Optimal refraction with monofocal intraocular lenses: no beneficial effect of astigmatism.
OBJECTIVE
This study aimed to determine the optimal spherocylindrical refraction in the monofocal, pseudophakic eye using power vectors in dioptric space.


METHODS
For parallel incident light the defocus of a spherocylinder may be described in dioptric space as: Defocus equivalent for distance fixation = D((SEP,M,x=∞)) = √SEP(2)+(1/2M)(2), where SEP = spherical equivalent power in dioptres (D) and M = astigmatic magnitude in D. In the pseudophakic eye the defocus for any fixation distance x is: Defocus equivalent for the fixation distance x = D((SEP,M,x)) = √(SEP-1/x)(2)+ (1/2M)(2). The cumulative defocus over a fixation interval is the integral of D((SEP,M,x)) . A minimal value for cumulative defocus will indicate a maximal unaided visual acuity (VA) over the chosen fixation interval. We calculated the summated defocus for various spherocylinders for fixation distances ranging from 0.5 m to 6.0 m.


RESULTS
Minimal cumulative defocus was present for pure spheres of -0.25 D to -0.5 D. No beneficial effect of the presence of astigmatism was detected.


CONCLUSIONS
In monofocal pseudophakia the highest possible VAs over the most extended fixation ranges may be achieved with slight myopic refractions without astigmatic components.
Department of Ophthalmology, Randers Regional Hospital, Denmark. KRISNAES@rm.dk
Kristian
K
Naeser
Jesper
J
Hjortdal
D000065:Accommodation, Ocular / Q000502:physiology*; D001251:Astigmatism / Q000503:physiopathology*; D002387:Cataract Extraction; D006801:Humans; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008433:Mathematics; D019591:Pseudophakia / Q000503:physiopathology*; D012029:Refraction, Ocular / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology