Eye Dictionary: C
carbonic anhydrase inhibitor. This is a class of drugs that are often used for treating glaucoma. These drugs work by decreasing the production of aqueous fluid inside the eye. Examples of this drug class include Trusopt (dorzolamide), Azopt (brinzolamide) and the combination drop Cosopt. This medication is also available as a diuretic pill Diamox which we sometimes use for treating resistant glaucoma. Diamox also helps decrease intracranial pressure in cases of pseudotumor cerebri.
cataract. A cataract is when the normally clear lens inside the eye becomes cloudy. This cloudiness is a normal aging process and occurs in everyone with time, though congenital and premature cataracts can occur in youth as well. A cloudy cataract can cause visual difficulties. One of
the earliest symptoms is glare or halos, especially with nighttime driving. Other symptoms include difficulty with fine visual details such as seeing distant road signs, reading small letters on television, and deciphering small print. As cataracts worsen, they can cause significant visual problems and even blindness. Fortunately, cataract surgery has advanced dramatically over the past few decades and cataracts are rarely a major problem these days.
cataract extraction. This is a fancy way to say cataract surgery. We say "extraction" because the cataract lens is removed from the eye during surgery. See cataract surgery for more details on the actual procedure.
cataract surgery. Cataract surgery is a procedure that involves removing the cloudy cataract from your eye and replacing it with a clear lens implant. This procedure takes only 15 minutes and with modern techniques can be done with no needles or stitches. A small microincision is created through the cornea to gain access to the cataract lens. The cataract is then vacuumed out using an ultrasonic probe. This is called phacoemulsification. A new intraocular lens (IOL) implant is
then injected back into the eye. This implanted lens folds very small but once inside the eye, unfolds like a blossoming flower. This replaces your cataract with a new clear lens, improving vision and eliminating glare. This is a high-tech, refined technique used by myself and most cataract surgeons due to its low rate of complication and rapid healing time.
cellulitis. This is an infection of the skin around the eye. The cause for cellulitis is sometimes obvious - a scratch on the skin or bug bite becomes infected. Many times, however, the initial insult is not discovered. A cellulitis infection spreads under the skin and causes skin redness, heat, and impressive eyelid swelling. When isolated to the superficial layers of skin, this type of infection is generally minor and is treated with oral antibiotics and careful monitoring. If the infection penetrates deeper through the septum layer of the eyelid, than the eyeball and ocular muscles can be involved. This is called post-septal or "orbital" cellulitis. This deeper infection is serious and usually warrants
hospitalization, IV antibiotics, and potentially, abscess drainage.
central retinal artery. This is the main artery that supplies blood to the eye, specifically the retina. The artery travels inside the optic nerve. Once the artery enters the back of the eye at the optic disk, it branches widely within the superficial layers of the retina. These coursing blood vessels can be examined during a dilated eye exam. This is the only artery in the body that is visible to the naked eye (i.e., not obscured by opaque skin). Some medical problems, like hypertension, can be detected by looking at this artery during an eye exam.
central retinal artery occlusion (CRAO). This is a blockage of the all-important central retinal artery that supplies blood to the inner eye. This blockage usually occurs from embolic sources, such as a cholesterol plaque from the carotid artery or a blood clot from an irregular beating heart. Unfortunately, the retina has no backup blood supply, so when the central retinal artery is clogged, retinal damage occurs rapidly. Symptoms are usually described as a "blacking out" of the vision or seeing a "curtain coming down" associated with severe vision loss. This vision loss is usually permanent and treatment is usually focused on finding the cause to avoid future embolic problems that might cause more eye problems ... or even a stroke.
central retinal vein. This is the main vein that drains blood out of the eye and away from the retina. This vein runs with the central retinal artery and leaves the eye through the optic nerve.
central retinal vein occlusion (CRVO). This is a blockage of the main vein that drains blood out of the eye. Without this drainage, blood can't get out of the eye and it backs up into the retina. The retina can become swollen with blood, causing serious problems. Depending upon the severity of the swelling, vision can be severely affected, though it sometimes improves with time (though rarely as good as new). Treatment may involve a fluorescein angiogram to evaluate the extent of damage and sometimes laser therapy or anti-VEGF injections if there is residual retinal swelling. One potential problem after a CRVO is neovascularization ... this is the formation of abnormal blood vessels inside the eye that can cause future retinal damage and, if the new vessels block the angle, a severe angle closure glaucoma as well.
