Phakic intraocular lenses, or phakic lenses, are lenses made of plastic or silicone that are implanted into the eye permanently to reduce a person's need for glasses or contact lenses. Phakic refers to the fact that the lens is implanted into the eye without removing the eye's natural lens. During phakic lens implantation surgery, a small incision is made in the front of the eye. The phakic lens is inserted through the incision and placed just in front of or just behind the iris.

What do they treat?

Phakic lenses are used to correct refractive errors, errors in the eye's focusing power. All phakic lenses approved by the FDA are for the correction of nearsightedness (myopia).

The cornea and natural lens of the eye focus light to create an image on the retina, much like the way the lens of a camera focuses light to create an image on film. The bending and focusing of light is also known as refraction. Imperfections in the focusing power of the eye, called refractive errors, cause images on the retina to be out of focus or blurred.

People who are nearsighted have more difficulty seeing distant objects than near objects. For these people, the images of distant objects come to focus in front of the retina instead of on the retina.

Ideally, phakic lenses cause light entering the eye to be focused on the retina providing clear distance vision without the aid of glasses or contact lenses.

Surgery is not required to correct nearsightedness. You can wear glasses or contact lenses instead to correct your vision. Depending on how nearsighted you are, and other conditions of your eye, other refractive surgery (surgery to correct refractive errors) options may be available to you, including PRK (Photorefractive Keratectomy) and LASIK (Laser Assisted In-Situ Keratomileusis).

Can they be removed?

Phakic lenses are intended to be permanent. While the lenses can be surgically removed, return to your previous level of vision or condition of your eye cannot be guaranteed.

What is the difference between phakic intraocular lenses and intraocular lenses following cataract surgery?

Phakic intraocular lenses are implanted in the eye without removing the natural lens. This is in contrast to intraocular lenses that are implanted into eyes after the eye's cloudy natural lens (cataract) has been removed during cataract surgery.

Anatomy of the Eye

The first part of the anatomy of the eye animated illustration shows an external side view of the eyeball with the parts labeled. The sclera, cornea, iris, pupil, and optic nerve are identified. The second part of the illustration shows an internal side view with the eye cut in half from front to back. It identifies the sclera, cornea, anterior chamber, iris, pupil, posterior chamber, natural lens, retina, and optic nerve.

How Phakic Lenses Work

The illustration of how phakic lenses work shows the side view of eye as if you cut it in half from front to back and you were looking at the inside. It shows light rays from a stop sign being focused by the cornea and lens onto the retina of an eye that needs no vision correction. It depicts the clear retinal image of the stop sign being sent to the brain by the optic nerve. When light rays come into focus on the retina, we see the object clearly.

The image of the same stop sign is focused in front of the retina in a nearsighted (myopic) eye. The light rays from the stop sign that fall onto the retina are out of focus creating a blurred image. The blurred retinal image is sent to the brain by the optic nerve. When light rays do not come into focus on the retina, we see the object as blurred.

The inset image shows the clear retinal image of the stop sign being sent to the brain by the optic nerve. This is the idealized results of the phakic lens bending light from the stop sign to redirect the focused image onto the retina. When light rays are redirected by the phakic lens onto the retina, the nearsighted eye sees distant objects more clearly.

You are probably NOT a good candidate for phakic lenses if:

• You are not an adult. There are no phakic lenses approved by the FDA for persons under the age of 21.
• You are not a risk taker. Certain complications are unavoidable in a percentage of patients, and there are no long-term data available for phakic lenses.
• You required a change in your contact lens or glasses prescription in the last 6 to 12 months in order to obtain the best possible vision for you. This is called refractive instability. Patients who are:
  • in their early 20s or younger,
  • whose hormones are fluctuating due to disease such as diabetes,
  • who are pregnant or breastfeeding, or
  • who are taking medications that may cause fluctuations in vision,
  are more likely to have refractive instability and should discuss the possible additional risks with their doctor.

