Optimization and Lens Personalization Parameters
About optimization and its benefits
Optimization is the lens calculation process to meet a set of visual performance requirements when following a list of constraints such as frame dimensions and type, prescription, interpupillary distance and pupilar heights in order to generate in advance center and edge thicknesses and aesthetics improvement. This technique is possible for both minus and plus power lenses because will consider the smallest blank size necessary to obtain the minimum possible thicknesses for the final diameter of the lens, balancing weight of the paired lenses and optimized lenses only where it is needed.
Lens optimization requires following input data:
MATERIAL DATA
- Refractive index
- Base curve
WEARER DATA
- Prescription
- Back vertex distance (BVD)
- Pantoscopic angle (Panto)
- Wrap angle (Z-Tilt)
- Inset
- Near working distance (NWD)
FRAME DATA
- PD (pupillary distance) for far vision for RE and LE separately
- Pupil heights for RE and LE separately or segment heights (in case of bifocal lenses)
- Frame type
- Frame shape
- Frame sizes: values of HBox (horizontal eyesize) and VBox (vertical eyesize) of the shape in boxing system
- DBL (bridge width)
CORRIDOR OPTIM GROUP
14
15
16
17
18
DESIGN MFH
14 mm
15 mm
16 mm
17 mm
18 mm
RECOMMENDED FH FOR EDGING
15 mm
16 mm
17 mm
18 mm
19 mm
Optimization is the act of finding the best solution from all possible solutions, the purpose is making lenses as fully perfect, functional and effective as possible.
Personalization parameters
Every patient is unique and wearing lenses should provide maximum comfort, clear images and natural eye movement. In order to produce the optimum lenses for each patient, it is strongly recommended to measure personalized parameters; this way the lenses will be designed with optical center matching perfectly with patient’s pupil and eye movements.
PERSONALIZED PARAMETERS
- Back vertex distance (BVD)
- Pantoscopic angle (Panto)
- Wrap angle (Z-Tilt)
- Inset
- Near working distance (NWD)
POW measurements parts
a. Holding part
b. Frame supporting curve
c. Frame reference line
d. Wrapping Scale
e. Wrapping indicator
f. Pupilar distance scale
g. Vertex distance scale
h. Ruler for box measurements
i. Pantoscopic indicator
j. Pantoscopic scale
Back vertex distance (BVD)
Back vertex distance (BVD) is the distance between the front of the cornea and back side of the lens. Increasing or decreasing the BVD values changes the optical properties by moving the focal point forward or backward, it changes the power of the lens relative to the eye.
How to measure it:
Align the BVD scale in horizontal position with the wearer’s cornea and measure the distance from cornea to back side of the lens, and the result is BVD value.
Pantoscopic angle (Panto)
Pantoscopic angle (Panto) describes the angle formed by the lens tilt in the vertical plane relative to the patient’s visual axis in the as-worn position. Pantoscopic angle is important because if the visual axis does not coincide with the optical axis of the lens, the patient is looking obliquely through a point that includes an amount of unwanted astigmatism and induced spherical power.
How to measure it:
The patient should be standing in a normal posture wearing the frame to be measured. The device should be vertically aligned with the frame reference line facing the patient’s eyewear, both upper and lower borders of the frame have to touch the frame supporting curve and centered in accordance to the frame reference line. On the pantoscopic scale the pantoscopic indicator will return the pantoscopic angle value.
Wrap angle (Z-Tilt)
Wrap angle (Z-Tilt) is the frame parameter that describes the horizontal angle of the lens plane in front of the eyes.
How to measure it:
Using device opened as illustrated below, the frame should be positioned so the center of the bridge lays over directly the Personalization key center screw. Make sure the Lens Edge Reference Lines reaches both corners of the frame and value of BVD is revealed.
Inset
Inset is the horizontal displacement of reading area towards the nasal side. If it is not specified, the inset is calculated exactly for each wearer considering all individual parameters (IPD, BVD, NWD and prescription).
Near working distance (NWD)
Near working distance (NWD) is the distance from the lens to the typical reading position of the wearer.
Lens optimization requires following input data:
NOTE: When some of the personalization parameters are not available, the final lens will be calculated using standard values for those parameters that are missing.
Wrap angle measuring
How to measure Frame Wrap/Z-TILT:
Place the frame, top side down, over the highlighted gray frame image. Ensure the frame is placed as it is shown in the picture. Record the angle of frame wrap from the extreme right side of where the lens ends, not where the frame ends.
Standard shapes for optimization
Compensation
The wearer is experiencing visual discomfort and reduced visual acuity when looking at an area that not coincide with the optical center of the lens, because he is focusing on a zone with oblique aberrations. This aberration is affecting negatively lenses’ visual fields especially in medium high powers or wrap frames.
One of the main advantages of freeform lenses is they can be calculated and produced with compensated powers. This way the effect caused by oblique astigmatism is corrected and the wearer will enjoy visual comfort and wider visual fields.
Conventional lenses vs Compensated lenses
In case of conventional lenses, the power prescribed by the eye medical doctor or optometrist will be calculated and produced taking into consideration that light follows perpendicular to the back surface of the lens. But when looking at lateral gaze directions the light does not follow perpendicular to the back surface and produces oblique aberrations and the effect is reduced visual acuity. When measuring the powers of a conventional lens, the lensmeter will display the prescribed powers.
For compensated lenses, DRP2 technology will calculate and change the power at each point considering all wearer’s personalized parameters (individual or standard values) in every gaze direction at various distances. With this methodology, oblique aberrations are minimized and the wearer’s vision and comfort are improved by changing the power at the back surface in every point so the user will perceive the power he needs in every gaze direction. In this case, when the lens is measured, the lensmeter will indicate the compensated power and not prescribed one.
On the envelope, the label attached will include both prescribed and compensated powers.