Point of Wear Measurements
If you want to experience a higher level of differentiation in your eye care needs then you need to trust the expertise of an eye care professional. You will recognize the in store difference and experience when an eye care professional will help customize and personalize your eyeglasses by considering point of wear measurements for your visual needs. As lens technology advances, customized measurements is important to deliver the full potential of ophthalmic lenses that will enhance your visual performance and vision correction experience. Only through the use of accurate and precise position of wear measurements and values will you be able to enjoy the fullest visual benefit of your Optometrist’s prescription (Rx).
With the advancement of free form manufacturing, it is now possible for real time lens design optimization that considers every aspect of how an individual’s lenses are positioned in front of their eyes. In order for your lenses to be optimized to enhance your comfort requires your eye care professional to provide the most fitting parameters when completing your eyeglasses.
What is Position of Wear?
Position of wear (POW) describes how your fitted eyewear has repositioned the lenses compared to the lenses used to test your vision in the exam room.
Position of wear is not all about adjusting your eyewear or sunglasses to make them fit as comfortable as possible. Occasionally, some of us may feel if our frames are fitted in a specific way, we see better. A good adjustment can be a solution, but for best visual satisfaction requires analyzing the position of wear and measuring the points of wear.
Benefits of Position of Wear
There has been significant increases in patient satisfaction when eye care professionals employ point of wear measurements. Optometrists have seen a significantly lower non-adapt rate when progressives are optimized with point of wear measurements. Since Opticians are noticing a variety of modern frame designs, shapes and styles, they can tell if visual performance will be affected if the lens selection and recommendations are not properly discussed. If you choose a frame with high wrap or a lot of pantascopic tilt, eye care professionals recommend that optimized lenses with proper measurements is essential to enhance visual performance and quality.
Types of Point of Wear Measurements and what to Expect
There are two ways to take point of wear measurements: manually and/or digitally. Before conducting the measurements, eye care professionals will make sure the frame style selected is properly fitted to the wearer’s preferred position. Once frame adjustments are made and the wearer is happy with the frame’s position, measurements can be taken.
Pupillary Distance (PD) – is the length between your eyes from your right to left corneal reflex when your eyes are fixated at a certain distance. There are generally two types:
- Distance PD or Far PD is measured when your eyes are fixated straight ahead and not converged.
- Near PD is measured when your eyes are converged at a single near point. Near PD can be measured at working distances of 25 cm, 33.3 cm or 40 cm. Working distances depend on the visual task such as reading or using the computer. Consult with your eye care professional to learn more.
Your PD can be taken by your eye care professional with a pen light and ruler, digital pupilometer, or advanced POW software and equipment. Multiple measurements will be taken to ensure accuracy.
Vertex Distance – is the length of the back of the lens to the tip of your cornea. How far or close a frame sits away from your eyes can affect your visual performance. This measurement is important for high power, free form, and/or high definition digital lenses.
Pupil Height or Ocular Center (OC) Height – is the distance of your corneal reflex to the bottom of the frame. Wearer’s posture and position of the frame is important to ensure accuracy. OC is essential with large frame shapes and when your eyes are not completely centered in the frame.
Seg Height – is a measurement commonly used for progressives and bifocal/trifocal to determine the vertical length from the beginning of the progressive addition to the lowest bottom of the lens in your frames.
Pantoscopic Tilt – is the amount of vertical angle between a wearer’s primary gaze and the intersection of the same with the plane of the lenses. It can also be explained as the rotation of lens bottom towards the cheeks. Pantoscopic angle is the angle of the frame front to the temple. The most important aspect is to make sure the wearer’s facial plane is as vertical as possible before the measurement is made. If Pantoscopic tilt is not accounted for, it can cause significant visual distress and discomfort.
Frame Wrap Angle (also known as face form and panoramic angle) – is the measurement to determine amount of wrap angle of the frame. An important aspect of wrap fitting is eyelash clearance. Having lenses that do not account for frame wrap can cause distortions, lens mounting and cosmetic concerns.
Base Curve – is the measurement to determine the amount of curvature of a lens in dioptric power. This is important to match the frame for proper lens mounting and to optimize lens performance based on your eye’s visual needs.
Frame Measurements – we also double check and provide all frame measurements to the lab to ensure proper lens manufacturing and fabrication of the lenses to securely fit into your frame.
How does Point of Wear Optimize your Prescription (Rx)?
The main benefit of point of wear optimization is to deliver the best representation of the prescription determined in the exam room. Compare the fitting values of the lenses used in an exam room versus how eyewear is fitted:
- Vertex Distance – typically averages 13 to 14mm.
- Pantoscopic Tilt – phoroptor lenses or trial frame are straight up and down, i.e., zero pantoscopic tilt.
- Frame Wrap Angle—Lenses are held in an absolutely flat plane, i.e., zero face form angle.
- Pupillary Alignment—Particularly with phoroptors, they accommodate PD in a binocular manner, and therefore cannot make allowances for monocular eye separation differences.
- Pupillary Height—The patient’s eye is typically aligned with the geometric (optical) center of the phoroptor’s test lenses and does not account for frame shape which can be larger or smaller.
- Vertex Distance – Fitted values can range from as close as 8mm to as far as 20mm.
- Pantoscopic Tilt- Fitted values range from 0 to 15mm; typically 6 to 8mm.
- Frame Wrap Angle – Also known as face form, fitted values range from 0 to 10 degrees. Wrap angle for sunglasses can range from 12 to as much as 25 degrees.
- Pupillary Alignment – Ideal measurements for an individual are monocular values. Differences between the eyes may range up to 4mm.
- Pupillary Height – Fitted values often find the pupil placed in most lens shapes between 3 and 7mm above the geometric and in some cases below the optical center of the frame and lenses.
By doing point of wear compensation takes the differences between exam room and fitted eyewear into account. These additional measurements allow the lens manufacturer to recalculate the prescription and make adjustments to optimize the lens quality and performance.
Both single vision and progressive lenses can benefit from point of wear optimization. Especially for stronger prescriptions, greater cylinder power and fitting situations where the wearer’s pupil is significantly above the mechanical center of the frame can greatly benefit from POW optimization. For progressive lenses, the reading zone is most improved with POW optimization.
Why Visit Us for a Personalized Experience?
Visit us to get the full experience of custom and personalized eyewear designed for you by our eye care professionals. Based on your visual and eyewear needs, we will provide top service such as customized prescriptions for any specific or all visual tasks, point of wear measurements, lens and frame recommendations based on your unique lifestyle, frame adjustments, frame repairs and much more. Buying online can never offer such detailed service to ensure your satisfaction and quality of the eyewear you receive. Visit or call us if you have any questions and we would love to help.