Contact Lens Power Research Articles

Two simple intraoperative measuring techniques: Keratometry by contact lens and intraocular lens power verification

Two simple intraoperative measuring techniques: Keratometry by contact lens and intraocular lens power verification

Changes in hydrogel contact lens power due to flexure.

When a hydrogel lens is placed on the eye, its power may change because of flexing of the lens. The correcting power of the lens when on the eye can be calculated by assuming that the lens flexes to the shape of the underlying cornea. Actual measurements of the correcting power of Hydrocurve lens on the eye were not in agreement with the calculated values. Assuming that the front and back surfaces of the lens flex by the same amount, the presence of a fluid lens between the hydrogel lens and the cornea would account for this discrepancy. For minus lenses of moderate and high power, it was found that the change in power was in the direction of more plus; for low minus and all plus lenses, the change was in the direction of more minus. Under the conditions of the present investigation, correcting power measured with the lens on the eye was in agreement with the calculated value for regular-thickness Hydrocurve lenses of -2.00 D and thin lenses of -0.75 D. This is interpreted to mean that lenses of these powers conform to the shape of the cornea so that the fluid lens is thin and plano. The clinical implications are discussed.

The effect of saline solutions of various compositions on hydrogel lens dimensions.

The most common method currently used to store and maintain hydrophilic gel contact lenses is in normal (0.9%) saline solution, which is made up nightly by the patient. This study was designed to evaluate the effects of saline solutions of various compositions on the base curve, power, diameter, thickness and light transmission of spin-cast hydrogel contact lenses. Nine randomly selected Bausch & Lomb Soflens™Contact Lenses were stored in these various solutions for 40 days. The major changes found were in the base curve and light transmission of the lenses stored in hypertonic solutions and solutions made with tap water. The dimensions of the lens stored in normal (0.9%) saline made with distilled water changed the least. - These findings are similar to those reported for lathe-cut hydrophilic contact lenses and show the importance of storing hydrogel lenses in properly made normal saline solution.

Corneal Section Verification in Refractive Keratoplasty

A GREAT deal of difficulty has been encountered in verifying the vertex power of flexible contact lenses by conventional technique. This problem is related to the flexibility and hydration of the lens. Refractive keratoplasty includes the separation of a corneal disc from the body of the cornea. We, in an attempt to verify vertex power of this section, have encountered the same verification difficulties presented by flexible contact lenses. The solution of this problem has been the adaptation of a contact lens technique originated at the Institute of Macromolecular Chemistry of the Czechoslovak Academy of Science. Method A soft-lens centrifuge was designed to solve this problem. Figure 1 shows two brass fittings, two nylon covers, and one polymethyl methacrylate contact lens with a flat peripheral lip. The hard lens was manufactured in a series of different radii, each lens having a paraxial vertex power of zero. The hard lens, with

FORM AND POWER OF CONTACT LENSES

Although this paper concerns the form and power of contact lenses, what I have to say holds true of regular lenses as well. The reason, or rather reasons, why I specify contact lenses are these : In the first place, while the oddities in lenses which I am going to mention are theoretically true of all lenses, practically they are feasible mainly in the small, sharply curved contact lenses. In the second place, it was while talking about contact lenses with a number of physicians that I learned of a few erroneous ideas commonly held regarding lenses in general and contact lenses in particular. It was to point out and correct these errors that I was prompted to present this subject. Incidentally, there is a good reason why physicians who have not gone into the theory of lenses extensively should get a few false notions about contact lenses, and this is