Alamo Optometry Blog

How Does the Eye Work?

(As appeared in Alamo Today, June 2009, pg. 29)

Last month I gave you an overview of our office. This month I thought I would give you an overview of the eye itself. It is an amazing organ that works in unison with our brains to allow us to visually interpret the world around us. They eye works similar to a camera. If any part of your camera is not working well, your photos will not turn out; similarly, if any of the structures or pathways of the eye are damaged, vision will be compromised.
The white part of the eye is called the sclera. The sclera is made of collagen and covers most of the eye. The clear front part of the eye is called the cornea. The cornea is where contact lenses are placed and is the first structure that light comes in contact with on its way to being focused on the retina.
Your pupil is the round black circle in your eye that gets bigger and smaller depending on the amount of light. The iris is the colored muscle fibers surrounding the pupil and controls the size of the pupil. The pupil and iris are like a camera’s aperture which is an open space that allows the light to pass through farther into the eye. Between the iris and cornea is the anterior chamber. This chamber is filled with a special fluid that gives the front part of the eye oxygen, protein, and glucose to keep it healthy. The light then travels to the lens of your eye.
The lens is similar to the lens of a camera; they help to bring the light into focus. The lens bends light further and sends it to the back of the eye. The lens is suspended in the eye by a bunch of fibers. These fibers are attached to a muscle called the ciliary muscle. The ciliary muscle changes the shape of the lens. When you look at things up close, the lens becomes thicker to focus the correct image onto the retina. When you look at things far away, the lens becomes thinner.
The biggest part of the eye sits behind the lens and is called the vitreous body. The vitreous body forms two thirds of the eye’s volume and gives the eye its shape. It’s filled with a clear, jelly-like material called the vitreous humor. After light passes through the lens, it shines straight through the vitreous humor to the back of the eye.
In the back of the eye is the retina. The retina contains photoreceptor nerve cells called rods and cones. Each eye has about 120 million rods and 7 million cones. The cones are mainly in the macula, the center of the retina. The cones are responsible for sharp vision and color vision. The rods are situated in the periphery of the retina and allow us to see at night. These cells take the light and transform them in to electrical impulses. These electrical impulses are then sent to the optic nerve. The optic nerve then transmits the information to the brain. Using a camera demonstration, you can call the retina the film of the camera. If your film goes bad you will not be able to view any pictures no matter what you do. The same goes with the retina. If the retina is damaged by macular degeneration or diabetes, you are not going to be able to fully process any pictures or images.
How the eye processes light is only part of the process. When you do not see well, the problem might be simple in that you are near-sighted or far-sighted and just need glasses or contacts. Also, any disease or trauma to any of the above-mentioned structures can be a cause of decreased vision. Anything from cataracts (clouding of the lens), diabetes, glaucoma (optic nerve deterioration), to almost any systemic disease can cause vision and ocular health concerns. That it why comprehensive exams with dilation that test more than vision alone can help ensure that the entire eye system is working as well as possible.

Dr. K. at Alamo Optometry is your hometown eye doctor for outstanding service, vision care, and designer eyewear. He can be reached at 925-820-6622 or visit his office at 3201 Danville Blvd., Suite 165 in Alamo.

Systemic Diseases and the Eye
Monday, February 2, 2009

(As appeared in Alamo Today February 2009, pg.33)

