vue Points de

INTERNATIONAL REVIEW OF OPHTHALMIC OPTICS REVISTA INTERNACIONAL DE ÓPTICA OFTÁLMICA

THEME

Visual fatigue TEMA

Fatiga visual

70

SPRING / PRIMAVERA 2014 BI-ANNUAL / SEMESTRAL © 2014 ESSILOR INTERNATIONAL

SUMMARY

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SPRING BI-ANNUAL © 2014 ESSILOR INTERNATIONAL

VISUAL FATIGUE IN NEAR VISION

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__ Visual fatigue - Jim Sheedy VISUAL FATIGUE THROUGH POSTURE

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__ Effect of multifocal lenses on eye and head movements in presbyopic VDU users with neck and shoulder complaints Michaela Friedrich, Jeanette Kothe, Hans-Jürgen Grein, Egbert J. Seidel

ACCOMMODATION

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__ The early signs and symptoms of presbyopia Ronald A. Schachar

YOUNG PRESBYOPES NEEDS

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__ Understanding the needs of pre-presbyopes and emerging presbyopes - Agathe Laurent VISION IMPACT INSTITUTE®

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__ The incredible paradox of vision - Jean-Félix Biosse Duplan UV AND EYE PROTECTION

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__ Eye-Sun Protection Factor. A new UV protection label for eyewear - Christian Miège

TO BE READ ALSO ON WWW.POINTSDEVUE.NET www.pointsdevue.net

EDITO

Jean-Pierre Chauveau Director of Publication

Dear Readers, In this new issue we focus on the subject of Visual Fatigue. This is an important and interesting topic and an increasing amount of research is going into the many causes of Visual Fatigue, making it a subject of increasingly widespread concern. Indeed vision is a sense that interacts strongly with the elements of our static and dynamic behaviours and which makes intensive demands on our brain. It is therefore important to take into account the way in which our visual system works, linked to the type of visual task concerned, so as to eliminate or minimise visual fatigue. Another specific characteristic of visual fatigue is that its symptoms can appear vague or even difficult to define verbally, and sufferers are not always aware of visual fatigue. The visual environment has also evolved a great deal over the past few decades, and documents are now read at increasingly near distances, using new devices such as tablets or smartphones, which may require increased visual effort. Jim Sheedy, who has done a great deal of work on the study of visual fatigue , has honoured us with a general article on the various causes, symptoms and treatments for visual fatigue, and underlines the fact that it is of primary importance that vision is well corrected, taking into account, whenever possible, the ergonomics of the visual task concerned.

Since visual fatigue is a feeling that can be relatively subjective, we thought that a qualitative study could shed light on the way in which each and every one of us talks about visual discomfort or proven visual fatigue. Agathe Laurent, from the Springvoice Institute presents the study she has carried out to achieve a better understanding of the visual needs of pre-presbyopes and emerging presbyopes. Jean-Félix Biosse Duplan, founder of the Vision Impact Institute®, whose mission is to increase knowledge of the socio-economic impact of poor vision, presents to us the challenges and issues arising at world level to ensure good quality vision for everyone, everywhere. As a follow-up to previous issues of the magazine, regarding the potential dangers of UV rays, Christian Miège has taken a look at available literature on the dangers of UV rays, produced by ophthalmologists, optometrists and dermatologists in 5 European countries, and gives us his opinion on the E-SPFTM UV protection factor. Finally, in our usual Art and Vision section, we are delighted to re-print for you an article by Philippe Lanthony on painting and accommodation, which considers the relationships between various vision distances in painting and the ensuing variations in accommodation.

We also invite you to watch the video interview with Jim Sheedy, available on www.pointsdevue.net Michaela Friedrich et al give an update on a study undertaken on the postural consequences of reading from computer screens, showing the importance of taking into account the configuration of work stations for reading on screen, with its consequences on musculoskeletal issues. One of the main ways of reducing or avoiding visual fatigue is to have good vision, with optimal accommodation comfort. However, accommodation diminishes with age, which can create visual discomfort, with visual fatigue arising well before the age of presbyopia. Ronald Schachar tells us about the eye’s physiology, how accommodation works and sets out the various symptoms that appear during pre-presbyopia for near reading.

Happy Reading

Director of Publication

ERRATUM : In the editorial committee for n°69 we omitted to welcome Laura de Yñigo, who takes over from Azucena Lorente. Our apologies for this error.

