Single vision boost lenses are designed to relieve eye strain at near focus. The demands of today’s digital devices can cause eye strain for all ages. These lens designs incorporate the benefits of a single vision lens with a minor dynamic ADD power at the bottom. The dynamic ranges for the designs span from about … Continued
Most lens manufacturers offer varying designs of computer progressives with many similarities in designs. These manufacturers each offer different computer lens designs within their portfolio. To fit a computer progressive, first determine the most important distances that the patient needs. Next, select a lens design that offers these distances. Then fit the lens in a … Continued
Just as you could put near at the bottom of a lined bifocal and intermediate at the top, you could also create something similar in a no-line design. These are often called computer lenses or office lenses. They come in multiple designs to match the needs of your patient. They can have near at the … Continued
Now that you understand the calculations, there are many custom pairs of eyewear that you can make for nearly any task. Musicians, speakers, and hobbyists may all have very specific distances that they need to work at. Understanding the exact distance where they work is the first step. This process begins by uncovering the patients’ … Continued
Let’s calculate the ADD power for a person in their mid-40s who needs glasses for computer work at an intermediate distance of 60 cm. Age-based ADD power: Mid-40s typically require +1.00 to +1.50 D for standard near tasks at 40 cm. For this example, we will assume that the doctor prescribed a +1.50 for the … Continued
Calculate the difference in demand power: the standard demand is +2.50 diopters at 40cm. This is important because the doctor will typically prescribe the ADD power (often based on age) to this distance of 40cm or about 16 inches. In order to calculate the difference in the demand power, subtract the result of the above … Continued
It is assumed that an average patient needs +2.50 diopters of demand power in order to read at 16 inches or about 60cm. As we age, we lose this accommodative ability of this demand power. For example, a patient who is prescribed an ADD power of +1.50 is assumed to have about +1.00 of accommodation … Continued
Adjusting for Specific DistancesThe ADD power is also influenced by the specific distance at which the near tasks are performed. Here’s a step-by-step method to adjust the ADD power for different working distances using the formula for dioptric demand: Determine the Near Working Distance:Standard near working distance is typically around 40 cm (16 inches). This … Continued
Presbyopia is an age-related condition where the eye gradually loses its ability to focus on near objects. The ADD power needed for reading or other close tasks generally increases with age. While individual needs can vary, here are typical guidelines that the eye doctor may refer to as a starting point when prescribing the ADD … Continued
This method involves using a formula to calculate the dioptric demand at each distance. In order to understand dioptric demand, we will look at the accommodative ability for each age group and the formula for demand.
1. Understand the multifocal prescription: A typical multifocal prescription includes values for distance vision and an ADD value for near vision. The format looks like this: OD (Right Eye): -2.00 (distance) +2.00 (add) OS (Left Eye): -1.50 (distance) +2.00 (add) 2. Identify the distance prescription: The distance part of the prescription is used for … Continued
Calculating the intermediate prescription from a multifocal (bifocal or progressive) prescription involves adjusting the prescription to focus on intermediate distances, typically around 20-30 inches, which is useful for tasks like computer work. This calculation typically involves using half of the ADD power value provided in the multifocal prescription. However, the patient’s needs may vary based … Continued
To calculate the intermediate power, there are two common methods: ratio and dioptric demand. The ratio method involves multiplying the prescribed near ADD power by a ratio which is related to the working distance. Basically, the ratio assumes that 16 inches or 40cm the percentage of add power is 100% (Be sure to check with … Continued
If the bifocal prescription includes a cylindrical correction (for astigmatism), you need to include this in the reading prescription. The ADD power value only affects the spherical component. This slide shows a sample prescription with astigmatism correction converted to single vision near focus. While the calculation is straightforward, it’s always a good idea to have … Continued
In order to derive the prescription for near vision from the bifocal prescription, simply combine the ADD power with the distance power to get the net near power. For a myope, the resulting number may be a negative number, and conversely it may be a higher positive number for a hyperope. In this particular scenario, … Continued
A typical bifocal prescription includes values for distance vision and an ADD power for near vision. The format looks like this:OD (Right Eye): -2.00 (distance) +2.00 (ADD)OS (Left Eye): -1.50 (distance) +2.00 (ADD) The distance part of the prescription is used for seeing far away. In the example above:OD: -2.00OS: -1.50 The ADD power value … Continued