occlusion amblyopia
A form of stimulus deprivation amblyopia that develops when an eye is constantly occluded for an extended period, particularly during the critical period of visual development. The obstruction of visual stimuli to the retina leads to abnormal development of the visual cortex, resulting in reduced visual acuity and contrast sensitivity in the affected eye. Occlusion amblyopia can occur due to various causes, such as congenital ptosis or media opacities.
occlusion therapy
The mainstay treatment for amblyopia, involving patching of the non-amblyopic eye to promote visual development in the amblyopic eye. The sound eye is covered with an opaque patch for a prescribed number of hours per day, forcing the brain to use the weaker eye. Occlusion therapy is most effective during the critical period of visual development in early childhood. Treatment duration depends on the severity of amblyopia and age at initiation. Compliance is essential for successful outcomes.
ocular myasthenia
A form of myasthenia gravis characterized by fluctuating weakness of the extraocular muscles, resulting in ptosis (drooping eyelid) and diplopia (double vision). Symptoms typically worsen with prolonged use of the eyes and improve with rest. It is caused by an autoimmune attack on acetylcholine receptors at the neuromuscular junction. Diagnosis involves clinical tests and antibody testing. Treatment includes medications to improve neuromuscular transmission and suppress the immune system.
ocular torticollis
Ocular torticollis is an abnormal head posture, such as head tilt, face turn, or chin up/down positioning, adopted to optimize visual acuity or maintain binocular single vision. Common causes include nystagmus, incomitant strabismus, and superior oblique palsy.
oculomotor nerve
The oculomotor nerve (CN III) is the third cranial nerve that innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique. It also provides parasympathetic input to the sphincter pupillae, constricting the pupil, and ciliary muscle, enabling accommodation. Oculomotor nerve palsy can cause ptosis, ophthalmoplegia, and pupillary dilation. Compressive lesions require urgent evaluation to rule out life-threatening aneurysms or tumors.
organic amblyopia
A decrease in visual acuity caused by an identifiable anatomic or pathologic abnormality in the visual system, such as retinal disorders, optic nerve anomalies, or visual pathway lesions. It is generally irreversible, even after treating the underlying cause. Organic amblyopia differs from functional amblyopia, which results from conditions like strabismus, anisometropia, or visual deprivation during the critical period of visual development and may be reversible with appropriate treatment.
orthophoria
Orthophoria is the optimal state of ocular alignment in which the visual axes are parallel and intersect precisely at the fixation point under binocular viewing conditions. It represents a perfect balance of the extraocular muscles without any latent deviation. The cover test is used to differentiate orthophoria from heterophoria and heterotropia.
orthopic fusion
A form of binocular fusion achieved by voluntarily diverging the eyes to fixate on two laterally separated fusible targets. The right eye directly fixates the right target, while the left eye fixates the left target. This differs from normal fusion, where both eyes converge to fixate a single target.
orthoptics (vision therapy)
Treatment approaches that aim to improve binocular vision and visual function through eye exercises and training techniques. Orthoptics focuses on strengthening eye muscles and enhancing eye alignment, while vision therapy encompasses a broader range of techniques to develop visual skills. Both involve personalized exercises guided by an eye care professional to improve coordination between the eyes.