DIOPTER / BASE CURVE
Standardized base curves were designed to conform to Oswalt’s equation (blue rectangles). Modern base curves have shifted downward, due to cosmetic preference for flatter lenses (red lines).
The Tscherning Ellipse above indicates the two lens base curves that are optically ideal for each dioptric power. The top curve represents Wollaston’s 1804 calculation. The bottom curve represents the flatter, more practicable calculation, introduced by F. Ostwalt in 1898, which became the basis for standardized lens base curves. Though modern base curve recommendations are slightly flatter due to cosmetic preference, Ostwalt’s calculation is still recognized as optically ideal.
IDEAL BASE CURVE
When the power of a lens is paired with its ideal base curve, the wearer enjoys clearer vision with minimal oblique astigmatism. When the base curve falls outside the ideal range for a given power, the wearer’s off-axis visual acuity diminishes precipitously. This has increased implications in a progressive lens, because the reading zone can only be accessed at an oblique angle. Patients with high add prescriptions are even more likely to feel confined by this limitation.
MULTIPLE IDEAL BASE CURVES
|Multiple Ideal Base Curves
A progressive lens has many powers from distance to near, hence it would be ideal for base curve to increase in diopter from top to bottom.
Digital lens technology has allowed the creation of progressive lenses out of single vision lens blanks. But pairing lens power to ideal base curve in this situation is complicated — and compromises are inevitable. A progressive lens has many powers, hence it has many ideal base curves, increasing in diopter from top to bottom. The distance zone power calls for a flatter base curve, while the near zone power calls for a steeper base curve.
However, when a free-form progressive lens is processed from a single-vision lens blank, the various powers must share a single base curve, one that may not be ideal for all zones. The Camber lens blanks offer an elegant solution that represents the next step in digital progressive technology. Magic Fusion® lenses, made from Camber lens blanks, offer wearers spacious, more comfortable fields of vision, in both the distance zone and reading area.
What is Camber
Camber is a name for a special, continuously increasing base curve.
Delivery times for different Fusion® lenses
Current delivery time in working days:
Gray & Brown
|Transitions® Signature™ VII
Gray & Brown
|1.53 Trivex||7||Coming soon||7|
Blanks for lenses with delivery time of up to 4 working days are in stock.
Blanks for lenses with delivery time of up to 7 working days are ordered with YoungerOptics.
Colouring: delivery time extends for 1 working day.
Mirror: delivery time extends for up to 4 working days.