Esotropia is a form of strabismus in which one or both eyes turns inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance. It is the opposite of exotropia and usually involves more severe axis deviation than esophoria. Esotropia is sometimes erroneously called "lazy eye", which describes the condition of amblyopia; a reduction in vision of one or both eyes that is not the result of any pathology of the eye and cannot be resolved by the use of corrective lenses. Amblyopia can, however, arise as a result of esotropia occurring in childhood: In order to relieve symptoms of diplopia or double vision, the child's brain will ignore or "suppress" the image from the esotropic eye, which when allowed to continue untreated will lead to the development of amblyopia. Treatment options for esotropia include glasses to correct refractive errors, the use of prisms, orthoptic exercises, or eye muscle surgery. The term is from Greek eso meaning "inward" and trope meaning "a turning".
In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an animal has eyes on opposite sides of its head and shares no field of view between them, like in some animals.
Strabismus is a vision disorder in which the eyes do not properly align with each other when looking at an object. The eye that is pointed at an object can alternate. The condition may be present occasionally or constantly. If present during a large part of childhood, it may result in amblyopia, or lazy eyes, and loss of depth perception. If onset is during adulthood, it is more likely to result in double vision.
An eye examination is a series of tests performed to assess vision and ability to focus on and discern objects. It also includes other tests and examinations pertaining to the eyes. Eye examinations are primarily performed by an optometrist, ophthalmologist, or an orthoptist. Health care professionals often recommend that all people should have periodic and thorough eye examinations as part of routine primary care, especially since many eye diseases are asymptomatic.
A phoropter or refractor is an ophthalmic testing device. It is commonly used by eye care professionals during an eye examination, and contains different lenses used for refraction of the eye during sight testing, to measure an individual's refractive error and determine their eyeglass prescription. It also is used to measure the patients' phorias and ductions, which are characteristics of binocularity.
A vergence is the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision.
The Worth Four Light Test, also known as the Worth's four dot test or W4LT, is a clinical test mainly used for assessing a patient's degree of binocular vision and binocular single vision. Binocular vision involves an image being projected by each eye simultaneously into an area in space and being fused into a single image. The Worth Four Light Test is also used in detection of suppression of either the right or left eye. Suppression occurs during binocular vision when the brain does not process the information received from either of the eyes. This is a common adaptation to strabismus, amblyopia and aniseikonia.
Fixation disparity is a tendency of the eyes to drift in the direction of the heterophoria. While the heterophoria refers to a fusion-free vergence state, the fixation disparity refers to a small misalignment of the visual axes when both eyes are open in an observer with normal fusion and binocular vision. The misalignment may be vertical, horizontal or both. The misalignment is much smaller than that of strabismus. While strabismus prevents binocular vision, fixation disparity keeps binocular vision, however it may reduce a patient's level of stereopsis. A patient may or may not have fixation disparity and a patient may have a different fixation disparity at distance than near. Observers with a fixation disparity are more likely to report eye strain in demanding visual tasks; therefore, tests of fixation disparity belong to the diagnostic tools used by eye care professionals: remediation includes vision therapy, prism eye glasses, or visual ergonomics at the workplace.
Hypertropia is a condition of misalignment of the eyes (strabismus), whereby the visual axis of one eye is higher than the fellow fixating eye. Hypotropia is the similar condition, focus being on the eye with the visual axis lower than the fellow fixating eye. Dissociated vertical deviation is a special type of hypertropia leading to slow upward drift of one or rarely both eyes, usually when the patient is inattentive.
A cover test or cover-uncover test is an objective determination of the presence and amount of ocular deviation. It is typically performed by orthoptists, ophthalmologists and optometrists during eye examinations.
Cyclovergence is the simultaneous occurring cyclorotation of both eyes which is performed in opposite directions to obtain or maintain single binocular vision.
Cyclotropia is a form of strabismus in which, compared to the correct positioning of the eyes, there is a torsion of one eye about the eye's visual axis. Consequently, the visual fields of the two eyes appear tilted relative to each other. The corresponding latent condition – a condition in which torsion occurs only in the absence of appropriate visual stimuli – is called cyclophoria.
