Part 1 of this two-part series considers the different methods of determining eye dominance and its relevance in practice.
Just as with having a dominant hand with which to write, or a preferred foot for kicking a ball, the concept of having a dominant eye has been around for a very long time. Rosenbach (1903) is credited with being the first author to refer to eye dominance.1 He claimed that most individuals have a dominant eye, even when the vision of the two eyes is equal. Interestingly, he found that if there was an inter-ocular difference in vision, the eye with the better vision was not necessarily the dominant eye, and this view has been confirmed in more recent research by Pointer.2 Pointer also showed that an individual’s handedness is not predictive of their eye dominance.3
The concept of dominance is very familiar to optometry students who need to learn to conduct retinoscopy, direct ophthalmoscopy and other monocular techniques with equal proficiency regardless of whether the right or left eye is being used. However, eye dominance is also widely known among the general public, especially by those who have occasion to use a monocular instrument, for example, a microscope or those who have participated in activities for work or pleasure when one eye needs to be selected over the other, such as in shooting or archery.
There are many claims in non-peer reviewed sources that knowing which eye is ‘dominant’ is important because it has practical relevance for how well we perform tasks in the real world. For tasks that necessitate viewing with only one eye, these claims are easy to appreciate. For example: “For accurate and reliable shooting it is important to ensure that the eye which is over the rib of the gun is fixed on the target.”4
However, other claims from the shooting fraternity are perhaps more open to question, for example, that: “In young men, eye dominance may not stabilise until the teens” and that: “There are also very significant sex differences ... Unlike men, few women have or develop eye dominance corresponding to their handedness. Indeed, few women are absolutely dominant in either eye. They usually have indeterminate eye dominance…”5
Interestingly, claims about the importance of eye dominance also stretch to tasks undertaken when both eyes are open. In such scenarios, it is less obvious how having a dominant eye can affect performance or how taking account which eye is ‘dominant’ could help to improve performance. Take for example, cricket – here is an extract from a book titled The Art and Science of Cricket by the late Bob Woolmer.6 In the section on stance for batting, Woolmer states: “…Just as you have a dominant hand, you also have a dominant eye, one that transmits visual signals to the brain more quickly and effectively than the other. This means that if you bat right-handed, and your right eye is dominant, a side-on stance means that your dominant eye is having to squint away to the left over the bridge of your nose, or at least look down a line that is slightly outside that of the ball. Opening up the stance, so that there is a more direct line of sight from your right eye to the bowler’s hand, can give you a better picture of the delivery. The same applies to left-eye dominant left-handers.”
The purported significance of eye dominance in sport is reflected in the information provided by some practitioners on their websites. Here is an example from the US: “Understanding which eye dominates may help an athlete adopt better strategies for improving athletic performance. Most athletes know they are either right-handed or left-handed, and they adjust body movements accordingly. But they may not realise that their dominant eye may process visual information more fully and accurately than their non-dominant eye. As an example, knowing which eye dominates can help an athlete achieve better head and eye positioning to interpret fast action in sports such as basketball or baseball. Some athletes are cross-dominant, meaning that a right-handed person is left-eye dominant or a left-handed person is right-eye dominant; this can be an advantage in some sports, but potentially a serious disadvantage in sports such as archery and target shooting where one side of the body is used to both aim and shoot.”7
Of course, for practitioners and their patients, the significance of eye dominance can extend well beyond the sphere of sport. In particular, as indicated by Pointer, “an indication of the laterality of ocular dominance informs the clinical decision-making process when considering certain ophthalmic refractive and surgical interventions.”8 The most common such clinical scenario is the likelihood of adaptation to monovision correction, where one eye is corrected for distance vision and its fellow is in focus for viewing at near.
The purpose of this article is to examine what the peer-reviewed literature says in relation to the measurement and significance of eye dominance. We are concerned here with the significance of eye dominance in visual normals, that is when the visual acuity is equal (or very nearly equal) and normal, or near normal, in the two eyes. Since the areas that have received most attention in relation to eye dominance are sport and ophthalmic refractive/surgical intervention, these are the areas that are concentrated upon here. Firstly, however, it is necessary to highlight potentially confusing terminology in this domain.
The term ocular dominance is often used to describe a preference for one eye over its fellow. However, ‘ocular dominance’ also appears in neurophysiology to describe the fact that neurons in the visual cortex are typically not equally responsive when stimulated via the right and left eyes. Thus, a neuron may be binocular (capable of firing when stimulated by either eye, as is the case with the vast majority of neurons in the visual cortex) but be much more responsive when stimulated via say, the right eye. Cells with similar ocular dominance profiles are arranged in so-called ocular dominance columns in the primary visual cortex.9 On the surface, this form of ocular dominance appears to have no connection with the concept of eye dominance that practitioners establish, for example, in monovision correction. However, recent studies suggest that this may in fact be incorrect. In other words, ‘ocular dominance’ of the neurophysiological and optometric types may in fact be linked; this will be considered in more detail in Part 2 of this series.
