Lasers have revolutionized many types of surgery over the last half century. This is especially true of eye surgery. Laser eye surgery is quick, close to painless, and stunningly accurate. It is done on an outpatient basis. There is no cutting or bleeding when you operate on an eye using a laser, and no special preparation is needed. Sounds like wizardry – but it is actually only creative applied science.
The eye is an obvious part of the body for laser treatment. Eyes are designed to collect light, and that is what lasers produce – a special kind of light that has unique and fascinating properties. There is no part of the eye that cannot be treated with some kind of laser.
Lasers are all around us. We use them all day long. Most of us own a laser printer, or a CD-ROM player. That bar code scanner on the checkout counter of your supermarket is a laser. Lasers now weld electronic circuits. They have revolutionized surveying and communications. Laser weapons are being developed that can vaporize an enemy. They are used to induce nuclear fission. That cloth in the clothes you are wearing was cut by a laser.Yet most people have no idea how they work. They don’t even know what the word “laser” means (it is an acronym for “Light Amplification by Stimulated Emission of Radiation”).
- After reading this chapter, you will know:
- How laser light is different from ordinary white light;
- How laser light is produced;
- Why and how lasers have completely changed the treatment of many blinding eye diseases;
- The names of different lasers used to treat the eye, and how they work.
Laser light differs from ordinary white light in three ways:
- Laser light is monochromatic, which means it has only one wavelength – unlike white light, which contains all the colors of the rainbow. (You see these colors when white light is separated with a prism.) Some lasers produce visible light, which is always of one specific color – for example, red, or green. Other lasers produce light that is not visible to the human eye – for example, one specific wavelength of infrared or ultraviolet radiation.
- Laser light is collimated, which is a fancy way of saying that every ray is accurately parallel. If a beam of laser light is shot to the moon and back, it will not spread out and disperse, but will arrive back the same shape and size it had when it left.
- Laser light is coherent, which means all its photons are waving together. Think of a room full of people who wander around randomly. If they all line up and march together in step, their motion is now coherent, and far more powerful.
Perfectly parallel, all-one-wavelength, marching -in-step laser light can do amazing tricks. It can be amplified to generate great power. It can be sharply focused with incredible precision. And it can be pulsed in unbelievably short bursts.
To make a laser, all you need is a solid, a liquid, or a gas, plus something to stimulate it – for example, a high voltage electric flash. Remember that picture of an atom you saw back in high school science? It showed positively charged protons in the central nucleus, with electrons (really, electron clouds) orbiting it. The energy from that flash will kick the electrons from their normal low energy level up to a high energy level. When the electrons fall back to their normal state, they will emit photons of light. All these photons now have the same wavelength, they are collimated, and they are coherent.
The theory of lasers was first put forth in 1958. The first practical laser was built – with lightning speed – in 1960. Very soon after lasers were developed, they began to be used to treat the eye.
The different lasers used in the eye all have different wavelengths, pulse patterns, pulse durations, repetition rates, and sport sizes. As a result, they are absorbed by the eye tissues at different depths, and they have different biological effects. Some lasers heat eye tissue, which is called “photocoagulation”, i.e. cooking using light. Other lasers work by photodisruption, i.e. creating miniature shock waves that rupture eye tissue without producing any heat or damage to collateral tissue.
Some lasers are designed to be used in the front part of the eye – the anterior chamber. Others are used in the back part, or posterior chamber. The excimer laser – the laser used in LASIK – treats the cornea, which sits over the anterior chamber of the eye.
The first time a laser was used to treat a human being took place at the Harkness Eye Institute of Columbia Presbyterian Medical Center, and the part of the body the laser treated was…the eye. The first laser used in the eye was a ruby – red – laser. The more adaptable and efficient Argon – green – laser soon supplanted the ruby laser.
The Argon laser treats the back chamber of the eye with unbelievable precision. Using this laser, I can place multiple tiny spots of heat – typically one half to one quarter the size of the head of a pin – into the retina. These tiny heat spots destroy abnormal and leaking blood vessels with stunning accuracy, curing and/or stopping the progression of blinding retinal diseases such as diabetic retinopathy.
