CATS - Cataract Formation and Contact Lenses
Learning Objectives:
Upon completion of this course, participants will be able to:
- Describe how pervasive, life-disrupting and downright menacing cataracts can be and how contact lenses provide a solution for some.
- List the characteristics of cataract formation, diagnosis, and management.
- Explain cataract removal, various replacement lenses, and other management tools.
Faculty/Editorial Board
Sam Winnegrad, ABOM, NCLEC, is a master optician who has instructed anatomy and physiology of the eye and other various ophthalmic courses for Roane State Community College in Harriman, Tennessee. He has also taught for Highline College's online optician program out of Des Moines, Washington. Sam is a technical speaker for the American Board of Opticianry and National Contact Lens Examiners. Sam holds a master's degree in business administration and a bachelor's in science, but above all, he treasures his license to practice opticianry.
Credit Statement
This course is approved for one (1) hour of CE credit by the National Contact Lens Examiners - NCLE, Ophthalmic Level 2. Course # CTWJHI118-2
INTRODUCTION
By age 6, full emmetropization occurs, with There are few conditions as pervasive, life disrupting and downright menacing as cataracts. Cataracts are defined as a clouding of the crystalline lens. The lens increasingly opacifies until light has difficulty passing through—making image formation progressively more challenging. Though prevalent, cataracts are often misunderstood. It can be challenging to educate patients on the anatomical changes they are experiencing and “walk them through” their visual changes. Over 3.5 million cataract procedures are performed yearly in the United States, and over 20 million are performed worldwide. With the aging baby-boomer demographic, those numbers are steadily rising, and with the surging trend of cataract cases, the numbers are on the upswing. The eyecare professional must be able to educate patients on how a cataract diagnosis may affect visual performance. Often, this is complicated for patients who wear contact lenses. While contact lenses do not exacerbate cataract formation, patients will often struggle with the psychological implications of their refractive changes and their impending surgical procedure. As eyecare professionals, properly educating our patients is the best way that we can serve them and begin to take care of their unique visual needs.
THE REFRACTIVE PATHWAY
The tear film is the first refractive medium of the eye. As
light waves encounter the eye, they pass through this medium
before entering the cornea. Though seemingly innocuous,
the tear film is intricately complex. There are three layers
of the tear film. The first layer, most external to the
environment, is called the lipid or oily later. The lipid layer’s
primary function is to prevent the tear film from premature
evaporation off the eye. The middle layer comprises the
brunt of the tear film and is called the aqueous layer. This is
the “watery” composition of the tear film. The aqueous layer
supplies most of the nutrition to the cornea and even houses
antimicrobial agents such as lysozyme. The innermost layer
of the tear film is called the mucoid or mucous layer. This
layer is produced by goblet cells of the conjunctiva. As the
name of the mucoid layer suggests, it is sticky and serves to
keep the tear film on the eye.
The mucoid layer turns the hydrophobic (repels water) cornea and conjunctiva into hydrophilic (loves water) surfaces. A healthy tear film is crucial for the patient to experience sharp vision. Not only must the tear film be of good quality and not evaporate too fast, but there must also be enough tears produced. Two standard tests used in contact lens fitting are the break-up-time and Schirmer’s tests. The break-up-time test determines the quality of one’s tears, while Schirmer’s test reveals the quantity of tears (i.e., Does this person produce enough tears to maintain a moist environment?). Keratitis sicca, also known as dry eyes, is a prevalent condition where patients are either not producing enough tears, or the tears they produce lack qualities that enable the eye to stay moist. If one’s tear film is not smooth, light that passes through the eye will not have consistent refractive properties, resulting in blurry vision.