VISUAL FATIGUE in near vision

VISUAL

FATIGUE

JIM SHEEDY, OD, PHD Pacific University College of Optometry OR, USA

__SUMMARY

Symptom category

Symptoms of discomfort are common among patients who spend considerable time performing tasks at near viewing distances – such as is common among computer users. Although the symptoms can be vague and seem elusive, they can usually be eliminated or reduced by diagnosis and treatment of the work arrangement and the visual system – including proper spectacle correction of presbyopia. This article summarizes clinical management of vision-related discomfort.

Visual symptoms

__BACKGROUND

Asthenopia

Symptoms Blur at near Post work blur at distance Slowness in focusing Double vision

Musculoskeletal symptoms

Neck and shoulder ache Back ache Sore wrist

Many of our patients have symptoms of discomfort associated with performing near tasks. Of course, the most common tasks performed at near involve reading – especially at computer displays [1]. Therefore it becomes the task of the practitioner to diagnose the conditions causing the symptoms and to devise a treatment plan to eliminate or at least mitigate the symptoms. The reading task itself, whether on hard copy or electronic display, is perhaps the most visually-demanding near task. Typical reading involves a series of 200 ms fixations sandwiched between 35 ms saccades – each saccade moves the eyes 7-9 characters further in the text. Although this is very demanding, we have discovered that it is the cognitive uptake system that limits reading speed in subjects with vision systems that are performing well – not the visual system. By manipulating the text size and legibility we have noted that fixation durations and frequency are altered, but the reading speed is maintained [2-5]. Actually, it is remarkable that many people can read for hours with no symptoms. Given that reading (near work) can be performed without symptoms under good conditions, it becomes our task to identify the reason(s) why our particular patient has symptoms of discomfort. I have observed clinically [6] and in laboratory research [7-9] that symptoms may occur when either the environmental conditions or the visual system capabilities are compromised. Resolving the patient symptoms often requires analyzing both the visual system and the environmental conditions under which they have the symptoms of discomfort [10]. __DIAGNOSIS Analysis begins with scrutiny of the patient symptoms. This can often directly lead the clinician to the correct diagnosis. The symptoms can be categorized into visual, musculoskeletal, and asthenopia as shown in Table 1.

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Points de Vue Magazine - n°70 - Spring - 2014

Headaches Eyestrain Eye fatigue Ocular dryness Glare sensitivity

TAB. 1

Three primary symptom categories.

__VISUAL SYMPTOMS Visual symptoms are the easiest to diagnose. They can easily result from an uncorrected refractive error – errors as low as 0.50 DC (Diopter Cylinder) can result in symptoms. Presbyopic patients should be properly corrected for the unique viewing distance of their computer, and will report blur or musculoskeletal ache if not. Typically presbyopic patients require an intermediate prescription in order to see their computer correctly. It is important to determine the distance at which they view their work (office computer displays are typically at a viewing distance of 50-60 cm). Demonstration and refinement of the near addition in free space can reassure both clinician and patient. Slowness in focusing, or distance blur after near work, is typically due to accommodative infacility. If so, tests of accommodative function can assess if this is a problem. It is best to test accommodative infacility directly using +/- lens flippers. Double vision (diplopia) is infrequently reported, but indicates a binocular vision difficulty when present. An intermittent diplopia usually indicates an intermittent strabismus. Analyze the binocular vision system to determine if there is an eso or exo strain on the visual system. The most common problem is a convergence insufficiency that causes intermittent exotropia at near distances.

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VISUAL FATIGUE in near vision

__MUSCULOSKELETAL SYMPTOMS Neck ache and back ache are quite common in computer-using patients. This can often be due to inappropriate location of the display or inappropriate spectacle correction of presbyopia. The top of the display should be near eye level. If not, then adjustments need made to accomplish this. Our visual system has a strong preference for looking down about 10 degrees – i.e. depressing the eyes about 10 degrees [11]. If the display center is not about 10 degrees below the eyes, then neck and back adjustments are made [12] resulting in strain. Neck and backache can also be caused by presbyopia-correcting spectacles that cause an awkward viewing distance or posture to see the computer display or other uniquely-located near work. It is very common for general-issue bifocals or progressive addition lenses (even though they might work for most other everyday tasks) to be guilty of this. Wrist, back, and shoulder pain or ache can also be caused by other work-related factors and referral to a workplace specialist is indicated.