The argon laser is a genuine miracle. It has revolutionized the treatment of diabetic eye disease. Diabetic retinopathy is a huge public health problem. It is the number one cause of blindness in adults in the US, according to the CDC. An estimated 4.1 million Americans have diabetic retinopathy, and a million of these have sight-threatening retinopathy. Since these years are the peak ages for working, untreated diabetic retinopathy has major economic consequences.
In 1976 – two years before I began my eye residency – researchers published the results of the first prospective randomized trial of the treatment of diabetic retinopathy using the argon laser. The researchers stopped the study early because it became blazingly obvious that patients who had been treated with the argon laser were doing much better than untreated ones.
Before the argon laser, all diabetics with retinopathy went blind. Since the argon laser, they almost all keep their vision – but only if their retinopathy is diagnosed and treated early. An estimated 50% of patients with diabetic retinopathy are not getting yearly eye exams. These people are often diagnosed too late for treatment to be effective.
The argon laser is also used to treat other retinal diseases, including retinal tears and detachments, vein occlusions and sickle cell eye disease. We once used this laser to destroy the abnormal blood vessels of wet macular degeneration, but now we inject a drug into the eye that inhibits these abnormal vessels. This drug is more effective, and has fewer side effects.
The argon laser has saved the sight of millions of people all over the world. There is an argon laser in every major eye hospital in the world today.
Lasers have also revolutionized the treatment of glaucoma. Glaucoma is the number two cause of blindness in the U.S., and the number one cause for African-Americans, who tend to get the disease younger and more severely. At least 2 million Americans have glaucoma, and approximately 80,000 have been blinded by it. This is a tragedy. This is evidence that, for some people, glaucoma, like diabetic retinopathy, is not being diagnosed and treated early enough. Nobody in the world should go blind from glaucoma today.
Most glaucoma is hereditary. If you have a close relative with glaucoma (a parent, or grandparent, a brother or sister) your risk of glaucoma doubles.
Your eyes have pressure inside them, like tires. High pressure will damage a tire. The same is true of an eye. Your eye is like a bathtub with the tap always on. Night and day, a clear nourishing fluid, called the aqueous humor (“aqueous” for short) circulates through the anterior chamber of your eye, bringing sugar and oxygen to your cornea and lens sugar, and taking away wastes.
After it has done its job, the aqueous humor exits your eye by passing through a slot – called the “angle” – which is where the front of your iris meets the back of your cornea. The angle leads into a tiny sieve called the “trabecular meshwork”. The trabecular meshwork then empties into the small veins on the surface of your eye. Normally, inflow of aqueous equals outflow, so the pressure inside your eye – which is measured in millimeters of mercury – is maintained between 8 and 22. (In some people, “normal’ can be as high as 24 or 25).
Glaucoma is, simply, high pressure inside your eye. Glaucoma is caused by a bad drain. If the aqueous humor does not drain properly, the eye pressure will go up. If your eye pressure gets too high, your eye will start to go blind. The higher the pressure, the faster you will lose your sight.
High eye pressure blinds your eye by destroying your optic nerve. Your optic nerve is the nerve that carries signals from your eye up to your brain, allowing you to see. Think of the optic nerve as an electric cord running to a lamp – the lamp itself could be working, but unless the cord is also working the lamp will not give out light.
Your optic nerve is very sensitive to pressure. If the pressure inside your eye is too high, your nerve will Start to die. Like all nerves, once damaged it never recovers.As it dies, first you lose peripheral vision, and, finally, central vision.
Glaucoma has been called the “sneak thief of sight”. You will not be able to tell if you have glaucoma if the pressure inside your eye goes up gradually, which is the case at least 95% of the time. Peripheral vision is the first to go in glaucoma. By the time you begin to notice blank areas in your sight, 85 to 90 percent of your optic nerve will have been destroyed.
Only your ophthalmologist can tell you whether or not you have glaucoma. If you visit your ophthalmologist every 2 years when you are under the age of 40, and every year after you are 40, if you do develop glaucoma it will be diagnosed at an early stage, and your sight will be saved.
Glaucoma is treated by lowering eye pressure. This can be accomplished by drops, by pills, by laser surgery, and/or by knife surgery.
There are two types of glaucoma.