• You may jeopardize your career. Some jobs prohibit certain refractive procedures. Be sure to check with your employer/professional society/military service before undergoing any procedure.
• Cost is an issue. Most medical insurance will not pay for refractive surgery.
• You have a disease or are on medications that may affect wound healing. Certain conditions, such as autoimmune diseases (e.g., lupus, rheumatoid arthritis), immunodeficiency states (e.g., HIV) and diabetes, and some medications (e.g., retinoic acid and steroids) may prevent proper healing after intraocular surgery.
• You have a low endothelial cell count or abnormal endothelial cells. If the cells that pump the fluid out of your cornea, the endothelial cells, are low in number relative to your age, or if your endothelial cells are abnormal, you have a higher risk of developing a cloudy cornea and requiring a corneal transplant.
• You actively participate in sports with a high risk of eye trauma. Your eye may be more susceptible to damage should you receive a blow to the face or eye, such as a blow to the head during boxing or hit in the eye by a ball during baseball. Your eye may be more susceptible to rupture or retinal detachment, and the phakic lens may dislocate.
• You only have one eye with potentially good vision. If you only have one eye with good vision with glasses or contact lenses, due to disease, irreparable damage, or amblyopia (eye with poor vision since childhood that cannot be corrected with glasses or contact lenses), you and your doctor should consider the risk of possible damage and/or loss of vision to your better eye as a result phakic lens implantation.
• You have large pupils. If your pupil dilates in low lighting conditions to a size that is larger than the size of the lens, you have a higher risk of experiencing visual disturbances after surgery that may affect your ability to function comfortably or normally under such conditions (e.g., while driving at night).
• You have a shallow anterior chamber. If the space between the cornea and the iris, the anterior chamber, is narrow, you have a higher risk of developing complications, such as greater endothelial cell loss, due to implantation of the phakic lens.
• You have an abnormal iris. If your pupil is irregularly shaped you have a higher risk of developing visual disturbances.
• You have had uveitis. If you have had inflammation in your eye, you may have a recurrence or worsening of your disease and/or may develop additional complications, such as glaucoma, as a result of surgery.
• You have had problems with the posterior part of your eye. If you have had any problems in the back part of your eye or are at risk for such problems, for example, proliferative diabetic retinopathy (growth of abnormal vessels in the back of the eye due to diabetes) or retinal detachment, you may not be a good candidate for phakic lens implantation. The phakic lens may not allow your eye doctor to get a clear view of the back part of your eye, preventing or delaying detection of a new or worsening problem, and/or the phakic lens may prevent or make treatment of a problem in the back of your eye more difficult.

The safety and effectiveness of phakic lenses have NOT been studied in patients with certain conditions. If any of the following apply to you, make sure you discuss them with your doctor:

• You have glaucoma (damage to the nerve of the eye resulting in loss of peripheral and then central vision due to too high pressure inside the eye), ocular hypertension (high eye pressure), or glaucoma suspect (some indications, but not clear, that patient has glaucoma). You may have a higher risk of developing or worsening of glaucoma as a result of phakic lens implantation.
• You have pseudoexfoliation syndrome (abnormal deposits of material in the eye visible on the structures in the front part of the eye, such as on the front of the natural lens and the back of the cornea). This syndrome is associated with glaucoma and weakness of the structures holding the natural lens in place (the zonules). You may have a higher risk of surgical complications and/or complications after surgery if you have this syndrome.
• You have had an eye injury or previous eye surgery.
• Your need for visual correction is outside the range for which the phakic lens has been approved. Ask your eye doctor if the phakic lens that he or she recommends for you has been approved to treat your refractive error and/or check FDA-Approved Phakic Lenses for the approved refractive range.
• You are over the age of 45 years old. Some phakic lenses have not been studied in patients over the age of 45.

Implanting a phakic lens involves a surgical procedure. As in any other medical procedure, there are risks involved. That's why it is important for you to understand the limitations and risks of phakic intraocular lens implant surgery.

Before undergoing surgery for implantation of a phakic intraocular lens, you should carefully weigh the risks and benefits and try to avoid being influenced by other people encouraging you to do it.

