1. Helmholtz's treatise on physiological optics. translated from German 1909;Gullstrand,1924
2. Uber die akkommodation des auges;Helmholtz;Arch Ophthalmol,1855
3. Presbyopia towards the end of the 20th century;Weale;Surv Ophthalmol,1989
4. Presbyopia – effect of refractive index;Pierscionek;Clin Exp Optom,1990
5. Ultrasound biomicroscopy monitoring of human ciliary body changes during accommodation in presbyopia;Bacskulin;Ophthalmologe,1996