Difficulty attempting to view distance objects is cause for most visits to the eye doctor. Road signs may seem a little blurry at first, then it becomes difficult to see the TV set or the jersey numbers on the basketball players at the arena. Examination by an eyecare professional usually results in a prescription change that corrects the blur. The blur may return over time. The person watches their prescription numbers increase year after year as lens thickness increases, dreading the day the doctor prescribes “coke-bottle” thick eyeglasses. The patient feels helpless in the wake of these increases. Many doctors discuss the vision change to the patient, insinuating prescription increases are normal and to be expected over time. The problem with this scenario is the development of the visual system (including the eye) is complete by adulthood. Then why is the vision changing? Genetic influences are the most likely cause of vision changes before adulthood and can be expected. Changes in distance vision should not continue to progress on a regular basis (excluding astigmatism) after the development of the visual system is completed through natural growth. The progression of Myopia (nearsightedness) during development of the visual system can be compounded by a dysfunction in the focusing mechanism (lens) of the eye, making the changes greater than they would have been through genetics alone. Any changes in vision after the complete development of the visual system is likely to have been brought about by problems causing over-focus (locking in of focus when viewing near objects) when looking at distance objects. Over-focus and failure to release focus to look at distance is a cause of progressive vision changes in adults. There are many ways to manage progression of distance blur.
THE NEAR TRIAD
The eye receives light and processes it as described in the section Anatomy of the Eye. This process is similar for viewing near and distant objects. Looking at distance objects differs from looking at near objects in how the musculature of the eye adjusts the focus mechanism, the Lens. Adjustment of focus for viewing near objects is termed Accomodation. When viewing distance objects (objects greater than 20 feet or 6 meters from our eyes), the eyes are aligned straight ahead and the line of sight of each eye is approximately parallel to one another. Light from the distance target enters the eye and is focused on the Retina, or light -sensitive tissue on the back of the eye. When looking from a distance target to a near target, the eyes must change focus. The eyes must also turn in towards each other to bring proper focus onto the near object (Convergence). This change in focus only occurs when looking from Distance to near. When looking up from near work, or near to distance, the eye un-focuses (releases accomodation) and the eyes straighten and the lines of sight go from being converged on a near target to being parallel again. The process of going from a position of convergence (looking at near) and accomodation (focusing at near) to being straight and unaccomodated for distance viewing is called divergence. The processes of convergence and divergence are controlled by the musculature surrounding the eye. These muscle actions for convergence and divergence are intertwined with the muscle that controls the focus for the lens of the eye so when the eye converges, the eye muscle focuses the lens for near and when the eye diverges, the eye muscle unfocuses the lens for distance. The eye muscles receive information for when to converge or diverge, direct the eyes to the left, the right, up or down based on information shared between the retina (image positioning information) and the nuclei (eye movement information). If an object passes to the left of you, the image of the object will fall on an area of the retina that corresponds to your left side. The nuclei will receive this signal and relay another signal to the eye muscles to look left in order to move the image of the object towards the area of the retina where the image is best viewed (the Fovea). Muscles inside the eye then control the process of accomodation and unaccomodation. When the act of focusing occurs, the mind assumes that a near object is to be viewed and convergence action kicks in. How does the mind know you are viewing a near target? When an object directly in front of you is brought closer to you, the image size of the object projected on the retina increases and the retinal image blurs. This slight amount of blur is the stimulus for the focus mechanism to kick in. Proximity of the object and blur are stimuli that activate the convergence/accomodation nuclei in the brain. The visual system transfers information about object proximity and blur to nuclei responsible for accomodation. Impulses are sent through the accomodation/convergence pathway. The impulses cause muscles inside the eye to increase the convexity of the lens of the eye. The increase in convexity increases focusing power, enabling focus at near. These stimuli cause accomodation for near and the eyes converge. When the object moves away from you, the image magnification on the retina decreases, the stimulus to converge and focus for near decreases as the eyes diverge to see the object at distance. The muscles in the eye cause the convexity of the lens to decrease, decreasing focusing power. This moves the point of focus out to distance. There is no convergence without accomodation and no accomodation without convergence. There is no divergence without unaccomodation and vice-versa.
