62(4):18. doi: https://doi.org/10.1167/iovs.62.4.18.

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      © ARVO (1962-2015); The Authors (2016-present)

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  • Supplements
I read with interest the recent investigation by Glasgow1 and was very impressed by the scientific approach to examine the surface layers. However, in estimating the likelihood of phospholipids being on the surface of the tear film, he quotes from Campbell et al. (ref 26) for the surface area of the tear film; this being 3.5 × 107Å2. This value from Campbell et al. is clearly wrong and it is difficult to discern where this calculation came from. Campbell et al. refer to a paper by Zaman et al., who measured a mean maximum palpebral height over a 5-minute period. This is the maximum height of the palpebral aperture before the next blink. From this, they estimate the surface area of the eye and use a formula to account for the curvature. Without going into details, their calculation is actually an underestimate because it does not account for the conjunctival regions. Nevertheless, they come up with a surface area of approximately 1.3 cm2. My estimate of the surface area of the exposed eye is approximately 2 cm2. Even if we halve this value, 1 cm2 represents 108 × 108 Å2 (1016 Å2). Clearly, this value is in excess of the value reported by Campbell et al., and so I think that the Glasgow data should be reappraised in the light of a much larger surface area for exposed surface of the eye (the tear film area). By my calculations, using this value as the surface area, it is very clear that only a minute proportion of molecules on the surface could be phospholipids; in reality, hardly any. 
Reference
Glasgow BJ . Evidence for phospholipids on the surface of human tears. Invest Ophthalmol Vis Sci. 2020; 61(14): 19, https://doi.org/10.1167/iovs.61.14.19. [CrossRef] [PubMed]
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