While most people would select the enhanced optical performance offered by the presbyopic lenses, these implants are not appropriate for all patients. There are a number of conditions and diseases which either decrease or totally neutralize the benefits these lenses can deliver. While many of these limitations are agreed upon by most cataract specialists, there may be room for debate among surgeons, so I will offer you my own guidelines (and preferences) based upon the specific ocular condition. Of course, I have a discussion with each patient who has any of these conditions and is considering optimizing his/her cataract procedure with an advanced technology IOL. Accordingly, these patients realize that their eyes are not 100% typical, and there is the very real possibility that the eyes will not see 20/20 after ANY type of IOL is implanted.
Macular Degeneration
Age-related macular degeneration (ARMD) is the subject of numerous articles, chapters and indeed textbooks. To attempt to describe it in any detail is well beyond the scope of this text. Suffice it to say that macular degeneration is typically an age-related loss of the cells which comprise the retina – the “film” where images are generated in your eye.
While there are a few dissenting opinions at the time this monolog is being printed, most surgeons queried will not recommend the use of multifocal IOLs in patients with moderate to severe macular degeneration. It is typically my custom NOT to implant multifocal presbyopic IOLs in eyes that have macular degeneration. The disease typically is progressive (that is, it gets worse as time passes) so it is questionable if a patient would appreciate any benefit with these lenses. In contrast, I have had success implanting accommodating intraocular lenses (the lenses which flex like our natural lens) in patients with early to moderate macular degeneration. Macular degeneration tends not to affect the performance of the accommodating IOLs – presumably due to their more physiologic mechanism of action.
Severe Dry Eye Syndrome
The cornea is the outer “window” and primary light-bending structure of the eye. The cornea is covered by a thin layer of tears, the precorneal tear film (PCTF). The tear film protects the eye from dust, allergens and infectious agents, as well as serving as an avenue for the immune system. Additionally, a stable, contiguous PCTF is vital for the cornea to fulfill its function as the eye’s primary focusing element.
Dry eye syndrome is the condition when the surface of the eye has a deficient or unstable PCTF. As a result, there are “dry spots” on the surface of the cornea. The dry spots can cause irritation to the extent that the patient experiences excessive tearing – this is caused by the dryness becoming a noxious stimulus which causes a physiologic response similar to the tearing that occurs when there is a piece of sand or dust in the eye. The excessive tear volume actually causes the vision to decrease, in addition to introducing the inconvenience of having tears running down one’s cheek in severe cases.
The patient’s vision may also be affected even when there is not any discomfort or excessive tearing. The dryness may cause an irregularity upon the surface of the cornea which results in light scattering. The process of light scattering introduces a source of inefficiency in the eye’s optical system. A cornea that scatters light is described by ophthalmologists as having aberrations. Aberrations are imperfections which cause light to defocus, resulting in a blurring of images, as light does not pass efficiently to the retina. Highly aberrated corneas prevent ALL IOLs from working optimally, but especially multifocal presbyopic lenses from working effectively. For this reason, I do not recommend placing multifocal intraocular lenses in eyes with severe dry eye.
In contrast, accommodating presbyopic lenses and astigmatism-correcting lenses may be placed in eyes with significant corneal optical aberrations; while the results may not be “perfect” 20/20 vision, the results of cataract surgery in patients with aberrated corneas can be quite gratifying.
Dry eye syndrome is not the only condition which results in cornea-based optical aberrations. Corneal scarring from disease or trauma may introduce optical aberrations. Radial keratotomy was a popular refractive surgery procedure in the 1980s and 90s. The keratotomy incisions induce optical aberrations, and actually induce multifocality of the cornea. Accordingly, most cornea specialists will not place a multifocal IOL in an eye that has had radial keratotomy. Instead, the use of the accommodating presbyopic IOL in “post-RK” eyes has resulted in some excellent outcomes as these patients enjoy the dual benefit of a multifocal cornea combined with an accommodating IOL.
The decision on whether to implant a presbyopic lens (or indeed perform cataract surgery at all!) in a patient with dry eye, or any eye that has corneal disease can be difficult. Among the factors to be considered preoperatively include the degree of dryness, cause of dryness, degree of visual debilitation, visual potential of the eye and patient expectations.
Diabetes Mellitus
The ocular sequelae of diabetes mellitus were among the leading causes of blindness in the United States in the mid to late 1900s. Diabetes affects virtually all of the body’s systems and the eye is no exception. Cornea, lens and retina are all potential targets of this disease. Diabetic retinopathy, like macular degeneration, is a disease which has been well chronicled, and an extensive discussion about diabetic ocular disease is beyond the scope of this text.
The process of diabetic retinopathy is caused by serum glucose compromising the competence of the vascular endothelium. That is, abnormally high levels of blood sugar cause blood vessels to leak into the retina, causing a loss of retinal function – again a process where the “film” of the camera is impaired. I generally do not recommend the multifocal presbyopic intraocular lenses in cases where the patient’s retinal function has been affected (although the accommodating lenses may be considered).
There is one diabetic condition where I typically do NOT recommend either type of presbyopic intraocular lens; the condition is called proliferative diabetic retinopathy. In proliferative retinopathy, the serum glucose has so adversely affected the retinal vasculature that there is a gross lack of oxygen being delivered to the retina. This lack of oxygen, or hypoxia, results in the growth of new abnormal retina vessels which have a tendency to actually bleed inside the eye. Eyes that have this degree of impairment from diabetes do not typically realize a significant benefit from presbyopic IOLs.