- PRIMARY OPEN ANGLE GLAUCOMA, or POAG, is by far the most common. In POAG, the drain is open, and it looks completely normal, but it does not work well, and as a result the eye pressure goes up.
- About 5% of glaucoma is ANGLE CLOSURE GLAUCOMA. This type of glaucoma usually occurs in far-sighted people, who have small, short eyes and therefore shallow front chambers of their eyes.
In angle closure glaucoma, your angle is narrow from the day you are born. As you get older, your lens gets bigger and bigger, and as it grows it pushes your iris forward. Eventually, it pushes your iris so far forward that it blocks your trabecular meshwork – just as a washcloth might block a bathtub drain. The blockage caused by your iris slams your drainage angle shut.
When a narrow angle slams shut suddenly, the eye pressure shoots up rapidly. This is a true eye emergency. The high pressure causes acute, severe pain – so bad you may vomit. Your vision becomes cloudy, as fluid inside your eye gets pushed into your cornea. The eye becomes red, especially right around the iris.
Ideally, a dangerously narrow angle should be detected on a routine exam, and a preventive treatment called a laser iridotomy should be performed before the angle closes. This is yet another reason why you need to get regular eye check-ups. Narrow angle glaucoma is hereditary. If you have it, your siblings and children should be examined.
When I was in my first year of residency in 1978 – which was just before the YAG laser was developed for use in the eye – I learned how to treat angle closure glaucoma by putting the patient under general anesthesia, slicing the eye open, hacking out a chunk of iris, and then sewing the eye up again. This caused a lot of bleeding. A cataract inevitably formed within a few years. Of course, this made the eye vulnerable to infection.
When I was in my second year of residency, eye surgeons began to use the Nd:YAG laser to punch a hole in the iris. What an improvement – minimal bleeding, no anesthesia except for one numbing drop, the eye is not opened so there is zero chance of infection, quick (five to ten minutes) surgery, and almost no pain.
The Nd:YAG laser – which stands for Neodymium-doped Yttrium Aluminum Garnet,YAG for short – gives off near-infrared, invisible, beams of light. It works by photo-disruption, not by photocoagulation like the Argon laser. Instead of heating tissue, the YAG sends extremely short (10 to 25 nanosecond) bursts of infrared light into the anterior chamber. (A nanosecond is one billionth of a second – this technology is so advanced it makes the head spin.) These pulses create minuscule explosions that cut through everything in their path.
If I see that your angles are dangerously narrow, I will open them up by creating a tiny (1/4 of a millimeter) hole – called an IRIDOTOMY – in the periphery of your iris, using the YAG laser. This will create a “trap door” for your aqueous to flow into your trabecular meshwork.
Aspirin and aspirin products must be avoided for 2 weeks prior to laser iridotomy sincet hey increase the risk of bleeding.For this reason, it is very important that you carefully check the contents of all “over the counter” preparations. Many headache preparations, cold remedies, and “hangover cures” contain aspirin. The chemical name of aspirin is acetylsalicylic acid.
This procedure takes about 5 minutes. You will have a trivial amount of discomfort during the procedure. Your only post-op assignment is to take steroid drops for four weeks afterwards.
If your laser iridotomy is done early enough, before your angle is scarred shut, there is an excellent chance you will be cured by the procedure alone. If the diagnosis is made late, you will probably need to take drops for the rest of your life. You make even need knife surgery to create an artificial passage from the inside of the eye to the outside to keep your eye pressure normal.
I also use the YAG laser to clear away the cloudy membrane – “secondary cataract” – that inevitably forms after modern day cataract surgery. After a period of time – the range is as early as a few weeks, to as long as ten years, but is usually three to five years – the capsule of the old lens, which holds the new clear plastic lens in place, clouds up, and the patient no longer sees clearly. After the YAG laser opens a hole in the membrane, the eye can see clearly again. A YAG capsulotomy is quick – three to five minutes – and painless.
If you are diagnosed with Open Angle Glaucoma, I will usually begin by treating you with eye drops. Some of these drops work by decreasing the production of aqueous humor. Others work by increasing its outflow. I will probably have to experiment to find the drop(s) that work best for you. Each drop has advantages and disadvantages – for example, beta blockers cannot be used if you have asthma or a slow heart rate.
