Importance of Aligning Lenses
Lens manufacturers have spent millions of dollars developing sophisticated single vision and multifocal lenses to improve clarity and comfort of vision. While these designs have been very successful, their performance is heavily dependent on the accurate positioning of the lens centre along the line of sight.
Lens alignment has traditionally been determined by the optometrist or optical dispenser marking the position of the pupil centre with a dot or cross on the dummy lens in the patient's frame. However, this method can be associated with a number of inaccuracies as the line of sight for most people does not pass through the pupil centre. Furthermore, unless the practitioner is exactly aligned with the patient these measurements would be incorrect.
Sophisticated instruments have been developed which eliminate such errors by compensating for the patient's head and eye positions far more accurately, as can be seen in the above image. It is possible to store these images, which means that they can be adjusted by the optometrist to cater for different types of visual tasks. For example, a bus driver who spends much of his time looking in the distance may require a different lens alignment from that of a computer operator engaged in near visual tasks. This instrumentation has greatly enhanced the performance of sophisticated lenses.