(Common Misspellings: centr, central, central ret, vein, occlu)
cephalexin. An oral antibiotic (trade name Keflex) that is often used for skin and sinus infections. This pill is available as an inexpensive generic. Some people find it a little harsh on the stomach.
(Common Misspellings: cefl,)
chalazion. This is a large lump that forms in the eyelid. They occur when one of the oil-producing meibomian glands that run along the eyelid margin become blocked. Oil backs up into the eyelid, and causes a large bump ... this can be tender at first but usually becomes painless with time. Sometimes warm compresses and massage can make these chalazions drain away on their own. Often, however, an inflammatory "capsule" will form around the oil and the bump remains no matter how aggressive you are with massage. In these cases we can manually drain the chalazion. This involves numbing the skin with lidocaine, flipping the eyelid over, and draining the chalazion from the inside of the eyelid (to avoid scarring on the outer eyelid skin). This speeds recovery, but the chalazion can still take many months to go away completely.
chemical injury. A chemical splash to the eye can be very painful and potentially blinding. Strong acids and bases can cause corneal scarring and permanent vision loss if not treated promptly. The most common chemical injuries seen are from household cleaners splashed into the eye. Other toxins include hair dye, ear medicines, and anti-fungal nail drops mistakenly used in the eyes. The treatment for any chemical injury is irrigation - immediately wash the eye out. The faster and more thorough you wash your eye, the better the ultimate outcome. In the emergency room, doctors will occasionally use a Morgan lens, a plastic cup placed in the eye that is attached to bags of saline to allow copious irrigation over 15-30 minutes. Chemical splashes are the only eye problem where we recommend a therapy "before" you even see the doctor.
chemosis. This is swelling of the conjunctiva skin, usually from allergy. The surface of the eye is covered by a very thin layer of skin called the conjunctiva. This skin layer is clear, but has blood vessels running through it that you can see when looking at the white of the eye in the mirror. Irritation to this skin causes fluid to collect under the surface and bulge this skin forward. This swelling can be quite impressive and alarming. As long as the vision is unchanged, however, this is rarely an emergency. Treatment usually involves allergy drops and occasionally steroid eye drops to decrease swelling.
choroid. The choroid is a layer of blood vessels that lie underneath the retina and supply some of the blood supply to the retina. The choroid circulation also helps remove the waste products from the photoreceptors (rods and cones) and processes them back into the circulatory system. Conditions like macular degeneration create a blockage between the choroid and retina, leading to retinal atrophy over time and vision loss.
chronic open angle glaucoma. This is the most common type of glaucoma. Glaucoma is usually described as high pressure inside the eye that causes damage to the optic nerve over time. The mechanism of this damage is not entirely clear ... but something about high pressure causes atrophy of the optic nerve over many years. The optic nerve is important because it connects the eyeball to the brain, and when damaged, the vision is permanently damaged. Most people with glaucoma have the "chronic open angle" variety, which is also called primary open angle glaucoma (POAG) or just plain "glaucoma." It is believed that something microscopic clogs the drainage "filter" inside the eye, leading to chronically elevated pressure. Unfortunately, there is no single test to determine if someone has glaucoma, so we look at several risk factors to determine risk and monitor progress. This includes eye pressure (obviously), visual fields (to evaluate peripheral vision), and OCT photographs of the optic nerve looking for changes that might indicate progression. Treatment is geared toward lowering the eye pressure with medication eye drops, laser therapies (SLT), and even surgery in advanced cases.
ciliary body. This is a ring of muscle that sits behind the iris (the colored part of the eye). The ciliary body has two main functions – to focus the vision and to produce aqueous fluid. To help the eye focus, the ciliary muscle can contract like a sphincter. The ciliary body is attached to the lens by zonules (strings) in a 360-degree ring (like the springs on a trampoline). When the ciliary muscle contracts, the tension on the zonular springs relaxes and the lens changes shape accordingly. This helps focus the eye to see near objects. The ciliary body also has cells that produce the aqueous fluid that fills the front chambers of the eye. The production (and drainage) of this aqueous fluid is what determines the internal ocular pressure of the eye, which is important in our discussion of glaucoma.