__ASTHENOPIA Asthenopia is a catch-all for the less-specific symptoms such as eyestrain. Our research has repeatedly shown [13-14] that these symptoms fall into 2 constellations both subjectively (i.e. patient sensations) and objectively (i.e. the inducing condition). We call these 2 constellations “external symptoms” and “internal symptoms”. They are summarized in Table 2. In general, the differentiation can be summarized as follows: • External symptoms – dry eye and caused by environment • Internal symptoms – felt inside the eye and caused by visual conditions The clinician can use this symptom differentiation to help guide the diagnosis and management of the patient. External symptoms indicate

a dry eye condition and possible environmental culprits such as lighting, display location, or text quality. Internal symptoms indicate an ophthalmic or visual problem related to accommodation, convergence, or refractive error. Clinicians may want to use the clinical tests shown in Table 3 to diagnose accommodative and binocular vision disorders.

__PATIENT TREATMENT AND MANAGEMENT After diagnosing the reasons, either environmental or visual, that cause or contribute to the symptoms of discomfort, then the appropriate treatment measures from those below can be used to treat the patient.

__FITTING THE PRESBYOPE To begin, the location of the primary work (e.g. computer display) must be determined. If a computer display location can be altered, then it should be located so that the top of the display is level with the eyes. If the display cannot be located differently, then its location should be noted and spectacles designed accordingly. Most younger presbyopes (near add of 1.25 D or less) can often use their regular bifocals or PAL for their intermediate work (e.g. computer display). This is because such patients have enough remaining accommodation that they are able to comfortably view and focus upon the intermediate task through the distant portion of their spectacle lenses. Presbyopic patients with a near add of 1.50 D or greater often require separate spectacles for performing near work comfortably if that near work is at a unique viewing angle or distance, such as commonly occurs at computers or on assembly lines. If the patient wears bifocals for everyday needs, then it is likely best to provide the patient with workrelated bifocals in which the top contains the intermediate prescription and the bottom contains the near prescription. Trifocals may be considered. If the patient wears PALs for everyday viewing, then it is best to provide Occupational Progressive Lenses (OPL) for the patient. OPLs are designed to provide extensive intermediate and near viewing areas. Usually the top of the lens also contains a small add of +0.500.75D. OPLs are very useful for most office and other indoor activities.

Clinical test Symptom sensations

External symptoms

Perceived location

Inducing conditions

Dryness

Bottom of Eyes

Decreased blinking

Burning

Front of Eyes

Overhead light glare

Irritation

Accommodation

NRA and PRA should each be 1.50D or greater

Accommodative flippers (+/-1.50D)

Expect 13 cycles/min monocularly, 10 cycles/ min binocularly

Phoria

Any esophoria may be a problem. Exophoria less than 6 PD is seldom a problem. Otherwise, see Sheard’s criterion

Sheard’s Criterion – base-out prism to first blur divided by the phoria. Only effective for analysis of exophoria [15-16]

Prism-to-blur should be twice the amount of the phoria.

Near Point of Convergence

Should be easily repeatable and closer than 8 cm. Note if patient has subjective difficulty in performing test.

Upward gaze Small font Flicker

Internal symptoms

Strain

Behind the Eyes

Accommodative stress

Ache

Inside the eyes

Convergence stress

Headache TAB. 2

Binocular alignment

Astigmatic refractive error

External and internal symptoms.

TAB. 3 www.pointsdevue.net

Findings

Positive and negative lens to blur (NRA and PRA)

Tests for accommodation and binocular alignment. Points de Vue Magazine - n°70 - Spring - 2014

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VISUAL FATIGUE in near vision

In prescribing adds and designing spectacles, it can be very useful to demonstrate the add and clear viewing distances in free space. If prescribing an OPL, it is also very useful to demonstrate the small distance blur through the top of the OPL so that there are no surprises at time of dispensing.

__LIGHTING Lighting is likely the most common environmental culprit insofar as causing and contributing to visual discomfort. All patients with near viewing symptoms should be counseled about eliminating glare from lights.