Risks

• You may lose vision. Some patients lose vision as a result of phakic lens implant surgery that cannot be corrected with glasses, contact lenses, or another surgery. The amount of vision loss may be severe.
• You may develop debilitating visual symptoms. Some patients develop glare, halos, double vision, and/or decreased vision in situations of low level lighting that can cause difficulty with performing tasks, such as driving, particularly at night or under foggy conditions.
• You may need additional eye surgery to reposition, replace or remove the phakic lens implant. These surgeries may be necessary for your safety or to improve your visual function. If the lens power is not right, then a phakic lens exchange may be needed. You may also have to have the lens repositioned, removed, or replaced, if the lens does not stay in the right place, is not the right size, and/or causes debilitating visual symptoms. Every additional surgical procedure has its own risks.
• You may be under treated or over treated. Many treated patients do not achieve 20/20 vision after surgery. The power of the implanted phakic lens may be too strong or too weak. This is because of the difficulties with determining exactly what power lens you need. This means that you will probably still need glasses or contact lenses to perform at least some tasks. For example, you may need glasses for reading, even if you did not need them before surgery. This also means that you may need a second surgery to replace the lens with another, if the power of the originally implanted lens was too far from what you needed.
• You may develop increased intraocular pressure. You may experience increased pressure inside the eye after surgery, which may require surgery or medication to control. You may need long-term treatment with glaucoma medications. If the pressure is too high for too long, you may lose vision.
• Your cornea may become cloudy. The endothelial cells of your cornea are a thin layer of cells responsible for pumping fluid out of the cornea to keep it clear. If the endothelial cells become too few in number, the endothelial cell pump will fail and the cornea will become cloudy, resulting in loss of vision. You start with a certain number of cells at birth, and this number continuously decreases as you age, since these cells are not replenished. Normally, you die from old age before the number of endothelial cells becomes so low that your cornea becomes cloudy. Some lens designs have shown that their implantation causes endothelial cells to be lost at a faster rate than normal. If the number of endothelial cells drops too low and your cornea becomes cloudy, you will lose vision and you may require a corneal transplant in order to see more clearly.
• You may develop a cataract. You may get a cataract, clouding of the natural lens. The amount of time for a cataract to develop can vary greatly. If your cataract develops and progresses enough to significantly decrease your vision, you may require cataract surgery your doctor will have to remove both your natural and your phakic lenses.
• You may develop a retinal detachment. The retina is the tissue that lines the inside of the back of your eyeball. It contains the light-sensing cells that collect and send images to your brain, much like the film in a camera. The risk of the retina becoming detached from the back of your eye increases after intraocular surgery. It is not known at this time by how much your risk of retinal detachment will increase as a result of phakic intraocular lens implantation surgery.
• You may experience infection, bleeding, or severe inflammation (pain, redness, and decreased vision). These are rare complications that can sometimes lead to permanent loss of vision or loss of the eye.
• Long-term data are not available. Phakic lenses are a new technology and have only recently been approved by the FDA. Therefore, there may be other risks to having phakic lenses implanted that we don't yet know about.

Initial Visit

Before deciding to have phakic intraocular lens implantation surgery, you will need an initial examination to make sure your eye is healthy and suitable for surgery. Your doctor will take a complete history about your medical and eye health and perform a thorough examination of both eyes, which will include measurements of your pupils, anterior chamber depth (the distance between your cornea and iris), and endothelial cell counts (the number of cells on the back of your cornea).

If you wear contact lenses, your doctor may ask you to stop wearing them before your initial examination (from the day of to a few weeks before), so that your refraction (measure of how much your eye bends light) and central keratometry readings (measure of how much the cornea curves) are more accurate.

At this time, you should tell your doctor if you:

• take any medications, including over-the-counter medications, vitamins and other supplements
• have any allergies
• have had any eye conditions
• have undergone any previous eye surgery
• have had any medical conditions.

Deciding to have Surgery

To help you decide whether phakic lenses are right for you, talk to your doctor about your expectations and whether there are elements of your medical history, eye history, or eye examination that might increase your risk or prevent you from having the outcome you expect. Before you sign an informed consent document (a form giving permission to your doctor to operate on your eye), you should discuss with your doctor:

• whether you are a good candidate,
• what are the risks, benefits and alternatives of the surgery,
• what you should expect before, during and after surgery, and
• what your responsibilities will be before, during and after surgery.

