Sports vision prescribing and dispensing

Transcription

1 Sports vision prescribing and dispensing Geraint Griffiths MSc, MCOptom 44 This article considers the pertinent factors to consider when prescribing and dispensing for sport. It evaluates the importance of binocular vision assessment, ocular dominance, contrast and elements to consider when dispensing to patients undertaking a range of sporting activities. Course code: C Deadline: June 20, 2014 Learning objectives To be able to ask appropriate questions relating to patient lifestyle (Group 1.1.1) To be able to prescribe and dispense optical appliances for a variety of occupations (Group 4.1.6) To understand the importance of binocular vision assessment in relation to sporting tasks (Group 8.1.3) Learning objectives To be able to ask appropriate questions relating to patient lifestyle (Group 1.1.1) To be able to prescribe and dispense optical appliances for a variety of occupations (Group 4.1.2) About the author Geraint Griffiths is chair of the Association of Sport and School Vision Practitioners, having published extensively in the field of sports vision. He is in independent practice at Optical3 in Leicester and the College of Optometrists councillor for the East Midlands region.

2 Introduction Sport is one of the biggest and most diverse occupations 1 and differs from most in the level of visual demand, which is often extreme. It emphasises the need for optometrists and dispensing opticians to work closely together with the athlete to achieve the best clinical outcome. On average, the competitive athlete s vision is no better than the rest of the population. 2 There is always a high percentage of visual deficiency amenable to correction, even in elite groups. Athletes with visual deficiency partaking in sports with a high visual demand may well be lost to that event. Optimal visual correction allows these players to compete on level terms. 45 Identifying visual deficiency High visual demand sports might include downhill skiing, ice hockey, shooting or tennis. Other popular sports, like football and rugby, may not have such a high acuity demand, but require other qualities such as peripheral awareness. The overall visual demand of the sport and refractive results will be important determinants in the design of the sports appliance and mode of correction and requires a structured task analysis and consideration of the following factors: Target size and distance Speed of target Speed of athlete Contrast of the target against its background Colour of target and background Ambient light levels (indoors or outdoors) Environmental pollution Precipitation and wind speed Reflectivity of the playing surface and surroundings Duration and energy demand of competition. Figure 1 The Brock string different coloured beads placed at various distances to assess anomalies of binocular vision The role of binocular vision As a profession, optometrists have a curious ambivalence towards binocular vision. While it is self evident that we have two eyes, because of our apparent cyclopean view of the world we somehow take the process of inter-ocular co-ordination for granted. Although most professionals are aware of the concept of eye dominance it is not generally measured in practice. However, binocular function cannot be understood scientifically in relation to sport without first measuring Figure 2 Dynamic fixation eye dominance. 3 In the first instance it is important to be able to connect eye dominance to the effect of the prescription. For example, a clay target shooter with divergence excess (decompensated distance exophoria) in the right eye would tend to miss to the right of the clay (too much lead when going from left to right) if this were his dominant eye and he shoots off his right shoulder. If attention swapped to the other eye because of decompensation associated suppression, the shot would miss to the left (not enough lead). If the left eye were dominant and the athlete shoots off the right shoulder, the problem would be compounded with the left eye readily taking over the aim; it is unlikely that this individual would get any pleasure from clay shooting. If a novice shooter were found to be left eye dominant but right handed with the same divergent slip in the right eye, then the dispensing advice would be, try to see For the latest CET visit