Other terms that are used to refer to the preference for one eye over its fellow for certain tasks include: ‘eye dominance,’ ‘sighting dominance,’ ‘sensory dominance’ and ‘ocular prevalence.’ The latter three terms can be considered as different forms of eye dominance.8
Sighting dominance refers to the eye that is used in forced monocular situations, such as when using a monocular microscope or when conducting retinoscopy. There are many different ways in which sighting dominance can be established.10 One is to point, using your index finger, to a distance target and establish, by closing each eye in turn, which of the two eyes is lined up with the target. Since the hand used for pointing could influence which eye emerges as ‘dominant’, the two hands should be intertwined, allowing the index fingers of both hands to point at the distant target (see Figure 1: Pointing test to determine sighting dominance showing: left – right eye dominance; middle – left eye dominance; right top – 'central' eye dominance). Another method is called the ‘hole-in-the-card’ and involves holding a rectangular card containing a small hole, typically around 3cm diameter at arm’s length and viewing a distant target, although near targets may also be viewed (see Figure 2: Hole-in-the-card method for determining sighting eye dominance. Here the left eye is dominant). As the patient views the target, the practitioner covers each eye of the patient in turn to discover which eye is viewing the target through the hole. Variations on this test include viewing a distant target while holding a hollow cylinder at arms-length with both hands, or making the aperture to look through using the patient’s hands. Another version of this test is to have the patient hold a Jackson cross-cylinder at arms-length (see Figure 3: Sighting eye dominance tested using the Jackson Crossed-Cylinder. Here the right eye is dominant). A number of authors have objected to the use of tests for sighting dominance where the patient is forced to choose one eye over the other, for example in the sighting test that involves the use of a cylinder or the hole-in-the-card.11,12 Instead, pointing tests are preferred as binocular vision is maintained13 and because the test can diagnose ‘central eye dominance’ where neither eye emerges as dominant (see Figure 1).11,12 The possible significance of central eye dominance is discussed in relation to sport in Part 2 (to be published in OT August 2016).
Since some individuals appear to have no strong preference and are considered ‘equi-dominant’, the advice is normally to run sighting tests on three occasions to establish if the same eye emerges as being dominant on each repeat. If the outcome is two-to-one (that is, one eye appears as dominant on two of the three tests, with the fellow eye appearing dominant on the other test), the implication is that there may be no strong dominance. The advantage of sighting tests is that they require visuomotor actions (vision in combination with the movement of a part of the body), just as in the real world, which might mean that the results they give may have greater significance outside the testing room.
A second means for examining eye dominance involves the use of tests that measure the balance of sensory input between the eyes. There are tests of sensory eye dominance. As opposed to a straightforward classification of an individual as right-eye or left-eye dominant, some of the tests in this category allow the strength of the dominance of one eye over its fellow to be quantified.10 Most of these tests use binocular-rivalry or stereo-disparate targets (see Figure 4: Binocular rivalry as a test of eye dominance. Mutually perpendicular gratings, which also differ in colour, are presented to the two eyes. At any one instant, most report perceiving one grating colour/orientation only, though there may be brief periods when the two gratings appear superimposed. As time passes, the precept changes from that registered via the right eye to that registered by the left eye. Sensory dominance is present if one eye's percept reaches awareness doe longer periods by comparison with that of the fellow eye. Image courtesy of Samantha Strong).
Binocular rivalry is thought to provide a particularly useful means for studying how sensory processing gives rise to eye dominance because it involves a changing percept without any change in the visual stimulus.14 Kommerell and colleagues distinguish between ocular dominance and ocular prevalence as follows: “Ocular dominance manifests itself in tests that contain stereo-objects with a disparity beyond Panum’s area, for example, in pointing a finger. These tests force subjects to decide in favour of one or the other eye. In contrast, ocular prevalence is determined using stereo-targets imaged within Panum’s areas. These tests allow a graded quantification of the balance between the eyes.”15 Thus with this terminology, ‘ocular dominance’ tests are tests of sighting dominance, and ‘ocular prevalence’ tests are tests of sensory dominance. Kommerell et al tests of sensory dominance include the Freiburg Ocular Prevalence Test in which stereo-disparate targets have to be aligned, and the Haase Stereo-balance Test which requires an estimation of the horizontal distance between stationary, stereo-disparate objects. These tests are much more commonly used in Europe. Another way to investigate sensory eye dominance is to introduce monocular blur, for example, using a +1.00DS or +1.50DS trial case lens and ask the patient to indicate whether they are less comfortable with the right eye blurred or the left eye blurred. This clinical evaluation is used in prospective monovision patients and will be discussed further in Part 2.