__DRY EYES Dry eye is a common complaint among office and computer workers. Very often the following conditions contribute to dry eyes and fixing them can improve the symptoms: 1. Lower the computer display – especially if the top of the display is above the eyes. 2. Reduce or eliminate glare from the patient’s field of view (see Lighting here after) 3. Correct refractive errors including presbyopia. 4. Make sure the text is not too small or viewed from a larger-thannormal distance. Most text should be 10 to 12 point in size, viewed with 100% screen magnification, and viewed from no more than 60 cm. 5. Eliminate any air drafts in the workers space. In addition to the above measures, it is advisable to provide artificial tears to be used only as needed. Counseling about work breaks and light rubbing of the lids may also be helpful. More severe cases of dry eye require additional measures such as punctual plugs.

__ACCOMMODATION AND BINOCULAR VISION Reduced amplitude of accommodation (for the patient’s age) and accommodative infacility can both be managed with either orthoptic training or prescription of plus lenses (usually +0.50 to 1.00D) for near work. Working patients often are unwilling to spend the time with an orthoptic program, and the plus lenses can cure the problem. Likewise, patients with esophoria at near are best treated with a near add, which reduces the eso stress on their binocular system. Patients with exo deviation, as often accompanied by convergence insufficiency, must be treated with orthoptics – lenses are not an effective treatment. Fortunately, convergence is the most easily trained visual function and can often be managed with push-up training alone.

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Points de Vue Magazine - n°70 - Spring - 2014

The most common lighting problem is shown in the picture below: light from luminaires (or windows) directly impinging the eyes of the patient – i.e. the light source is very bright in the peripheral field of the patient. This can be demonstrated to the patient by taking the patient to an office location with a bright overhead light, and requesting the patient to shield their eyes from the offending light with their hand. Patients should be encouraged to note the improved comfort by doing so. The patient can then be instructed to repeat the test at their work place to test if lighting is a problem. If lighting is determined to be a problem, then possible interventions include: turning off the offending light, use blinds or drapes on windows, remove white surfaces, use partitions, rotate the work station, use indirect lighting, or wear a visor.

__WORK ARRANGEMENT For visual and musculoskeletal comfort, the work to be viewed most often must be directly in front of the person and located so that the person views it with eyes depressed at least 10 degrees and no more than 30 degrees. For computer displays, intended to be used with an upright posture, the top of the display should be at eye level, resulting in eye depression to view all elements of the display. Upright posture while maintaining the normal convex curvature of the lower spine can be important to long term comfort. Arms should be supported by chair arm rests to avoid tension across the shoulders. Variable positioning, such as adjustable height desks and chair also can improve patient comfort. vue Points de

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visual fatigue in near vision

REFERENCES 1. Sheedy, JE. Vision problems at video display terminals: a survey of optometrists. J Am Optom Assoc 63, 687-692, 1992. 2. Tai, Y.-C., Yang, S.-N., Hayes, J. R., Sheedy, J. E. (2010). Effect of character spacing on text legibility. Presented in the Annual meeting of American Association of Optometry. November, 2010: San Francisco, CA. 3. Yang, S.-N., Tai, Y.-C., Hayes, J. R., Doherty, R. A., Corriveau, P. J., & Sheedy, J. E. (2010). Effects of font size and display quality on reading performance and visual discomfort of developmental readers. Presented in the Annual meeting of American Association of Optometry. November, 2010: San Francisco, CA.

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4. Tai Y, Sheedy J. Blink is not just a random event in reading. Optom Vis Sci 2006;83:E-abstract 060065.

induced asthenopia. Optom Vis Sci 2007; 84:E-abstract 075095.

13. Sheedy JE, Hayes JR, Engle J. Is All Asthenopia the Same? Optom Vis Sci. 2003;80:732-739.

5. Tai YC, Sheedy J, Hayes J. Effect of letter spacing on legibility, eye movements, and reading speed. Vision Sciences Society abstract 2006;248.

10. Sheedy JE. How to eliminate visual symptoms - treat the eyes and fix the environment: A report from the VDT Eye Clinic. Work With Display Units ‘92, Technische Universitat Berlin, Institut fur Arbeitswissenschaft, Berlin, D-23, 1992.

14. Gowrisankaran S, Sheedy JE, Hayes JR. Eyelid squint response to asthenopia-inducing conditions. Optom Vis Sci,2007;84(7):611-619.

