Front Surface Bifocal Lens

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The P.C.L Bifocal Lens is a one piece translating bifocal lens, which is solely designed and manufactured by P.C.L, with comfort, precision and performance in mind.
The object of the P.C.L design is for a smooth transition between the distance curve and the reading curve for patient comfort and to keep protein and calcium deposits to a minimum.
The lens is designed so that it positions low on the eye, leaving sufficient clearance between the top of the lens and the superior limbus. This is so that on the downward glance the lens moves up freely for use of the reading segment, which is truncated to enhance movement. It has been found through patient testing, that when truncating the lens it causes it to become unstable in the eye, with the lens found to be riding high.
This problem appears to be caused by the loss of secondary and periphery curves at the bottom of the lens and/or a lack of weight in the lens. To rectify this problem P.C.L has designed an alternative inside curve design. The design is such that the secondary and periphery curves are manufactured eccentrically with a .7 mm offset producing a secondary curve which is .7 mm wider at the bottom of the lens. Once the lens has been truncated it still has some secondary curves left for stability ( fig 1 ).

Eccentric Curves

Also manufacturing these lenses with a distance power of – 4.00 and higher, with a 3 prism gives the weight back to them that they lose at that range of powers using a 2 prism. This also helps keep the lens in the lower position in the eye.
The secondary curves should be fitted flatter compared to the fitting of a normal lens.
The P.C.L design recommends 0.1 flatter than normal, which is necessary for a smooth upward transition as well as for the lens to drop quickly after a blink. Each individual patient may need a slightly flatter or steeper periphery for the necessary movement. This is why free diagnostic lenses made to the patient’s parameters are manufactured from P.M.M.A to make sure the perfect fit is obtained.
We recommend that diagnostic lenses are ordered with a segment height 1 mm under natural centre of lens. This segment height can be checked when fitted on the patient and increased or decreased accordingly for the final lens. The reading segment transition line is designed so that if the lens swings slightly the vision does not move back into the distance curve.
It has been found that the introduction of free P.M.M.A trial lenses made to the patients Rx has been very successful towards obtaining the right fit which is very important for the performance of this lens.
Dianostic Button
We also have a stock of these diagnostic lenses on call for the practitioner, one or many lens can be on loan free of charge from our Bifocal Diagnostic lenses List.
We are willing to change the lens parameters in any way for the individual patient fit. The P.C.L standard which we recommend to start with is :
Starting Parameters bottom
Bifocal Dia 1st

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