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Archive for October, 2012

New study: eye movement problems in dyslexic children

The authors say that studies comparing binocular eye movements during reading and visual search in dyslexic children are inexistent. In the present study they examined ocular motor characteristics in dyslexic children versus two groups of non dyslexic children with chronological/reading age-matched. Binocular eye movements were recorded by an infrared system (mobileEBTH, e(ye)BRAIN) in twelve dyslexic children (mean age 11 years old) and a group of 9 chronological age-matched and 10 reading age-matched non dyslexic children. Two visual tasks were used: text reading and visual search. Infrared devices permit recording eye movements on a graph for further analysis.

Independently of the task, the ocular motor behavior in dyslexic children is similar to those reported in reading age-matched non dyslexic children: many and longer fixations as well as poor quality of binocular coordination during and after the saccades.

Note: If the age reading scores are similar in both groups of children, and one of the group includes dyslexic children, we could assume that the group of children called “normal readers” have not scored very high on the reading task (like the dyslexics). That would explain the behavior of eye movements (ocular motor) of the two groups is similarly ineffective. Difficult to understand?

According to the authors, for the two groups of dyslexic and non dyslexic children, the two tasks (reading and visual search) produced similar effects in terms of fixations and in terms of binocular coordination. It is believed that reduced visual and attentional span (or “visuo-attentional window”) which limits the number of letters that can be processed simultaneously, could have a similar impact on reading and visual search, due to the visuo- attentional demand similar in both tasks. Most likely, at least for these two groups of children for whom reading skills are not yet well structured, reading and visual search has important requirements in the spheres of vision-perception, attention and space processing. 

In contrast, chronological age-matched non dyslexic children showed a small number of fixations and short duration of fixations in reading task with respect to visual search task; furthermore their saccades were well yoked in both tasks. The atypical eye movement’s patterns observed in dyslexic children suggest a deficiency in the visual attentional processing as well as an immaturity of the ocular motor saccade and vergence systems interaction.

Recording of eye movements during reading (first column) and visual search (second column). We observe that the number and duration of fixations of the dominant right eye for a dyslexic child (11 years old), a non-dyslexic child 9 years old and a 11 years old non-dyslexic. The dyslexic child shows more fixations and regressions (backward movements). In the second case, the eye movements of the non-dyslexic child of 9 years old are more efficient but still lack precision if we compare the movements of the 11 years old non-dyslexic child.

Source: Bucci MP, Nassibi N, Gerard C-L, Bui-Quoc E, Seassau M (2012) Immaturity of the Oculomotor Saccade and Vergence Interaction in Dyslexic Children: Evidence from a Reading and Visual Search Study. PLoS ONE 7(3): e33458.

 Note: please click on «Reference» in the upper right corner of the page to get more information about eye movements in dyslexic children.

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New study supports orthokeratology for myopia control and for astigmatism correction

The Faculty of Health and Social Sciences at Hong Kong’s Polytechnic University issued a press release today on the results from two studies on orthokeratology. One, called the “ROMIO” study (Retardation of Myopia in Orthokeratology), was a single blind, randomized, controlled clinical trial on the effectiveness of orthokeratology for myopia control.  The other, called the “TO SEE” study ((Toric Orthokeratology-Slowing Eyeball Elongation), looked at the effectiveness of orthokeratology for astigmatism correction.

Brief description of orthokeratology

Patients who wish to receive an orthokeratology treatment must undergo a comprehensive oculo-visual exam and specific measures of the shape of their eyes to see if they are good candidates for the treatment. Using computer software, the optometrist is able to design special contact lenses adapted to the shape of the eyes of each candidate. These contact lenses are rigid gas permeable lenses and are made from high oxygen content materials, which can be worn during sleep. The aim is to reshape the cornea in order to obtain perfect vision the next day without having to wear glasses or contact lenses.

Orthokeratology is the only non-surgical treatment that allows you to be free of corrective lenses like eye-glasses and contact lenses. For cons, the treatment must be continuous.

Progression of myopia 

Myopia and its progression is a serious problem. Not only does it cause a gradual decrease in the uncorrected vision, but it ensures that the individual needs thicker and thicker and more expensive glasses. In addition, severe myopia increases the risk of retinal tear.

After 24 months of research, the ROMIO study found that the increase in eyeball length (also called “axial length” — the progression of myopia is measured by observing the elongation of the eyeball) in a group of subjects that were treated with orthokeratology was 0.36mm.  In the group that was not treated with orthokeratology and only wore spectacles, the eyeball length was 0.63mm longer. The results indicate that orthokeratology slowed down the progression of myopia by 43%.

Astigmatism

Researchers at the same university also concluded the “TO-SEE” (Toric Orthokeratology-Slowing Eyeball Elongation) study which looked at 37 children aged 6 to 12 years to study the potential of orthokeratology for the reduction of astigmatism. The team found that toric design orthokeratology lens retainers effectively reduced astigmatism by 79% after one month of wear. At the end of 24 months, the eyeball length of the participants was 0.31mm which indicated that myopia was also being controlled.

Orthokeratology is a reversible treatment and can be stopped anytime. The results of these two studies show that orthokeratology is a safe and effective solution for refractive error correction, myopic control and astigmatism reduction.