Angular vision deficiency: «Mum, the letters are dancing!»

Luca thinks reading is rubbish. He avoids it whenever possible. He also finds writing difficult. He slips in the lines, twists the letters and makes lots of spelling mistakes. He often has a headache and is tired. «You just have to practise harder,» he is often told. But no matter how hard he tries, the letters just «jump out» in front of him. Luca only gets help when he is diagnosed with an angle vision defect as the cause of his problems.

Angular defective vision - What kind of disease is it?

Angular defective vision is not a visual defect or disease in the strict sense. «Rather, it is a latent deviation of the eyes from their optimal position when at rest,» explains Daniel Bruun, ophthalmologist and eye surgeon from Kreuzlingen TG. «However, this deviation can have an impact on simultaneous vision on both sides.»

Latent strabismus

In order to create a three-dimensional image, the two individual images that are created on the retinas of the two eyes must be merged by the brain into a single spatial image. This process is known as fusion in technical jargon. «For optimal fusion, the two eyes should always be aligned in the same way,» says Bruun. «In the vast majority of people, however, there are naturally small deviations inwards or outwards in the relaxed eye position, and more rarely upwards or downwards.» This deviation from the ideal state is called angular misalignment.
In ophthalmology, it is also referred to as heterophoria or hidden strabismus. "Hidden because the slight misalignment only becomes visible when the eye is at rest - for example when tired or with the eye covered," explains the strabismus expert. «As soon as the eyes focus on an object, the brain readjusts the deviation in a fraction of a second so that the eyes are synchronised again.» Unlike real strabismus, latent strabismus is therefore not noticeable in everyday life.

80 per cent of all people have so-called hidden strabismus, also known as angle vision deficiency.

Around 80 per cent of all sighted people have an angle defect. Most people can cope with the constant extra work that the brain and eye muscles have to do to achieve optimum fusion without any major problems. «However, a certain percentage develop strain-related complaints, which can sometimes have a massive impact on their quality of life,» says Bruun.

Angular defective vision can make you ill

«A clear sign of possible problems with hidden strabismus is when patients repeatedly see double vision,» says eye expert Daniel Bruun. «Frequent headaches, especially in the evening, can also be a sign of this.» Children also show symptoms such as frequent stumbling, poor orientation in space and problems following moving objects such as balls. Tasks that require concentrated eye work, such as handicrafts, colouring or cutting out, are consistently avoided.
Affected schoolchildren often suffer from concentration difficulties and show severe abnormalities in reading and writing. «It is typical that the children prefer to avoid reading, almost stick their nose to the paper when asked to do so, only make halting progress and often slip in the line,» says Daniel Bruun. «When writing, the lines cannot be held and the words are illegible and/or incomplete.»

Complex diagnosis

Angular misalignment only needs to be treated if it causes problems. «I always compare it to slight knock knees or bow legs, which are not a disease in themselves,» emphasises the strabismus expert. «It's only when symptoms such as pain due to incorrect weight-bearing occur that something needs to be done.»
A very detailed medical history is required to determine whether the symptoms described are due to eye strain caused by angle vision deficiency or have another cause. «You need a lot of experience and sensitivity here, especially with children,» says Daniel Bruun.
In addition, other possible causes, such as existing genuine visual defects, must be ruled out or treated professionally. «Unfortunately, this comprehensive and time-consuming examination is not particularly well remunerated by health insurance companies,» says Bruun. «As a result, it is not economically lucrative for many ophthalmologists and is therefore neglected.»

If standard examinations do not reveal any abnormalities, angle vision deficiency often remains unrecognised and untreated for years.

There are currently only a very small number of ophthalmologists in Switzerland and neighbouring countries who deal more intensively with the issue of angle vision deficiency. The victims of this development are affected children and adults whose angle vision deficiency often remains unrecognised and untreated for years because standard examinations do not reveal any abnormalities.
Ruth Schmid, mother of three children with angle vision deficiency and founder of a Swiss self-help group in Winterthur, has had such experiences herself and knows many families who could only be helped after a long ordeal with prism glasses or strabismus surgery. She says: «Parents of affected children are often more likely to find help from an optician than an ophthalmologist.»

