S Afr Optom 2006 65 (4) 150 − 156 A retrospective analysis of heterophoria values in a clinical population aged 18 to 30 y e a r s NT Makgaba* Department of Optometry, University of Limpopo, Turfloop campus, P. Bag X1106, Sovenga, 0727 South Africa <[email protected]> Abstract with a mean of 0.08 pd right hypophoria (SD Information on heterophoria values in South = ± 0.96). The distributions of heterophoria Africans is scanty. The purpose of this paper at distance and near were non-normal. There therefore, is to present information on the dis- was no significant gender variation in the tribution of heterophoria in a clinical popula- horizontal values for distance vision and the tion aged 18 to 30 years, which hitherto is not vertical (distance and near) ones. However, available. The data presented here was obtained there was a statistically significant gender varia- from the record cards of 475 black South tion in the near horizontal values (p > 0.05). African patients examined at the Optometry There was no significant variation in hetero- clinic, University of Limpopo (Turfloop cam- phoria values with age. The data presented pus) between 2000 and 2005. The patients were here will be useful for comparison with simi- examined by final year students under the super- lar data from South Africa or other countries. vision of qualified optometrists. Heterophoria was measured for each patient using the von Keywords: Heterophoria, horizontal pho- Graefe method. The horizontal heterophoria ria, vertical phoria, esophoria, exophoria. for distance vision (6 m) ranged from 16 prism diopters (pd) esophoria to 12 pd exophoria with a mean of 0.74 pd exophoria (SD = ± 2.84 pd). Introduction For distance vision, esophoria ranged from Heterophoria often simply called phoria has 0.5 to 16 pd with a mean of 3.08 pd (SD = ± been defined in many ways by researchers. 3.09), while exophoria ranged from 0.5 pd to Carey1 has discussed the issue of definition 12 pd with a mean of 2.21 pd (SD = 1.82 pd). adequately, and hence will not be discussed here For near vision (0.4 m), the horizontal phorias any further. An interesting definition of this ranged from 17 pd esophoria to 15 pd exopho- condition is that of Kommerel and Kromeier2 ria with a mean of 3.84 pd exophoria (SD = ± who defined it as a non-primarily existing ocu- 4.80 pd). The near esophorias ranged from 0.5 lar deviation but a reaction to an interruption to 17 pd with a mean 4.88 pd (SD = ± 3.41), of the sensory-motor-feedback control system. while the exophorias ranged from 1.0 to 15 pd This definition agrees with the claim by Von with a mean of 6.30 pd (SD = ± 2.58). Vertical Noorden3 that ocular misalignment in hetero- heterophoria for distance vision ranged from 5 phoria is held in check by the fusion mechanism. to 3 pd right hyperphoria with a mean of 0.05 According to this author3, in patients with het- pd right hyperphoria (SD = ± 0.76) whereas at erophoria, motor fusion is adequate to provide near it ranged from 4 to 6 pd right hyperphoria * BOptom Received 24 August 2006; revised version accepted 10 December 2006 The South African Optometrist − December 2006 150 NT Makgaba proper alignment of the eyes; this, however, both distances. According to these authors8, ver- does not mean that the patient with heterophoria tical heterophoria is less likely to alter between necessarily has normal sensory fusion. When distance and near vision. Slight incomitancy and there is a high degree of heterophoria, there may relative vertical prism in anisometropia may, be suppression and a high stereoscopic thresh- however, cause differences in the angle of a old, but motor responses are sufficient to keep vertical heterophoria as gaze depresses for close the eyes aligned2. Heterophoria measurements work. This view differs from those of Schor are very vital during binocular vision assess- and Ciuffreda9 and Dowley10 who reported that ment as its values are used in the diagnosis there is a high prevalence of distance ortho- of binocular vision anomalies such as diver- phoria in the population despite a large number gence excess and convergence insufficiency. of mechanical, neural and sensory variables. There are several methods used clinically to Decompensated heterophoria is associated evaluate heterophorias. In all of these methods with several symptoms11-17 such as photophobia, fusion must first be broken to achieve dis- eyestrain, headaches, decreased stereopsis, pain sociation of the eyes, allowing evaluation of in the eyes, diplopia, poor visual performance11-17 heterophoria4. The methods may differ in the and dizziness is associated with vertical het- ability to control accommodation adequately erophoria18. Diagnosis such as convergence in the level of proximal convergence induced insufficiency characterized by an exophoria and in the method by which heterophoria is which is