6. Sheedy JE. Video display terminal users: clinical findings. Amer J Optom Physiol Opt 65, 38p, 1988. 7. Sheedy JE, Gowrisankaran S. Viewing compromised visual stimuli causes dry eye symptoms: role of the orbicularis muscle. Vision Sciences Society abstract 2006;26. 8. Nahar N, Gowrisankaran S, Sheedy J, Hayes J. Eyelid squint response to visual and cognitive stress. Optom Vis Sci 2007;84:E-abstract 075096. 9. Gowrisankaran S, Nahar N, Sheedy J, Hayes J. Visual and cognitive load determines severity of near work

11. Menozzi M., Buol A. v., Kruege H. and Miege Ch.. Direction of gaze and comfort: discovering the relation for the ergonomic optimization of visual tasks. Ophthal. Physiol. Opt., 1994, Vol. 14, 393-399, October. 12. Sheedy JE, Parsons SP. Vertical yoked prism - patient acceptance and postural adjustment. Ophthalmic and Physiological Optics 7: 255-257, 1987.

15. Sheedy JE, Saladin JJ. Phoria, vergence and fixation disparity in oculomotor problems. Am J Optom Physiol Optics 54(7): 474-478, 1977. 16. Sheedy JE, Saladin JJ. Association of symptoms with measures of oculomotor deficiencies. Am J Optom Physiol Optics 55(10): 670-676, 1978.

Points de Vue Magazine - n°70 - Spring - 2014

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VISUAL FATIGUE through posture

EFFECT ON I N

OF

EYE

MULTIFOCAL

AND

HEAD

P R E S B Y O P I C

N E C K

A N D

V D U

S H O U L D E R

MICHAELA FRIEDRICH University of Applied Sciences Jena, Departement of Optometry Germany

The findings of this study suggest that in the case of presbyopic subjects with neck-shoulder discomfort, a VDU workplace may significantly contribute to the manifestation of a pathological stereotype (eye mover) in horizontal gaze shifts. An optometric treatment based on multifocal spectacle lenses may be envisaged in presbyopic VDU users to reduce levels of neck and shoulder discomfort. The multifocal lens design typically induces more head movement in the horizontal direction, thereby reducing the levels of physical inactivity at VDU workplaces. Any relevant effects associated with the type of multifocal lens design could not be confirmed, although both the eye mover design and the occupational lens design contributed to a greater extent to the reduction in subjective neck and shoulder discomfort. The influence on eye/head movement in the vertical direction was not investigated.

MOVEMENTS U S E R S

W I T H

C O M P L A I N T S

JEANETTE KOTHE Optometrist Germany

EGBERT J. SEIDEL Clinical Center Weimar Sopien- and Hufeland Klinikum Physical and Medical Rehabilitation Germany

HANS-JÜRGEN GREIN University of Applied Sciences Lübeck, Department of Optometry Germany

__SUMMARY

LENSES

that not only the amplitude but also the frequency of head movements is higher in PAL wearers [16], [11]. There was no difference between the various types of lens designs [14]. The ratio of head and eye movements while fixating an eccentric target represents a typical and reproducible behaviour in each individual [17], [19], [9], [21]. In the literature, a distinction is made between two types of motor functions involved in gaze shifts [2], [9], [1]. Head movers mainly use head movements to identify a peripheral object (i.e. for gaze shifts with an amplitude of less than 10°). Eye movers mainly move their eyes while performing gaze shifts with an amplitude of more than 20°. In both types, however, the sum of head and eye movement amplitudes is identical and corresponds to the position of the peripherally fixated objects [17]. Beyer & Seidel 2007 reported that in patients with neck and shoulder complaints, the share of eye movers (eye movements contributing more than 50 % to gaze shifts) amounts to 90% [3]. This percentage may in part be due to changes in combined eye/head movement when working at VDUs.

