Glossary of Common Vision Terms
A relationship between the Convergence Dioptre to Accommodation Dioptre. The measurement is done with a range of differing Dioptre Lenses. The affect of the change in Lens Dioptre is plotted against the magnitude in change of Convergence Prism Dioptre (PD) to form the AC/A Ratio. For a normal AC/A ratio of 1 there should be no change in PD for differing Lens dioptre's
Also called Anomalous retinal correspondence is binocular sensory adaptation to compensate for a long-standing eye deviation (i.e. strabismus). The fovea of the straight (non-deviated) eye and non-foveal retinal point of the deviated eye work together, sometimes permitting single binocular vision.
Accommodative infacility or accommodative inertia occurs when the accommodative system is slow in making a change, or when there is a considerable lag between the stimulus to accommodation and the accommodative response. The patient often reports blurred distance vision immediately following sustained near work. Some have considered this infacility to be a precursor to myopia.
Movement of the eye outwards away from the nose
Movement of the eye towards the nose
Amblyopia (also called lazy eye) is a type of poor vision that usually happens in just one eye but less commonly in both eyes. It develops when there’s a breakdown in how the brain and the eye work together, and the brain can’t recognize the sight from 1 eye. Over time, the brain relies more and more on the other, stronger eye — while vision in the weaker eye gets worse.
It’s called “lazy eye” because the stronger eye works better. But people with amblyopia are not lazy, and they can’t control the way their eyes work.
Amblyopia starts in childhood, and it’s the most common cause of vision loss in kids. Up to 3 out of 100 children have it. The good news is that early treatment works well and usually prevents long-term vision problems.
Amplitude of Accommodation (AA)
The amplitude of accommodation is a measure of the closest point at which the eyes can focus: it is the range from the far point to the near point in dioptres. Because it is measured from the far point, the measurement needs to be taken with the distance correction in place
Aniseikonia
A condition where the eyes have a mis-matched prescription. Eg One eye is long sighted, the other is short sighted. This can lead to Amblyopia.
Treatment includes:
Visual Therapy: This should be done whilst in conjunction with wearing contact lenses (Contact lenses cause a much smaller change in size of the image than glasses).
Anisometropia
Anisometropia is a condition where the two eyes have significantly different refractive powers, meaning one eye may be more nearsighted (Myopia), farsighted(Hyperopia/Hypermetropia), or have more astigmatism than the other. This disparity can cause difficulties in achieving clear vision with both eyes simultaneously and may lead to issues like eyestrain, headaches, or double vision.
Blepharitis is an inflammation along the edges of the eyelids. The eyelids can become irritated and itchy, and appear greasy and crusted with scales that cling to the lashes. People with blepharitis sometimes wake with their eyelids stuck together. Others may wake with dried tears around their eyes and a feeling of sand in their eyes.
Convergence insufficiency happens when the nerves that control your eye muscles don't work the right way. Normally when you focus on something up close, both of your eyes turn in. When people with convergence insufficiency look at something up close, one eye turns out.
A Development Optometrist (also often called a Behavioral Optometrist or Functional Optometrist) specializes in behavioral optometry which is a specialty in the field of optometry that is concerned with how your eyes and visual system function and is interested in how your behavior affects vision or how your vision influences your behavior
Dichoptic
Distinctly separate eyes. Having dichoptic eyes is what provides us with the ability to observe depth.
Diplopia
Double vision, which is also called diplopia, causes people to see two of the same image—whether horizontal, vertical or diagonal—instead of one. Sometimes double vision can just be an irritating but benign problem called strabismus
Divergence excess can be described clinically as exophoria or exotropia at far greater than the near deviation by at least 10 prism diopters (PD). Divergence excess can be further divided into true or simulated DE on the basis of responses to occlusion. In simulated DE, occlusion dramatically affects slow vergence, increasing the angle of deviation slightly at distance and significantly at near. Occlusion does not affect true DE.
Emmetropia is the medical term for perfect vision, or 20/20 sight. It's a naturally occurring condition where the eye has no refractive errors, and light focuses perfectly on the retina. People with emmetropia can see clearly at all distances without corrective lenses, squinting, or straining their eyes
Exophoria the outward eye misalignment is only temporary and occurs when the individual is tired or stressed, or during close vision tasks when the eyes are unable to move across the line of text smoothly due to eye teaming difficulties. Exotropia the outward eye movement is more frequent and noticeable.