The cornea is the most refractive medium of the eye, supplying an average of +43.00 diopters of strength. It comprises five distinct layers, from anterior to posterior; the layers of the cornea are Epithelium, Bowman’s, Stroma, Descemet’s and Endothelium. The cornea is primarily made up of collagen. These fibers lay perfectly parallel to one another, allowing for complete transparency. The average contact lens prescription is around 1.50 diopters—yet the cornea supplies +43.00 diopters and is only 0.5 millimeters thick in the center, thinning to 0.1 millimeters at the periphery. It is truly an amazing tissue.
In addition to the visual Furthermore, the cornea has no blood vessels running through it to supply oxygen and nutrition. If the cornea had blood vessels within the tissue, it would impede vision. Instead, the cornea receives its nutrition through the tear film and blood vessels that end in loops at the limbus and through the process of deturgesence, where the endothelial layer of the cornea pumps aqueous fluids throughout the corneal tissue. When light enters through the cornea, ideally, it enters at the same angle. If the cornea is flatter or steeper along varying meridians, this will change how light behaves as it passes through the eye. Corneal astigmatism is where the cornea is not perfectly spherical and has varying degrees of steepness. This condition causes light rays to focus at varying points on the retina. The keratometer measures the cornea’s dioptric strength and thus, the steepest and flattest meridians. Using the keratometer, one can determine the amount of corneal astigmatism.
The crystalline lens supplies, on average, +17.00 diopters of strength in its relaxed (non-accommodative) state. It is the eye’s internal lens, yielding roughly one third of the eye’s overall refractive power for distance vision. In its accommodative state, the crystalline lens becomes thicker, and its refractive power increases by as much as +13.00 diopters, accommodating near focus. The crystalline lens is transparent, like the tear film and the cornea. Also, much like the cornea, the crystalline lens can be the object of astigmatism in the visual pathway. One common cause of this is called lens subluxation. Lens subluxation is a displacement of the crystalline lens from its normal position. While the keratometer measures corneal astigmatism, we measure crystalline lens astigmatism by subtracting the corneal astigmatism (K readings) from the total astigmatism found in the manifest refraction. For example, if a patient refracted with -4.00 diopters of total astigmatism, and the keratometer determined that there were -2.50 diopters of corneal astigmatism, we would infer that there are -1.50 diopters of crystalline lens astigmatism. The crystalline lens is composed of distinct layers. The innermost layer is the fetal nucleus. Working outward, we encounter the embryonic nucleus, adult nucleus, cortex, epithelium and capsule. The lens is biconvex and is responsible for accommodation, which is the ability of the eye to change its focus from distance to near objects. As the ciliary muscles tighten, the zonule fibers loosen, allowing the crystalline lens to relax, increase in thickness and gain accommodative amplitude for near vision. A cataract is a clouding of the crystalline lens. Next, we will look at some of the distinct types of cataracts.
CATARACTS
Congenital cataracts are cataracts that are present at birth. There are quite a few known reasons why cataracts may develop in newborns. The most common cause is if the birth mother has measles or rubella. There is a strong link between these illnesses and congenital cataract development in the child. Other causes include trauma, diabetes, infection and reaction to medications. Cerulean cataracts are one specific type of congenital cataract that manifests bilaterally (both eyes) as tiny blue dots throughout the crystalline lens. This type of cataract generally does not require any intervention. If a cataract is causing significant vision loss, a surgical procedure will be required. It is crucial that after the baby’s lens is removed, it is either replaced with an intraocular lens or that the child is prescribed contact lenses or eyeglasses. Many times, contact lenses are the best option. In most cases, if an IOL is implanted, it would need to be replaced through adolescence, which involves multiple procedures. When babies are fit with contact lenses, an extended wear lens is generally fit to simplify care management. Detection and surgical intervention are vital for these young children, as their mental and physical development is at stake. Occasionally, congenital cataracts are not detected at birth, and conditions such as amblyopia, otherwise known as “lazy eye,” develop as the brain circumvents the eye that contains the cataract. Newborns should have their eyes examined after birth, and parents should be encouraged to bring their children to an eye doctor starting at age 3 to detect conditions such as these.