Agreement between tests
Most ‘sensory eye dominance’ and ‘sighting dominance’ tests are quick and straightforward to administer, and require little or no additional clinical equipment. However, it is of interest to know if there is consistency in the same individual between the results of these different test types? If not, a number of questions immediately present themselves:
- Which test type reveals the true dominance?
- Within sensory eye dominance and sighting dominance tests, are results consistent in individuals?
- If there is poor consistency between test results in individuals, could it be the case that the concept of having a dominant eye is in some way flawed and in need of revision?
We will now consider the first two of these questions, the answers to which will have significant implications for the final question, and we will return to that question at the end of the article. A number of studies have examined the agreement between the results of sensory eye dominance and sighting dominance tests. The test-retest reliability and the effect of testing distance has also been studied.16 Rice and colleagues found excellent test-retest reliability for each of the eye dominance tests they examined.16 They used the ‘hole-in-the-card’ test for assessing sighting dominance when viewing was at distance and at near, and interestingly, they found that the results of eye dominance testing frequently depended upon the testing distance. They found that the results of eye dominance testing frequently depend upon the testing distance.
Most studies comparing eye dominance assessed using sensory- and sighting-test types have found that little agreement exists between the results.17,18 For example, Pointer found agreement between the eye that was ‘dominant’ using ‘sensory’ and ‘sighting’ test types in only 50% of their participants – that is, a level of agreement that is no better than would be expected by chance.8 Ooi and He also concluded that sensory eye dominance couldn’t be equated with motor eye dominance as revealed by sighting tests.19 As early as 1943, Cripes found that sighting tests often gave results which depended upon the test type and the same is true, possibly even more so, in sensory eye dominance tests. For example, Suttle and colleagues found that the agreement between sighting and sensory dominance test results show poor agreement, and that sensory dominance is not a significant element of vision in most individuals with normal vision.20 In contrast, only a small number of studies have found a correlation between sighting dominance and sensory dominance test results.21,22 Kommerell et al found that there was agreement in 75% of the individuals between the eye that was ‘dominant’ according to the ocular dominance (sighting) and ocular prevalence tests, although the sample size was small (20 participants).15
The reasons for the between-study differences in findings are far from obvious but, on the balance of evidence at the present time, it seems safe to conclude that sensory and sighting dominance test results show poor agreement, that even within one test type (sensory or sighting) the eye which emerges as ‘dominant’ is often not consistent, and that at least part of this variability between test results may be due to the test distance. Laby and Kirschen recommend that, if the evaluation is to be accurate, only tests of eye dominance that allow for the maintenance of binocular vision should be used.23 Indeed, Johansson and colleagues suggest the “plausible occurrence of forms of eye dominance under binocular viewing conditions.”24
Thus it appears that many factors (some internal to the patient but numerous additional factors relating to the test, including the test-type, viewing distance and conditions of testing) influence the results obtained in eye dominance tests. Add to this the finding that eye dominance may not be absolute but more graded and we have a complicated picture. Until more is known about the significance of the various internal and external factors, and the issue of graded dominance, the value of eye dominance test results will probably remain extremely limited.
Is right eye dominance more common?
Despite differences in results when different tests are used, studies of sighting dominance generally find right-eye-dominance to be much more common than left-eye-dominance. For example, Chia and colleagues reported 58% and 30% were right and left eye dominant, respectively, with the hole-in-the-card test, with the remaining 12% having no eye preference.25 Another study found left-eye and right-eye sighting dominance in 32% and 68% of participants.26 In tests of sensory eye dominance, the incidence of right- and left-eye dominance appears to be much more balanced.19
Factors known to affect which eye emerges as ‘dominant’ include the test type is sighting or sensory, and also whether the test allows a diagnosis of central dominance (see Figure 1). In Part 2 of this series, we will see that the gaze angle and hand used during testing can also influence dominance. Although the test-retest variability on any one test may be low, the results in any one individual may be highly variable as either eye can be ‘dominant’ in different circumstances. Thus, the concept of having a single, unchanging dominant eye may be flawed. Studies that compared test results using a range of different test have found that no clear ocular dominance exists in most individuals.10 Instead, there is frequently an alternating balance between the eyes in visual normals. This could explain the great variability both between and within different kinds of tests. Overall, these findings raise the question as to what, if anything is the clinical significance of eye dominance.