A brief synopsis before continuing: To view objects at distance (greater than 20 feet or 6 meters), the visual system causes the focus mechanism to un-focus or relax. When looking at near, the vision system causes the lens of the eye to accommodate to focus on a near point. This accomodation is achieved by increasing the convexity of the lens of the eye. Accomodation is the process of moving the distance point of focus on the retina to the near point of focus by increasing or decreasing the convexity of the lens of the eye. To look at it in a different light (no pun intended) accomodation is the process of moving a distance point of focus to a near point of focus by increasing convexity of the lens. Spasm of accomodation, or pseudo-myopia occurs when the convexity achieved for the near point of focus “locks in” and won’t release again to view distance objects clearly. An example of “locking in” is seen in college students. Many patients in the late 20’s and early 30’s report having had perfect vision until sometime during or immediately after their college years. The first change they note in vision was blur at distance after reading, studying or hours of computer work. They report looking up from a book after a study session, then blinking a few times or squinting to see far away again. There far away vision gradually returned, but slower and slower until the distance vision was slightly blurry permanently. Then, going for an eye exam where the chief complaint they tell the doctor is distance blur, they are prescribed eyeglasses for distance, see better and become dependent on the glasses, but the whole time the near problem was never addressed. So, their vision blurs at distance, is tweeked in an eye exam and the problem continues. If the student had only told the doctor that the problem was the change in focus from distance to near, they may have been prescribed glasses to help them focus at near (reading or computer glasses). That may have solved the problem and halted a problem that gradually leads to a need for glasses at distance full time. Clearing someone’s distance vision is no-brainer for your eye-care professional. You could leave a patient alone in the examination room with the ‘better #1 or better #2 machine and within 5 minutes they could find a prescription that could clear the bottom line of the eye chart. The person determines whether 1 or 2 is better at distance, gets shown to the optical and another nearsighted person is created. The problem was not at distance, but at near. The blur is not the consequence of continued development of the visual system. It is the first sign of visual change secondary to false distance blur, or Pseudo-myopia. People concentrate on print or virtual pixel images 16 to 19 inches in front of their nose for hours on end. After focusing at near for extended periods of time, the focusing system may lock in on the near image. When the person looks up, the distance image appears blurry. The neurological signal to focus for near is not letting go and blur is caused by looking at the distance object through the near focus. The person is looking far away, but their eye hasn’t let go the focus from the book or computer screen! The person is unable to relax accomodation for near back to distance. When they go for an eye exam, often distance glasses are prescribed. Distance glasses clear blur, but the problem of near over-focus remains and the cycle of annual prescription changes and increases continues. If the near point vision problem is not addressed, the progression of pseudo-myopia will eventually lead to more dependence on the distance prescription. Real doctoring involves identifying the cause of the changing vision and making recommendations to slow the vision changes down, stop them or reverse them.
The latest research on myopia is showing that depriving someone of peripheral vision might be another cause of increase in myopic prescriptions. When we look out at a distance, we use our central and peripheral vision. When we look close to read or do computer work, we use less of our peripheral vision. Lack of stimulation of the periphery over long periods of time can lead to prescription Ã¬creepÃ® if one is genetically geared towards myopia. In order to minimize the effect one should increase their reading distance or computer working distance.
Human beings are highly adaptable organisms. The body will alter function to accommodate needs for which the system isn’t able to compensate for. After enough use, the adaptation, if successful, may become part of the system for which it was meant to modify. Incipient nearsightedness brought on by focus problems is an adaptation our technological society is adopting. Most people in school or in white-collar occupations spend 6 to 10 hours of their waking day involved in near activities. Pseudo myopia, or false near focus is the bodies’ modification for increased need to see at near. For many of my patients, clear distance vision is needed only for driving to and from work and going to the movies. If we continue to evolve in this manner, our descendents will find no need for glasses continuously perched on the bridge of their noses anymore. People will be buying cars with prescription windshields. Of course, this is an exaggeration. In this day and age, the need for clear, comfortable, functional vision at distance is not as great as that at near. The old paradigm for prescribing glasses may need to be tossed out the window if we, as doctors, are to truly manage patients vision problems. As an eye care provider I feel a responsibility to identify and solve problems, instead of offering crutches (eyeglasses/contact lenses) for patients to become more and more dependent on. I’m talking about solid management of the underlying vision problem, not the symptoms alone.