Background Ocular magnification and aniseikonia after cataract surgery has been widely
ignored in modern cataract surgery. The purpose of this study was to analyse ocular
magnification and inter-individual differences in a normal cataract population with
a focus on monovision. Methods From a large dataset containing biometric measurements
(IOLMaster 700) of both eyes of 9734 patients prior to cataract surgery, eyes were
indexed randomly as primary (P) and secondary (S). Intraocular lens power (IOLP) was
derived for the HofferQ, Haigis and Castrop formulae for emmetropia for P and emmetropia
or myopia (-0.5 to -2 dpt) for S to simulate monovision. Based on the pseudophakic
eye model in addition to these formulae, ocular magnification was extracted using
matrix algebra (refraction and translation matrices and a system matrix describing
the optical property of the entire spectacle corrected or uncorrected eye). Results
With emmetropia for P and S the IOLP differences (S-P) showed a standard deviation
of 0.162/0.156/0.157 dpt and ocular magnification differences yielded a standard deviation
of 0.0414/0.0405/0.0408 mm/mrad for the HofferQ/Haigis/Castrop setting. Simulating
monovision, the myopic eye (S) showed a systematically smaller mean absolute spectacle
corrected ocular magnification than the emmetropic eye (-0.0351/-0.0340/-0.0336, respectively,
relative magnification around 2%). If myopia in the S eye remains uncorrected, the
reduction of ocular magnification is much smaller (around 0.2-0.3%). Conclusion Vergence
formulae for IOLP calculation sometimes implicitly define a pseudophakic eye model
which can be directly used to predict ocular magnification after cataract surgery.
Despite a strong similarity of both eyes, ocular magnification does not fully match
between eyes and the prediction of ocular magnification and aniseikonia might be relevant
to avoid eikonic problems in the pseudophakic eye.