Exudative (or serous) retinal detachment (ERD) occurs when fluid accumulates in the subretinal space between the sensory retina and the retinal pigmented epithelium (RPE) resulting in retinal detachment. Causes for fluid accumulation include inflammatory, infectious, and neoplastic diseases of the choroid or retina
Also see:
An eye condition in which the directions that the eyes are pointing at rest position, when not performing binocular fusion, are not the same as each other, or, "not straight". This condition can be esophoria, where the eyes tend to cross inward in the absence of fusion; exophoria, in which they diverge; or hyperphoria, in which one eye points up or down relative to the other.
See Hyperopia
Hyperopia
Long-sightedness: Hyperopia (also known as hypermetropia). This condition occurs when distant objects can be seen more clearly than close ones because the light entering the eye focuses behind the retina.
Irlen Syndrome (Scotopic Sensitivity Syndrome)
A perceptual processing disorder, It is not an optical problem. It is a problem with the brain’s ability to process visual information. This problem tends to run in families and is not currently identified by standardized educational, psychological, optometric, or medical tests. This problem can manifest itself differently for each individual. Irlen Syndrome is not remediable and is often a lifetime barrier to learning and performance.
Present day understanding is that this condition cannot be corrected by Vision Therapy
Myopia, also known as near-sightedness and short-sightedness, is an eye disease where light from distant objects focuses in front of, instead of on, the retina. As a result, distant objects appear blurry while close objects appear normal. Other symptoms may include headaches and eye strain. Severe near-sightedness is associated with an increased risk of macular degeneration, retinal detachment, cataracts, and glaucoma.
Micropsia is a condition affecting human visual perception in which objects are perceived to be smaller than they actually are. Micropsia can be caused by optical factors (such as wearing glasses), by distortion of images in the eye (such as optically, via swelling of the cornea or from changes in the shape.
Nystagmus is the involuntary movement of the eye. This can be an oscillation in the eye in the horizontal plane or vertical plane or even a circular motion involving both planes. This presents problems with the patient being able to focus on a scene and can lead to amblyopia of both eyes. One possible solution is the use of Syntonics, which utilises the differing coloured filters to stimulate parts of the brain in order to reduce and eliminate the condition
Typical Syntonic filters for Nstagmus are listed below
- Blue-Purple - Slows down the movement of the Eye which helps focus and fixate
- Yellow - Trains the brain and eye to focus see more distinctly.
- Bluey Green - Trains the brain to improve strabismus.
- Purple - helps Binocular Vision
- Royal Blue - Helps with vertical alignment.
Doctor of Optometry (Optometrist)
Optometrists are at the frontline of eye care. By carrying out detailed examinations, they are helping to improve eye health across the country. By making a detailed examination of the eye, optometrists may be able to identify whether a patient has conditions such as diabetes or high blood pressure.
See Also:
Orthoptics is a profession allied to the eye care profession. Orthoptists are the experts in diagnosing and treating defects in eye movements and problems with how the eyes work together, called binocular vision. These can be caused by issues with the muscles around the eyes or defects in the nerves enabling the brain to communicate with the eyes. Orthoptists are responsible for the diagnosis and non-surgical management of strabismus (cross-eyed), amblyopia (lazy eye) and eye movement disorders.
A progressive addition lens (PAL) is a type of multifocal that offers a smooth, seamless transition between zones of increased add power. Unlike simple bifocals and trifocals, PALs provide the desired add power without breaks, ledges, lines or abrupt jumps between distance and near viewing zones.
Phoria represent the collective term for Exophoria and Esophoria. Phoria's are not generally visible but can become visible when broken down into Exotropia and Esotropia under certain test conditions.
Phoria can break down into a tropia. This means that a patient is able to keep both eyes teamed together, but at times one eye deviates
A phoropter is an instrument comprised of cylinders, prisms, and lenses that measures the eye's refractive error to help determine and eye prescription. Phoroptors can also be used to measure the eye's natural resting position, near-distance focal ability, binocular vision and eye movements
PHOROPTER
Positive relative accommodation (PRA)
Positive relative accommodation (PRA) in biology, is a measure of the maximum ability to stimulate eye accommodation while maintaining clear, single binocular vision. This measurement is typically obtained by an orthoptist, ophthalmologist or optometrist during an eye examination using a phoropter
Anytime subretinal fluid accumulates in the space between the neurosensory retina and the underlying retinal pigment epithelium (RPE), a retinal detachment occurs. Depending on the mechanism of subretinal fluid accumulation, retinal detachments traditionally have been classified into Rhegmatogenous, Tractional, and Exudative retinal detachment.