About the author
Professsor Brendan Barrett is professor of visual development at the University of Bradford where he is the module leader for Refraction and Refractive Error and also teaches on the binocular vision module. He is currently an external examiner for the undergraduate ophthalmic dispensing programme at Glasgow Caledonian University and the undergraduate programme at Aston University. His research interests include amblyopia, vision and sport, and vision and reading.
- Rosenbach, O. Ueber monokulare Vorherrschaft beim binokularen Sehen. M€unchener Medizinische Wochenschrift, 1903. 30, 1290– 1292
- Pointer JS. The absence of lateral congruency between sighting dominance and the eye with better visual acuity. Ophthalmic Physiol Opt. 2007 Jan;27(1):106-10
- Pointer JS. Sighting dominance, handedness, and visual acuity preference: three mutually exclusive modalities? Ophthalmic Physiol Opt. 2001 Mar;21(2):117-26
- http://www.shotspot.co.uk/?page_id=805, accessed 13/1/16)
- http://www.shootinguk.co.uk/features/eye-dominance-and-your-shooting-13003, accessed 13/1/16)
- Bob Woolmer’s The Art and Science of Cricket5 (Struik Publishers, 2008)
- http://www.allaboutvision.com/sportsvision/skills.htm#dominanteye accessed 13/1/16)
- Pointer JS. Sighting versus sensory ocular dominance. J Vision 2012;5(2):52-55
- Millodot’s Dictionary of Optometry. Definition for ocular dominance
- Seijas O, Gómez de Liaño P, Gómez de Liaño R et al. Ocular dominance diagnosis and its influence in monovision. Am J Ophthalmol. 2007 Aug;144(2):209-216
- Portal JM, Romano PE. Patterns of eye-hand dominance in baseball players. N Engl J Med. 1988 Sep 8;319(10):655-6
- Portal JM, Romano PE.Major review: ocular sighting dominance: a review and a study of athletic proficiency and eye-handdominance in a collegiate baseball team. Binocul Vis Strabismus Q. 1998;13(2):125-32
- Laby DM, Rosenbaum AL, Kirschen D. Re: Portal JM, Romano PE: Ocular dominance, central, etc. and baseball. Binocul Vis Strabismus Q. 1998;13(3):165-6
- Platonov A, Goossens J. Eye dominance alternations in binocular rivalry do not require visual awareness. J Vis. 2014 Sep 2;14(11)
- Kommerell G, Schmitt C, Kromeier M et al. Ocular prevalence versus ocular dominance. Vision Research. 2003, 43: 1397-1403
- Rice ML, Leske DA, Smestad CE et al. Results of ocular dominance testing depend on assessment method. J AAPOS. 2008 Aug;12(4):365-9
- Blake R, Camisa J. Sighting dominance and binocular rivalry. Am J Optom Physiol Opt 1978;55:208-13
- Porac C, Coren S. The relationship between sighting dominance and the fading of a stabilized retinal image. Percept Psychophys. 1982 Dec;32(6):571-5
- Ooi TL, He ZJ. Sensory eye dominance. Optometry. 2001 Mar;72(3):168-78
- Suttle C, Alexander J, Liu M, Ng S, Poon J, Tran T. Sensory ocular dominance based on resolution acuity, contrast sensitivity and alignment sensitivity. Clin Exp Optom. 2009 Jan;92(1):2-8
- Kommerell G, Schmitt C, Kromeier M et al. Ocular prevalence versus ocular dominance. Vision Research. 2003, 43: 1397-1403
- Handa T, Mukuno K, Uozato H et al. Efects of dominant and non-dominant eyes in binocular rivalry. Optom Vis Sci. 2004;81:377-83
- Laby DM, Kirschen DG. Thoughts on ocular dominance-is it actually a preference? Eye Contact Lens. 2011 May;37(3):140-4
- Johansson J, Seimyr GÖ, Pansell T. Eye dominance in binocular viewing conditions. J Vis. 2015;15(9):21
- Chia A, Jaurigue A, Gazzard G et al. Ocular dominance, laterality, and refraction in Singaporean children. Invest Ophthalmol Vis Sci. 2007 Aug;48(8):3533-6
- Ehrenstein WH, Arnold-Schulz-Gahmen BE, Jaschinski W. Eye preference within the context of binocular functions. Graefes Arch Clin Exp Ophthalmol. 2005 Sep;243(9):926-32.