As many of you may or may not be aware, almost every systemic disease can have ocular effects. Any disease, including cardio-vascular, auto-immune, intestinal, and cancer can and do affect the eye. The eye is no different from any other organ in the body; it receives and needs blood and oxygen to survive. If this is affected or reduced, vision and/or ocular health will definitely be affected. These can vary from a prescription change, cataract formation, or retinal disease, to name a few. That is why it is very important to let us know of any systemic ailments and medications, as these can have a profound effect on the eyes. For the purposes of this article, I will just cover the two most prevalent diseases, diabetes and high blood pressure.
Diabetes affects about 8 percent of the population in the United States and is characterized by either a deficiency in insulin production (type 1) or insulin resistance (type 2). The main ocular effect of diabetes is retinopathy, which is a disease of the retina. Diabetic retinopathy can lead to poor vision and even blindness. Most of the time, it gets worse over many years. At first, the blood vessels in the eye get weak. This can lead to blood and other liquid leaking into the retina from the blood vessels. This is the most common kind of retinopathy. If blood sugar levels stay high, diabetic retinopathy will keep getting worse. Due to the poor retinal blood flow through the damaged blood vessles, new blood vessels grow on the retina. This may sound good, but these new blood vessels are weak. They can break open very easily, even while you are sleeping. If they break open, blood can leak into the middle part of your eye in front of the retina and change your vision. This bleeding can also cause scar tissue to form, which can pull on the retina and cause the retina to move away from the wall of the eye (retinal hole or detachment). Retinopathy can also cause swelling of the macula of the eye. This is called macular edema. The macula is the middle of the retina, which gives you your sharp 20/20 vision and color vision. When it swells, it can make your vision much worse. The only way to diagnose this is a comprehensive dilated optometric examination. Annual exams can help detect retinopathy and monitor retinopathy before it affects your vision.
High blood pressure, or hypertension, is another vascular disorder that forces your heart to work harder to pump blood through your arteries. This can lead to hardening of the arteries and subsequent heart failure. In addition to all of the other body organs it can affect, the eye can also be compromised. The blood vessels of the retina over time can narrow and cause a decrease in blood to the retina. Compromised blood flow can cause swelling of the optic nerve and macula, which over time can lead to decreased vision and possible stroke in the eye. Since this is something that can not be self-monitored, an annual dilated examination can help in the detection and monitoring of this potentially blinding disease.
To help combat these diseases, the absolute best thing you can do is to keep the disease under control. The more your blood sugar and blood pressure are under control, the less likely eye consquences will be an issue. That means visits to your doctor and taking your medications, life-style changes, etc. as prescribed. Keep in mind that just because you “feel” fine and have your diseases under control, the fact is you still have the disease. Besides the ocular consequences, you also have heart, liver, kidneys, brain, and other organs that need to be monitored to help avoid any long-term or life-threatening issues. Along with your regular doctor visits, annual eye exams should be on your list to keep these devastating diseases monitored and under control.

Dr. K. at Alamo Optometry is your hometown eye doctor for outstanding service, vision care, and designer eyewear. He can be reached at 925-820-6622 or visit his office at 3201 Danville Blvd., Suite 165 in Alamo.

(As appeared in Alamo Today Nov 2008 edition, pg.28)

Presbyopia, or the “short-arm syndrome“, eventually affects everyone. Your lens, which is in the inside of the eye, continues to grow throughout life. As it becomes thicker and denser, it becomes less flexible, and this is what causes a decrease in your near focusing ability. Overall, your focusing ability is best when you are born, and decreases from that point on. Usually the symptoms of presbyopia include pushing reading material farther away, the need for good lighting, eyestrain, and fatigue, begins in your low-to-mid 40′s. As you age, your ability to focus decreases. As your accommodation decreases, which will happen regardless if you wear glasses full-time, part-time, or never, you will need more power to make up the difference. This process will cease in your upper 50′s to around 60 years of age. After that point, you might need some fine-tuning in your glasses or contacts, but the constant change will stop. Even though this is a completely normal process, there are several methods to help.

Progressive Lenses: These lenses have the advantage of 1 pair of glasses giving you clear vision at distance, intermediate, and close. Another advantage is that they have no lines; cosmetically they look like single-vision lenses. There will be adaptation necessary for this type of lens because you have a smaller area to use for near compared to a single vision lens. In addition, for heavy computer users, computer progressives are available. These lenses do not correct for distance vision, but allows a wider field of view compared to regular progressive out to about 7 feet. With the proper frame size and motivation, well over 90% of patients do very well with all types of progressives.

Bifocal Lenses: This lens will allow you to see well at distance and near. However, intermediate vision eventually will become compromised. These lenses don’t require the adaptation that progressives do, but the “line” will be evident.

Single Vision Glasses for Near Work: Some people choose to have separate glasses for distance (if needed) and near. The nice thing is that there is no adaptation required; you can use any part of the lenses to see. However, the compromise is that you will need to remove or slide them down your nose to see clearly outside of a few feet.

Contacts: Some people are still under the impression that once presbyopia hits, you can no longer wear contacts. These days, that could not be farther from the truth. Assuming you can comfortably wear contacts, there are basically 3 options:

Multifocal contacts allow you to see distance and near with each eye. All of the power is centered in the middle of the lens, and you just pay attention to the object in focus. These require very little adaptation and care of the lenses is no different than any other type.

