This article is more than 5 years old. Information may no longer be current.
Lens exchange can improve patient’s functional vision, surgeon says
The aging of the crystalline lens affects visual function in several ways, studies show.
Click Here to Manage Email Alerts
Improving functional vision through lens exchange may be “the new paradigm for lens removal,” according to Jorge L. Alió, MD, PhD.
![Jorge L. Alió, MD, PhD [photo]](/images\OSN\200602b\alio.jpg) Jorge L. Alió |
“We are changing the paradigm of lens exchange at this moment,” Dr. Alió said, speaking at the American Academy of Ophthalmology meeting in 2005. “Because if the optical quality of eyes implanted with new IOL technology is better than before surgery, removing the crystalline lens may have a quantitative clinical indication, especially if there the a possibility to compensate for the degradation of other functions of the lens, such as loss of accommodation.”
The aging process in the human lens is manifested not only by loss of accommodation but also by increased light scattering and progressive decay in optical function, Dr. Alió said.
“When this lens dysfunction reaches the moment at which the vision is impaired, that is the moment of cataract,” he said.
An upcoming challenge for ophthalmology will be finding objective ways to document these degradations in the lens that lead to reduced quality of functional vision, he said.
Identifying lens aging
The optical performance of the human lens begins to degrade much earlier than most people think, Dr. Alió said. Accommodation begins to decline between the ages of 25 and 30 years.
“This decadence of accommodation is indeed starting earlier than is generally accepted,” he said. Contrast sensitivity also declines as part of the degradation process, he said.
Changes in the physiology of the lens with age include an increase in the complexity of lens fibrin sutures, which increases light scattering, and changes in lens protein synthesis and oxidation, which lead to a decrease in transparency, Dr. Alió said. In addition, he said, the water content and the density of the lens increases, which increases the refractive index of the lens.
“All these changes have a role in this process [of visual degradation] and indeed have an impact on visual function,” he said.
Irregular changes in the lens thickness also result in an increase in spherical aberration and a reduction in accommodation, Dr. Alió said.
“The lens aging, of course, is associated with a decrease in vision,” he said. “But how does this optical decline correlate with visual quality?”
There has to date been no way to measure the role of crystalline lens dysfunction separately from other factors in aging vision, he said.
Clinical testing
In an attempt to document the changes that cause degradation in the performance of the crystalline lens over time, Dr. Alió and colleagues have performed several types of clinical testing, including wavefront measurement, modulation transfer function measurement, and densitometry and axial biometry of the lens. These measurements were done in 72 subjects aged 8 to 80 years.
“You can find 80-year-old human beings with a crystalline lens if you look for them,” Dr. Alió joked.
Modulation transfer function demonstrates the decay of visual function in eyes from 30 to 80 years of age, Dr. Alió said. The change is manifested by an increase in blur at the retina, which indicates increased scattering of light, he said.
Many changes in the lens happen around age 40 years or even earlier.
“At around the age of 40, we have a dramatic increase in the density of the embryonic nucleus, and in other areas the increase in density starts earlier,” he said.
Wavefront measurements show that global aberrations increase significantly throughout life, Dr. Alió said.
“If we explore, for instance, the spherical aberration, one of the main aberrations that changes through life, we can see that these changes affect spherical aberrations later in life, which parallels with anatomic changes. It is around age 40 to 50 when spherical aberration is evidently significantly higher than before,” he said.
“The only aberration that is really increasing significantly is the spherical aberration at the fourth order,” Dr. Alió said. “And this increase is not only linear, but is significant through life.” Aberrations above the fourth order were not seen to increase significantly with age in these studies, he said.
The change in spherical aberration in the whole eye is not paralleled by changes in corneal aberrations, he said, leading to the conclusion that changes in the lens are responsible.
Improving vision
Dr. Alió said new methods of clinical testing are needed to document these changes in the human crystalline lens that affect visual function.
“We face a major effort in the development of new, objective examination techniques of the intraocular structures and new IOL technology aiming to better restore visual function, because the goal is to restore vision with better function and better quality of life,” he said.
For Your Information:
- Jorge L. Alió, MD, PhD, can be reached at Vissum, Instituto Oftalmologico de Alicante, Avda. de Denia, s/n, 03016 Alicante, Spain; 34-965-150-025; fax: 34-965-151-501; e-mail: jlalio@vissum.com.
- Daniele Cruz is an OSN Staff Writer who covers all aspects of ophthalmology.