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The effects of outdoors on Myopia

The following article is presented to you by Pablo Sanz and Miguel García
Disclaimer: For all the general public and specialists, some technical knowledge might be required.

Let en-light our blog, pick our sunglasses and let´s talk about the influence of outdoor time on the onset, development as well as progression of myopia. Besides, as far as 100 years ago (1), some studies started to conjecture about ambient light and its impact on the development of the eye. Starting to be considered as plausible public action to stop myopia prevalence increase, especially in those areas with high risk of development such as East Asia, the topic triggered interest again.

For more in-depth treatment of the issue of outdoors effect we should keep in mind different terms such as time exposure and light intensity, because many factors could contribute to this “shielding effect“.

During the last years a large number of research studies investigated the hypothesis that time spent outdoors protects against the development and progression of myopia.

Since the beginning of this hypothesis, all researches pointed to this direction. Earlier, it was shown in chickens (2) and children that ambient light plays an important role at compensation of myopic defocus and onset of myopia. While at early stages in humans, it was though that physical activity could have a major input, Rose et al (3) showed that light conditions where the key.

To get a better overview on this matter we should introduce the sentence scientific evidence.

  • But what´s evidence?

In a scientific environment, there is no place for believes, and the evidence relies in the studies published and their repeatability. If we want to grade the evidence they give, we do so according to the type of article, as following pyramid illustrates.

Evidence piramyd
Fig 1. Pyramid of evidence

As pointed out by the pyramid, meta-analysis are the highest source of evidence in science. And a recent meta-analysis from Xiong et al, 2017 (4), analyzed over 25 studies and they concluded that time outdoors prevent the development, but has no effect on slowing progression of eyes that are already myopic.

Other studies that looked into the possible use of longer outdoor hours to prevent myopia (5) as public policies, concluded that an extra hour could have greater impact on the onset and development of myopia in children between 5 to 8 years. Similar recommendation were given by He et al 2015,(6) where they claimed that 45 min of outdoor activities for schools in China could prevented myopia onset.

“Although research about understanding the exact mechanism is still underway, based on current results approximately 3 hours of outdoor activity during a day may be considered protective against myopia.”

– Verkicharla, 2016 (7)

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What is Myopia?

The following article is presented to you by Pablo Sanz and Miguel García
Disclaimer: For all the general public, not technical knowledge is required.

Originally described by the ancient Greeks as “myopos”, this condition makes reference to how the myopic people squint their eyelids to create a sharp and clear image.

But what´s myopia? And why they do this characteristic grimace? Let us begin with how the image is formed into the eye.

In a normal eye, the ray-lights coming from far distance pass through the different mediums inside the eye creating a sharp point on the retina.

On the other hand, if we are dealing with any error condition, we have a mismatch between this focused image and the retina, where our light receptors reside. Both ray schemes are shown below:

Raylight image formation

Note that this is an easy approximation, while even in the best ideal case, a point refracted by crossing a circle(pupil) is not a point. Far from this, due to the eye aberrations, this merged point is always a stain/blur.

So, myopia also known as short-sightedness or nearsightedness , constitutes a failure of matching image formation and receptors location, being the image formed in front of them as shown in the right scheme.

Using a more accurate definition, myopia has been defined as a common optical aberration of the eye in which the conjugate focus of the retina is at some finite point in front of the eye, when the eye is not accommodating.

Some signs related to myopic subjects are primarily: blurred distance vision or out of focus image and deteriorated vision in low lighting conditions while better vision at short distance than hyperopes.

*Why they squint their eyes? With this characteristic gesture they are simulating a pinhole, reducing the amount of rays arriving to the eye and generating an artificial pupil of smaller size. This pupil reduces the size of the blur on the retina but also the amount of light and the area you can see.

As this post is supposed to be an easy explanation on myopia, further comprehension about aberrations of a myopic eye can be found in other entries:

Myopia and eye aberrations (Not available yet)

This refractive error is caused by many factors, but basically due to elongation of the eye.

  • Which is the prevalence of myopia?

Now, knowing what this refractive error is, you might be curious to know the predominance of this eye condition around the world.

