CUSTOM CONTACT LENSES
Virtual Fitting of standard diameter RGP lenses using a topographer.
Take a minimum of 2 images of each cornea and note if there is any difference. If little or non then proceed to the virtual fitting.
Note the parameters of the virtual lenses should be entered into the computer, for the full range of base curves diameters and peripheries.
Click on lens fitting and note fluorecein pattern in the centre, this pattern will show as green if thicker than 0.30 microns and will show as a dark area if less than that.
Ideally you want minimum clearance. Which will show as dark or just light green. The periphery should show as a clear green band with no touch at the edge.
The area between the base curve and peripheral curve will show a blending with minimal touch.
Note when choosing a diameter, it should be about 1 to 2 mm,s less than the corneal diameter (HVID)
For corneas with 2 mm or more of toricity, it may be worth considering a toroidal base curve to assist with stability. Use the Custom base curve selection software to determine the powers of the toric or bitoric lenses.
For high powers increase diameter by 1/2 mm and check fluoresceine pattern.
Note topographers vary as to how to achieve a good fit, read the manual for your particular model.
Take K readings, 2 in each meridien (should be close if not redo) and note axis and readings.
Note spectacle RX, vertex distance and axis.
Utilising the Custom fitting software, enter this information and note the following..........
1/ residual cylinder
2/ the corneal cylinder difference and axis.
3/ If suggested goto a Toric design
4/ In the toric design enter the base curves you want.
5/ note if using a toric base curve what is the residual cylinder, if neccessary goto a bitoric.
6/ call custom who will advise on lens diameter and material.
7/ Due to the high oxygen permeability of modern materials, the diameter can be as large as you need to obtain centration and comfort.
Note pupil size in normal light, HVID and PA.
If the patient is a previous wearer of soft or RGP lenses it is advisable to get the patient to leave their current lenses out for 3 or 4 days prior to measuring the cornea.
Special consideration should be given to wearers of back surface aspheric lenses, as there is usually a distortion of the corneal shape.
(refit using the original K,s and a larger diameter for stability, use a high DK material and check topography monthly until original K,s have become established.)
K's and RX