Horizontal Heterophoria

High degrees of comitant esophoria or exophoria are often accompanied by a small vertical component. In these cases, the treatment will be that which is appropriate to the primary condition, but prism relief of the hyperphoria may help.

Incomitant Deviations

Paretic conditions involving the elevator or depressor muscles may begin as hyperphoria and develop later into strabismus. It is important that this early sign of pathology is detected. The sudden onset of intermittent vertical diplopia and/or other symptoms, and the incomitant nature of the deviation, are the main diagnostic features. The most common cyclovertical incomitancy is superior oblique underaction, so it is important to look carefully for cyclophoria in all cases of hyperphoria and skew deviation is another differential diagnosis ( Chapter 17 ). Congenital incomitant deviations are frequently accompanied by a vertical element, but symptoms are usually absent.

Unilateral High Myopia (Heavy Eye Syndrome)

Heavy eye syndrome involves anisometropia, usually with high myopia, and hyperphoria or hypertropia. The more myopic eye is hypotropic or hypophoric. The notion that the disorder results from a ‘heavy’ myopic eye is incorrect: the cause is an abnormally low muscle path of the lateral rectus in the involved eye ( Yanoff & Duker, 1999 ). The vertical deviation ranges from 2–25Δ, although there is no correlation between the amount of anisometropia and the amount of hypotropia. Elevation of the low eye may be limited. Frequently, the head tilts to the side of the hypotropic eye.

Tilted Spectacles, Unilateral Toric Contact Lenses, and Anisometropia

If spectacles are incorrectly fitted or the frame becomes bent, a vertical prism element may be introduced which initially shows as hyperphoria. Usually, the patient adapts quite quickly to this abnormal prism and the hyperphoria reduces. When this occurs, hyperphoria will be present when the glasses are removed, or the spectacle frame straightened. This will disappear after a few days.

Toric contact lenses, most commonly disposable soft lenses, often contain a vertical prism to aid lens orientation. The strength of prism ranges from 0.52Δ to 1.15Δ which, in patients who only require monocular correction of astigmatism, might cause symptoms in sensitive patients ( Sulley, Hawke, Lorenz, Toubouti, & Olivares, 2015 ).

Corrections for anisometropia may also produce hyperphoria when the eyes are not looking through the lens optical centres. Again, adaptation to this variable prismatic effect usually occurs after a few days of using the anisometropic correction, but difficulties can arise with a correction for marked anisometropia particularly where no glasses have been worn before ( Chapter 11 ). Similarly, problems may arise if a refractive correction has changed markedly (e.g., after a cataract extraction operation). A near hyperphoria can result when multifocal spectacles are prescribed to a patient with significant anisometropia ( Chapter 11 ).

A spectacle correction which has not been correctly balanced between the two eyes may also cause hyperphoria. The same applies to uncorrected anisometropia.

Removal of Cause of Decompensation

Care must be taken to explore the visual working conditions and any stress or ill health that may be the cause of the decompensation. These should receive attention before other aspects of management.

Refractive Correction

In some cases, the provision of a correction for previously uncorrected refractive error will alleviate the hyperphoria without any other treatment. Balancing the refractive correction is very important in hyperphoria.

In the case of marked anisometropia where no previous correction has been worn, a partial correction of the more hypermetropic eye may prevent disturbance by vertical prismatic effects when the patient is not looking through the optical centres of the lenses. The correction is reduced in the more hypermetropic eye until the vertical heterophoria is compensated when looking through the lenses a little above or below the optical centres. This can be judged by Turville’s ‘nodding test’. Traditionally the infinity balance septum is used, and the patient asked to raise and lower their head in a slight nodding motion until the reduced sphere does not create a change of level in the two letters. Nowadays, it is more common to carry out a version of this test with the patient slowly nodding whilst viewing the vertical Mallett fixation disparity test. This correction may be increased to a fuller prescription with subsequent glasses (see also Chapter 11 ).

Eye Exercises

Eye exercises to improve the vertical fusional reserves very seldom prove successful, and do not seem to help in making the hyperphoria compensated. This is not surprising as vertical vergence may not be disparity driven ( Ygge, 2000 ) and, unlike horizontal vergence, is not influenced by emphasising the need for accuracy during vergence changes ( Stevenson, Lott, & Yang, 1997 ). However, one study (a non-controlled trial) indicated that it might be possible to change vertical fusional reserves with exercises ( Luu et al., 2000 ). When the hyperphoria is associated with horizontal heterophoria, exercises to increase the horizontal fusional reserves will often result in the vertical heterophoria becoming compensated ( Cooper, 1988a ).

Relieving Prisms

Most primary hyperphoria can be readily relieved by weak vertical prisms, although randomised controlled trials are lacking ( Doble et al., 2010 ). As explained earlier, the smallest prism that will neutralise the fixation disparity with a Mallett unit can be prescribed. As noted in Chapter 8 , such vertical prism relief may also help any decompensated horizontal heterophoria ( Sheard, 1923 ; London and Wick, 1987 ).

Referral

Incomitant hyperphoria with intermittent diplopia of recent onset indicates the need for medical investigation. When there is a high degree of hyperphoria and congenital incomitancy which gives rise to intolerable symptoms, surgical relief is sometimes considered. Medical advice should be sought.

Dissociated Vertical Deviation (DVD)

This is a comparatively unusual anomaly which is also known as ‘alternating sursumduction’. Although it could be mistaken for hyperphoria, the clinical appearance is not the same. It is usually seen during the cover test. When one eye is covered with an occluder or a dark filter it slowly deviates upwards, possibly by as much as 40Δ. This differs from hyperphoria in that, whichever eye is covered, there is an upward movement of the eye behind the cover. When the cover is removed, the eye slowly recovers to the fixation position. The upward movement is not always equal in the two eyes, and sometimes it can be absent in one eye, giving the appearance of a ‘unilateral hyperphoria’. In all cases, if a neutral density filter bar is placed before the uncovered eye and the density of the filter increased, the eye under the cover will slowly move down. When the density of filter is reduced, the covered eye moves slowly up again. This is called the Bielschowsky phenomenon.

DVD is usually associated with a history of infantile esotropia syndrome (p. 227). There is sometimes a cyclorotation of the occluded eye ( Burian & von Noorden, 1974 ). Various surgical approaches have been used for DVD, but the evidence-base for these is weak ( Hatt, Wang, & Holmes, 2015 ).

When DVD exists without any other deviation or anomaly, there are usually no symptoms and no independent treatment is required. If it exists with other conditions, treatment appropriate to the primary condition can be considered. Occasionally, patients with DVD complain that one eye deviates spontaneously and this is noticed by other people. The condition rarely produces symptoms ( Mallett, 1988a ), but if the condition is cosmetically unacceptable surgery is indicated ( Kanski, 1994 ).