A Perifocal-Psa lens central refraction range from +0.75D to 0.0D, with a cylinder up to 4.0D. the Additional index (a) in contrast to Perifocal-Ps indicates the presence of a zone to support accommodation. The lens has an asymmetric progression on both sides of the optical center horizontally and a downward progression. The value of the nasal (towards the nose) progression is 2.5D with the beginning of the progression in 4.5mm from the optical center and the saturation of the progression in 24mm from the optical center horizontally. The value of the temporal (in the direction of the temple) progression is 3.0D with the beginning of the progression at 3mm from the optical center and the saturation of the progression at 24mm from the optical center horizontally. The amount of downward progression – 1,25 D with the beginning of the progression in 2mm from the optical center in a downward direction and saturation in 9mm from the optical center, the point of saturation of downward progression is offset 2mm toward the nose, relative to the vertical passing through the optical center. One of the important features of the Perifocal-Psa lens is the short progression corridor of the zone for supporting accommodation, which, unlike standard progressive lenses for supporting accommodation, provides the user with a higher motivation to get the visual axis into this zone when working near. Also, unlike the Perifocal-P lens, the Perifocal-Psa lens is divided into right and left. The front surface of the lenses has visible yellow markings indicating its optical center, horizontal, and progression to support accommodation (just like the Perifocal-Msa lens).
Thus, the optical features of the Perifocal-Ps and Perifocal-Psa lenses can provide conditions for increasing the effectiveness of therapeutic effects on the eye and the visual system as a whole in preventing the development of myopia in children with myopia predictors.