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.
panoramic vision
An expansion of the peripheral visual field that can occur in some patients with exotropia, particularly those with intermittent or divergence excess types. Due to the misalignment of the eyes, each eye sees a different portion of the visual field. The brain combines these two separate images, resulting in a wider field of view compared to normal binocular vision.
Panum’s area
A region in the retina of one eye that corresponds to a specific point in the other eye. Stimulation of any point within Panum’s area simultaneously with the corresponding point in the fellow eye results in a single fused percept, allowing for a small degree of retinal disparity while maintaining single binocular vision. The size of Panum’s area varies, being smallest at the fovea and increasing peripherally. It plays a crucial role in sensory fusion and stereopsis.
paresis
A partial paralysis (palsy) of an extraocular muscle, resulting in weakness and reduced movement in its field of action. This results in an incomitant deviation, where the misalignment is more pronounced in the direction of the paretic muscle.
paresis of accommodation
A reduction or complete loss of accommodative ability due to paralysis of the ciliary muscle. It can occur unilaterally or bilaterally and may result from damage to the oculomotor nerve or ciliary ganglion. Symptoms include blurred near vision and reduced accommodative amplitude.
penalization
A treatment method for amblyopia that involves decreasing vision in the fixating eye with pharmacologic agents or optical lenses to encourage use of the amblyopic eye.
Percival’s criterion
Asthenopia is likely to occur when the vergence demand falls outside the middle third of the total fusional vergence range—the fusional vergence system should operate within a comfortable range to avoid excessive strain.
period of visual immaturity
The critical period in early childhood, typically from birth to 7-8 years old, when the visual system is highly sensitive to abnormal visual experiences. Disruption of normal visual development during this time can lead to suppression, anomalous retinal correspondence, and amblyopia.
peripheral fusion
Sensory fusion in which images in the extrafoveal peripheral portions of the retinae are combined, excluding the foveae. It has a wider fusional range than bifoveal fusion but cannot support high-acuity vision or fine stereopsis alone. Peripheral fusion contributes to the overall binocular visual field and perception of visual direction.
photophobia
An abnormal sensitivity to light, causing ocular discomfort or pain. It can be associated with various eye conditions, such as corneal abrasions, uveitis, and retinal disorders, as well as neurological conditions like migraine, meningitis, and traumatic brain injury.
physiologic diplopia
A normal phenomenon in binocular vision where objects not being fixated are seen as double. It occurs when images of non-fixated objects fall on non-corresponding retinal points outside of Panum’s fusional area. Objects closer than fixation produce crossed diplopia, while objects farther than fixation cause uncrossed diplopia.
pleoptics
A dated and ineffective method of treating amblyopia, pleoptics involves intensive stimulation of the fovea in the amblyopic eye using techniques such as bright lights to dazzle the eccentric fixation point while protecting the fovea, and using after-images to encourage foveal fixation. The goal is to eliminate eccentric fixation and improve visual acuity.
Pleoptics has largely fallen out of favor, with studies finding mixed results compared to conventional occlusion therapy.
positive relative accommodation
The maximum amount of accommodation that can be stimulated while maintaining clear, single binocular vision at a fixed distance, typically 40 cm. It is measured by adding minus spherical lenses binocularly until the patient reports sustained blur, with the total minus lens power representing the PRA value. High PRA (>2.5D) may indicate accommodative excess or uncorrected myopia, while low PRA (<1.5D) suggests accommodative insufficiency or an over-minused refraction.