Anisometropia and aniseikonia calculation in aphakic eye
Introduction
Currently we solve aphakic states with implantation of posterior intraocular lens or anterior IOL or the lens is implanted in eye lens capsule. Earlier we don’t use any IOLs so patients had induces high anisometropia and resulted aniseikonia. Sometimes when surgery is complicated we have to use aphakia these days.
Goals
- Calculate axial refraction of the aphakic eye
- Calculate adequate spectacle correction of the aphakic eye
- Calculate anisometropia in aphakia
- Calculate size of the aniseikonia in monocular aphakia
Equipment
Writing equipment, calculator.
Methods
Calculate axial refraction of the aphakic eye
Axial eye refraction is calculated from modified imaging formula on the base of knowledge refractive index of intraocular fluid (n’), corneal refractive power (φ´R) and axial length of the eye (a´R= dO). .
Calculate adequate spectacle correction of the aphakic eye
For calculation of adequate spectacle correction of the aphakic eye we need to know vertex distance of the spectacle lens (measure it from the frame) and axial refraction of the aphakic eye.
Calculate anisometropia in aphakia
For optical power of the aphakic eye we need to know Gullstrand formula. Difference between total optical power of the aphakic eye and emmetropic eye show us level of anisometropia.
Calculate size of the aniseikonia in monocular aphakia
Ratio between total refractive power expressed in percent of aphakic and emmetropic eye show us aniseikonia.
Results
Calculate axial refraction of the aphakic eye
AR =
Calculate adequate spectacle correction of the aphakic eye
S´B =
Calculate anisometropia in aphakia
𝛗´em = 58,64 D
𝛗´af =
𝚫 𝛗´=
Calculate size of the aniseikonia in monocular aphakia
𝛃 em/af =
Discussion
If we correct aphakia with spectacle lens we try to increase visual acuity and decrease aniseikonia. If we correct aphakia with spectacle lens we usually induce anisometropia 10 D, i.e. 20 % of aniseikonia. From eye physiology we know that patients are able to fuse 5 % of aniseikonia. If the anisometropia is present in patient from childhood he is able to fuse aniseikonia around 14 %.
In adults aphakia usually is very sudden and leads to diplopia if is corrected with glasses. If we use contact lenses we can decrease the aniseikonia. Currently most of aphakic eyes are corrected with intraocular lens (IOL).
Conclusion, notes, comments
Calculate size of anisometropia and aniseikonia in aphakia corrected with contact lens. Will be successfully accepted by patient?