Lenses what is bc

Fortunately, fitting soft lenses is a relatively simple task. Unlike GP lenses, for which several parameters must be tailored for patients, many soft lenses provide choices of, at most, two different base curves and a single diameter. Their pliability and flexibility allows to them to fit virtually the entire population, making them nearly one-size-fits-all.

Studies show that a single base curve of 8. Table 1 displays these parameters for some commonly worn soft contact lenses. By employing an optimal base curve and diameter, these mass-marketed soft lenses have a high probability of achieving a good fit when prescribed for a random individual in the population. This convenience is quite advantageous for practitioners because it can substantially reduce the time it takes to find a good-fitting soft lens.

Patients can also benefit from this by avoiding the need to endure round after round of trialing and re-trialing several different pairs. However, there is a cost for this convenience. When contact lenses fit reasonably well on almost everyone, the act of fitting and assessing the fit of a contact lens becomes an overlooked and ignored process. When this occurs, contact lenses themselves become viewed as a commodity rather than as a medical device.

In this day and age, it is extremely easy for existing and potential contact lens patients, or even non-patients, to obtain contact lenses and contact lens education online. There are many distributors that sell them online without ever requiring a prescription from the buyer. There also are numerous resources available on popular video hosting sites, some of which unfortunately feature unqualified and untrained persons who erroneously educate the public on how to use contact lenses.

Some of these videos have literally been viewed, at minimum, hundreds of thousands of times, suggesting their wide and far-reaching impact. Although, to be fair, there are some videos that advise properly and emphasize the importance of visits to an eyecare professional.

However, in the former, the spread of misinformation is a disservice to the general public. Interestingly, many of these videos fail to discuss how a contact lens should fit on the eye or what to do if the contact lens does not fit. For practitioners, it may be easy to neglect properly assessing the fit of a soft lens because it is expected to fit well.

While parameters are quite easy to choose from, we should not expect that any soft lens can be applied on the eye and perform well. It is a well-known fact that comfort is a major driving force for contact lens success, with discomfort being the primary reason why patients discontinue lens wear. A soft lens that does not have sufficient coverage may irritate the cornea with its edge. Soft lenses that are poorly fitted may result in decreased ocular surface integrity.

Tight-fitting lenses, although appearing to fit more comfortably, 2 , 9 , 10 when excessively tight will reduce tear exchange, leading to a buildup and trapping of metabolic waste and toxins under the lens.

For these reasons, the process of contact lens fitting and the assessment of contact lens fit are both vital to healthy contact lens wear. The fitting of soft contact lenses essentially comes down to selecting a lens with the appropriate sagittal height.

It was thought that steeper corneas theoretically exhibited a higher sagittal height and should therefore be fitted with steeper lenses. Likewise, it was thought that flatter corneas with the same given diameter exhibited lower sagittal height and should therefore be fitted with flatter lenses Figure 1. Figure 1. The idea is similar with contact lenses, where r1 and r2 would be base curves and d would be lens diameter. Axis AX : Astigmatism is caused by the irregular curvature of the eye; the axis is a figure which determines the angle of the correction needed in order to see clearly.

The Axis is always a number between 0 and degrees. Addition ADD : If you suffer from presbyopia it affects your near vision, the Addition figure determines what level of correction you need to be able to see clearly at a close distance.

This is a number between 0. Dominant : Multifocal or bifocal contact lens wearers will see that the correction is determined by a dominant and non-dominant eye. This is the dominant figure, and is usually marked with a "D" and "N" to express which eye is which. Contact Lenses by Brand. Contact Lenses by Type. Eye Care. How to read your contact lens prescription Your contact lens prescription allows you to purchase contact lenses that match your requirements from opticians or online suppliers.

Do I need a prescription for contact lenses in the UK? Desio brands are available in two curvatures and sizes and these measurements might not be included in the prescription. Account Login Register. Skip to Content. Compare Products. Darker Lighter. Home how to read your prescription. Myopia Commonly known as near-sightedness or short-sightedness is a condition of the eye where the light that comes in does not directly focus on the retina but in front of it, causing the image that one sees when looking at a distant object to be out of focus, but in focus when looking at a close object.

The opposite of myopia is hyperopia long-sightedness. Hyperopia or Hypermetropia Commonly known as being farsighted or longsighted, is a defect of vision caused by an imperfection in the eye often when the eyeball is too short or the lens cannot become round enough , causing difficulty focusing on near objects, and in extreme cases causing a sufferer to be unable to focus on objects at any distance. As an object moves toward the eye, the eye must increase its optical power to keep the image in focus on the retina.