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. Subsequently, one may also ask, is Base Curve important with contact lenses? Optician's answer. A base curve measurement represents how curved your contact lens is. This measurement affects how a contact lens sits on the front surface of your eye, and is quite important. Changing this value, even by a small amount, can cause blurred vision and discomfort if it's not suitable for you.
Secondly, is there a difference between 8. The difference between an 8. Contacts are the same as shoes in a sense. Matching the curvature or diameter of a different brand does NOT mean it will fit the same, or even fit close sometimes. Most patients will fall in the range of 8.
Typically its better for soft lenses to fit flatter than steeper. Soft lenses cover the entire cornea and actually extends past the limbal area by a few mm. Acuvue Oasys contacts come in 8. There is a difference in fit of the 8. Yes they do matter. The BC, or base curve , is measured based on your cornea's curvature. Wearing the wrong size of contact lens may not worsen your vision but definitely will cause discomfort. Here we will go through with you what will be the wrong base curve and wrong diameter symptoms.
Estimated reading time: 5 minutes. Some did not aware that wearing poorly fitted contact lens can cause serious harm to your overall eye health. This condition can cause a person to be forced to wear eyeglasses or undergo laser vision correction. People with contact lens intolerance are not able to apply lenses to their eyes without pain, or wearing them for more than a few minutes.
But if the lens is moving too much, it can be telling you that the contacts is too big for your cornea. Having different materials of contact lenses can also make a difference in the way the lens fits. Compared with soft contact lenses, gas permeable contacts may move even a little more than that, which is two to three millimeters.
It is necessary to trace the reasons for the discomfort so that you could make an intelligent choice the next time, you are offered vision correction lenses. Diameter is yet another factor but patients have reported problems of symptoms more with wrong base curve than size. Key Words:. Palabras Clave:. Full Text. Introduction During the evolution of soft contact lens fitting, base curve radius selection has been always a matter of concern. Methods We conducted a prospective, double-masked, randomized and clinical comparative study.
Table 2. Criteria for assessing the lens movement. Grade Descriptor Explanation -2 Extremely inadequate The lens does not move on blink. Figure 1. The authors have no proprietary interest in any of the materials mentioned in this article. Young, S. Poorly fitting soft lenses affect ocular integrity. CLAO J, 27 , pp.
Holden, S. On the confortmity of soft lenses to the shape of the cornea. Am J Optom Physiol Opt, 58 , pp. Bibby, A. A model to explain the effect of soft lens design specifications on movement. Am J Optom Physiol Opt, 60 , pp. Int Eyecare, 2 , pp. Effects of base curve on the fit of thin, mid water contact lenses. ICLC, 20 , pp. Dumbleton, N. Keir, A. Moezzi, Y. Feng, L. Jones, D. Objective and subjective responses in patients refitted to daily-wear silicone hydrogel contact lenses.
Optom Vis Sci, 83 , pp. Efron, N. Brennan, J. Currie, J. Fitzgerald, M. Determinants of the initial comfort of hydrogel contact lenses. Am J Optom Physiol Opt, 63 , pp. The critical initial comfort of soft contact lenses.
Clin Exp Optom, 80 , pp. Wichmann, I. Algorithm AS An efficient and portable pseudo-random number generator. Applied Statistics, 31 , pp. Efron grading scales for contact lens complications. Contact Lens Complications, pp. Keay, D. Sweeney, I. Jalbert, et al. Optom Vis Sci, 77 , pp. Covey, D. Sweeney, R.
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