How high is a high prescription?
How long is a piece of string? The highest powered spectacles that we have ever made at our practice were a set of -35.00 diopter lenses for a worker at a Mongolian orphanage. This is certainly well above the normal power range 0f around 0.00 to 4.00 diopters but shows that limits are made to be pushed! How did they look? They were very thick indeed but the patient was happy to report that the trees outside their window now had leaves and they could function in their role at the orphanage, so they got the job done.
One of our more recent efforts was a -22.00D lens that we made for a patient. Again our patient was happy with the resultant vision and this time we managed to get some photos of the finished job too.
What did we do?
First and foremost the power of the prescription as written is examined. In this case we were able to determine that the test was performed with the frame at one distance from the eye but the new spectacle frame was sitting much closer. This results in a need for compensated powers to ensure that the prescription in the new spectacles is the same as that experienced in the eye test. By doing this we can ensure that the patient is getting exactly what the doctor ordered.
In some cases this can result in a remarkable change in powers so it is vital that these things are considered, not just for extremely high powers but even for prescriptions that may not seem overly strong at first glance.
We also made sure that the lenses made use of an appropriate material and lens design that balanced thickness reduction with the visual requirements of the patient. By making use of our in house design facilities it was possible to gain visual acuities and visual fields that enabled this patient to retain their drivers license, something they had previously been told was impossible.
Various eye conditions can result in a patient having asymmetric powers (i.e. one eye needing a much stronger prescription that the other). Lenses made for these patients will give different image sizes and rates of image movement, the effects for the patient can range from mild discomfort to extreme visual distress and nausea. Patients who have had one cataract removed and are waiting on the other to be operated on will often experience this condition known as anisometropia (unequal refractive power).
In many cases it is possible to overcome the difference in powers by manipulating the relative curvatures of the lens surfaces as well as several other factors. Lenses made to correct this condition are known as iseikonic lenses and can look a little interesting with various curves and thicknesses, but if the end result is clear, comfortable vision these are small considerations.
Many people are unaware of what prism actually is, but those who do need it are very aware as it enables them to get one clear image of the world rather than double vision. The causes of prismatic prescriptions are varied but can include issues with the muscles of the eye or even traumatic injuries to facial bones.
We use prism to help a patient ‘fuse’ the two images received by the eyes and the amounts required to do this will vary according to each case. Most patients who need it will have somewhere between 0.50D and 2.00D, the highest we have seen was 26.00D which was one of the most challenging cases we have experienced.
In some cases the amount of prism required will vary between distance and near vision. These require special solutions as we need to bring many disparate elements together in one pair of spectacles. One of the best solutions for these is actually one of the oldest lens designs, the ‘Franklin Split Bifocal’. At Hannaford Eyewear we are proud to manufacture our own Franklin Split Bifocals on site which means that you can be sure that we are working with you to reach your optimal vision.