In an optimum fit lenses will move post blink vertically. Toric lenses will also appear as pictured. A lens that rides high and does not move with the lid is a high riding fit. This is usually due to lid interaction and corneal shape, altering the lens will not centre high riding lenses. Some lenses will drop and not move, especially high plus powers, reducing the lens diameter 0.5mm will reduce the weight and thickness of the lens. Lenses that are high or low riding will limit the bifocal effect. Alter the BOZR to create movement. If this is not possible mono-vision or distance CLs and over readers may give better patient satisfaction.
Assess the acuity with a distance chart after 10 minutes for lens settling. Check the lens power with spherical over refraction ensuring as much plus as possible. With toric lenses align cross-cyl with the rotation of the flat axis marks.
Perform a binocular over refraction-
With the patient looking at a distance target with both eyes maximise plus in each eye using 0.25 D increments.
Most VDU monitors are in the distance visual field requiring a +0.50 over-correction in the distance Rx or modified monovision (dominant eye DV and NV, non-dominant VDU and NV). Laptop screens are often in the near visual field. If there is a demand for VDU vision force plus in the non dominant eye until a VDU target is clear, ensure distance acuity is acceptable.
Using a realistic near text (news print N8) ensure minimum plus, presenting +0.25D increments to both eyes until target is acceptable
If necessary adjust the lens fit and incorporate the over refraction prior to giving the lenses to the patient for the trial period.
The distance zone can be increased if DV is poor and lenses de-centre slightly. The distance zone can be decreased if NV is poor and lenses de-centre slightly or pupils are small.
If either the fit or power of the lens need altered forward the information to the lab or specify the parameters for the new lens.
Patients should be made aware that there will be visual blur due to the corneal moulding effect of this back surface design. Blurring is temporary and will last for around two hours.