Specialist GP Lens Fitting

Correction of Presbyopia

The major advantage that RGP lenses have over their soft counterparts is that they move with each blink. This can be used to allow the wearer to utilise different parts of the OZ in different directions of gaze. Either segmented or varifocal designs are available.

The segmented designs use a prism-ballast to ensure that the lens orientates correctly, whereas multifocal designs tend to be centre-near or centre-distance with the power gradually changing towards the periphery.

Factors such as lid position, pupil size and palpebral aperture do need to be taken into consideration with these designs and will dictate which design is more appropriate.

If a new wearer is considering these lenses or a soft lens user is moving over to RGP lenses as presbyopia becomes a problem, a single vision fit is suggested first to establish wearing time and fit prior to embarking on the bifocal/multifocal fitting. This also reduces the number of variables, although some fitters may disagree.

Segmented bifocal lens

The image above shows a segmented bifocal with the segment aligned with the lower pupil margin. The position of the segment is determined at the time of ordering, but can be lowered by truncating the bottom edge of the lens if the segment sits too high. As there is no way to raise the position if it proves too low, the ECP is advised to aim high to start with - normally 1.5mm below datum and a 1.5 prism base down is a good starting point.

Again, a good relationship with a laboratory with more than one design in their inventory is essential. The rewards from this type of fitting in terms of patient satisfaction and referrals, make it worth the initial investment in time.

Keratoconus/Irregular Cornea

The use of RGP lenses to correct these conditions is well established, however advances in the measurement and understanding of these conditions brought about by improved instrumentation and lathing techniques has contributed to the huge growth of diagnosis and treatment of these conditions.

Apart from the well-known market leaders, most laboratories have developed specialist lenses for the treatment of these conditions, along with the expertise to assist the ECP in successfully correcting all types of irregular corneal problems.

Early Keratoconus corrected with a regular spherical lens

Improvements in designs and materials have seen a resurgence in the fitting of semi-scleral lenses and the advantages of this type of lens are numerous. The corneal surface is entirely vaulted, which means that any irregularity on the surface does not affect the stability of the lens. The weight of the lens is borne by the sclera and the tear lens corrects any astigmatism or distortion. The lens movement is similar to that of a well-fitted soft lens and the edge of the lens is under the upper lid, minimising lid/lens interaction and resulting in comfort akin to that normally associated with a soft lens. The results with this type of lens can be quite stunning for patients who have struggled with poor comfort and fluctuating vision with other lenses.

High Dk materials such as Optimum Extra permit long wearing times and with support from the right laboratory, fitting techniques are not onerous.

 
Semi-scleral lens with single fenestration