Contact lens and process for fitting

Abstract

A contact lens with a central region (10) that is optimally less than approximately 1.9 millimeters in diameter and that is preferably overcorrected by approximately 25% to 100% over the correction needed for reading. Unexpectedly, the central region (10) does not impair distance vision, but compensates for presbyopia and therefore alows a user to focus on objects within a range of near and intermediate distances. A method for fitting the contact lens is also provided.

Description

[0001] This invention relates to a contact lens that restores the ability to focus on objects within a range of distances near to the user (referred to as "natural accommodation"), while retaining the ability to see distant objects. More specifically, this invention relates to a contact lens with a conventional spherical concave surface conforming to the curvature of the eye (base curve) and having a non-conventional convex surface (optic curve) combining spherical and non constant aspherical curvature resulting in an optical system that provides true monocular presbyopic correction (correction of presbyopia in each eye independently, instead of partial or full distance correction in one eye and partial or full near correction in the other) and restores the phenomenon of "natural accommodation." Additionally, the invention affords a methodology of fitting that substantially reduces the skill and experience required by the contact lens fitter to a very basic level while affording a h...

AI Technical Summary

Benefits of technology

[0031] The invention incorporates both concentric and aspheric design principles and can be produced with a high add power correction or a low add power correction. In addition, the lens system offers two accommodation zone diameters for different sized pupils to achieve maximum near point acuity without reduction in distance visual acuity.

[0033] The accommodation zone should cover approximately 50% of the pupil area for maximum success in distant, intermediate and near visual acuity. The accommodation zone functions to restore the phenomenon of natural accommodation by creating a very small area of over magnification in the center of the pupil of approximately 25% to 100% over the near vision correction required by the indicated reading add power. Surprisingly, distance vision will not be substantially impaired if the accommodation zone covers 50% or less of the pupil area. Further, the function of natural accommodation will be restored to an unexpectedly great extent.

[0034] Although the inventor is not sure (and the validity and enforceability of any patent issuing hereon shall not be affected by the accuracy or inaccuracy of this explanation), the inventor believes that, in near vision, a user's pupils constrict, so that the accommodation zone occupies a large enough portion of the pupil area for the accommodation zone to become effective. Normal reading correction is prescribed for approximately 15 inches (approximately 38 centimeters). Accordingly, the overcorrection of the accommodation zone (sweet spot) allows the user to see from 8 inches to 15 inches, thus restoring the function of natural accommodation. In distance vision, however, the pupil will be normally dilated, so that the accommodation zone is small enough that the brain ignores the image generated by it. The constriction of the pupil for near vision is known as "accommodative pupil response."

[0035] The accommodation zone is blended to the distance zone 4 via two zones of non constant aspherocity which allows true monocular correction of near, intermediate and distant vision. Near vision correction, when tested at the standard distance of approximately 15 inches (approximately 0.38 centimeters) offers normal best corrected acuity and when reading material is brought closer to the eyes, up to about eight inches (approximately 20 centimeters), near acuity remains stable and often improves due to the increased near power created by the sweet spot.

[0036] Due to the non constant aspheric transition from the sweet spot to zone 4, adaptation problems associated with prior designs of concentric or aspheric multifocal contact lenses are substantially reduced or eliminated completely.

[0038] The fitting of lenses according to this invention requires accurate centering of the lens over the pupil of the eye in order to achieve the expected results. To determine the location of the sweet spot relative to the pupil is often difficult because the pupil may not be aligned with the center of the cornea or for other reasons. Thus, the invention also incorporates the use of a diagnostic trial lens with a white ring corresponding in diameter and location to the sweet spot. The exact position of the center of the contact lens can be determined and the relative position of the sweet spot to the pupil and the percentage of pupil covered by the sweet spot is easily observed. The use of the diagnostic lens allows the fitter to very quickly determine the proper sweet spot size, which increases the chances of successful fitting. For example, if the accommodation zone does not align within the pupil, the fitter knows that the standard lens design will not work and a custom lens design with an offset accommodation zone will be required.

Problems solved by technology

Normally between the ages of 40 and 45, presbyopia or old sightlessness is brought about by loss of elasticity of the crystalline lens of the eye, causing blurred vision at near points due to the reduction of the ability of the eye's natural lens to accommodate the changes in curvature necessary to focus on both near and distant objects.

These contact lenses, although very innovative in design, met with only limited success because the only readily available material was Poly Methyl Methacrylate (Plexiglass), also known as PMMA, which does not transmit oxygen.

As bifocal and multifocal designs of the period were quite thick and heavy compared to conventional distance correction contact lenses, these presbyopic contact lenses were uncomfortable to wear for substantial periods of time.

Additionally, the fitting of these bifocal and multifocal contact lenses required considerable time and skill on the part of the contact lens fitter.

However, lens thickness and resultant patient discomfort continued to be a problem.

Alternating vision lenses have proven to be successful in RGP designs, but have met with little success when designed in soft contact lenses.

Perhaps the reason that alternating vision soft contact lens designs were not as successful as the same design concept in RGP materials was because lens translation is necessary for this design to be successful.

Soft lens material by its nature caused this modality to fail as there was insufficient rigidity in the soft lens to remain properly positioned on the lower eyelid and often the lens would slip underneath the lower eyelid during translation.

As alternating presbyopic designs proved to be unsuccessful in soft contact lens designs, most of the development work with soft contact lenses was done in the area of simultaneous presbyopic correction with concentric designs or aspheric designs.

However, conventional monovision becomes less satisfactory as presbyopia becomes more advanced because the needed add power increases and visual accommodation has deteriorated further, so that the visual imbalance exceeds the brain's ability to select the desired image from the appropriate eye.

However, if aspheric corrections are increased in attempts to achieve higher add powers, the images become too different for the brain to suppress the undesired images, resulting in blurred vision.

Even at add powers of +0.75 to +1.25 diopters, many patients suffer some blurring or ghosting with multifocal contact lens designs because their brains are not able to completely separate the desired image while simultaneously completely suppressing the undesired images.

However, this creates even more blurring and ghosting.

Still, only limited success is achieved because providing add power of +0.75 to +1.25 (or more) usually results in reduced distance acuity.

When attempting to fit moderate to mature presbyopes, this modified monovision almost always results in a visual compromise similar to that of conventional monovision.

Although concentric center add multifocal designs have the ability to correct higher add power requirements, most individuals fitted with this type of lens experience moderate to significant amounts of visual discomfort due to ghosting of images or a 3-D effect, at near distances.

These effects diminish with adaptation, but still cause a high portion of wearers to discontinue the use of this type of presbyopic contact lens.

The reality of the existing art of presbyopic correction with simultaneous vision contact lenses is that no currently available lens system, be it aspheric or concentric, provides monocular multifocal correction for moderate to mature presbyopia.

Additionally, no currently available multifocal contact lens has the ability to restore the phenomena of natural accommodation and successful results are difficult to achieve and require considerable time and experience on the part of the fitter.

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