3 Test Significance 46 Retinoscopy High and low contrast LogMAR vision Dominant eye Objective muscle balance 9 Brock string (see Figure 1) Look for gross errors, anisometropia, astigmatism Demonstrates real life vision at low contrast and identifies the possibility of reduced contrast sensitivity Ocular dominance can cause problems in aiming and depth perception Muscle balance measure gives the athlete a better appreciation of binocular imbalance, which can be related directly to sporting deficit and refractive error Measures binocular vision anomalies in the sporting context raising underlying visual problems to a conscious level The Eye Bright Test for colour preference and light sensitivity 10 Dynamic fixation 8 (see Figure 2) Colour preference gives an indication of light sensitivity and the tint to be prescribed Gives a measure of eye speed and tracking ability and indication of innate skeletal muscle physiology (proportion of fast to slow twitch fibres) Table 1 The diagnostic screening elements of sporting visual performance if you can shoot off your left shoulder ; we would then stabilise the aim of the left eye by prescribing the required prism in front of the right eye. Divergence excess even in the non-dominant eye will tend to distract the dominant eye as the visual system tries to maintain single vision. It can lead to a head turn to the left, as the divergence of the right eye is favoured. Aiming and anticipation are the two primary sporting visual skills. 4 Aiming is the role of the dominant eye; it gives positional sense in relation to the object of regard whether it is a tree we are trying to avoid on a ski slope, or a ball we are hoping to catch. To anticipate the arrival of an object, whether we are running towards it or it is being thrown to us, requires accurate depth perception; this allows us to judge the distance of the object and how fast it is moving. In sports such as tennis, where the primary sporting skill is depth perception, it doesn t matter which eye has the fixation disparity (FD) as long as the FD is corrected to maintain stereopsis. Athletes can be divided into Type I dominance (right eye, hand and foot) and Type II (any left tendency in hand, eye or foot). It is particularly important that the non-dominant eye is fully corrected in Type I players. 3 The lessons learnt from sport is that these principles apply to all occupations, from the highest-flying tennis player or downhill skier to the office worker and long distance lorry driver. 5 The energy demand of the visual system Within the brain, the visual system ranks amongst the highest energy-consuming systems. 5 In the presence of a binocular vision anomaly, particularly while undertaking a challenging visual task, these demands will be significantly increased, highlighting the importance of managing decompensated phoria in these individuals. Cross dominance Problems can occur in all occupations when the dominant eye is not the same as the dominant hand (cross dominance); this can affect the way in which, for example, the bat is aimed at the ball in cricket or the club in golf and how a footballer kicks (aims at) the ball. 6 Prismatic effect The effect of prism can make all the difference to the performance outcome in sport and involves consideration of: The binocular effect of corrected myopia and hyperopia The effect of even low levels of uncorrected astigmatism on accommodation and, therefore, binocular balance The prismatic effect of inaccurate lens centration and anisometropia The absence of a prismatic effect in contact lenses.

4 Reflective learning Having completed this CET exam, consider whether you feel more confident in your clinical skills how will you change the way you practice? How will you use this information to improve your work for patient benefit? 1. History and Symptoms 2. Dominance a. Type I (right) b. Type II (left tendency) 3. Proportions of primary visual skills a. Aiming b. Anticipation 4. Type of sport a. Dynamic b. Control Table 2 Protocol for investigating sports vision deficiency Dihedral Angle Lens power Type of sport The type of sport gives an indication of potential ocular hazards and the need for eye protection and the required strength of the frame. Sport can be broadly divided into two types, dynamic and controlled Elements of visual performance a. Refractive error (retinoscopy) b. High and low contrast vision c. Eye dominance d. Muscle balance e. Fixation disparity f. Colour preference and light sensitivity (Eye Bright Test) g. Dynamic fixation 6. Subjective refraction 7. Full eye examination Sphere Cylinder Axis Prism base 0 Trial frame In wrap frame 28 In wrap frame Table 3 The effect of dihedral angle on dioptric lens power in in Examples of dynamic sports include athletics, squash and hockey, whereas archery, bowls and snooker are categorised as controlled sports. In reality, for many sports, it is generally a mixture of the two in varying proportions. Figure 3 Measurement of dihedral/face form angle. Image courtesy of r+h The diagnostic elements of sports vision performance The principles of assessing sporting visual performance 4 require that the task is broken down into its single diagnostic elements (individual sporting visual skills). Any deficiency in the primary skills of aiming and anticipation can then be addressed. Seven diagnostic elements of visual performance including dynamic fixation 7 are proposed, which are common to all occupations, including sport (see Table 1). These elements of visual performance form the basis of the sports vision screening battery evolved to measure and demonstrate visually related sporting deficiency. For example, demonstrating and explaining the implication of poor low contrast vision, a fixation disparity, or a strong colour preference are an essential part of breaking down the barriers between practitioner and athlete. When justifying a correction to an individual athlete or team two things need to be achieved: Demonstration of a visual deficit in any of the elements of sporting visual performance Relation of poor sporting performance to this deficiency. Investigation of visual related sporting deficiency The primary sporting visual skills of aiming and depth perception and the diagnostic elements of vision, including dynamic fixation, form the basis for a protocol for investigating visually related sporting deficiency. When the tests are used to screen a team of athletes they can justify clinically any optometric or dispensing intervention (see Table 2). The diagnostic tests show how data can be directly related to visual deficiency and well-understood dispensing measures. Deficiencies in any of the diagnostic elements of sporting visual performance in an initial screening each have their own dispensing implications. For example, poor muscle balance (objective muscle balance test) or sensory fusion (fixation disparity) will affect depth perception and possibly aiming, both critical factors in sporting performance. Prism correction is used to solve these problems where required. 47 For the latest CET visit

