Contact Lenses For Mature Wearers
Considerations for the Aging Patient
Changes With Age
Let’s face it: as we grow older our bodies go through changes. These changes typically aren’t for the better. Our skin loses its elasticity and begins to thin and get wrinkled. Bones become less calcified and more brittle. We begin to lose muscle mass as they begin to atrophy and become harder to maintain. Our neurosensory system begins to slow down and we react to stimuli more slowly. Our gastrointestinal system may develop ulcers, acid reflux or not digest foods as efficiently. Cardiovascular disease may become an issue as cardiac muscles begin to weaken or exhibit signs of disorder. Incontinence often becomes a concern. Women go through menopause. Men produce less testosterone. Our immune systems are not as strong as they once were. To put it bluntly: growing old isn’t for sissies!
Just as our body goes through changes, our eyes are not immune from being affected by the ravages of time. The first perceptible effect of aging many of us encounter is the inability to focus on close objects. This is due to a thickening and lack of elasticity found in the suspensory ligaments which work to allow the crystalline lens to focus. This would facilitate the need for bifocals, readers, or monovision/bifocal contacts. Any of these modalities would correct for problems not only at a distance, but also give us that extra boost we need to read or do things up close.
Physiological Changes and Aging
On a cellular level, our eye is also undergoing changes. The conjunctiva which is the protective covering found on the sclera, contains mucous cells which help to lubricate and protect the eye. As we age, these cells grow fewer in number. Tear production is also effected. Not only the quantity of tear produced, but also the quality. The lack of mucous cells and quality tear production will result in a patient experiencing dry eyes which can interrupt the corneal tear film and diminish visual acuities.
The retina is prone to diseases such as age-related macular degeneration, glaucoma, and diabetic and hypertensive retinopathy. System diseases or medications used to treat them are of vital importance to the overall health of the retina. The retina has a high degree of vascularization (meaning blood flow) to help nourish it. In fact, fundus examinations (when your eyecare practitioner examines the retina), are the only way doctors are allowed to get a clear view of part of the vascular system without having to do invasive surgery. Whatever may be happening in your body, as long as there is some degree of vascularity to it, may show up in the retina layers of your eyes. This is why routine eye health exams are incredibly important as we age. Polls have been conducted showing that of all our senses, vision is at the top of the list for being one most people would least like to lose or have compromised.
Muscle weakness is another concern. The muscles responsible for squeezing the eyelids shut begin to weaken. The toll gravity takes on your eyelids making them sag will sometimes begin to obscure the visual field and in some cases will require surgery. This poses an anatomical consideration to the eyecare professional whenever considering whether lenses will be a good fit. All of these things are considered by your eyecare professional when determining whether it is feasible to continue to wear your contacts or if certain lens materials will be beneficial over others.
Visual Function As We Age
As our bodies decline with age, so does our visual function. 1% of the population over 50 is blind; however, of the remaining statistic which is left, 1 in 6 patients report some decline in visual function. The reasons are varied, but it’s important to understand the process of eye goes through as we age and the decline of visual function as it does. At about age 40, it starts becoming more difficult for patients to see objects up close. This is a condition known as presbyopia. It’s important to realize the refractory ability of the eye is dictated by two things: the cornea and the crystalline lens. The cornea is responsible for roughly 1/3 of the ability of the eye to perceive objects clearly. The curvature of the cornea will determine whether a patient is nearsighted, farsighted or astigmatic. The remaining 2/3 of the ability of the eye to focus clearly resides with the crystalline lens. The crystalline lens is found in the anterior chamber of the eye and is held in place by a series of ligaments called the zonules of Zinn (sounds like a science fiction movie, huh?). These “zonules” are basically suspensory ligaments which help to hold the lens in place, but also act on the lens when viewing objects at a distance or up close. Before the age of forty, when we move our eyes from viewing objects at a distance to viewing them up close, the crystalline lens will instantly flex allowing us to see objects at any focal length clearly. This process is known as accommodative reflex or simply accommodation.
