lens surfacing is the process undergone in an optical which involves grinding a prescription power into a semi-finished blank.
the process has aided the improvement of the vision of the program vision 2020 as debated by the ODBRN group of eye care professionals.
A lens is a transparent medium that transfers light effects and enhances vision.
Types of the lens ;
Table Of Contents
Concave and convex lenses
- Single vision lenses
Kinds of lenses lens materials:
Surfacing a lens in the surfacing laboratory is the practical work of an optician, an optician is an eye care professional who specialized in the fitting, production, prescribing, and dispensing of corrective eye wears for the correction of refractive errors.
Kinds of refractive errors;
LENS SURFACING PROCESS:
The surfacing of the lens involves a tedious process of grinding a prescribed power into which has to do with the ability of an optician to grind a particular prescription giving to him or her into a semi-finished lens blank.
The process of surfacing a lens:
Axis marking; the axis marking of the lens is the first step taking while surfacing a lens blank using the axis marker to notify the axis of the lens. by placing the blank on-axis desk properly centered and match that axis foot mat to get your axis marked at the immediate center of the lens
The lens taping of the lens involves covering the immediate center of a lens with the tape for blocking.
This involves covering the lens with a blocker using a hot alloyed solution to hold the lens ready for grinding.
Lens grinding; the lens grinding involves the reduction in the size of the hence grinding the particular lens power into the lens using the grinding machine which is operated by setting the adjustment wheels according to the lab tool of the prescription.
Calculation of lab tool; the calculation of the lab tool for every prescription which involves using the clock like the tool to get the base curve of the lens Calculations
- Lap tool: to get your base curve (1st reading) you either add the gauge reading to the sphere (if it is of minus power) or minus the sphere from the base curve (if it is of plus power).
To determine the cross curve, the base curve reading would be added to the cylinder.
Eg. Rx: OD: +0.25/-0.50 X 90 GR: 600
OS: +0.50/-0.50 X 90
R.E = 600-025 = 575, then 575 + 050 = 625
L.E = 600-050 = 550, then 550 + 050 = 600
Therefore, the lapping tool reading for the right eye is 575/625 and for the left eye is 550/600.
- Decentration: achieved by either grinding in a prism or by moving the optical center of the lens. Dec = FFP – PPD/2
E.g.: Aloha has a PD of 68mm to be fitted into a lens of PD 70mm. how much Decentration would be required and in what direction?
Solution: Dec = FPD – PPD/2 = 70-68/2 = 2/2 = 1mm.
Since the decentration is positive, it will be inward.
iii. Minimum Blanc Size (MBS)
MBS = ED + 2(DEC)
E.g. A = 52mm, PPD = 67mm, DBL = 17mm, ED = 55mm
Solution: MBS= ED + 2 (DEC) = 55+2(1) = 57.
- Transposition: It is simply converting the lens prescription from minus cylindrical notation to plus cylindrical notation. The optical properties and power remain the same.
E.g. Rx +0.25/-0.50 X 90 wills Lens Clock
This is a mechanical handheld dial indicator that is used to measure the dioptric power of a lens. A lens clock measures the curvature of a lens surface. A lens clock measures the curvature of the lens surface but gives the result as an optical power in diopters assuming the lens is made of a material with a particular refractive index. It is called a Geneva Lens Gauge, Lens Measure, or Lens Clock.
A lens generating machine is an optical device used to grind in lens prescription into the Blanc. It works with the aid of compressed air for a firmer grip of the button. It has different wheels serving different purposes; the sphere, cylinder, and axis wheels respectively. It uses water and has a circulatory system; i.e. the used water is brought up again after the cut-out lens is filtered from it.
This is a machine used for the smothering of a lens after its prescription has been generated. It makes use of compressed air too for gripping the lapping tool and also to aid the pin holding down the button.
In advanced laboratories there are often two; one for polishing and the other for fine. Contrary to the previously mentioned, one could be used for both, whereby the water channel after polishing with water. When it’s time for a fine, the waste pipe could be disconnected to avoid the slurry wasting, a bucket or bowl could then be placed for collecting the slurry as the process is in progress. The machine works with a timer often programmed with about 45 seconds maximum for a period.
This machine is of two kinds; automatic and manually operated. It is used for the cutting of lenses after surfacing before they are fitted into the desired frames. The automatic edger works with little aid.
Lens surfacing is general laboratory activity that involves grinding the power of a prescription into a semi-finished blank to satisfy its corrective purposes and increase vision.