Astigmatism – A Primer

Astigmatism – A silent and invisible thief.

No one should expect parents to understand how vision works, let alone how this might affect their children – even though they might observe very clearly the effects of significant visual impediments. Astigmatism, (or ‘cyl’ for ‘cylinder’ when in a glasses prescription) is a term that people sometimes hear, but even more rarely understand. This article gives a brief overview of astigmatism and why it constitutes a significant physical disability, and cause of many apparent learning and developmental concerns.

Start with this, the basics: Astigmatism defined by American Optometric Association

“Uncorrected astigmatism and hyperopia (farsightedness) are arguably the most common physical cause of idiopathic apparent learning disabilities including reading, balance/coordination, defiance/emotional disturbances.”

Most descriptions of astigmatism are described in terms of blur, but there is much more going on. Consider that human optics, like any optical system, is designed for certain tasks more than others. So, one would not use a telescope to view bacteria in a Petri dish. If the tool is not suited to the task, there will be challenges in fulfilling outcomes. In the near-tasking world of the classroom, there is a great need for, among other things, clarity of the visual signal. This is especially true for high-detail visual tasking such as reading. With astigmatism, the child struggles to render a clear image, but there is more to the story.

Astigmatism affects learning and development in the following important ways:

1. Low astigmatism (>0.75D-2.00D) causes low-to-moderate asthenopia  (generlized strain, discomfort, and pain in, around, and behind the eyes) in the range of 4 to 6 on a 10-point scale. Light amblyopia is possible, with visual acuities moderately impacted in the higher ranges.
2. Moderate astigmatism (>2.00D-5.00D) will cause severe acute and chronic headaches and asthenopia, depending on environment and tasking. This range is likely to lead to moderate amblyopia, and so subsequent deficits in spatial perception, fine motor control of the hands, coordination concerns, limited depth perception/stereopsis, and significant deficits in visual acuity.
3. Higher levels of astigmatism (>5.00) are not as likely to induce asthenopia and headache as the accommodative process is incapable of acquiring any sort of retinal image clarity and so effectively it simply does not engage. Amblyopia will be profound in these cases, with accompanying deficits in spatial awareness, depth perception, fine motor control, coordination, and a visual acuity in the range of legally blind.
4. Reading is affected as a function of increasing astigmatism, with anything >0.75 becoming significant.
5. Moderate to high astigmatism will also promote speech impediments as the child cannot visualize mouth movements.
6. Moderate to high astigmatism also impacts upon socialisation in that many fine points of facial microexpressions cannot be appreciated and are therefore not learned at an early age.

There are also different varieties of astigmatism:

1. Hyperopic (Farsighted) Astigmatism: The focal planes are behind the retina, requiring continuous focus to keep the image as clear as possible. This is the worst configuration for near work.
2. Mixed Astigmatism: One focal plane is in front of the retina (myopic) and the other behind (hyperopic). This may lead to additional blur occasionally at distance, but will not generally be as burdensome as hyperopic astigmatism for the classroom.
3. Myopic astigmatism: Both focal planes are positioned in front of the retina. Since the eye cannot use its focusing system to resolve a myopic eye, glasses are required. There should be minimal discomfort with distance viewing in the blur zone, but this would increase as the target (text, say) is drawn near so that the child can begin to resolve the detail. For schoolwork, the child is much more likely to experience asthenopia and headache given tasking is generally done in the near distance, where the child can see more easily.

Studies show a high prevalence of astigmatism among Aboriginal/- Indigenous children. In Alberta, for  example, and this is fully consistent with my readings over some 1500 kids in Southern Alberta. At Siksika, the mean cyl was 1.00D, sufficient to impact on reading and spur headache/migraine.

It is not so much blur that provokes emotional/defiant responses, but the physical pain/burden of the constant accommodative strain and subsequent asthenopia and headache – a constant irritant, worsening from 0.50D to 4.00D, then beyond that, the ciliary response wanes as blur increases beyond the image resolving capacity of the eye.

Uncorrected astigmatism and hyperopia (farsightedness) are arguably the most common physical cause of idiopathic apparent learning disabilities including reading, balance/coordination, defiance/emotional disturbances.

Inasmuch as parents should know their children’s health details such as immunization history and allergies, it is critical to get a reading on child visual function – does your child have significant astigmatism? You won’t know unless you measure, and you cannot know ‘how’ your child sees – they do not have your eyes. This is especially important in the case of suspected learning or behavioural concerns where astigmatism is known to impact upon cognitive development and processing, language skills, spatial perception, and emotional regulation.

Resources:

• Prevalence of Astigmatism in Native Americans
• Astigmatism and Reading Fluency
• Correcting Bilateral Astigmatism Restores Children’s Reading Fluency
• Amblyopia in Astigmatic Infants and Toddlers
• Prevalence of high astigmatism, eyeglass wear, and poor visual acuity among Native American grade school children
• Visual Impediments to Learning
• Search PubMed for Astigmatism