Visual stress: problems in the focusing system
If you avoid reading, have difficulty concentrating, maintaining attention, get tired when doing close-up tasks, or notice that it takes time to see clearly when looking far or near, it is likely that your accommodative system is stressed.
Accommodation is the focusing ability of our visual system. That is, the ability to clearly see objects at different distances. When functioning properly, the accommodation mechanism allows for precise and rapid focus changes. However, this system is frequently disrupted by certain near vision habits, such as prolonged use of electronic devices, reading with small font, or poor posture at close working distances, among others.
We can change focus and obtain sharp images thanks to the crystalline lens, a "lens" that we naturally have inside the eye. This "lens" changes its power—it "bulges" or "thins"—depending on the distance to the object we are looking at. A small muscle called the ciliary muscle is responsible for tensing or relaxing the ligaments that connect it to the lens, thus making the change in power effective. When the muscle relaxes, the ligaments tighten, and the lens's power decreases. Conversely, when the muscle contracts, the ligaments relax, and the power increases. To give you an idea, the diopters of the lens when we focus on a distant object are approximately 19. While if we focus on an object located 10 cm from the eye, the power increases to about 30 diopters. When we focus on a near object, in addition to the change in lens power, the pupils also constrict (miosis) and convergence is triggered. This triple action is called the proximal triad.
The visual system is not prepared to withstand prolonged work with near vision. Changing human customs and habits has made the accommodative function of vital importance in everyday life. However, the overexertion we subject this system to when performing sustained near tasks produces visual stress, which leads to symptoms such as blurred vision, eyestrain, diplopia (double vision), or suppression of information from one eye. This stress can dominate the body's physiological functions: it produces an activation of the sympathetic nervous system, which alters heart rate, releases adrenaline, dilates the bronchial tubes, increases blood pressure, and dilates the pupils. Pupil dilation, in turn, in relation to the proximal triad, causes excessive convergence to meet accommodative demands. A vicious circle develops, causing the ability to focus to decrease further and possibly leading to accommodative dysfunction such as excessive accommodation, insufficient accommodation, low accommodative flexibility, paralysis, or accommodative spasm.
In conditions where accommodation does not function correctly, some signs and symptoms become apparent:
- Aversion to doing close-up tasks
- Avoid reading
- You have trouble concentrating
- Double vision (diplopia)
- Fatigue after performing tasks in close vision
- Blurred vision when reading or looking from a distance
- Headache
- Excessive tearing when reading
- Common mistakes when reading or writing
- Changes in prescription (refraction): pseudomyopia usually manifests
Accommodation disorders, so common today, can usually be treated with vision therapy exercises aimed at integrating accommodative skills. As a result, the symptoms described above disappear, along with the visual stress associated with focusing problems.