You should have the opportunity to ask your doctor questions during this discussion. Ask your doctor for the Patient Labeling of the lens that he or she recommends for you. Give yourself plenty of time to think about the risk/benefit discussion, to review any informational literature provided by your doctor, and to have any additional questions answered by your doctor before deciding to go through with surgery and before signing the informed consent document. You should not feel pressured by anyone to make a decision about having surgery. Carefully consider the pros and cons.

Within weeks of surgery

About one to two weeks before surgery, your eye doctor may schedule you for a laser iridotomy to prepare your eye for implantation of the phakic lens. Before the procedure, your eye doctor may put drops in your eye to make the pupil small and to numb the eye. While you are seated, you doctor will rest a large lens on your eye. He or she will then make a small hole (or holes) in the extreme outer edge of the iris (the colored part of your eye) with a laser. This hole (holes) are to prevent fluid buildup and pressure in the back chamber of your eye after phakic lens implantation surgery. This procedure is usually performed in an office or clinic setting, not in an operating room, and usually only takes a few minutes.

After the iridotomy procedure, the doctor may have you wait around awhile before checking your eye pressure and letting you go home. The procedure should not prevent you from driving home, but you should check with your eye doctor when you schedule your appointment. You will be given a prescription for steroid drops to put in your eye at home for several days to reduce inflammation from the iridotomy procedure. It is important that you follow all instructions your doctor gives you after the iridotomy procedure.

Possible complications of laser iridotomy include:

• iritis (inflammation in the front part of the eye)
• increase in eye pressure (usually within 1 to 4 hours after the procedure)
• cataract (clouding of the natural lens) from the laser
• hyphema (bleeding into the anterior chamber of the eye, behind the cornea and in front of the iris, that can cause high pressure inside the eye)
• injury to the cornea from the laser that can result in clouding of the cornea
• incomplete opening of the hole all the way through the iris
• closure of the new opening
• rarely, retinal burns

Your doctor may ask you to stop wearing contact lenses before your surgery (anywhere from the day of the surgery to a few weeks before).

Before your surgery, your eye doctor may ask you to temporarily stop taking certain medications that increase the risk of bleeding during surgery. How long before surgery you may need to stop these medications depends upon which medications you are using and the conditions they are treating. You and your eye doctor may need to discuss stopping certain medications with the doctor who prescribed them, since you may need some of these medications to prevent life-threatening events. For example, you may need medications that stop blood clotting to keep from having a stroke.

Within days of surgery

Your doctor may give you prescriptions for antibiotic drops to prevent infection and/or anti-inflammatory drops to prevent inflammation to put in your eye for a few days before surgery.

Arrange for transportation to and from surgery and to your follow-up doctor's appointment the day after surgery, since you will be unable to drive. Your doctor will let you know when it is safe for you to drive again.

Your eye doctor will probably tell you not to eat or drink anything after midnight the night before your surgery.

The Day of Surgery

Just before surgery, drops will be put in your eye. You will have to lie down for the surgery and remain still. If you cannot lie down flat on your back, you may not be a good candidate for this surgery. Usually, patients are not put to sleep for this type of surgery, but you may be given a sedative or other medication to make you relax and an i.v. may be started. Your doctor may inject medication around the eye to numb the eye. The doctor also may give you an injection around the eye to also prevent you from being able to move your eye or see out of your eye. You will have to ask your doctor to find out exactly which of these types of anesthesia will be used in your case. Your eye and the surrounding area will be cleaned and an instrument called a lid speculum will be used to hold your eyelids open.

The doctor will make an incision in your cornea, sclera (the white part of your eye), or limbus (where the cornea meets the sclera). He or she will place a lubricant into your eye to help protect the back of the cornea (the endothelial cells) during the insertion of the phakic lens. The doctor will insert the phakic lens through the incision in the eye into the anterior chamber, behind the cornea and in front of the iris. Depending upon the type of phakic lens, the doctor will either attach the lens to the front of the iris in the anterior chamber of the eye or move it through the pupil into position behind the iris and in front of the lens in the posterior chamber of the eye. The doctor will remove the lubricant and may close the incision with tiny stitches, depending upon the type of incision. Your doctor will place some eye drops or ointment in your eye and cover your eye with a patch and/or a shield. The surgery will probably take around 30 minutes.

