Paraxial power of the pseudophakic eye
The pseudophakic eye corresponds to a system made up of two thick elements (the cornea and the intraocular lens). It is treated as a single virtual system whose anterior interface is equivalent to the principal object plane of the cornea and the posterior interface the principal image plane of the IOL It includes an anterior limit or interface and a virtual posterior limit or interface, a total paraxial power (De), and the position of its principal planes (He, H’e) can be determined.
The paraxial power of the anterior interface is then equated to the total power of the cornea (Dc), and the power of the posterior interface is equated to the total power of the IOL (Di). The use of Gullstrand’s formula calculates the total power of the compound pseudophakic eye and depends on the respective powers and distance between the cornea and the IOL.
In this context, the distance between these two interfaces refers to the effective lens position with thick lens elements (ELPT). This distance extends from the principal image plane of the cornea (H’c) to the principal object plane of the implant (HI).
It, therefore, depends not only on the anatomical distance separating these two elements (S1S3) but also on the position of their respective principal planes.
We can apply the paraxial formulas that calculate the power of the pseudophakic eye assimilated to the sum of the corneal and IOL using Gullstrand’s formula and determine the position of its principal planes.
The position of the principal planes of the total eye is referenced from the principal object plane of the cornea (principal object plane) and from the principal image plane of the IOL (principal image plane).
It is proportional:
– (principal object planeà: to the ratio between the object focal length and the object focal length of the posterior surface
– (principal image plane): to the ratio between the image focal length and the image focal length of the anterior surface