Starting at around age 40, the elasticity of these ligaments begins to diminish as they begin to harden with age. Since these ligaments are not nearly as flexible as they once were, the accommodative ability of the eye weakens. In steps the eyecare professional with your first set of bifocals or readers. The bifocals you are prescribed take the place of the ability of the crystalline lens to flex. In the optical game, bifocals are known as “adds.” The reason for this is very simple: bifocals are power “added” to your distance prescription to offset the effects of presbyopia.
Decline of Dynamic Vision
There are three primary components to dynamic vision or vision at all: the cornea/crystalline lens, the retina and the visual cortex of the brain. What is “dynamic vision?” Quite simply, dynamic vision is the ability to perceive objects clearly and identify them as they move. For example, you’re on a trip and it seems as though you’re not able to read the road signs until you get close to them. This is an example of dynamic visual acuity not being what it once was. You may go to your eye doctor with this complaint. He or she may check your visual acuities with your glasses or contacts, but you see well. 20/20 vision the doctor tells you. You’re skeptical. These are the facts. The eye chart is stationary and so are you. What isn’t really measurable is your “dynamic” visual acuity. The ability of the three components of vision mentioned earlier are not working quickly as they did at one time. It’s no one’s fault: not you, not your doctor, not your glasses or contacts. Once again, father time has dealt you a blow. As with all other aspects of our body, our brains slow down as well. The visual cortex may be receiving visual information quickly, but the interpretation is something to be desired.
The same can be said for contrast sensitivity. Tests have been conducted for patients over the age of 50 in which they were told to drive near road signs and indicate when they could see them clearly. The same test was administered to patients between the ages of 19 to 30. All the patients tested had 20/20 vision. The test results were quite interesting. It was determined that patients over 50 must get 25% closer to the road sign before being able to discern what it indicated. The reasons for this discrepancy were simple, contrast sensitivity declines with age. Our senses decline with age. This includes the ability to distinguish color and colors in certain lighting conditions. The retina contains certain cells which are responsible for the perception of light (which allows us to see) and the perception of color. These photoreceptive cells are known as rods and cones. As we age, the responsiveness of these photoreceptor cells begins to decline. Even though we may have 20/20 vision, the chemical processes responsible for allowing us to perceive differences in contrasts (i.e., driving up to road signs), may not allow the visual cortex to efficiently due it’s job in making distinctions. The problem is compounded even more if a patient has been diagnosed with certain macular disorders. For example, one of the biggest complaints found in patients with macular degeneration is not only the unfortunate loss of central vision, but also the loss of contrast sensitivity. Certain studies have shown that with the addition of amber tinted lenses, a small part of this contrast sensitivity may be restored allowing some relief to the patient. Sadly, as this condition worsens, contrast sensitivity as well as overall visual function will be lost.
Stereopsis or 3-D Vision
Vision is definitely a group effort. The eyes perceive images which are relayed through the retina and optic nerve to the brain where they are interpreted. The eyes work as a team. Typically, one eye may be better than the other eye at perceiving images. Just as we are right handed or left handed so too are our preferences for either our right or left eye. This is known as dominance. Ever wonder how to determine whether your right or your left eye is dominant? Pick an image at a distance. Point at the object straight on. Now, close your left eye and observe where the image is in relation to your finger. Now, switch eyes, closing your right eye. Well, which eye allowed the finger to appear closer to the object? This is your dominant eye.
Not only do our eyes have dominance, but they also work together to bring us three dimensional images through a process called binocularity. Our perception of this image is referred to as stereopsis. Ever listen to a radio in either a stereo or mono setting? The stereo setting has a more robust sound, right? The same principle can be applied to vision. We can see things clearly looking at something with one eye (monocularly), but we perceive it much better with both eyes (binocularly). This allows us to catch balls, judge distances when driving or simply grasp something as it is handed to us. There are a few structures in the eye which allow all of this to happen. It’s important to think of the eye as a camera and film. Images are brought into focus with the cornea and crystalline lens, the image then proceeds to the retina where it is captured by the macula and more specifically the fovea, then transmitted the optic nerve to the photolab or the visual cortex of the brain. In addition to providing the sharpest image available to the brian, the fovea is also responsible for highly resolute images needed to perceive spatial relationships. This means that even if the images viewed by each eye appear to be slightly different, the brain is able to sort it out and the image may be fused properly. However, the brain has some difficulty sorting out these images when the visual field of a patient is compromised. What is the visual field? It’s easy to find and therefore understand. Focus on a small object across the room. Are you aware of objects out of the corner of your eye? Hopefully, the answer is yes. How is this possible? The totality of everything you see in your peripheral vision accounts for what is termed your visual field. Why is this important in how it relates to stereopsis? Remember how we said how the brain sorts out spatial relationships transmitted to it from the fovea? Well, interpreting those spatial relationships only work well if the patient has good peripheral vision. Otherwise, they become harder to discern. Unfortunately, another sign of aging is a decline in our peripheral vision. Since this declines, so too does the ability of spatial relationships to be easily recognized. Therefore, perceiving images in three dimensions becomes a lot more difficult and our stereopsis begins to suffer.