After the surgery is over, you may be brought to a recovery room for a couple of hours before you will be allowed to go home. You will be given prescriptions for antibiotic and anti-inflammatory drops to use at home as directed. You will be given an Implant Identification Card, which you should keep as a permanent record of the lens that was implanted in your eye. Make sure you show this card to anyone who takes care of your eyes in the future. You will be asked to go home and take it easy for the rest of the day.

Immediately After Surgery

After the surgical procedure, you may be sensitive to light and have a feeling that something is in your eye. You may experience minor discomfort after the procedure. Your doctor may prescribe pain medication to make you more comfortable during the first few days after the surgery. You should contact your eye doctor immediately if you have severe pain.

You should see your eye doctor the day after surgery. Your doctor will remove the patch and/or shield and will check your vision and the condition of your eye. Your doctor will instruct you on how to use the eye drops that you were prescribed for after the surgery. You will need to take these drops for up to a few weeks after surgery to decrease inflammation and help prevent infection. Your doctor may instruct you to continue wearing the shield all day and all night or just at night. You should wear the shield until your doctor tells you that you no longer have to do so. The shield is meant to prevent you from rubbing your eye or putting pressure on your eye while you sleep and to protect your eye from accidentally being hit or poked while it is healing.

As You Recover

Your vision will probably be somewhat hazy or blurry for the first several days after surgery. Your vision should start to improve after the first several days, but may continue to fluctuate for the next several weeks. It usually takes about 2 to 4 weeks for the vision to stabilize. Do NOT rub your eyes, especially for the first 3 to 5 days. You may also experience sensitivity to light, glare, starbursts or halos around lights, or the whites of your eye may look red or bloodshot. These symptoms should decrease as your eye recovers over the next several weeks.

You should contact your doctor immediately if you develop severe pain or if your vision or other symptoms get worse instead of better. Follow all postoperative instructions given to you by your surgeon and surgical center.

Remember to:

• Wash your hands before putting drops in your eye.
• Use the prescribed medications to help minimize the risk of infection and inflammation. Serious infection or inflammation can result in loss of vision.
• Try not to get water in your eyes until your doctor says it is okay to do so.
• Try not to bend from the waist to pick up objects on the floor, as this can cause undue pressure to your eyes. Do not lift any heavy objects.
• Do not engage in any strenuous activity until your doctor says it is okay to do so. It will take about 8 weeks for your eye to heal.

Long-term

Your doctor will instruct you to return for additional follow-up visits to monitor your progress. Initially, these visits will be closer together (a few days to a few weeks apart) and then they will be spread out (several weeks to several months apart). It is important to go to all these appointments, even if you think you are doing well, so that the doctor can check for complications that you may not be aware of.

Because you will have a permanent implant in your eye with long-term risks, and especially since all these risks are not known at this time, you will need to be followed by an eye doctor on a regular basis for the rest of your life. Endothelial cell counts will have to be performed on a regular basis. You and/or your doctor should maintain records of these measurements, so as to be able to estimate the rate of cell loss. It is especially important for you to have your endothelial cells counted before you and your eye doctor consider any other intraocular procedures, such as cataract surgery, that will decrease the endothelial cell count even further.

Annual eye exams are usually recommended. However, if you have any problems with your vision or your eyes, such as flashing lights, floating spots, or blank spots in your vision (symptoms of a retinal detachment), you should see an eye doctor right away and inform him or her that you have a phakic lens implant. When participating in sports or other activities during which you might injure your eye, like home improvement work, always wear protective eye wear, such as safety goggles.

Use the following checklist to help you guide your discussion with your doctor about phakic lenses.

Know what makes you a poor candidate

• Do I have any conditions that would increase my risks?
• Are the size of my pupils under low lighting conditions bigger than the size of the lens? If so, what are my additional risks?
• Is my anterior chamber shallow? If so, what are my additional risks?