Nuclear sclerotic cataracts are a natural part of the aging process. This is the most common type of cataract. As we age, the cells of the crystalline lens die and migrate toward the center or nucleus of the lens. These protein-based cells compound and eventually turn the lens opaque, stiff and yellowish. This hardening of the nucleus makes vision incredibly difficult and will eventually require surgery when the impairment affects the patient’s quality of life. Nuclear sclerotic cataracts generally take many years to develop. The average patient age at the time of procedure to remove nuclear sclerotic cataracts is 74 years old, although these cataracts may develop much earlier in life. Nuclear sclerosis of the lens can produce varying symptoms. Some of the more common symptoms related to this formation include having difficulty discriminating between shades of the same color, experiencing glare and seeing halos around lights. Double vision is sometimes also associated with nuclear sclerotic cataracts. One interesting symptom of nuclear sclerosis is that many patients experience a transient improvement in their near-focus vision as the lens is ripening. Frequently, patients will have swift refractive changes during the development of their cataracts— which is a common symptom associated with nuclear sclerosis.
Cortical cataracts are another common opacity of the crystalline lens. As the name implies, these cataracts form within the cortex of the lens, which is around the nucleus and close to the outer edge. Cortical cataracts take shape as white wedges that produce long projections growing toward the nucleus of the lens. Visually, upon slit lamp evaluation, these cataracts look like the spokes on a bicycle wheel. Unlike nuclear cataracts, which form when cells die and migrate toward the center of the lens, cortical cataracts form when the cortical cell fibers experience a metamorphosis, and the membrane becomes compromised. Some symptoms that are associated with cortical cataracts include blurry vision, difficulty driving at night, issues with glare and even seeing lines in the visual field. Other scotomas, which can be defined as a partial loss of vision in the visual field, can also manifest with cortical cataracts. As with nuclear sclerotic cataracts, cortical cataracts are generally a product of aging; however, these opacities can also form secondarily from trauma or disease.
Posterior subcapsular cataracts are the most common cataract diagnosis in patients less than 60 years of age. Younger patients may develop this type of cataract because it is closely linked to outside forces such as radiation exposure, trauma and corticosteroid use. The posterior subcapsular cataract will also sometimes develop in patients who experience chronic intraocular inflammation. With this cataract, an opacity forms in the back of the crystalline lens directly behind the capsule, as the name implies. Though these cataracts are generally not large, their positioning along the visual axis causes quite a disruption. Posterior subcapsular cataracts start as micro-opacities and will gradually increase in density as plaque builds. Patients with this type of cataract will have trouble driving at night and face excessive glare. They may also experience blurry vision at a near point focus, more so than at a distance focus. Those suffering from posterior subcapsular opacities will also have a difficult time seeing in bright lighting. Due to the rapid progression of this type of cataract, patients may experience dramatic differences in their vision within only months of initial diagnosis.
Traumatic cataracts describe a clouding and opacification of the crystalline lens that develops as a result of blunt or penetrating trauma to the eye. Each year in the United States, there are an estimated 2.4 million eye injuries. Fortunately, many of these eye injuries are preventable with proper eye protection. Statistically, most of these eye injuries occur within the younger male demographic. The crystalline lens is susceptible to other maladies outside of traumatic cataract formation. The lens may decenter from its original position, referred to as subluxation. The crystalline lens may also luxate, completely dislocating from the lens zonule fibers. Most traumatic cataracts occur because the lens proteins swell and become intumescent as a result of the force. Visually, a traumatic cataract will appear as a rosette or radiating star (stellate) pattern. Though beautiful to observe through biomicroscopy, this swelling and clouding of the lens will need to be addressed by an ophthalmologist to restore vision. Traumatic cataracts are not usually simple surgical cases. Often, when a traumatic cataract is caused by a penetrating injury, there are multiple issues that need to be resolved. Is the globe open? Do the cornea and the anterior chamber need to be repaired prior to the lens being replaced? The entirety of the visual pathway must be considered.