Nearsightedness has been estimated that affects 1.6 billion people worldwide and during the year 2020, 2.5 billion people would be affected by myopia. (1)(2)

‘Myopia Prevalence, based in birth and educational level in Europe, Meta-Analysis’ Click in the image for more information.

Furthermore, the prevalence of myopia varies with age and other factors: genetic, ethnicity, geographic location, environmental factors, lifestyle, etc. As you can found in the following post:

Risk Factors 

Current recommendations for Myopia (Not available yet)

Typically appears between 6 and 12 years of age, and the mean rate of progression is approximately 0.50 Diopters per year, based on studies of mostly Caucasian children. (3, 4)

The prevalence of myopia is approximately 25% in the western population and much higher (70% to 90%) in different regions of Asia (5, 6).

Among persons the prevalence is about 35% to 40% in their 20s to 40s and decreases to about 15% to 20% among those in their 60s, 70s, and 80s. (7, 8)

All these values led us to think that this optical condition is emerging as a major public health concern, generating an economic burden for each individual with myopia that does not have to go unnoticed. (9) For this reason, the research myopia field is focused on understand and reduce all the factors that may produce the increase and development of myopia.

Stay up-to-date, Keep on reading and

Myopia in Science!

  • References.
(1) Kempen JH, et al. The prevalence of refractive errors among adults in the United States, Western Europe, and Australia. Arch Ophthalmol. Apr 2004;122(4):495-505.

(2) Holden BA, et al. Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050. Ophthalmology. 2016 May;123(5):1036-42.

(3) Jensen H. Myopia progression in young school children and intraocular pressure. Doc Ophthalmol 1992;82:249-55.

(4) Parssinen O, Hemminki E, Klemetti A. Effect of spectacle use and accommodation on myopic progression: final results of a three-year randomised clinical trial among schoolchildren. Br J Ophthalmol 1989; 73:547-51.

(5) Shortt AJ, Allan BDS. Photorefractive keratectomy (PRK) versus laser-assisted in-situ keratomileusis (LASIK) formyopia. Cochrane Database Syst Rev 2006; (2):CD005135 3. Dirani M, Islam FMA, Baird PN. The role of birth weight in myopia – the Genes in Myopia twin study. Ophthalmic Res 2009; 41:154–159

(6) Saw SM, Tong L, Chua WH, Chia KS, Koh D, Tan DT et al. Incidence and progression of myopia in Singaporean school children. Invest Ophthalmol.Vis.Sci. 2005; 46:51-7.

(7) Vitale S, Ellwein L, Cotch MF, et al. Prevalence of refractive error in the United States, 1999-2004. Arch Ophthalmol 2008; 126:1111-9.

(8) Katz J, Tielsch JM, Sommer A. Prevalence and risk factors for refractive errors in an adult inner city population. Invest Ophthalmol Vis Sci 1997; 38:334-40.

(9) Zheng YF et al. The economic cost of myopia in adults aged over 40 years in Singapore. Invest Ophthalmol Vis Sci. 2013 Nov 13;54(12):7532-7.

1st Annual Meeting

The following article is presented to you by Pablo Sanz and Miguel García
For all the general public, some statements may require deeper knowledge of science.

During the last week of November, on the shores of the Neckar River (Tübingen, Germany) and just a few minutes walking from the place where Kepler observed its first eclipse though a projection of one hole at the vaults of Tübingen Cathedral, our First Annual Meeting was held consisting of all the early stage researcher (ESR), supervisors and members of the MyFUN program.

Throughout this meeting, the project teams met together, stroked up a friendly conversations and suggestions about how each project can starts out with the best possible resources and support available.

The main purpose of each of these projects remain to try and achieve better knowledge and answers regarding the myopia development, considering three specific research Work Packages (WP):

  • WP1: Unknown features of the visual feedback-control loop for eye growth. (Projects: 1, 2, 3, 4, 5, 6).
  • WP2: Biological features of the visually-guided signalling cascades controlling eye growth. (Projects: 7, 8, 9, 10).
  • WP3: Visual performance, adaptation and training. (Projects: 11, 12, 13, 14).