In the fields of optometry and ophthalmology, the Lancaster red-green test is a binocular, dissociative, subjective cover test that measures strabismus in the nine diagnostic positions of gaze.
The Maddox rod test can be used to subjectively detect and measure a latent, manifest, horizontal or vertical strabismus for near and distance. The test is based on the principle of diplopic projection. Dissociation of the deviation is brought about by presenting a red line image to one eye and a white light to the other, while prisms are used to superimpose these and effectively measure the angle of deviation. The strength of the prism is increased until the streak of the light passes through the centre of the prism, as the strength of the prism indicates the amount of deviation present. The Maddox rod is a handheld instrument composed of red parallel plano convex cylinder lens, which refracts light rays so that a point source of light is seen as a line or streak of light. Due to the optical properties, the streak of light is seen perpendicular to the axis of the cylinder.
The prism cover test (PCT) is an objective measurement and the gold standard in measuring strabismus, i.e. ocular misalignment, or a deviation of the eye. It is used by ophthalmologists and orthoptists in order to measure the vertical and horizontal deviation and includes both manifest and latent components. Manifest is defined by the eye deviating constantly or intermittently, whereas latent is where the deviation is normally controlled but becomes present when the eyes are dissociated. A PCT reveals the total deviation and cannot distinguish between latent and manifest strabismus as you are using an alternate cover test.
Bagolini striated glasses test, or BSGT, is a subjective clinical test to detect the presence or extent of binocular functions and is generally performed by an optometrist or orthoptist or ophthalmologist. It is mainly used in strabismus clinics. Through this test, suppression, microtropia, diplopia and manifest deviations can be noted. However this test should always be used in conjunction with other clinical tests, such as Worth 4 dot test, Cover test, Prism cover test and Maddox rod to come to a diagnosis.
The prism fusion range (PFR) or fusional vergence amplitude is a clinical eye test performed by orthoptists, optometrists, and ophthalmologists to assess motor fusion, specifically the extent to which a patient can maintain binocular single vision (BSV) in the presence of increasing vergence demands. Motor fusion is largely accounted to amplitudes of fusional vergences and relative fusional vergences. Fusional vergence is the maximum vergence movement enabling BSV and the limit is at the point of diplopia. Relative fusional vergence is the maximum vergence movement enabling a patient to see a comfortable clear image and the limit is represented by the first point of blur. These motor fusion functions should fall within average values so that BSV can be comfortably achieved. Excessive stress on the vergence system or inability to converge or diverge adequately can lead to asthenopic symptoms, which generally result from decompensation of latent deviations (heterophoria) or loss of control of ocular misalignments. Motor anomalies can be managed in various ways, however, in order to commence treatment, motor fusion testing such as the PFR is required.
The Maddox Wing is an instrument utilized by ophthalmologists, orthoptists and optometrists in the measurement of strabismus. It is a quantitative and subjective method of measuring the size of a strabismic deviation by dissociation of the eyes brought about by two septa which are placed in such a way as to present fields to either eye separated by a diaphragm at the centre. The right eye sees a red and white arrow, each of which point to a scale with numbers seen by the left eye; the red arrow points to the vertical red scale and the white arrow points to the horizontal white scale. A third arrow located to the right and below the horizontal white scale is used to measure torsion
The FourPrism Dioptre Reflex Test is an objective, non-dissociative test used to prove the alignment of both eyes by assessing motor fusion. Through the use of a 4 dioptre base out prism, diplopia is induced which is the driving force for the eyes to change fixation and therefore re-gain bifoveal fixation meaning, they overcome that amount of power.
Ernest Edmund Maddox was a British surgeon and ophthalmologist. He was a specialist in abnormal binocular vision and phorias. He made advances in optical treatments and invented several devices to better investigate eye conditions, including Maddox rod, double prism Maddox, red glass Maddox, Maddox cross and Maddox wing. As a keen amateur astronomer he also invented the starfinder, a device to home in on stars and constellations.
