References in periodicals archive ?
b) An aspherical design with BOZR of 7.65 and a TD of 10.4mm
c) A spherical design with a BOZR of 7.65 and a TD of 8.5mm
The measurement of central corneal curvature by keratometry purely for the purpose of choosing the BOZR of the initial soft lens is, therefore, not particularly helpful.
A common theory is that as a lens dehydrates there is a steepening of the BOZR, the consequences of which are a reduction in lens movement.
Typically, the BOZR is reduced (creating a steeper curve) to create a tighter fit to eye as a result of an increase in lens sagittal depth (sag), and increased to loosen the fit due to a decrease in lens sag.
* If a lens is fitted steeper than K, a positive tear lens is created, requiring more negative power in the over-refraction to neutralise the effect (that is the tear lens power increases by +0.25 for each 0.05mm that the BOZR is made steeper, therefore an extra -0.25 over-refraction) (see Figure 1i
* For BOZD between 7.00 and 7.40, each principal BOZR is fitted 0.05mm flatter than K readings
Generally speaking, practitioners using 'in house or system lenses' only have to deliberate about the total diameter (TD), back optic zone radius (BOZR) and back vertex power (BVP).
* For toric corneas with 1.00-2.50 D of astigmatism (0.2mm and 0.5mm difference between K readings), the lens should be fitted with a BOZR that is 2/3 of the way towards the flattest K
b) Alter the BOZR to 7.90mm and reduce the maximum wearing time
a) Back optic zone radius (BOZR) and lens thickness b) Back optic zone radius (BOZR) and back optic zone diameter (BOZD) c) Back optic zone radius (BOZR) and back vertex power (BVP) d) Back optic zone diameter (BOZD) and lens thickness
If excessive rotation is observed, then the BOZR should be steepened and the TD increased.