During all the Early Stage Researchers presentations we could get some of the specific objectives, and the key activities regarding all the projects. All this information is listed below:

  1. Accommodation and undercorrection.

ESR Name: Dmitry Romashchenko. Supervisors: Linda Lundström; Peter Unsbo.

Purpose: To study the interactions between the position of the image shell, determined by the accommodation, and the retinal image quality, which is used by the retina to adjust the rates of eye growth. The data will be analyzed for single cases in high details rather than statistical measurements for average values.
The main target is to know in detail what happens with accommodation during undercorrection and with no correction of myopia and how this affects the defocus error signal in the peripheral retina.

  1. Why suddenly myopia?

ESR Name: Andrea Carrillo Aleman. Supervisors: Frank Schaeffel; Marita Feldkaemper; Sandra Bernhard.

Purpose: to analyse accommodation behaviour, using infrared photorefraction, and clarify whether the development of myopia may start because accommodation gives up to compensate for the lenses, generating an error signal on the retina.

  1. More progression with new spectacles?

ESR Name: Miguel Garcia Garcia. Supervisors: Siegfried Wahl; Arne Ohlendorf.

Up to date the single vision spectacles wear are the most used way to correct myopia, besides the different availability of treatments to slow its progression. For that reason, a deeper knowledge of how them act over the eye structures is required.

Purpose: to test the ocular structures in young subjects, just becoming myopic, in close detail by daily or at least weekly measurements with low coherence interferometry, OCT, and photorefraction, before and after new corrective lenses are prescribed.

  1. Crystalline lens and myopia.

ESR Name: Geethika Muralidharan. Supervisors: Susana Marcos; Carlos Dorronsoro; Sergio Barbero; Daniel Pascual; Enrique Bustos.

Purpose: to investigate statistical differences in lens thickness, and lens geometry between myopes and emmetropes, as well as their potential relationships with the magnitude of refractive error, ACD, ACV and AL and investigate the astigmatic axis of the lens surfaces in relation to the corneal astigmatic axis, and the degree of compensation of corneal and internal astigmatism in myopes and emmetropes.

  1. Sign of defocus and eye growth.

ESR Name: Najnin Sharmin. Supervisors: Brian Vohnsen.

Purpose: to study monocular and binocular accommodation with fast wavefront sensing and adaptive optics (>100 Hz) by setting up a stimulation system that will automatically eliminate size, contrast, and brightness clues by use of tuneable liquid filters. It will be tested on myopes if there are marked differences in response between the two groups.

  1. Near work and myopia.

ESR Name: Manto Chouliara. Supervisors: P. Artal; P. Prieto; J. Tabernero; J. Fernandez.

Purpose: to study the image defocus on the retina with yet unachieved precision and resolution in both myopic and emmetropic subjects, and in both eyes at the same time. The question of whether there is a significant “lag of accommodation” during binocular reading will be answered.

  1. In vivo markers of myopia development: changes in fundal reflectance.

ESR Name: Barbara Swiatczak. Supervisors: Frank Schaeffel; Marita Feldkaemper.

Purpose: To find out whether changes in fundal reflectance relate to metabolic state and biochemical signals associated with changes in eye growth, we will sample fundal reflectance in chickens in high detail while their eyes are covered with diffusers, negative lenses and positive lenses for variable periods of time. Using a custom developed procedure to measure the spectral fundal reflectance in alert chickens (derived from white light photorefraction), we will determine the time courses and magnitude of changes in fundal reflectance for different light exposures in chickens.

  1. Inter-individual variability of myopia.

ESR Name: Sandra Gisbert Martinez. Supervisors: Frank Schaeffel; Marita Feldkaemper; Sandra Bernhard.

Purpose: to track the development of deprivation myopia in individual chickens by at least one measurement of ocular biometry and refractive state per day. The slope of refractive change over time will be determined (the gain). Individual gains will be correlated with the patterns and frequency ratios of the different cone types as determined by the analysing the oil droplets in retinal flatmounts.

  1. Inheritance of the peripheral optics of the eye.

ESR Name: Dibyendu Pusti. Supervisors: P. Artal; P. Prieto; J. Tabernero; J. Fernandez.

