Strabismus is considered one of the most common binocular vision disorders in ophthalmology. It occurs when the two eyes do not move in the same direction in a coordinated manner. Strabismus is generally divided into manifest strabismus and latent strabismus. Manifest strabismus is a visible deviation that can be noticed with the naked eye, where one eye turns inward, outward, upward, or downward clearly. In contrast, latent strabismus, also known as phoria, appears only when the visual system is under stress or when binocular fusion is disrupted during clinical examination. The treatment of strabismus using vision therapy has gained significant attention in modern academic references, especially regarding the effectiveness of exercises in manifest strabismus compared with latent strabismus. Difference Between Manifest and Latent Strabismus Manifest strabismus (Tropia) represents a clear loss of eye alignment and is often caused by muscular, neurological, or sensory fusion abnormalities. In this condition, the brain fails to maintain proper eye alignment continuously, making the deviation constant or intermittent and clearly noticeable. Latent strabismus (Phoria), on the other hand, is a hidden deviation that does not appear during normal vision because the brain compensates for the misalignment and maintains binocular fusion. However, when the patient becomes fatigued, performs prolonged visual tasks, or undergoes a cover test, the deviation temporarily appears. Latent strabismus is considered less severe because the visual nervous system can still control eye alignment most of the time. Treatment of Latent Strabismus with Vision Therapy Scientific references issued by the American Academy of Ophthalmology indicate that latent strabismus, especially convergence insufficiency, is among the eye disorders most responsive to vision therapy, also known as orthoptic therapy. These exercises aim to strengthen the eyes’ ability to converge and maintain binocular vision. Some of the most commonly used exercises include: Pencil push-up exercises toward the nose Computer-based convergence exercises Lens and prism exercises Binocular fusion training in the clinic These exercises are effective in treating latent strabismus because the primary problem is functional rather than structural. In other words, the eye muscles are relatively healthy, but the neurological coordination between the eyes requires training and improvement. Therefore, the brain can gradually restore binocular balance with consistent therapy. Clinical studies have shown that patients with convergence insufficiency often suffer from symptoms such as headaches, eye strain, difficulty reading, and blurred near vision. These symptoms improve significantly after regular vision therapy exercises. Treatment of Manifest Strabismus with Vision Therapy Manifest strabismus differs from latent strabismus in both the nature of the defect and the degree of deviation. Therefore, the response to vision therapy is limited in most cases. Manifest strabismus is usually associated with a clear imbalance in the eye muscles or severe sensory fusion weakness, making exercises alone insufficient to restore normal eye alignment. International ophthalmology references confirm that exercises may only be helpful in some mild cases of intermittent manifest strabismus, such as intermittent exotropia associated with convergence weakness. In such cases, exercises may improve temporary eye control and reduce symptoms, but they do not completely treat the underlying cause. In cases of constant or large-angle manifest strabismus, the main treatment usually includes: Corrective eyeglasses Treatment of amblyopia if present Use of prisms in some cases Surgery to adjust the strength of the eye muscles The limited effectiveness of exercises in manifest strabismus is mainly due to the fact that the deviation often results from muscular or neurological abnormalities beyond the capability of simple functional training. In addition, the brain may suppress the image coming from one eye to avoid double vision, making restoration of binocular balance more difficult. Why Are Vision Therapy Exercises More Successful in Latent Strabismus? The success of exercises in latent strabismus compared with manifest strabismus can be explained by several scientific reasons, including: Presence of effective binocular fusion: Patients with latent strabismus generally retain a relatively good ability to fuse images, which can be strengthened through training. Absence of severe muscular abnormalities: Eye muscles in latent strabismus are relatively balanced, whereas manifest strabismus may involve significant muscular defects requiring surgical intervention. Brain adaptability to training: The visual nervous system in latent strabismus can adapt to exercises and restore coordination between the eyes. Small angle of deviation: The deviation in latent strabismus is usually mild, making it easier to control with exercises. Conclusion Differentiating between manifest and latent strabismus is essential for selecting the appropriate treatment. Latent strabismus, especially convergence insufficiency, responds well to vision therapy because binocular fusion and visual balance are still preserved. In contrast, manifest strabismus, particularly constant or large-angle cases, is generally not adequately treated with exercises alone and may require other interventions such as glasses or surgery. Therefore, each case should be evaluated by an ophthalmologist or strabismus specialist to determine the type of strabismus and select the most appropriate treatment plan according to modern scientific principles.