Angular aberration has no effect on reading performance

By Prof. Dr. Dr. R. Werth

When looking at a distant object, the axes of both eyes are directed toward this object so that the image of the object is projected onto corresponding points on the retina in both eyes. The brain can then merge (fuse) the images from both eyes into a single image. However, even if one eye is not focused precisely on the object to be viewed and one eye axis is aligned as if the object to be viewed were slightly in front of or behind the object actually being viewed (i.e., in the Panum area) and the image of the actual object to be fixed is not projected exactly onto corresponding areas of the retina, the images on the retinas of both eyes can still be merged into one object by the brain. However, this only applies to minor deviations of both eye axes.

Deviation from ideal eye position

If the eyes tend to deviate slightly from the ideal eye position, this slight deviation can also be compensated for spontaneously by the deviating eye correcting its position. For example, if a prism is held in front of the eye of a person with normal vision so that the fixed object is no longer projected onto a point on the retina that corresponds to the point on the retina of the other eye (non-corresponding retinal point), the eye in front of which the prism is held automatically performs a compensatory movement. This causes the fixed object to reappear at a corresponding retinal point.

Experiment with prisms

Even when normal readers were artificially induced to deviate their eye axis inward or outward by placing prisms of up to 6 prism diopters in front of their eyes, this had no effect on their reading performance. (Dysli and Vogel 2014). Double vision only occurs when the deviation of one eye is so great that no compensatory eye movement can correct it and the brain can no longer merge the two retinal images.

Angular vision aberration

“Angular vision aberration” is a term that is not used in scientific medical optics. Angular aberration refers to a slight misalignment of the eyes that only appears in the measurement procedure proposed by H.-J. Haase and has been interpreted as a form of heterophoria, i.e., latent strabismus. The aim is to determine the weighting (prevalence) of one eye in vision.

Valence test for heterophoria according to Haase

In the Haase valence test, a mark must be fixed at a distance of 5-6 m. Above or below the mark to be fixed, a triangle is presented approximately 1.5 m in front of or behind this mark. If neither eye is dominant in this directional perception, i.e., if both eyes are equivalent, both triangles are seen in the center of the fixation mark. However, if the triangles are perceived as being offset to the side of the center of the fixation mark, this is interpreted as greater weighting (prevalence) of one eye. If there is prevalence of one eye, according to Haase, this should be converted to equivalence by placing prisms in front of the eye. If there are different degrees of prevalence for triangles in front of and behind the fixation mark, this is interpreted as a sign of a slight misalignment of the eyes and a fixed image is not projected onto exactly the same areas of the retina in both eyes (Schroth V, ldschinski 2001; IVBS 2912).

This slight difference in the prevalence of both eyes should be corrected using prisms so that the prevalence of one eye disappears. However, studies have shown that the prevalence of one eye is the norm in people with normal vision and can be detected in 70 to 80% of the population without affecting visual performance in every case (Kommerell and Kromeier 2002; Kříž and Skorkovská 2017). Studies have also shown that the prevalence of one eye measured by Haase’s test is not a reliable measurement and that the prevalence of one eye can only be corrected by prisms in exceptional cases (Schroth, Jaschinski 2007).

Dependence on body posture

The heterophoria detected by the measurement method proposed by Haase and its correction using prisms, as advocated by Haase, had no influence on reading performance (Jainta and Joss 2019). A comparison of children with dyslexia and normal readers showed no causal relationship between mild vertical heterophoria and reading performance. Heterophoria appeared to occur depending on the children’s posture (Quercia et al. 2015).
Our studies on children with dyslexia (Werth 2006; 2018; 2019, 2021; Klische 2017) clearly show that dyslexia is not a consequence of heterophoria. All studies involving more than 350 children show that a dramatic improvement in reading performance occurred immediately when the following sub-skills important for reading were controlled by software in such a way that they were appropriate for reading:

Simultaneous recognition

  • Fixation times
  • The time from the presentation of the material to be read to the correct pronunciation
  • Eye movements

Literature

Dysli M, Vogel N, Abegg M. Reading performance is not affected by a prism induced increase of horizontal and vertical vergence demand. Front Hum Neurosci. 2014; 8; 431. doi:10.3389/fnhum.2014.00431.

Schroth V, ldschinski W Beeinflussen Prismen nach H.-J. Haase die Augenprävalenz?
Klein Monatsbl Augenheilk 224, 2001, 32-39.

IVBS, Internationale Vereinigung für Binokulares Sehen. Richtlinien zur Anwendung der MKH. 2012

Kommerell, G., Kromeier, M. Prismenkorrektion bei Heterophorie. Ophthalmologe 99, 3–9 (2002). https://doi.org/10.1007/PL00007112.

Kříž P, Skorkovská Š. Distance associated heterophoria measured with polarized Cross test of MKH method and its relationship to refractive error and age. Clin Optom (Auckl). 2017 Mar 31;9:55-65. doi: 10.2147/OPTO.S123436. PMID: 30214361; PMCID: PMC6095580.

Schroth V, Jaschinski W. Beeinflussen Prismen nach H.-J. Haase die Augenprävalenz? [Do prism corrections according to H.-J. Haase affect ocular prevalence?]. Klin Monbl Augenheilkd. 2007 Jan;224(1):32-9. German. doi: 10.1055/s-2006-927268. PMID: 17260317.

Jainta S, Joss J. Binocular advantages in reading revisited: attenuating effects of individual horizontal heterophoria. J Eye Mov Res. 2019 Dec 9;12(4):10.16910/jemr.12.4.10. doi: 10.16910/jemr.12.4.10. PMID: 33828742; PMCID: PMC7880141).

Quercia P, Quercia M, Feiss LJ, Allaert F. The distinctive vertical heterophoria of dyslexics. Clin Ophthalmol. 2015;9:1785-1797. Published 2015 Sep 25. doi:10.2147/OPTH.S88497.

Werth R: Therapie von Lesestörungen durch Erkennen und Beheben der Ursachen
Ergotherapie und Rehabilitation 9 (2006b) 6-10.

Werth R: Rapid improvement of reading performance in children with dyslexia by altering the reading strategy: a novel approach to diagnoses and therapy of reading deficiencies. Restor Neurol Neurosci 36, 2018, 679-691 2018.

Werth R: Dyslexic readers improve without training when using a computer-guided reading strategy. Brain Sci. 2021, 11(5), 526

Werth R: What causes dyslexia? Identifying the causes of dyslexia and effective compensatory therapy
Restorative Neurology and Neuroscience , 37, 2019, 2019, 1-18.

Klische A , Leseschwächen gezielt beheben. Tectum, Baden-Baden, 2007.