Ciloxan. This is the trade name for the antibiotic eye drop ciprofloxacin (commonly called Cipro"). Ciprofloxacin is a fluoroquinolone antibiotic that has good general bacterial coverage and is good for infections of the cornea. It may not be as powerful as the newer (and more expensive) medicines in the same class, however, such as moxifloxacin (Vigamox) and gatifloxacin (Zymaxid).
ciprofloxacin. This is an antibiotic eye drop that is also available in pill form - it is commonly called "cipro." This antibiotic is in the fluoroquinolone class of drugs and therefore has good general bacterial coverage ... including covering most strains of pseudomonas (a particularly virulent bacteria found with many contact lens). Newer medicines in this class include moxifloxacin (Vigamox or Moxeza), gatifloxacin (Zymaxid) and Besivance.
color blindness. This is when a person has a difficult time with color vision. Cones are the light receptors in our eyes that detect color and there are three types: red, green, and blue detectors. If any of these color-sensors are abnormal, color-detection will become flawed and a person may be considered "color blind." Many of the genes that control the development of these color cone cells are located on the Xchromosome. Males, who have only one X-chromosome to rely on, are more likely to have developmental color problems. In fact, about 8% of men have some color issues (usually difficulty with subtle red-green hues) while only 0.4% of women have this problem. There are a few conditions that can affect color as well, such as an active bout of optic neuritis and long-term use of the arthritis medication Plaquenil (though this is rare).
Combigan. This is a combination glaucoma drop. It containsbrimonidine (i.e., Alphagan) and the beta-blocker timolol. This drop is usually used twice a day. Combination drops like this decrease the number of drops you have to take and tends to improve eye comfort by minimizing exposure to preservatives like BAK. This convenience may cost more, however, as both brimonidine and timolol are available as generics when bought and used separately. Cones are the photoreceptor in our retina that let us see in color. Cone cells are located deep in our retina and come in three different varieties, each sensitive to a different color spectra: red, green, and blue. Cones are very important for daylight vision and also for detecting fine visual needed to read small print. The macula, the central part of the retina that's responsible for our fine vision, is composed primarily of cones with more rods located in the peripheral retina. People with color blindness typically have a genetic problem with one of their cone types.
conjunctiva. This is the thin layer of skin that covers the white part (the sclera) of the eyeball. The conjunctiva is very thin and has blood vessels coursing through it that you can see when looking in the mirror. The conjunctival skin also loops over and forms the inside of the eyelids themselves. This "looping" is what keeps objects like eyelashes and contact lenses from slipping completely behind the eye. When irritated, the conjunctival blood vessels dilate and make the eye look "pink." This is called pink-eye, or more formally conjunctivitis. If a blood vessel breaks, blood can collect under the conjunctival skin and cause an impressive subconjunctival hemorrhage.
conjunctivitis. This is an irritation or infection of conjunctiva and is sometimes called "pink eye." There are many causes for conjunctivitis, but these usually fall into three categories: allergic, bacterial, and viral infection. With allergic conjunctivitis, the eye is typically irritated and "itchy." The eyelids can become puffy, and fluid can collect under the conjunctival skin and bulge it outwards (which looks quite scary). Viral conjunctivitis is what we usually think of as "pink eye." This is a viral infection of the eye similar to the common cold. Just like a cold, there is no effective treatment other than symptomatic relief and careful hygiene (as viral infections are quite contagious). Bacterial conjunctivitis usually affects only one eye and is associated with purulent (gunk or pus) discharge. This is treated with antibiotic drops. It is often hard (even for the eye doctor) to determine the exact cause of a conjunctivitis. If your eye is red you should see your eye doctor, especially if there is any change to the vision.
contacts. Contacts are plastic lenses that are placed directly onto the eye to improve vision. There are two main varieties: soft contact lenses, and hard rigid gas permeable (RGP) lenses. Most people use soft contacts as they are more comfortable and inexpensive, though hard RGP contacts are easier to manipulate with the fingers and get into the eye. Soft contacts have gotten so cheap that they are now available in disposable form and no longer require the extensive cleaning regimens of the past. Advanced toric contacts can now fix astigmatism and multifocal contacts can sometimes help with reading vision. Colored contacts have color pigment silk-screened on the plastic to change eye color - I don't recommend these as they have a high rate of eye infection. The newer contact lens designs allow much more oxygen to permeate through the plastic and have been approved for extended wear so that you can sleep in them ... I don't necessarily recommend this either, as wearing contacts for extended periods dramatically increases the likelihood of infection, GPC, and corneal ulcers. Contact lenses are much harder to "fit" than glasses as they come in different steepness and diameters, thus contacts usually require a "fitting" for the first-time user and a refitting with any
major prescription changes.