Know all the benefits, risks, and alternatives

• What are the benefits of the phakic lens for my amount of nearsightedness?
• What are the risks of having the phakic lens implanted?
• What is my risk of needing a corneal transplant in the future, if I have the phakic lens implanted, based on my age and my endothelial cell count?
• What could happen if I get hit in the eye or head after phakic lens implantation that might be different from what could happen if I did not have the lens implanted? Are my chances greater for a more severe injury after phakic lens implantation?
• Can the phakic lens be removed? What are the risks of removing the phakic lens?
• What other options are available for correcting my nearsightedness?

Know preoperative, operative, and postoperative expectations

• Will I need to limit my activities after treatment? If so, for how long?
• What quality of vision can I expect in the first week, first few months, and a year after surgery?
• What is the possibility that the phakic lens will not completely correct my vision or that my prescription might be worse than before surgery? What options for additional treatment will be available to me, if needed?
• How likely is it that I will need to wear glasses or contact lenses immediately after surgery and as I grow older?
• Should I have the phakic lens implanted in both eyes?
• What vision problems might I experience if I have the phakic lens implanted in only one eye?
• How long will I have to wait before having surgery on my other eye?

Know what the costs are

• How much will the surgery and follow-up cost? Will my health insurance cover this surgery?
• Will there be additional costs if I need additional procedures because the phakic lens implanted in my eye is too strong or too weak or because I have astigmatism? What is the likelihood of this happening?

Accommodation: the ability of the eye to increase its focusing power. As an object is viewed closer up, greater focusing power is needed to continue to see it clearly.

Anterior Chamber: the fluid-filled space in the eye between the back surface of the cornea (endothelium) and the front of the iris.

Antibiotic: a medication to treat or prevent infection from bacteria.

Anti-inflammatory: a medication to reduce inflammation (the body's response to surgery, injury, irritation, or infection).

Astigmatism: a distortion of the image on the retina caused by irregularities in the refractive power of the cornea and/or lens.

Cataract: cloudiness of the natural lens inside the eye that can blur vision.

Cornea: the clear, transparent cover over the iris and pupil on the front part of the eye. The cornea is the first part of the eye that bends (or refracts) the light and provides most of the focusing power of the eye.

Corneal Edema: abnormal fluid build-up in the cornea that can cause haziness and swelling of the cornea and resulting blurred vision.

Corneal Transplant: surgical treatment where the patient's cloudy cornea is cut away and a clear cornea, donated by someone who has died, is sewn into its place.

Crystalline (Natural) Lens: the eyes natural lens that bends light (refracts) to provide some of the focusing power of the eye. The eye's natural lens is able to change shape allowing the eye to focus at different distances.

Diopter: unit of measurement of refractive error. A negative diopter prescription for glasses or contact lenses signifies an eye with nearsightedness and positive diopter prescription signifies an eye with farsightedness.

Double Vision: seeing two images of a single object instead of one.

Endothelial Cells: the cells that line the inner surface of the cornea in a single layer (endothelium). They are responsible for pumping fluid out of the cornea to keep it clear. These cells gradually decrease in number over a lifetime. They can die off faster than normal from damage during surgery or after surgery. If the number of endothelial cells becomes too low, your cornea becomes cloudy, you lose vision and may require a corneal transplant.

Endothelium: the innermost layer of cells lining the inner surface of the cornea.

Farsightedness (Hyperopia): the inability to see near objects as clearly as distant objects. The need for accommodation to see even distant objects clearly, because the focusing power of the eye is too weak when the eye is not accommodating. Light rays come to focus behind the retina instead of on the retina when the eye is not accommodating.

Glare: scatter from bright light that causes discomfort and can decrease vision and the ability to perform tasks like driving.

Glaucoma: a group of eye diseases characterized by pressure that is too high for the optic nerve (the nerve that sends the signal of images created by the eye to the brain) to withstand. Damage to the optic nerve from glaucoma results in loss of peripheral and then central vision. Glaucoma may be treated with medications or surgery to try to stop further damage to the optic nerve and further loss of vision.

Halos: hazy rings around lights.