__INTRODUCTION __PURPOSE Computers have now become an integral part of today’s work environment. In 2011, almost 21 million people in Germany had been working at visual display units (VDUs) [20], [5]. About 80% of individuals sitting in front of a PC for more than three hours a day usually complain about discomfort, including, for example, visual strain, headaches or pains in the neck and shoulder area [14]. According to Hayes et al. (2007) there is a correlation between eye and body symptoms in 81% of the cases as well as between eye strain and back/neck strain in about 64% of the cases [12]. Sitting in front of a computer screen will lead, in the long run, to unnatural postures (lack of movement, sustained immobile posture) as well as to changes in gaze shift behaviour [7]. Changes in the oculomotor function may also involve changes in neck muscle activation patterns [6]. The main focus of the study was to determine how the visual system is influenced by the optics and the design of an individualized multifocal spectacle lens. Von Buol (2002) has demonstrated that changes in eye and head movements occur depending on the type of eyeglasses and near addition [21]. According to Guillon et al. (1999) progressive addition lenses lead to higher amplitudes of head movement compared to single vision lenses [10]. Selenov et al. (2002) and Han et al. (2003) reported

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Points de Vue Magazine - n°70 - Spring - 2014

The purpose of this study was to investigate whether a multifocal lens design is able to influence individual levels of discomfort in VDU users suffering from neck and shoulder strain. The study involved testing three different lens designs. Specifically, the blurred vision areas in the periphery of the lenses should, over a three-month period, induce the subjects to use more head movements during lateral gaze shifts – with the aim of reducing levels of discomfort caused by neck and shoulder strain. __MATERIAL AND METHOD Study design The subjects were randomized and single-blind divided into different interventions. Four groups were set up (Fig. 1). The subjects in group I, II and III (eye movers) were randomly given one of three different multifocal lens designs (Head/eye mover design or occupational lens). Group IV was the control group (comprising both head and eye movers) with no intervention.

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VISUAL FATIGUE through posture

study group group I + II eye movers

group III eye movers

eye or head movers

fitted with progressive addition lenses

fitted with occupational lenses

no optometric treatment

head mover design FIG. 1

group IV

eye mover design

Splitting of subjects into different groups: groups I, II and III are provided with multifocal lens designs; group IV receives no optometric treatment.

__TEST SUBJECTS All subjects (n0=122, 24 males and 98 females, aged 51,73 ± 4,46 years) showed an age-related reduction in their amplitude of accommodation and had already been wearing reading glasses, progressive lenses or bifocals prior to entering the study. They have all been working at VDUs (for more than 4 hours a day) and suffered from neck and shoulder discomfort (self-reported symptoms > 3 according to the visual analogue scale).

are eye movers. These subjects were given VDU corrective spectacles fitted with multifocal lenses. After three months, a follow-up check was performed. Data processing Data from n=100 subjects could be evaluated before and after the study (study groups I, II and III nV=52, control group nK=48). For the complaints in the neck and shoulder area (SNA) and the head/ eye ratio (HER), mean values and standard deviations were respectively calculated. Results were checked for statistical relationships between pre-study and post-study data.

__LENS DESIGNS USED FOR THE STUDY __RESULTS The spectacle frames and the different multifocal lens designs used under this study were provided free of charge by Essilor. The various types of lens designs were randomly allocated by the lens supplier. The designs included three different types of PAL’s, a head and an eye mover design as well as occupational lenses (“mid-distance” variable focus lenses). __TESTS

HER and discomfort levels across the entire study group before and after the study In the investigated group of subjects, the HER ranged somewhere between 0 to 1 both before and after the study. On average, it rose from 0,36 ± 0,22 at the start of the study to 0,48 ± 0,22 at the end of the study. Consequently, after three months, the test subjects used more head movements for lateral gaze shifts than before the beginning of the study.

Assessment of individual discomfort levels To evaluate subjective discomfort, the test persons were asked to assess their individual discomfort levels by using the Visual Analogue Scale (VAS) for the following question: “How would you rate your pain in the neck and shoulder area on a scale of 0 to 10, with 0 being no pain at all and 10 being the worst possible pain ?” Determination of the head/eye ratio (HER) In order to determine subjects’ head to eye ratio, Essilor’s Vision Print® System was used during the study (Fig.2) involving the determination of the head/eye mover ratio (HER) (mean value calculated from three measurements). Optometric eye exams and tests To test relevant optometric parameters under this study, standardized optical/optometric methods were used, i.e. visual acuity determination, refraction & determination of distance and near correction, heterophoria tests (using the Polatest) and finally determination of lens centration data. Test procedure The group of test subjects comprised both head and eye movers (n0=122), half of them having received an optometric treatment. As these optometric interventions were to be tested on eye movers only, 61 subjects with typical eye mover gaze behaviour (HER: 0