Purpose: to be able to find out in how far the pattern of peripheral aberrations and refractive errors is inherited. These data have important implication for the understanding of the roles of peripheral defocus on the development of myopia. They also have implications for the prediction of the risk of myopia in humans.

  1. Stiles-Crawford Effect and Myopia.

ESR Name: Alessandra Carmichael Martins. Supervisors: Brian Vohnsen.

Purpose: A  system  that  allows  measurements  of  the  psychophysical  and  the  optical Stiles‑Crawford  effects for the foveal  and parafoveal regions, respectively, will be built. Both techniques will be applied on healthy subjects and on subjects with different degrees of myopia. Previous studies have indicated a slight reduction in directionality for highly myopic eyes with psychophysical techniques but this remains to be confirmed with objective measurements. With this project, such decrease will quantify and clarify its relationship to accommodation as well as to emmetropisation.

  1. Myopia, cycloplegia, and training of accommodation.

ESR Name: Pablo Sanz Diez. Supervisors: Siegfried Wahl; Arne Ohlendorf.

Purpose: to study the plasticity of accommodation in myopes and to investigate if accommodation can be trained or shifted and whether the level of tonic accommodation is paradoxically higher, and why. During this project a continuously recording photorefractor sampling at 100 Hz that emits a sound with the frequency coupled to accommodation tonus will be used. Emmetropic and myopic subjects will be trained to achieve their most relaxed accommodation state and differences in their adaptable amplitudes will be determined.

  1. Visual performance with bifocal correction to inhibit myopia.

ESR Name: Neeraj K. Singh. Supervisors: Prof. Susana Marcos

Purpose: An Adaptive Optics and Simultaneous Vision Simulator (SimVis) developed in the host laboratory will be used to mimic experimentally bifocal corrections of different patterns (concentric vs angularly segmented; centre vs peripheral near add; different addition magnitudes) and measure visual performance of young observers with bifocal corrections: accommodation, visual acuity & visual perception.

The lag of accommodation with bifocal corrections and variation in visual performance across different bifocal corrections (different patterns and near additions) will be determined. The investigators aim to propose the most suitable bifocal correction to interfere with myopia development.

  1. Adaptive optics technology to assess myopia development and correction.

ESR Name: Nikolai Suchkov. Supervisors: B. Jaeken; J. Fernandez; P. Artal

Purpose: To develop a new generation of adaptive optics visual simulator, allowing to measure high ametropes and pathologic patients. The device will allow to measure virtually any eye, and to simulate a solution, correcting both low and high order aberrations. For the increased dioptric range, a tunable lens will be used, allowing to modulate defocus in a range of ± 10D, meanwhile a spatial light modulator will be compensating for the rest of aberrations. The stimulus for subjective measurements will be provided by a digital light processing projector. In order to simulate solutions for different pupil sizes, a motorized exit pupil will be introduced.

  1. Asymmetry in the effects of defocus on vision.

ESR Name: Petros Papadogiannis. Supervisors: Linda Lundström; Peter Unsbo.

The detection of the sign of defocus by the foveal as well as by the peripheral retina is essential for the control of both accommodation and eye growth. The amount of additional blur cannot provide this information since it is symmetrical when the same amount of defocus is imposed in either direction. However, asymmetries in visual performance under positive and negative defocus have been found for both foveal and peripheral vision in myopes, but not in emmetropes .

Purpose: The foveal and peripheral vision will be evaluated with different amounts and signs of defocus for myopic and emmetropic subjects under natural conditions. As the chromatic and higher order aberrations (more irregular optical errors) of the eye can give sign-dependent blur, the same measurements also have to be performed under controlled optical conditions. For this purpose, a peripheral adaptive optics system will be used to remove any asymmetries in the optical blur during the vision evaluation. The system will also be updated for high-resolution foveal measurements.

During the following days, the first Winter School took place, giving the chance to the ESR to enter widely in some threads due lectures from PIs and experts and some workshops at the AugenKlinik (EUKT), Tübingen.

Here we let you some pictures from the lectures, and the social events from afterwards.

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Stay up-to-date, Keep on reading and…

Myopia in Science!