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D. M. Silver, A. Csutak; Human Eye Dimensions for Pressure-Volume Relations. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5019.
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To measure the dimensions of human eyes, to ascertain their correlation with refractive error, to calculate their volumes, and to generate a volume-dependent pressure-volume relation.
Using a micrometer with 0.025 mm accuracy, the anterior-posterior (AP), horizontal (H), and vertical (V) dimensions of eyes from 40 male and 62 female deceased donors were measured. Age, spherical refraction and cylindrical refraction were also obtained. All eye measurements were made within hours of death. Eye volume was calculated assuming an ellipsoidal geometry for the eye. T-tests were used to compare particular measurements and features.
The measured (mean +/- SD) dimensions of the eyes were: male AP 24.1 +/- 0.9 mm, H 23.4 +/- 0.9 mm, V 23.2 +/- 0.9 mm; female AP 23.5 +/- 0.8 mm, H 23.0 +/- 0.9 mm, V 22.9 +/- 0.8 mm. Refractive parameters were: male spherical -0.65 +/- 1.59, cylindrical -0.26 +/- 1.49; female spherical -0.21 +/- 1.42, cylindrical -0.68 +/- 1.40. Ages were: male 70.1 +/- 10.9 years; female 67.8 +/- 14.0 years. Comparing male to female, there were statistically significant differences for AP length (p=0.001), and H length (p=0.03); the other parameters were not significantly different (p > 0.05) between male and female. For both male and female eyes, statistically significant greater length was found for AP compared to either H or V lengths (p < 0.001), while H and V lengths were not significantly different from one another. AP length was longer for eyes with higher myopic refractive error, and there was a positive correlation between longer AP and longer H and longer V (R2 = 0.4). Calculated eye volumes were: male 6,032 +/- 620 muL; female 5,712 +/- 566 muL. The difference in eye volume was statistically significant (p= 0.009) between male and female. However, the volume dependence for both male and female eyes was captured with the dependence of volume on AP, V(AP) = 600 x AP - 8400 muL (R2 = 0.7). Inserting this equation into the pressure-volume relation of Silver and Geyer gives ΔV = V(AP) x (-8.03 x 10-3 + 4.87 x 10-3 ln P + 3.90 x 10-5 P), where ΔV is the change in volume corresponding to the intra-ocular pressure P.
On average, male and female eyes differ significantly in size, hence in eye volume. However, the range of eye volumes exhibited for both males and females is manifest in AP length. Therefore an AP dependent eye volume equation can be used to account for eye volume when using pressure-volume relations for calculating outflow facility from tonography and pulsatile ocular blood flow from intraocular pressure pulsations.
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