Fig. 69. Effect of the position of a spectacle lens on retinal image size in 5-D axial myopia. Object subtends 0.1 radians. a. Length of the eye is 25.2 mm. The chief ray height is 1.8 mm. This is the blurred image size. b. Correction lens at the first focal point shifts the principal plane to within 22.9 mm of the retina. The power of lens and eye is 58 D. The image size is 1.72 mm, as in emmetropia. c. Fitting the correction lens at the refracting surface reduces the power of the eye and lens system to 53 D. The principal plane remains at the vertex. The image is 1.89 mm long. d. Fitting the correction lens in contact with the cornea results in the principal plane H' for the system being shifted to within 25.02 mm of the retina, in a power of 53.4 D, and in an image size of 1.87 mm.