Hyperopia: see: farsightedness

Inflammation: the body's response to surgery, injury, irritation, infection, or some foreign substances, often associated with pain, heat, redness, swelling, and/or loss of function.

Informed Consent: the process of obtaining a patient's permission for a procedure after the patient and doctor have discussed the risks, benefits, and alternatives of the procedure and the patient understands them.

Informed Consent Document (Consent Form): a form listing the most common and worst possible risks of a procedure, the alternatives to the procedure, and the possible benefits of the procedure, which the patient signs to document their agreement to have the procedure at the end of the Informed Consent process.

Intraocular: inside the eye.

Intraocular Lens: a lens that is surgically implanted inside the eye.

Intraocular Pressure: the pressure of fluid inside the eye.

Iris: colored ring of tissue suspended behind the cornea and immediately in front of the lens separating the anterior chamber from the posterior chamber.

Iritis: inflammation of the front portion of the eye that can lead to scarring inside the eye and glaucoma.

Iridotomy incision of the iris.

Laser Iridotomy: production of a small hole in the outer edge of the iris using a laser beam.

Myopia: see nearsightedness.

Nearsightedness (Myopia): the inability to see distant objects as clearly as near objects, because the focusing power of the eye is too strong. Light rays come to focus in front of the retina instead of on the retina.

Optic Nerve: the large nerve of the eye that carries visual signals from the retina to the brain to allow sight. Damage to the eye's optic nerve results in loss of vision or blindness. Once the optic nerve is permanently damaged, it cannot be repaired or replaced by a transplanted optic nerve.

Over Correction: the refractive error of the eye is corrected too much causing someone who is nearsighted to become farsighted or someone who is farsighted to become nearsighted.

Peripheral Iridectomy: surgical removal of part of the iris near its outer edge.

Phakic: with the natural lens of the eye; from the Greek word "phacos" meaning lens.

Phakic Lens: an intraocular lens that is implanted in the eye with the eye's natural lens still in place.

Posterior Chamber: the space in the eye between the back of the iris and the front of the vitreous (the jelly-like substance that fills the space in the back central portion of the eyeball).

Pseudoexfoliation: abnormal deposits of white, flaky material seen on the structures in the front part of the eye that may be associated with cataracts and high pressure in the eye or glaucoma.

Pupil:the black hole in the center of the iris that changes size in response to changes in lighting. It gets larger in dim lighting conditions and smaller in bright lighting conditions.

Pupillary Block: blockage of the flow of fluid from the posterior chamber to the anterior chamber of the eye through the pupil. This can cause the pressure to build up inside the eye and can result in glaucoma.

Refraction: a test to determine the refractive power of the eye; also, the bending of light as it passes from one medium into another.

Refractive Error: imperfections in the focusing power of the eye, so that light rays are not brought into sharp focus on the retina, causing blurred vision that can usually be corrected with glasses or contact lenses. Nearsightedness (myopia), farsightedness (hyperopia), and astigmatism are refractive errors.

Refractive Power: the ability of an object, such as the eye, to bend light as light passes through it.

Refractive Surgery: general term referring to many different procedures to correct the refractive error of the eye.

Retina: a thin layer of sensory tissue that lines the inside wall of the back part of the eyeball. The retina acts like the film in a camera to capture images created by the focusing power of the cornea and the lens and transform them into electrical signals that are sent to the brain through the optic nerve.

Retinal Detachment: separation of the retina from its attachments to the back of the eyeball often resulting in loss of vision. Flashing lights, floating spots, and blank spots in vision can be symptoms of a retinal detachment.

Sclera: the white, protective outer layer of the eyeball that is continuous with the cornea in the front of the eye.

Shallow Anterior Chamber: narrowness of the space between the cornea and the iris.

Under Correction: the refractive error of the eye is not corrected enough leaving someone who is nearsighted still nearsighted or someone who is farsighted still farsighted to a certain degree.

Uveitis: general term for inflammation of the eye. Inflammation can be in the anterior (iritis), intermediate, and/or posterior portion of the eye.

Visual Acuity:the sharpness of vision; the measurement of the eye's ability to distinguish object details and shape.