Challenges exist in getting post-cataract patients to wear spectacles comfortably

If these patients can’t see comfortably with their new spectacles, you won’t benefit, either.

Issue: November 1, 1999

ByHenry L. Trattler, MD

A successful outcome of modern cataract surgery is good vision without the use of eyeglasses. More often than not, however, we must give eyeglasses to our post-cataract patients. Patients usually decide the success of their surgery by how well they are able to see with their new eyeglasses. They may tell you, “Yes, I can see clearer, but I’m having trouble with my new glasses.” That pair of glasses in their hand is something that they can hold up and use as an object to measure their satisfaction or dissatisfaction with your care. If they can’t see comfortably with their new spectacles, your patients are not going to give glowing reports about you to their family or friends. You won’t get the benefit of the referrals that we all still depend upon to help our practices grow.

Achieving satisfaction

So what do we need to do to get patient satisfaction in wearing glasses after cataract surgery?

Consider the fundamentals: removal of the crystalline lens reduces the refractive power of the emmetropic eye from 58 D to slightly less than 43 D. An aphakic spectacle averaging +11.0 D is needed to correct the hyperopia induced by the lens removal. The removal of the crystalline lens also changes the anterior focal length of the eye, moving it from about 16.7 mm from the retina to 23.2 mm from the retina. Image size on the retina is determined by the magnification induced by the position of the necessary correction. Although a posterior chamber implant induces no magnification in image size on the retina, there is a 3% increase with anterior chamber implants, a 6% increase with contact lenses and a 25% increase with aphakic spectacles. Most people can tolerate up to 6% differences in image size between eyes; otherwise, the difference in image size will create anisekonia. Contact lenses or intraocular implants are necessary to balance vision with unilateral cataract removal.

Knowledge is power

But how do we use this knowledge to get patient satisfaction?

History-taking is the foundation for proper decision-making in the care of our patients. If a patient is myopic and has been able to see clearly up close their whole life, then changing the optics of their eye by the use of an implant focused for distance vision may not be of help to that patient. Although perfect 20/20 distance vision without glasses may give great satisfaction to the ophthalmologist, the patient may be very disappointed in having to wear glasses for any close activities. Likewise, an unsatisfactory surgical result also can occur if a myopic patient develops a significant unilateral cataract that is removed and replaced by implant focused for distance. Although a myopic patient may volunteer that they have used contact lenses previously, do not assume that they can use a unilateral contact lens in the non-operated eye without putting them to a test for their ability and willingness to wear it. If the refractive difference between the two eyes after surgery is greater than 2 diopters, then there will be anisometropia and the patient will probably be uncomfortable. Trying to correct anisometropia with spectacles may lead to frustration and possible failure.

What are the reasons that the eyeglasses are uncomfortable? There is a prismatic effect created when the patient looks away from the optical centers of their glasses. When looking through the optical centers, there is no prismatic effect. When the person looks down to read, they are now looking 10 mm below optical centers of their lenses. With myopic corrections, there is a base-down prismatic effect. With hyperopic corrections, there is a base-up effect. With similar corrections for each eye, the prismatic effect of displacing the object will not be noticed since it will be the same in both eyes. However, if the disparity of the postoperative refraction is greater than 2 diopters between the eyes, then there can be a vertical phoria producing diplopia. This is especially apparent when they use a bifocal segment to read. For example, if one eye is –2.00 D and the other is –5.50 D, there will be a 3.5 D base-down vertical imbalance. This vertical imbalance will destroy fusion and cause diplopia.

Treating vertical imbalance

How can we treat this vertical imbalance? There are differences in bifocal segment design and optics. A round-top bifocal segment has a base-down effect while a flat-top segment has base-up effect. If a vertical phoria is pre-existing or induced by anisometropia following cataract implant surgery, the use of dissimilar bifocal segments can be used to correct this. The round-top bifocal segment will limit the off-axis base-up effect of the more hyperopic correction, while the flat-top segment will minimize the base-down effect of the more myopic lens. Bicentric or slab-off grinding of a reading segment also can be used to correct the vertical imbalance. In these situations, a good optical laboratory will do the necessary calculations to produce the lenses for solving the problem.

While spectacle corrections with slab-off grinding or dissimilar bifocal segments are tools that we can use, avoiding anisometropia by proper implant selection is probably the main rule to follow. Patients after cataract surgery who can wear their glasses comfortably are your best advocates.

For Your Information:

Henry L. Trattler, MD, can be reached at 8940 N Kendall Drive, Suite 400-E, Miami, FL 33176; (305) 598-2020; fax: (305) 274-0426; e-mail: htrattler@hotmail.com. Dr. Trattler has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.