greater at near than at distance, or quantified. The duration and the degree of divergence excess, characterized by exophoria dissociation when fusion is disrupted will greater at distance than at near are associated also affect the measurements in that a lon- with many symptoms19. Decompensated hetero- ger duration of dissociation will increase ver- phorias may become significant after a working gence adaptation5. Therefore heterophoria val- day and they can result in ocular symptoms ues may vary from one procedure to another. and visual discomfort20. Jaschinski-Kruza and Heterophoria has been attributed to four Schweflinghaus21 found a relationship between main categories of etiologies namely: anatomi- tonic convergence and psychosomatic symp- cal, refractive, uniocular activity and trauma6, 7. toms. Also, Hasebe et al.22 found that fatigue The anatomical causes include abnormal inter- reduces tonic accommodation. These studies pupillary distance, exophthalmos and/or endo- imply that after a working day there is high inci- phthalmos. Also, an abnormality of the fascia dence of visual and psychosomatic symptoms. or ligaments of extraocular muscles may be a Fixation disparity and associated phoria (the cause of an imbalance. Refractive causes relate degree of prism required to eliminate fixation to the relationship between accommodation and disparity) have been thought to be an indicator vergence. For example, an uncorrected hypero- of a decompensated phoria which give rise to pia has a tendency to induce a shift towards symptoms19. Yekta et al.20 found a statistically esophoria. The repeated use of one eye (for significant increased dissociated exophoria and example, watchmakers) has also been suggested associated exophoria after the normal close as a possible cause of heterophoria6, 7. Von working day. They20 also found that at the end Noorden3 also reported that innervational fac- of the working day 63 of the 84 subjects com- tors which comprise of nervous impulses reach- plained of visual symptoms. They, therefore, ing the eyes can result in heterophoria. This concluded that there is fixation disparity and implies that all these ocular and visual abnor- symptoms associated with close work which is malities have the ability to interrupt fusional more likely to be related to binocular stress and innervation thereby precipitating heterophoria. decompensated heterophoria. Also, Hasebe et Heterophoria can be vertical, horizontal or al.22 reported that fatigue reduces tonic accom- oblique (cyclophoria). A small heterophoria is modation, therefore individuals such as stu- present in 70-80% of the population2. Bennett dents who are exposed to a lot of near work are and Rabbetts8 reported that people are exophor- likely to have decompensated phorias which ic both at distance and near or esophoric in both may result in symptoms. There are reports that and also, the angle of deviation might differ in age influences heterophoria23-26. According to 151 The South African Optometrist − December 2006 A retrospective analysis of heterophoria values in a clinical population aged 18 to 30 years 23 Kephart and Oliver , distance heterophoria Table 1. A summary of heterophoria measurements. Positive has a slight tendency towards greater esophoria values refer to exophoria and right hyperphoria while nega- with age. The validity of this claim has been tive refer to esophoria and right hypophoria. The units are in prism diopters (pd). questioned because accommodation decreases with age which may lead to greater divergence Heterophoria Range (pd) Mean (pd) Standard 25, 26 Deviation and hence an increase in exophoria . This view (pd) 25 agrees with the reports by Freier and Pickwell Horizontal at far -6 to 12 0.74 2.87 that exophoria increases with age. Also, Yekta et Exophoria 0.5 to 12 2.21 1.82 al. 26 reported an increase in exophoria, associated Esophoria -16 to -0.5 -3.08 3.09 phoria and fixation disparity with age. An increase in exophoria for near vision with age has been Vertical at far -5 to 3 0.05 0.76 24, 25 11 Right hyperphoria 0.5 to 3 0.22 0.5 reported . Although Waline et al. however, Right hypophoria -5 to -1 -1.30 0.99 found no significant changes of distance hetero- Horizontal at near -17 to 15 3.84 4.80 phoria with age. There is a general consensus that Exophoria 1 to 15 6.30 2.58 age has an effect on heterophoria. Although het- Esophoria -0.5 to -17 4.88 3.41 erophoria has been studied in South African chil- Vertical at near -4 to 6 -0.08 0.96 dren27, but no information could be found in the Right hyperphoria 0.5 to 6 0.19 6.51 Right hypophoria -4 to -1 -1.61 0.95 literature on heterophoria in South African adults. It was, therefore decided to examine the distribu- tion of this condition in adults in a clinical setting. Table 2. A summary of heterophoria values according to gender for distance and near vision.