Rhegmatogenous retinal detachment is the most common type of retinal detachment. It can happen if you have a small tear or break in your retina. When your retina has a tear or break, the gel-like fluid in the center of your eye (called vitreous) can get behind your retina.
Retinal detachment is painless. Early symptoms of rhegmatogenous detachment may include dark or irregular vitreous floaters (particularly a sudden increase), flashes of light (photopsias), and blurred vision. As detachment progresses, the patient often notices a curtain, veil, or grayness in the field of vision
See also:
Scleral buckling is an ophthalmic surgical technique that has been successfully employed as a primary or adjuvant procedure to repair rhegmatogenous retinal detachments.
Scotopic Sensitivity Syndrome
See Irlen Syndrome
Syntonics or optometric phototherapy, is the branch of ocular science dealing with the application of selected light frequencies through the eyes. It has been used clinically for over 70 years in the field of optometry with continued success in the treatment of visual dysfunctions, including strabismus (eye turns), amblyopia (lazy eye), focusing and convergence problems.
An inward eye turn, or Esotropia, typically requires Red light, while for an outward eye turn, Exotropia, Blue light is recommended.
Further Reading
The most common cause of tractional retinal detachment is diabetic retinopathy — an eye condition in people with diabetes. Diabetic retinopathy damages blood vessels in the retina and can scar your retina. As the scars get bigger, they can pull on your retina and detach it from the back of your eye.
See also:
Unlike phorias, tropias occur during binocular conditions—i.e. when the two eyes should be working simultaneously to view a target.
Another name for a tropia is strabismus or “eye turn”. This occurs when one, or both eyes, do not align properly to view a central target.
Another name for a tropia is strabismus or “eye turn”. This occurs when one, or both eyes, do not align properly to view a central target.
Fusional vergence dysfunction occurs when the eyes are well aligned (orthophoria), but negative and positive fusional vergence ranges are decreased, resulting in fatigue, eyestrain, headaches, and lack of concentration.
Individuals with fusional vergence dysfunction have both reduced positive and negative fusional vergence ranges. The only treatment option for fusional vergence dysfunction is vision therapy centered around increasing the amplitude of both vergence ranges.
Fusional Vergence Dysfunction (vergence insufficiency) Patients with fusional vergence dysfunction often have normal phorias and AC/A ratios but reduced fusional vergence amplitudes Their zone of clear, single binocular vision (CSBV) is small.
Vertical heterophorias may be either comitant and idiopathic or noncomitant, due to muscle paresis or other mechanical cause. One of the most common causes of newly acquired vertical diplopia or asthenopia with vertical deviation is longstanding, decompensated, fourth nerve palsy, which results in superior oblique paresis. These patients demonstrate a hyperphoria in primary gaze that is initially greatest during depression and adduction of the affected eye. Over time, secondary overaction and contracture of the inferior oblique muscle may overshadow the initial fourth nerve palsy. Thus, the deviation may be largest during elevation and adduction of the affected eye.
The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and then reaches the visual cortex. The area of the visual cortex that receives the sensory input from the lateral geniculate nucleus is the primary visual cortex, also known as visual area 1 (V1), Brodmann area 17, or the striate cortex. The extrastriate areas consist of visual areas 2, 3, 4, and 5 (also known as V2, V3, V4, and V5, or Brodmann area 18 and all Brodmann area 19).
Both hemispheres of the brain include a visual cortex; the visual cortex in the left hemisphere receives signals from the right visual field, and the visual cortex in the right hemisphere receives signals from the left visual field.
View of the brain from behind. Red = Brodmann area 17 (primary visual cortex); orange = area 18; yellow = area 19
Vision Therapy
Vision therapy is a program that aims to improve a person's visual abilities. It uses a variety of ways – such as eye exercises, testing, occlusion (patching) lenses and prisms – to treat a range of visual problems. Vision therapy may be used to treat problems such as: amblyopia (lazy eye)
VT
See Vision Therapy
VTOD
A Doctor of Optometry (Optometrist) specialising in Vision Therapy