convergence. This is when the eyes turn inwards. For example, the eyes need to converge when looking at close objects such as when reading a book. People with a convergence insufficiency have a hard time with this and may have double vision when reading. Treatment may involve prism reading glasses and occasionally eye exercises to strengthen the inner eye muscles.
cornea. The cornea is the clear window in the front of our eye that lets light inside. If you were to touch the "colored part of your eye" with your finger, you'd be touching the cornea. The cornea is an extremely important part of vision - it acts as a fixed lens and actually provides the majority of the focusing power of the eye. Opacities of the cornea, from past infections or trauma, can severely limit fine visual acuity. The cornea has 5 distinct structural layers. The surface layer is called the pithelium. This layer is very thin and can scratch off if a foreign body gets in the eye. This is called a corneal abrasion. The middle layer is called the stroma - if an injury gets into this middle layer, scarring can form with possible visual consequences. The inside layer of the cornea is very thin and called the endothelium. This inner layer is important as the cells in this layer contain "pumps" that suck fluid out of the cornea. The cornea is clear because it is relatively dehydrated compared to other tissues in the body. If the pump mechanism of the inner cornea is injured or abnormal (such as in Fuchs' dystrophy or after a traumatic cataract surgery) the cornea can become too wet and cloudy.
corneal abrasion. A corneal abrasion occurs when the surface layer of the cornea (the clear tissue that covers our eye) gets scratched. This usually occurs when a foreign body, like a piece of sand, gets into the eye. The surface layer of the eye is extremely thin and scratches easily. Fortunately, this tissue also heals quickly and most abrasions heal within a few days. Unfortunately, this process can be painful as there are more nerve endings in the cornea than anywhere else in the body. Treatment is usually geared toward avoiding infection with antibiotics. If the abrasion is large, painful, or healing slowly, other treatments may be instituted like patching the eye closed or putting a "bandage" contact lens on the eye. When an abrasion becomes infected, we call this a corneal
ulcer. Most abrasions heal with no long-term consequences.
corneal thickness. The cornea is the clear window that makes up the front of the eye. It has a normal thickness of 540 microns and this can be measured in the office with a handheld device called a pachymeter (see pachymetry). Corneal thickness is important for a couple of reasons. When we check eye pressure using applanation tonometry (the blue light on the slit-lamp microscope) we press on the eye to measure how "hard" the cornea "feels." A thick cornea can give a falsely high pressure reading while a thin cornea can give a falsely low pressure. Thin corneas have been found to be an independent risk factor for glaucoma. Also, if you are contemplating LASIK surgery, you need to have a thick enough cornea to be a good candidate.
corneal topography. This is the measurement of the surface characteristics of the cornea. See topography for more information on this topic.
corneal transplant. A corneal transplant is when part of the cornea is replaced surgically. This may be necessary because of corneal opacities from past infections, traumatic scars, or decompensation of the cornea from prior intraocular surgeries. Several congenital abnormalities, such as keratoconus, may also need a corneal transplant to rehabilitate vision. Traditionally, a full thickness corneal transplant involves removing the central cornea and replacing it with a donor corneal button. This is done with extremely small stitches under a surgical microscope. These stitches are usually removed one by one over time. Certain conditions, such as Fuchs' Dystrophy, require only partial corneal transplants (called a DSEK) and have a much faster healing time. Because of advances in contacts and cataract surgery, corneal transplants are done much less often these days. This type of surgery is usually performed by a corneal specialist.
corneal ulcer. This is when an infection (bacterial, fungal, or viral) invades the cornea, the normally clear window that makes up the front of your eye. The cornea is unique because it is one of the few tissues in the eye that is clear, allowing us to see bacterial infections with no opaque skin blocking our view. Corneal ulcers usually look like a small white spot on the surface of the eye, though they are usually so small that they can only be seen using the slit lamp microscope. These infections can occur after a corneal abrasion, with contact lens use, and sometimes randomly with no obvious cause. Treatment is aggressive and involves antibiotic drops (often multiple antibiotics) to nip the infection in the bud as quickly as possible. Ulcers can be severe and penetrate all the way through the cornea and result in loss of the eye (very rare). Ulcers can also create scarring of the normally clear cornea. This scarring can limit the vision and necessitate a corneal transplant if severe enough.
