Back Vertex Compensation Calculator

FAQs

How do you calculate the back vertex distance? The back vertex distance (BVD) is typically measured in millimeters (mm) and is the distance from the back surface of the spectacle lens to the cornea of the eye. It’s calculated by subtracting the thickness of the lens from the total length of the glasses arms or the bridge.

How does back vertex distance affect prescription? Back vertex distance affects the effective power of the lens. As the distance increases or decreases, the power experienced by the wearer changes. This alteration can impact the accuracy of the prescription, particularly for higher power lenses.

What is the normal range for back vertex distance? The typical range for back vertex distance in eyeglasses is between 10mm to 14mm, although it can vary based on the design of the frames and individual characteristics of the wearer’s face.

What is vertex compensation? Vertex compensation is the adjustment made to the prescription to account for the change in lens power caused by the back vertex distance. It ensures that the wearer experiences the intended power despite the distance between the eye and the lens.

What does BVD 12 mean for glasses? A BVD of 12 for glasses indicates that the back surface of the lens is 12mm away from the cornea of the eye.

Why is the back vertex distance important? Back vertex distance is crucial because it affects the power of the lens and thus the accuracy of the prescription. An incorrect back vertex distance can lead to visual discomfort and distortion.

What happens if PD is off by 2mm? A deviation of 2mm in the pupillary distance (PD) can cause visual discomfort, decreased clarity, and potentially induce headaches or eyestrain due to improper alignment of the optical centers of the lenses with the eyes.

What is the rule of thumb for vertex distance? The rule of thumb is that for every 3mm change in back vertex distance, the effective power of the lens changes by approximately 0.25 diopters.

What is the average BVD? The average back vertex distance typically falls around 12mm, but this can vary depending on factors such as frame design and individual facial characteristics.

What does vertex mean on glasses prescription? Vertex on a glasses prescription refers to the distance between the back surface of the lens and the cornea of the eye, typically measured in millimeters.

What changes when vertex distance changes? When vertex distance changes, the effective power of the lens changes, impacting the clarity and comfort of vision for the wearer.

What is a compensated RX? A compensated RX is a prescription that has been adjusted to account for factors such as vertex distance, pantoscopic tilt, and frame wrap, ensuring accurate vision correction.

What is the back vertex power? The back vertex power refers to the effective power experienced by the wearer due to the combination of the lens power and the back vertex distance.

What is the back vertex power of a contact lens? The back vertex power of a contact lens is typically zero because the lens sits directly on the cornea, eliminating the need for compensation due to vertex distance.

How do I read my eye prescription? Eye prescriptions include information such as sphere (Sph), cylinder (Cyl), axis, and sometimes additional parameters like prism and near addition. The values indicate the required lens power and correction for any refractive errors.

What is the BVD on a Specsavers prescription? BVD on a Specsavers prescription refers to the back vertex distance, specifying the distance between the back surface of the lens and the cornea of the eye.

What does BVD 11 mean on an eye prescription? BVD 11 on an eye prescription indicates that the back vertex distance is 11mm.

What is BVD 11 eyes? BVD 11 eyes may refer to a prescription indicating a back vertex distance of 11mm for each eye.

Is 20/12.5 vision good? A visual acuity of 20/12.5 is excellent, indicating that you can see at 20 feet what a person with normal vision can see at 12.5 feet.

How do you measure vertex glasses? Vertex glasses are measured by determining the distance between the back surface of the lens and the cornea of the eye, typically using specialized equipment in an optical laboratory.

What adjustment do you make to increase pantoscopic tilt? To increase pantoscopic tilt, you would adjust the angle of the frame so that the top of the lenses tilts away from the face and the bottom of the lenses moves closer to the cheeks.