Strabismus is a change in the alignment of the eyes that can appear at different stages of life, and its causes range from neurological disorders to trauma. When it appears in adulthood, it usually has specific effects that require careful investigation. Diplopia, or double vision, is one such effect and tends to occur more frequently in adults when there is an eye misalignment. This happens because at this stage of life, the brain is no longer able to adapt in the same way as it was in childhood.
“The child, with a more adaptable brain, avoids diplopia by developing a suppression mechanism, that is, the brain ignores the image of one eye and begins to see with one eye at a time. Adults do not have this ability. Therefore, when strabismus begins in adulthood, diplopia occurs,” explains ophthalmologist David Kirsch, from Hospital Vilar de Olhos, a unit of the Vision One network.
Binocular vision — achieved when the eyes are aligned and images are correctly projected onto the macula, the central area of the retina — expands the field of vision and allows depth perception. “Binocular vision is important because it gives us a larger visual field and also gives us stereoscopic imaging, which is the concept of depth, as when an image seems to jump off the screen in a 3D cinema,” says the doctor. When this alignment is lost, such as in strabismus, the images no longer come together properly, causing double vision. Symptoms may appear suddenly or develop gradually, depending on the cause.
Strabismus that appears in adulthood may be related to more complex conditions, including neurological causes. “It can be caused by paralysis of the nerves responsible for eye movements, such as the oculomotor nerve, abducens nerve or trochlear nerve. This paralysis can be caused by high blood pressure, diabetes, tumors or aneurysms. Therefore, it is important to investigate the cause quickly,” advises Dr. David.
The doctor also lists other causes, such as myasthenia gravis — a disease that affects communication between nerves and muscles, causing weakness — Graves’ syndrome, which changes the function of the thyroid gland and can affect the eyes, and fractures in the area around the eyes, which can limit movement.
Excessive use of screens can lead to strabismus, and thus double vision
Milder and more common strabismus cases are often related to current lifestyle. According to Dr. David, prolonged use of mobile devices is a frequent factor in the office. “Screen-related strabismus occurs because when focusing on close objects, the eyes make a convergent movement, that is, they turn toward the nose to maintain focus. In some predisposed people, this repetitive effort can lead to strabismus compensation.” Diplopia, in these cases, can be subtle and mixed with eye strain. If the condition does not resolve spontaneously, treatment may include placing prisms in glasses, using botulinum toxin or surgery, depending on the individual indications.
Due to the increase in screen time, the doctor recommends paying attention to visual habits. “The ideal is to follow the 20-20-20 rule: keep a distance of at least 20cm from the screen, take a break every 20 minutes and look into the distance for 20 seconds, to help relax your eyes,” advises Dr David.