The Big Three: Diabetes, High Blood Pressure and High Cholesterol
Systemic diseases typically associated with older patients will cause a decline in vision as well. Many older patients often suffer from diabetes, high blood pressure, high cholesterol, heart disease, arthritis or other diseases which can impact their vision. In addition to systemic diseases, female patients typically go through menopause between the ages of 45 and 55. The key to prevent many of the harmful effects of these diseases is prevention or at minimum good management once diagnosed.
If blood glucose levels are not well controlled, a patient may experience a change in the refractive state of the crystalline lens as it absorbs glucose. This can cause blurred vision, but is by far the least harmful effect of diabetes with respect to vision. There are several blood vessels found in the retina. When a patient experiences proliferative diabetes, these vessels may begin to leak in certain spots. These are referred to as microaneurysms and may occur anywhere along the lining of the retina. They become problematic when they obscure the macula (where central and peripheral vision occur), or if blood leaks into the vitreous which can interrupt the transmission of light to the retina hindering the ability of the eye to transmit images to the brain. They key to prevent problems associated with diabetic retinopathy is to be examined by your eyecare professional regularly. Measures can be taken to prevent vision loss when a patient suffers from this disorder which may prevent blindness.
Patients with high blood pressure may also rupture vessels in the retina or vitreous causing visual acuities to become compromised. The eye may undergo swelling (or edema) resulting in what is known as a refractive shift, causing vision to blur. Another risk is hemorrhages associated with blood vessels under too much pressure. If these vessels leak they can cause a decrease in visual acuity or blindness until the hemorrhage is stopped and reabsorbed into the tissues. The key to preventing hypertension from affecting your vision is to keep your blood pressure in check and under control by a combination of medication, appropriate diet and exercise.
Patients with high cholesterol are more prone to blockages. Since blood vessels feed and nourish the tissue of the retina. These problems may occur here as well. Patients with high cholesterol are more prone to plaque build-up in the blood vessels of the eye. These plaques are known as Hollenhorst plaques. They are associated with patients who also suffer from atherosclerosis, a condition in which patients are at a higher risk for stroke. Just as a blood clot will choke off oxygen to certain areas of the brain during a stroke, Hollenhorst plaques may impede the flow of blood in the retina causing a retinal vein occlusion which if left untreated may cause death to the retinal tissue. Since the optical system is part of the central nervous system, this tissue cannot be replaced.
The Effects of Medications
Medications used to treat many of these conditions may also cause toxicity to the tissues of the eye and should be carefully monitored by your eyecare professional at regular eye health exams. Typically the side effects of these medications result from long term use, but many patients are living longer and the side effects should be carefully observed. For instance, drugs used to treat hypertension may not only cause your eyes to become dry disturbing the corneal tear film and your vision, but may also cause damage to the retina. Patients who have use medications for rheumatoid arthritis can easily damage the nerve fiber layer at the back the eye causing long term damage to the retina. Antidepressants change the chemistry of the brain and how information from neurons is processed. Additionally, these medications may cause damage to the optic nerve resulting in a loss of visual field or other visual disturbances. Medications have vastly improved the quality of our lives, especially with an ever increasing aging population. The important thing to remember with respect to vision is to provide your eyecare provider with a list and dosage of all medications your taking and to see your eye doctor for routine, regular eye health exams.