If you are unable to remember to take your drops, or if all drops have intolerable side effects, I will suggest a Laser Trabeculoplasty.
In the 1970s, researchers Witter and Wise discovered the Argon laser could be used to heat the drainage channel of the eye – the trabecular meshwork – in patients with glaucoma, and thereby increase the flow rate of liquid out of the eye. They called this procedure “Argon Laser TrabeculoPlasty”, or ALTP. I learned how to perform ALTP when I was an eye resident, and used it to help many patients.
Then in the mid-1990s, Latina developed an even better laser for trabeculoplasty. He called it the Selective Laser. The selective laser is sometimes called a “cold laser”, because its light is absorbed only by the trabecular meshwork pigment.It is a frequency doubled (ultraviolet) YAG laser that can produce ultra-short pulses, which means there is minimal heat, and almost no scar tissue. I immediately switched from the Argon laser to the Selective Laser to treat the trabecular meshwork of patients with open angle glaucoma. This technique is called Selective Laser Trabeculoplasty, or SLTP.
I use the Selective Laser to put half-millimeter spots of ultraviolet light into the trabecular meshwork so it will drain more freely. This procedure is almost painless.
I will do your SLTP on an outpatient basis. It will take about 10 minutes. You may resume normal activities immediately. It has a success rate of around 85%, and very few side effects. It does wear wear off with time – at a rate of about 10% each year – but I can repeat it.
I have already described modern-day cataract surgery using phacoemulsification in Chapter Twelve, “Good Hands and a Good Head”. To recap, I make a tiny incision, by hand, into the eye, using a sterile blade. Then I create a circular incision in the capsule of the lens, using tiny forceps. I then insert a small ultrasound probe into the eye, to break up and suck out the cloudy lens.
Some cataract surgeons now perform cataract surgery using a femtosecond diode laser. This laser has a similar wavelength to the YAG laser, in the infrared, but its effect on eye tissue is different because the pulse duration is much shorter. The YAG laser is pulsed in nanoseconds, while the femtosecond laser is pulsed in one quadrillionth of a second, i.e. 10-to-the-minus-fifteenth of a second. This unimaginably short burst of energy generates a shock wave that produces even less heat and damage to nearby tissue than the YAG laser.,
In laser cataract surgery, the femtosecond laser, not the hand of the surgeon, makes the incision into the eye and into the lens capsule. This same laser then softens the cataract before it is removed. Since the use of this laser during cataract surgery is not covered by insurance, you will have to pay an extra $4,000 to $6,000 out of pocket per eye.
The potential advantages of laser cataract surgery are:
- Less energy is used to break up the cataract, which is supposedly gentler on the eye;
- The incision into the eye and into the lens capsule are made by a machine instead of by hand, hypothetically providing more precision and accuracy, and an extra edge of safety.
Studies have not shown that laser cataract surgery results in fewer complications, or provides better options, than traditional cataract by phacoemulsification. Both traditional and laser cataract surgery are almost painless, have a quick recovery time, and require no stitches.
Laser cataract surgery adds another level of complexity and expense. There are more ways the procedure can go wrong, for example, if there is a glitch in the software – which happened in May of 2018 to the Catalys Precision Laser System.
As in all surgery, the outcome depends in large part on the skill and experience of your surgeon.
These amazing lasers – Argon, YAG, and Selective – have allowed me to save the sight of tens of thousands of eyes.
All these widely-used lasers are designed to be used in eyes that have a serious disease that threatens to destroy vision. The benefit is enormous, and there are virtually no complications if these lasers are used properly. They are not used in normal eyes, and they are not used for cosmetic reasons.
The excimer laser – a powerful ultraviolet (invisible) laser that, like the YAG laser, emits nanosecond pulses – has a completely different purpose. Unlike the other lasers used in the eye, it is not designed to heal eyes that have a serious problem. It is used for purely cosmetic reasons: to eliminate the need for distance glasses. LASIK is the eye equivalent of breast augmentation, a tummy tuck, a face lift, or a nose job. Excimer laser treatment of the cornea has been a disaster, as the next chapter will show.