Monovision allows you to see distance out of one eye and reading out of the other. Your need for reading glasses is minimal; they usually are only required for small print like reading medicine bottles. This modality does require some getting used to, since you are artificially changing the power of one eye to read. Greater than 75% of patients get comfortable with monovision after the initial week or so. If you are happy with the comfort of your current contacts, this allows you to remain in them and just change the power in one eye.

Distance contact with reading glasses is also the choice for many people. This allows clear distance vision out of both eyes, and clear reading through the glasses. Even though you still need glasses for near work, the contacts still give you the flexibility for sports, recreation, and other activities where detail near work is not needed.

As you can see, all is not lost when your accommodation (focusing ability) decreases. It is a completely normal process; but the advantage we have now is that we have several tools to help solve the problem. Depending on your personality, activities, and prescription, we will determine what will work best for you and help guide and assist you in the process.

Dr. K. at Alamo Optometry is your hometown eye doctor for outstanding service, vision care, and designer eyewear. He can be reached at 925-820-6622 or visit his office at 3201 Danville Blvd., Suite 165 in Alamo.

(As appeared in Alamo Today Sept 2008 edition, pg.27)

This question comes up often in practice as parents are questioning whether or not a screening at school or their child’s pediatrician is sufficient to ensure good vision and eye health. Obviously, each parent must make their own decision; however, here are some of the glaring differences between a screening and a comprehensive examination.

Vision screenings conducted at school or in a doctor’s office test for distance vision only. Since distance vision is defined at 20 feet, a child might pass this without any difficulty, but gives no information whether a child can read a book and use the eyes well as a team up close. If the screening is done at school, a rough determination of prescription and eye alignment is attempted without the use of any machines. This information is then used to either pass or fail the child. However, the standards for pass/fail are arbitrary and can differ from clinic to clinic and child to child. The last thing to consider about a screening is who is conducting the test. Most of the time it is a doctor’s assistant or nurse at the pediatrician’s office, and at schools, an optometrist or school nurse conducts the screening. However, in both circumstances, the ability for the child to focus on the tasks at hand and for the tester to get accurate results are often compromised due to the noise and distractions of other children and students waiting to be tested.

Comprehensive eye examinations should be conducted by an eye care professional. Optometrists have the necessary training and experience to make a diagnosis of vision, binocular vision, and health status and to recommend treatment if needed. Often, the necessary equipment and tests to fully evaluate the status of the eyes are not available at a vision screening. Here are just some of the highlights of a pediatric exam at our office.

Visual acuity at distance and near is determined. Since a child needs to be able to see and function at many distances, simply testing distance only is not sufficient. In addition, the focusing ability is also assessed. Your child needs to focus on the board or overhead and then to their notes or book and back all day long. The ability for sustained focusing also allows your child to attend to reading and writing for a period of time.

The exact prescription for good comfortable vision is determined. Amblyopia, or “lazy eye”, occurs in about 8% of the pediatric population, and is when one or both eyes cannot be corrected to 20/20 vision. The need to correct this is important early in life to help both eyes develop and see well. Sometimes glasses or contact lenses are needed and sometimes they are not; however, knowing the exact status of the eyes is paramount.

Binocular vision, color vision, eye movements, and depth perception are all tested. If your child cannot move his/her eyes well to track objects, or to differentiate colors well, activities such as reading, sports, and copying information from the white board will be affected. Good eye alignment allows the muscles in the eye to converge (come together) and diverge (move apart) depending on the task. This allows for good depth perception and a precise eye alignment so the brain can fuse what it sees from each eye into a single, clear image.

Finally, the health of both the front and back (retina) part of the eyes is determined by examining all structures through the use of a microscope and lenses. We will also measure of the pressure in the eyes, and use drops if needed to make the health assessment process easier.
Even though most screenings figure out which children need to be evaluated further, it is based on decreased distance visual acuity alone. As stated above, many things aid or are a detriment to good and comfortable vision, and are usually not evaluated at a screening. My recommendation is to have your child’s eyes examination early (preschool age or by kindergarten), and if a recommendation for a vision evaluation is given, we would be more than happy to examine your child and give you an honest recommendation based on the findings of the exam.

Dr. K. at Alamo Optometry is your hometown eye doctor for outstanding service, vision care, and designer eyewear. He can be reached at 925-820-6622 or visit his office at 3201 Danville Blvd., Suite 165 in Alamo.