Secondary cataracts may sometimes develop after cataract surgery. In these instances, after an intraocular lens is implanted, the lens capsule itself will grow an area of scar tissue. This new growth will generally cause visual issues such as clouding and dimming of vision that will make the patient think that their cataract has grown back! However, patients are relieved to discover that it is nothing more than a posterior capsular opacity, or PCO. This opacity occurs in the back of the lens capsule that surrounds the newly implanted IOL. Physicians will perform a YAG capsulotomy to clear the opacity using a laser. In most cases, this is a onetime occurrence and does not need to be repeated.
PROCEDURES
The earliest known cataract procedures were performed in the 5th century B.C.—about 2,500 years ago! A quick survey of these early “surgeries” would make anyone thankful that they are living in the modern age of technology. Nowadays, patients will make positive remarks such as, “Was that it?” after their minimally invasive, pain-free procedure. During the 5th century B.C., physicians used a technique called couching. Couching is when they would jab a blunt object into the patient’s eye in hopes that they would break the zonule fibers and dislodge the lens. The aftermath would leave the crystalline lens sitting within the anterior chamber. These patients would also be unable to focus lights without any aid of eyeglasses or intraocular lens options. Obviously, the results were not wonderful, but it would permit light to pass through and reach the retina for some vision. A less destructive, yet equally as concerning method of cataract removal began to be used a few hundred years later, where a sharp object would penetrate the eye and cut the zonule fibers. This procedure led to the same results but with fewer complications (as one would imagine there would be with getting jabbed in the eye). The earliest recorded cataract removal was in Paris, France, in 1748, which is somewhat recent considering the grand scale of history. It was not until 1949 that the first successful intraocular implant was performed. Being able to replace the crystalline lens with an implant was a game changer, but it did not gain popularity until the 1970s as a widely accepted procedure.
Presently, the most common cataract procedure is called phacoemulsification. The prefix phaco translates to “lens” in Greek, and emulsification means to “break down into small particles.” Phacoemulsification is a process whereby the surgeon enters the anterior chamber and emulsifies the crystalline lens within the capsule, aspirates it out and then replaces it with an intraocular implant. Generally, topical anesthetics are used. However, in some cases, a local anesthetic injection is necessary. In limited cases, general anesthesia is administered, but this is usually reserved for children or adult patients with special needs or circumstances. After creating a small incision, the ophthalmologist will use a phacoemulsification probe to vibrate and break down the cataract rapidly. Sometimes, the nucleus of the lens is difficult to emulsify, and a secondary chopper tool is necessary. The surgeon will then introduce an aspiration probe to suction out the remnants of the lens. Lastly, the ophthalmologist will insert and correctly orientate the intraocular lens into the remaining lens capsule bag.
Prior to the commonplace use of intraocular lenses, patients who had their cataracts removed were considered aphakic, meaning that they literally had “no lens.” Considering that the average crystalline lens supplies roughly +17.00 diopters of necessary power, these patients would have to wear incredibly high prescription contact lenses or eyeglasses to be able to focus after lens removal. In modern times, physicians insert IOL implants into their aphakic patients during surgery to restore, and many times improve their patient’s refractive abilities to near perfect vision. Each IOL is hand selected based on multiple variables to yield the best visual results. Older technology IOL implants were rigid and made of polymethylmethacrylate, whereas newer lenses are pliable and can be folded upon insertion, requiring a smaller incision. Recent advancements in technology have paved the way for toric and multifocal intraocular lens implants, though these options usually carry a hefty out-ofpocket expense for patients. Never in history have patients been able to see so sharp and vivid after cataract surgery. Surgeons can dictate the vision that they want for their patients with incredibly accurate results.
