Richard A. Levinson, M.D. > Glossary of Terms

Glossary of Terms

In astigmatism, the cornea is shaped more like a football than a basketball. Patients with astigmatism have distorted vision because light rays are refracted unequally through the misshapen cornea. Of all myopic patients, 50% or more have astigmatism as well. Astigmatism is very precisely corrected with Laser Vision Correction, and especially with Custom Wavefront.

Ectasia refers to distention or weakening of the cornea. This results in progressing, blurred, distorted vision that may not be correctable with glasses or contact lenses and may, rarely, require a corneal transplant. Ectasia can occur naturally as a disease of the cornea, called keratoconus. If patients have keratoconus, they are not candidates for Laser Vision Correction. Ectasia can, also, develop following Laser Vision Correction in approximately 1/2000 cases of LASIK. Ectasia is mostly avoidable if patients are screened appropriately pre-op to make sure the corneas have adequate corneal tissue and structural integrity to safely tolerate LASIK. Ectasia is more common in younger patients under the age of 30. Ectasia is less common with PRK than LASIK. I typically recommend PRK for patients under age 30 to avoid the risk of ectasia.

The Excimer Laser is used in Laser Vision Correction to reshape the cornea. The word Excimer is short for Excited-Diamer. The Excimer Laser uses two diamers, or gases, Argon and Fluoride, to generate the Laser energy. When I was in elementary school, I used a magnifying glass to focus the sunlight on a piece of paper, and burn a hole in the paper. A Laser functions on a principle similar to this. However, a Laser uses just one wavelength of light, whereas sunlight has a wide band of wavelengths. Also, Lasers have all the waves “in phase”, allowing for very high concentrations of focused energy. Each Laser wavelength has different physical properties. It happens that the Excimer Laser, which is in the ultra-violet range with a wavelength of 193 nanometers, breaks carbon-carbon bonds. This releases vaporized molecules, without cutting or damaging surrounding tissue. Each pulse of the Excimer Laser removes .25 microns, 0.00004 of an inch, of tissue. (A human hair is 50 microns. The Excimer Laser removes 1/200 of a hair with each pulse of energy.

A Femtosecond Laser is a Laser that has an extremely fast rate of firing. A femtosecond Laser fires a shot of energy at a rate of every .000000000001 second. These lasers are used to make extremely precise incisions. Femtosecond Lasers have to two applications in Eye Surgery. They are used to make the flap in LASIK and they are also used to make the incisions in cataract surgery.

Hyperopia is the medical term for farsightedness. Hyperopia occurs when an eye is too short for the cornea’s curvature, and light rays entering the eye focus behind the retina. The term ‘farsighted’

means that you are able to see ‘far’ objects clearly without correction, but objects nearer appear blurry

A Laser Vision Surgeon is an Ophthalmologist, an M.D., an Eye Surgeon. Laser Vision Surgeons use Laser technology to reshape the cornea to treat nearsightedness, farsightedness, astigmatism and presbyopia.

Myopia is the medical term for nearsightedness. Myopia occurs when an eye is elongated or the cornea is too curved, causing light rays entering the eye to fall short of the retina, creating blurred vision.

The term ‘nearsighted’ means that you can see ‘near’ objects without correction, but objects in the distance are blurry. Myopia occurs in various degrees. The more myopic you are the more blurred objects appear in the distance, the higher your eyeglass prescription and the thicker your glasses. 95+% of all myopic cases have corrections less than -10.00 diopters and are correctable with Laser Vision Correction

An ophthalmologist is an M.D., a Medical Doctor. Ophthalmologists have, at minimum attended four years of college, four years of medical school, one year of internship in medicine or surgery, and three years of residency training in ophthalmology at a university medical center. Ophthalmologists are trained to diagnose and treat medical and surgical eye diseases. Only Ophthalmologists can perform Laser Vision Correction Surgery. Ophthalmologists also provide primary routine eye care including glasses and contact lenses.

An Optometrist is not a Medical Doctor. Optometrists have, at minimum, two years of college and four years of optometry school. Optometrists are well trained in fitting glasses and contact lenses. Optometrists have some training in treating eye disease with medicines but not to the extent and level of training of Ophthalmologists. Optometrists do not perform surgery.


The cornea is the clear, front part of your eye that is reshaped by the Excimer Laser in Laser Vision Correction.

A painless test performed to measure the corneal thickness, also a part of our complimentary consultation. The purpose of pachymetry is to determine if you have enough corneal tissue to safely perform Laser Vision Correction. We want to leave enough residual corneal tissue after Laser Vision Correction to ensure that the cornea will maintain adequate structural integrity and not develop ectasia.

Presbyopia is the normal process of aging, where the natural lens of the eye loses some of the flexibility that characterizes a younger eye. As a result, the eye has more difficulty adjusting from distance vision to close vision. This normally occurs around the age of forty and is usually corrected with the aid of reading glasses or monovision.

Punctal plugs are used to treat moderate to extreme dry eyes. We initially use lubricating eye drops (artificial tears) to treat dry eyes after Laser Vision Correction. However, if dry eye symptoms still persist, punctal plugs are inserted.

Punctal plugs are small, soft silicone plugs that are inserted into the puncta. Have you ever noticed that you have a small hole in your upper and lower eye lids near where the two lids come together near the nose? These are the puncta, ie holes, where the tears drain out of the eye. Plugging these holes is like plugging the drain in your sink; it will prevent your tears from draining out of your eye and will keep your eye moister, decreasing the symptoms of dry eye. The plugs are easily inserted and this is done right in my office. There is no cutting, suturing or needles involved and takes just a few seconds to insert. The plugs, which are about the size of a grain of sand, can be left in the punctal opening indefinitely and are rarely associated with complications. The plugs can be easily removed, if needed, but are usually left in place without problem indefinitely.

A painless procedure that takes a picture of your eye to map the surface curvature of the cornea, also a part of our complimentary consultation. The topographical map will mathematically model the shape of your cornea to determine the structural integrity of your cornea. Topography is extremely valuable in identifying corneas that will develop warpage after Laser Vision Correction and should, therefore, not be treated.