The Perifocal-Msa lens is a spectacle lens for restraining the development/progression of myopia with accommodation support. Additional index (sa) in contrast to Perifocal-M indicates: (s) – an earlier start of the addition and its faster saturation with higher values horizontally relative to the optical center of the lens; (a) – the presence of a zone to support accommodation.
Perifocal-Msa - the range of Central refraction from -0.25D to -10D, with a cylinder up to 4.0D. the Perifocal-Msa lens, as well as Perifocal-Ms, has an asymmetric progression on both sides of the optical center horizontally. The value of nasal (towards the nose) addition 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 temporal (in the direction of the temple) addition is 3.0D with the beginning of the progression in 3mm from the optical center and the saturation of the progression in 24mm from the optical center horizontally. The Perifocal-Msa lens, unlike Perifocal-Ms and Perifocal-M, has a zone for supporting accommodation, in the form of a downward progression with an addition of 1.25D.
The progression starts at 2mm from the optical center downwards with a saturation in 9mm from the optical center, the saturation point of the progression downwards is shifted by 2mm towards the nose, relative to the vertical passing through the optical center. One of the unique optical features of the Perifocal-Msa lens design is the short corridor of progressionfor the accommodation support zone, which, unlike many existing progressive lenses used to support accommodation in myopia in children, significantly increases the user's motivation to get the visual axis into this zone when working near. Also, the value of the addition of 1.25D is the most optimal for supporting accommodation in myopic children, given the results of scientific studies showing that the myopic eye is configured for perception in the middle spatial frequencies.
Unlike the Perifocal-M lens, the Perifocal-Msa lens is divided into right and left lenses. On the front surface of the lenses there is a visible yellow marking indicating the optical center and horizontal, an oval indicates the area for supporting accommodation (the presented marking is also applied to the Perifocal-Psa lenses).
Thus, the Perifocal-Msa lens, unlike all known spectacle lenses that differentially corrects central and peripheral refraction, has an additional function in the form of accommodation support. The Perifocal-Msa lens can be used in cases of progressive myopia correction accompanied by a decreased accommodation values, symptoms of accommodation weakness and / or habitual excessive accommodation stress.