On occasion, in the coming weeks after surgery, patients will experience what seems to be the return of their cataract; however, this is not the case. This is usually a posterior capsular opacity, as mentioned earlier. This opacity occurs in the back of the lens capsule that surrounds the newly implanted IOL. To remove this second cataract, a Yttrium Aluminum Garnet, or YAG, capsulotomy is performed. The procedure is painless, so patients do not require anesthesia. After dilation, the entire YAG capsulotomy generally takes less than five minutes as the surgeon lasers holes in the opacities on the posterior capsule. Restoration of vision may be immediate or may take a few weeks.
CATARACT POST-OPERATIVE EXPECTATIONS
After cataract surgery, patients will follow up with their surgeon or a co-managing optometrist for a one day, one week and one-month follow-up appointment. At the one-day post-operative appointment, the doctor will ensure that the surgery went as planned, and that the eye is beginning to heal. Another primary focus of this exam is to ensure that patients understand their drop regimen and that they have an opportunity to have any questions answered. Normal findings on the day after the exam may include a reduction in visual acuity, foreign body sensation, redness, residual dilation and a slight flare in the anterior chamber.
At the one-week post-operative appointment, the
doctor will ensure that the point of incision is
healed well enough that any prescribed antibiotics
can be discontinued. Any inflammation of the anterior
chamber should have resolved or at least greatly
reduced from the one-day appointment. This
appointment is also generally when the surgeon will
evaluate the second eye for cataract removal.
A comprehensive dilated examination is performed at the one-month follow-up. The purpose of the one-month exam is to ensure that the eye is well healed, and vision has been restored. A final post-operative refraction is performed at the onemonth appointment. This is when the doctor will write out an eyeglass or contact lens prescription.
WEARING CONTACT LENSES AFTER SURGERY
Though most cataract surgeries severely reduce or eliminate the need for corrective lenses, there are still various scenarios wherein patients may benefit from the use of contact lenses. At times, post-cataract visual outcomes still leave a residual need for some form of correction. One month after cataract surgery, if the eye has healed properly, the patient may begin wearing contact lenses again. Those patients who still need distance correction may wear contact lenses with reading glasses over them for near or computer use or a multifocal option. More often than not, patients will not need distance correction, so the prescriber may opt for a multifocal design or monovision fit. Multifocal contact lenses, even with little or no distance correction, offer patients an option to be able to focus well at all distances without the hindrance of eyeglasses. These lenses have improved rapidly over the last decade; however, they still require proper fitting to ensure that they behave properly on the eye. Some patients prefer monovision. This is when a patient only wears one contact lens—which will generally be for up close correction. The brain will learn to choose which image it prefers, but this takes time, willingness and patience. Monovision is a definite compromise, as binocular depth perception is challenged. Other options, such as modified monovision, are also used where a patient may wear a multifocal lens and make a single vision contact in the opposing eye. Inquiring about the patient’s specific lifestyle habits will help guide the contact lens fitting process. For example, a patient who spends eight hours a day working on a computer may not appreciate the compromised vision that a monocular fit may offer.
CONCLUSION
With cataract cases on the rise, there is an evergrowing need for eyecare professionals who understand and can communicate with patients regarding their care. As our population ages and individuals live longer lives than ever, this is translating into an overabundance of patients with questions surrounding their unique visual situation. With modern technology and years of surgical advancements, what once was a blinding, life-altering condition is now easily treated with minimal risk of complications. From the barbaric couching procedures of long ago to the present micro-surgeries, there has been a whirlwind of progression. The future of cataract care is even brighter, with scientists working to develop intraocular lenses with autofocusing mechanisms. Newer trifocaltype IOLs are already available. The advent of newer contact lens materials has made fitting patients’ post-surgery a safe and healthy option; however, with the refractive outcomes of most cataract cases, this can be a trying process. Many times, patients experience wonderful distance correction yet must negotiate their inability to accommodate. This only highlights the need for proper patient education. Patients who understand their prognosis and limitations are much more likely to be pleased with their visual outcome.