Measurement and correction methodology according to Haase

In the 1950s, master optician Hans-Joachim Haase developed a special measurement method known as the H.-J. Haase measurement and correction method - MKH for short. Formerly known as the Polatest, the MKH is now mainly used by opticians and a few convinced ophthalmologists who have joined forces in the International Association for Binocular Vision (IVBS). «With MKH, the eye position is measured separately using polarisation filters, but while maintaining fusion as in natural vision,» explains Fritz Gorzny, Vice President of the IVBS and ophthalmologist from Germany. Unlike conventional eye tests, both eyes are involved in the visual process when measuring MKH. Polarisation filters in the measuring glasses ensure that each eye can still be measured individually.
«During the measurement itself, the patient must then analyse polarised test images, which are preceded by different prism lenses until the images from both eyes subjectively hit the sharpest point of both retinas and display the test image correctly.»
The aim of the measurement is to determine the exact deviation of the eyes in so-called prism dioptres. These values can then be used to produce prism glasses that compensate for the measured deviation and relieve the strain on the eyes during daily visual work. «As the eye muscles can become tense due to years of strain, the strength of the prisms may need to be increased later,» emphasises Fritz Gorzny. «In less than two per cent of cases, the final number of prisms can be so high that a strabismus operation becomes necessary.»

Movement helps the brain to retain information in the mind.

Criticism of the MKH method

One critic of the MKH, for example, is Gabriela Wirth Barben, an ophthalmologist specialising in strabismus and paediatric ophthalmology in St. Gallen. She describes angular defective vision as an artificial product: «The Haase measurement method measures values in a state artificially created by polarisation filters, which has nothing to do with natural vision.» Wirth Barben also criticises the fact that the subsequent increase in prisms artificially increases the squint angle. «The result is a squint operation that would not have been necessary at all without prism glasses.»

Véronique Glauser, President of Swiss Orthoptics and lecturer at the Centre for Training in Healthcare in Winterthur, is similarly critical. She considers Haase's measurement method to be insufficient and advises additional tests. «As specialists in binocular vision, orthoptists examine the interaction of both eyes under natural conditions and carry out not just one, but different tests,» explains Véronique Glauser.

The child's social environment should also be included in the assessment.

What should parents with affected children do now?

Both supporters and critics agree that all other possible causes for the symptoms must always be expertly ruled out before treating an angle vision defect. Véronique Glauser advises that the child's social environment should also be taken into account. «A divorce situation, pressure of expectations from parents or bullying at school can also lead to headaches and school failure.» Only then does Wirth Barben recommend contacting a clinic with an orthoptics department or an ophthalmologist experienced with children who works together with an orthoptist for further clarification.
Fritz Gorzny believes that optometrists with proven experience in the field of angle vision deficiency and who work with prism glasses are the right people to contact. Bruun offers his patients prism glasses on a trial basis after the measurement. If the symptoms do not improve, the cause lies elsewhere and the patient can simply return the glasses.

About the author:

Symptoms due to angle vision deficiency

• Temporary double vision
• Headaches, especially in the evening
• Concentration difficulties
• Also abdominal pain in small children
• Stumbling, running into obstacles, problems catching the ball
• Avoidance of handicrafts, colouring, cutting out
• Problems with reading: Line skipping, faltering reading, rapid fatigue
• Problems with writing: spidery writing, lines are not held, letters are twisted

What are prism glasses?

The lenses of prism glasses are prismatic. This makes them look like two round wedges. In ophthalmology, prismatic lenses are used for certain strabismus disorders to bring together double images. In the case of angular defective vision, they are intended to compensate for the measured deviation of the eye at rest. Due to the additional expense, prism glasses are more expensive than normal glasses and the lenses are heavier.

Information for those affected by angle vision deficiency:

• The Swiss self-help group Winkelfehlsichtigkeit no longer meets actively, but runs its own website at www.winkelfehlsichtigkeit.org.
• The German self-help group Winkelfehlsichtigkeit is still active and offers information and addresses of contact persons in Germany, Austria and Switzerland at www.shgwf.de/cms/.
• Forum: Exchange of experiences on binocular vision At www.optometrieonline.de/forum/5 those affected can exchange information.
• IVBS - International Association for Binocular Vision An association of optometrists and ophthalmologists who specialise in angle vision problems. www.ivbs.org