Estimating principal plane positions for ocular power calculations in children and adults

To develop an age-dependent model to estimate the positions of the ocular and lenticular principal planes (pps) for use in ocular and axial power calculations.

Ocular power of the eye (P_eye ) and axial power (P_ax ) were calculated based on previously published average data of the ocular biometry and refraction in newborn infants, children and adults, as well as the associated pp positions. Next, regressions of the pp positions were made as a function of the logarithm of age, which were subsequently used to estimate P_eye and P_ax . These regression-based estimates were compared with the original data for validation. Finally, this procedure was repeated using the Atchison myopic eye model to determine the influence of myopia on the regression estimates.

In adults, the corneal pps almost coincide at 0.058 mm in front of the cornea. The first lenticular pp position relative to the corneal apex is described by the equation: 5.809 - 0.697·exp(-0.211·Age) (r²  = 0.96), and the second lenticular pp by 6.026 - 0.684·exp(-0.232·Age) (r²  = 0.95). The first ocular pp position relative to the corneal apex is at 0.293·exp(-0.232·Age) - 2.2·10^-3 ·Age + 1.723 (r²  = 0.99) and the second ocular pp is located at 0.392·exp(-0.181·Age) - 2.4·10^-3 ·Age + 2.093 (r²  = 0.99). Estimates of P_eye and P_ax derived from these regressions led to minor differences from the original values (0.00 ± 0.06D and 0.00 ± 0.10D, respectively). These errors were not affected by ocular refraction between -10D and 0D, with errors of + 0.12 ± 0.00D and -0.02 ± 0.05D for P_eye and P_ax , respectively.

The proposed regression models of the pp positions are sufficiently accurate to estimate P_eye and P_ax reliably. Interestingly, although the adult lens undergoes considerable physiological changes, its pps remain fixed with respect to the corneal apex.