Why after simple glaucoma patients frequently change lenses
Answers
Answer:
Explanation:
Multifocal lenses may be inadvisable option for glaucoma patients
For a number of reasons, multifocal lenses are likely to have a negative effect on quality of vision in these patients, surgeon says.
Ocular Surgery News Europe Edition, October 2009
Carole Burillon, MD
Carole Burillon
PARIS — Multifocal lenses are not an advisable option in glaucoma patients, according to one surgeon speaking at the French Society of Ophthalmology meeting.
“This topic is extremely interesting because chronic primary open-angle glaucoma is a frequent pathology and cataract surgery a frequent procedure in elderly patients. In addition, filtration surgery and cataract surgery are often performed together,” Carole Burillon, MD, said.
“On the other hand, premium lenses are becoming increasingly popular, and many glaucoma patients who undergo cataract surgery now ask for this kind of implants,” Dr. Burillon said.
Halos and reduced contrast
Monofocal implants have a continuous, uniform optic surface that directs light rays toward a single focal point in the retina. Multifocal lenses, however, distribute the incoming light to multiple refractive points, for near, intermediate and distance vision, Dr. Burillon said.
Refractive models, such as the ReZoom (Abbott Medical Optics), have optical zones that alternate near and distance vision through different, dedicated optical zones. They are pupil-dependent, so the amount of incoming light energy varies considerably according to the number of optical zones that are exposed by the diameter of the pupil, and this contributes to halo formation at night time.
Diffractive lenses, such as the Tecnis (AMO), are less pupil-dependent. They direct the light at the same time toward the two near and distance foci. However, each of these two optical zones uses 41% of the light, and the remaining 18% light rays are redirected to higher refractive orders, which generate halos, she said.
Apodized optics, such as the AcrySof ReSTOR (Alcon), integrate the two technologies and reduce photic phenomena because of a more gradual transition to the two points of focus.
“All multifocal lenses, however, perform better in bright light, and a low light may create problems,” Dr. Burillon said.
Apart from photic phenomena, a major drawback of multifocality is that the distribution of light to several refractive points results in loss of contrast.
“This can indeed be a problem in glaucoma patients, who already suffer of reduced contrast sensitivity,” she said.
A reduction of contrast sensitivity is found in 30% of glaucoma patients with no visual field changes, in 60% of normal tension glaucoma patients, who are often diagnosed when the disease is already at a fairly advanced stage, and in 93% of the patients with visual field defects
Explanation:
A group of eye conditions that can cause blindness.
With all types of glaucoma, the nerve connecting the eye to the brain is damaged, usually due to high eye pressure.