Presbyopia Correction: Surgical Reversal
Presbyopia is that common age-related condition in which the eyes lose their ability to focus on close objects. Two popular methods exist for surgically addressing it:
- Lens replacement – use of an intraocular lens to replace the natural lens. This is the same procedure that is done for cataracts.
- LASIK monovision -- the adjustment of one eye’s cornea for distance vision and the other for near vision
The eye’s lens is where its accommodative ability is. That is the ability to switch focus quickly from near to far and have everything clear. This is done by the lens changing its curvature according to how far away the objects are. To clearly image a distant object, the lens does not need to steepen itself very much because light from distant objects does not need to be sharply refracted (bent) in order to focus on the retina. But to clearly see a nearby object, the lens does need to steepen so that it can sharply bend that incoming light and focus it on the retina.
Lens replacement and monovision do not try to change the lens or change its ability to accommodate. Lens replacement removes it and LASIK monovision works on the cornea.
Theories of Presbyopia Causation
The cause(s) of presbyopia are not well-established. Until recently, the most commonly-accepted theory has been the Helmholtz theory. It postulates that aging causes the lens to become stiffer and less able to change its curvature. It was developed by a German physician, Hermann von Hemholtz, who lived between 1821 and 1894, and who invented the first ophthalmoscope which allowed eye doctors to see clearly inside a patient’s eye.
The Schachar theory of causation
More recently, support has started moving towards a different theory proposed In 1992 by one Dr. Ronald Schachar. It proposes that presbyopia is caused by the continued growth of the eye’s lens throughout a person’s life. The growth expands the lens into the area around it which is needed by the ciliary muscle that controls it. Thus there is less space for the muscle to operate and it can no longer steepen the lens’ curvature to clearly focus near objects.
Based on that theory, there are some new surgeries for treating presbyopia which are still in testing to gain approval from the Food and Drug Administration (FDA).
Three Presbyopia Surgeries Being Tested
The ciliary muscle which controls the lens curvature is beneath the sclera – the white area of the eye. These three surgeries are designed to create more space for the ciliary muscle by modifying the sclera.
Surgical Reversal of Presbyopia (SRP) with Scleral Expansion Bands
The eye surgeon implants four tiny plastic inserts, each about the size of a grain of white rice. They are positioned directly below the surface of the sclera, expanding the distance between the lens and the ciliary muscle. This gives the muscle room to relax fully, which steepens the lens curvature.
In the FDA tests, results so far are mixed, with some patients experiencing vision improvement and others not achieving any. Safety concerns about the procedure include the possibility of infection, degradation of the implants over time, and compromised blood circulation in the eye.
Anterior Ciliary Sclerotomy (ACS)
The eye surgeon makes multiple incisions (usually eight) in a radial pattern on the patient’s sclera. This increases the amount of space around the lens where the ciliary muscle is.
Although not specifically FDA approved, ACS does not require the use of any unapproved drugs or devices and therefore can be performed legally in the United States. Few published results exist of its effectiveness but some early studies have shown minor improvements in presbyopic vision (an average increase of about one diopter). Others have shown no improvement, but have concluded that this procedure weakens the sclera significantly so that it will rupture more easily.
A variation of the procedure has been tested in Japan, called ACS-SEP, for Anterior Ciliary Sclerotomy with Silicone Expansion Plugs. This study was done on 12 people with presbyopia. The same incisions were made in the sclera but this time they were filled with silicone plugs. The plugs were sutured in position to the exact same depth as the incision was made (95% of scleral thickness). Results showed 1.5D of improvement over 18 months. The plugs prevent the sclera from weakening.
These researchers found that the pressure inside the eyes dropped by about 6 mmHg. That was an unexpected phenomenon and further research is ongoing to determine whether ACS-SEP might be of use for glaucoma patients. Increased intraocular pressure (IOP) is a common symptom of glaucoma and a cause of damage to the optic nerve.
Laser Presbyopia Reversal (LAPR)
This is similar to ACS, but uses a laser instead of a surgical knife. The laser vaporizes tissue in eight radial lines on the sclera. This removal of tissue thins the sclera and increases the amount of space for the ciliary muscle beneath it. For more detail on LAPR, please see our Laser Presbyopia Reversal article.
If you would like to locate a highly-qualified and experienced ophthalmologist and are in the Silicon Valley area, please contact Dr. Gary Kawesch in San Jose, California.