5 48 Lens performance Vision and sporting performance are directly related so everything should be done to maximise lens performance and maintain light transmission through the lens including: Anti-reflection coatings to increase light transmission Hard coats, sustain lens performance/ transmission Hydrophobic and oleophobic coatings to keep lenses clean and repel water High index materials to keep lens thickness and weight down Aspheric lenses to minimise peripheral distortion Filters for blue light, ultra violet and visible non-ionising radiation maximise contrast 10 and maintain visual acuity 11 Trivex and polycarbonate materials, including polarized and Drivewear to protect the globe and adnexa from trauma and non-ionising radiation High base curve wrap lenses to maximise peripheral awareness and eliminate side incident non-ionising radiation. Wrap lenses One of the most important characteristics of the generic sport frame is its wraparound construction. The mechanical advantages of this type of frame in sport are: Protection from side incident ultraviolet, visible and infrared radiation Protection from wind and foreign bodies Unrestricted peripheral field when glazed with high base curve lenses. The power of wrap lenses has to be recalculated (see Table 3) to take into account off-axis viewing and changes in material thickness, which occurs in larger lenses of this type. Dispensing requires an additional measure of face form angle (see Figure 3). More sophisticated methods are available now using a tablet computer, 3D imagery and the measurement of parallax (for example Shamir). Sports frames There is a large range of sports frame available from various manufacturers, including Norville, Rudy Project, Oakley, Carl Zeiss, Nike, Maui Jim, Inland and Academy Eyewear. Some are easily recognisable appliances such as snooker specs, swimming goggles and shooting specs, whereas others have more specialised features including ventilation, brow protection and spectral filters. Sports frames are generally made of very tough and light polyamide (Nylon). SPX (Silhouette) and TR90 are examples of this material. Ideally sides will be detachable in case of an accident and adjustable vertically. The tips that grip the back of th e head can be covered with silicone to prevent slipping and the sides can be interchangeable with a headband. The nose and the temples should be protected with silicone pads and the rim inset to prevent the lens being forced out by direct impact. In some sports, for example cycling or clay shooting, adjustable pads are very useful to raise and lower the frame. The choice of appliance and mode of correction depends on the athlete and the sport. Manufacturers will give guidance on the application of the sport frame and filters, but the practitioner needs to design the ideal appliance around the athlete and establish the available solutions to find the one that most closely matches the desired benefits. It is helpful to have no more than three frames in mind for each sport (some frames will cover more than one sport), which are kept in stock. Contact lenses Contact lenses are a key mode of correction in sport and binocular visual development with important optical properties and will be the subject of a future article. 16 Conclusion The relationship between vision and sporting performance is not fully understood. The principles of sports vision and consideration of dominance type give a better understanding of the visual and physiological requirements of each athlete. This helps to identify and quantify the key visual tasks in each sport, which is an essential precursor to successful dispensing for sport. Exam questions Under the enhanced CET rules of the GOC, MCQs for this exam appear online at /exams. Please complete online by midnight on June 20, You will be unable to submit exams after this date. Answers will be published on /exam-archive and CET points will be uploaded to the GOC every two weeks. You will then need to log into your CET portfolio by clicking on MyGOC on the GOC website ( to confirm your points. References Visit clinical, click on the article title and then on references to download.