Cosopt. This is a combination glaucoma drop. It contains dorzolamide (Trusopt) and timolol. It is usually used twice a day. A preservative-free version is now available, though it is more expensive.
cranial nerve palsy. The head and face are innervated by twelve separate "cranial" nerves. Each of these nerves has a different function. For example, the first cranial nerve (CN1) controls smell, while the eighth nerve (CN8) controls hearing. The main nerve we are concerned with is the second nerve (CN2) which is the optic nerve and transmits visual signals to the brain. The other nerves we watch are the ones that control eye movement ... this is the third (CN3), fourth (CN4) and sixth (CN6) nerves. If these "motility nerves" become damaged we call this ”palsy." Most cranial nerve palsies occur because of vasculopathic problems like diabetes or hypertension where the nerve doesn't get enough oxygen and shuts down. This is usually temporary and improves over six months. Other causes are more concerning, such as a tumor or aneurysm pushing on the nerve. See the entries on third nerve palsy, fourth nerve palsy, and sixth nerve palsy for more information.
cromolyn. An older allergy drop. I never prescribe cromolyn giventhe plethora of newer allergy drops available.
cross-eyed. This is when the eyes turn inwards toward the nose. In medical circles, we call this esotropia. This alignment problem can be congenital or arise in adulthood from a cranial nerve palsy or a stroke. In childhood, crossed eyes are usually corrected with strabismus surgery. The goal is to straighten the eyes for primary vision (when looking straight ahead and reading) to help with stereoscopic vision and avoid the formation of amblyopia. Prism glasses can also help alleviate double vision.
Crystalens. This is a premium implant used in cataract surgery that allows people to focus at both distance and near. Standard implants are fixed focus lenses, like a magnifying glass, and are only calibrated for one distance (i.e., you will need reading glasses after surgery). The Crystalens has a unique hinge design that allows it to rotate forward and back ...kind of how a telescope focuses. This more closely simulates the action of the original lens inside our eye and may eliminate your need for reading glasses after surgery. The effect of the Crystalens has had mixed results ... many people have good focal range afterwards, but others have much less effect (or the bifocal effect goes away after a few years). The nice thing about this lens, however, is that even if the bifocal effect doesn't work or wears off, the lens itself is just as clear as a standard lens implant and so no loss of actual "acuity" or "crispness" is suffered by choosing this lens. We are currently using more Restor lenses in our own practice, however, as the bifocal effect seems to be a little more predictable. Florence Henderson (the mother on the old Brady Bunch TV program) had a Crystalens for her own eye surgery and is featured in some of their commercials.
cyclopentolate. This is a moderate strength dilating drop used in the office to enlarge the pupils. This dilating drop lasts longer than tropicamide and is usually reserved for dilating children as they have strong eye muscles and are harder to dilate. This drop also has cycloplegia effects and is helpful when performing cycloplegic refraction in children. I occasionally prescribe cyclopentolate to help with photophobia (eye pain) for people with internal eye inflammation, such as from iritis or uveitis.
cycloplegia. This is when the eyes are dilated using eye drops. Certain dilating drops make the pupil larger, but they also paralyze the muscles inside the eye that control lens focusing. This paralysis is called cycloplegia. This effect is helpful when checking the vision in children (we call this cycloplegic refraction) as kids tend to "strain" when reading the eye chart. Eliminating this strain through temporary "cycloplegic paralysis" gives a more accurate prescription. Cycloplegia can also be helpful for pain control in people with ocular inflammation, such as iritis or uveitis. By paralyzing the muscles inside the eye, they don't spasm asmuch around bright lights, which makes the eye more comfortable overall. The cycloplegic drops we use in our office include tropicamide (most adults) and cyclopentolate (children). Atropine is the longest acting cycloplegic and was originally obtained from the belladonna nightshade plant - it was used in Victorian times to make women look "beautiful" by dilating their eyes. Most people have difficulty reading while dilated with cycloplegia drops.
cycloplegic refraction. This is the method for checking glasses prescription in children. Children have strong muscles inside their eye that make it hard to measure their vision during a refraction. They can "strain" while reading the eye chart, throwing off our measurements. By using cycloplegia dilation drops, we temporarily paralyze these eye muscles and can capture a more accurate glasses check. Many children require their eyes to be dilated this way and this can really extend your office visit time tremendously.