As the UK’s population continues to age, practitioners are aware of the need to expand their services to include additional magnification solutions for their elderly patients. This first article in a two-part series will focus on the functionality, design and use of simple, hand and stand magnifiers that may be dispensed at practice level
Optical practitioners are becoming increasingly aware that as the population continues to grow, services will need to evolve to meet the increasing demands of an elderly population and especially from those whose vision has been affected by an age-related condition. It is well documented that age-related macular degeneration (AMD) is the most prevalent cause of visual impairment in the over 65 age group,1,2 accounting for over 50% of all UK certifications,2-4 suggesting that despite recent advancements in both prevention and treatment, AMD remains a significant burden.
There is a wealth of products on the market to assist visually impaired patients. But choosing a long- term, successful product for a patient is not always straightforward and requires a review of the patient’s clinical, refractive and psychological status. Using a magnification device is almost always a compromise compared to ‘standard’ reading spectacles, but is something that many patients are willing to make, especially when it can return a degree of previously lost independence. However, all too often, motivated patients are let down by an inadequately designed and poorly manufactured product. The objective of this article, therefore, is to outline the generic design features of hand and stand magnifiers and to highlight what makes a low vision aid successful and ultimately an indispensable lifeline to a patient.
A proactive approach to light and magnification
Many practitioners are still reluctant to get involved in providing devices to their visually impaired patients, often due to either lack of product knowledge or a perception of limited financial reward for clinical time. However, most individuals who experience a degree of visual impairment have already tried using a magnifier, whether bought at a local hardware store or by a family member over the internet.
Optical practitioners understand the concept of light, lens power and magnification more than most in the associated healthcare professions. We also appreciate far more about the effects of macular disease than the local hardware store, so it would seem natural that patients should approach their optometrist or dispensing optician to determine which magnifier may be best to address their needs.
Practices that have successfully integrated a low vision service take a more proactive approach by introducing the concept of light and magnification as an alternative, or in addition to, standard spectacle correction for both hobbyists and those with low vision, rather than considering low vision aids as an ‘end of the road’ product for the visually impaired.
The importance of good design
With more practices investing in optical magnification it can be daunting trying to decide which products or product line to choose. In recent years, there have been a number of exciting new products entering the marketplace. Successful manufacturers have invested wisely, not just in good product components and design but have held discussions with focus groups and end- users to review the functionality of the product.
If a patient with low vision uses additional magnification to do basic daily tasks, then they should expect their magnifier to have the same quality optics as a spectacle lens. All too often there are cheaper, poor quality products that appear within the marketplace, offering inferior quality lenses with distortion or aberrations and casing that becomes brittle or discoloured over a short time period. Similarly, there are products boasting a high quality lens with a superb ergonomic handle but other features such as a fiddly battery compartment or a flimsy switch mechanism lets the product down. Before investing, it is important to take time to review the products carefully and be reminded that what may appear useful for a sighted individual may not be as useful for someone suffering from a visual impairment.
Lens power, magnification and lens design
With such a wide variety of hand magnifiers available containing spherical, biconvex, aspheric or aplanatic lenses, it is important that practitioners consider the benefits of each with their visually impaired users or hobbyists in mind.
Single lens powers for optical devices range from approximately +4.00D to +50.00D. Most devices contain just one lens although some hand or stand magnifiers may contain a double lens system to either increase overall magnification, field of view, or both. At the lower powers, magnifiers can afford to have a larger lens diameter. Standard spherical lenses tend to be used in the economy ranges but will suffer from aberration and distortion in the higher powers. Biconvex lenses offer larger lens diameters, particularly in the lower power range and if the patient requires stronger magnification, then an aspheric lens will reduce weight and thickness while controlling distortion and aberrations.
Lens quality can vary significantly between product ranges. A few manufacturers have tried to reduce weight by creating a ‘blended’ lens, where the stated power is only central to the lens then tapering off slightly towards the edge. For those patients with central vision loss this may not be the best option for them. Aplanatic lenses produce an edge-to-edge distortion free image, particularly relevant for those suffering from central distortion or scotoma.
With visually impaired users, a major factor influencing reading performance is the field of view through the lens.5 In higher powers, the overall diameter of the lens is significantly reduced and, therefore, practitioners need to assist patients in managing their expectations with reading fluency when using a device with a restricted field of view.
In the lower power range there is also the option to create a larger, rectangular lens, and maintain good quality optics. A rectangular lens is useful for reading a column of print, for example (see Figure 1: A +10.00D rectangular lens will comfortably cover a column of newspaper print while still achieving the full magnification). Weight, lens quality, and cost restrict the manufacture of a usable aspheric rectangular lens beyond approximately +10.00D as a low vision device, unless the lens is created by multi-order diffractive (MOD) optics. MOD lenses have been introduced in several low vision devices, providing higher-powered lenses for both hand-held devices and high-powered spectacles offering a significant reduction in weight and thickness compared to similar powered aspheric lens designs (see Figure 2: An illumination +16.00D credit card-sized magnifier of only 6mm thickness produced by multi-order diffractive optics). They also boast excellent quality optics but should not be mistaken for the familiar Fresnel lenses used in low-cost ‘sheet’ magnifiers, which have significantly more chromatic aberration.
In addition to the quality of the optics, it is also practical to have a lens that is hard coated. Devices are often carried loosely in bags and pockets, rather than within boxes or pouches to allow quick and easy access. Those with a visual impairment may not be aware of lens degradation and so may wrongly believe they have experienced a drop in vision. In lens designs without a hard coating, practitioners need to warn patients accordingly so that additional care may be taken when handling or transporting the device.
Other design features
Despite a good quality lens, some designs are let down by poor quality casing. The ideal scenario is to have a durable casing that adds little weight. Several products in the current marketplace are more prone to discolouration, especially if the patient is a smoker. Others become brittle and crack over a relatively short time. Within a hospital setting where devices may be ‘recycled,’ it is important to consider durability when factoring in restrictions on budget for replacement devices.
With elderly users in mind, handle shape and thickness is an important feature for those with weak or arthritic hands. An ergonomic handle is preferable with a material that is easy to wipe clean without degrading the plastic and ideally with contrasting colours to improve the device’s visibility around the home.
By far the vast majority of illuminated devices used in low vision benefit from an LED (light emitting diode) light source. LEDs emit more light per watt than incandescent light bulbs (tungsten/tungsten-halogen) and are more energy efficient, radiating very little heat. Furthermore, efficiency is not affected by shape or size so LEDs can be incorporated easily within a device without adding extra weight or bulk. An LED will light up very quickly, achieving full brightness in under a microsecond and has approximately 35,000 to 50,000 hours of useful life. Previously used incandescent bulbs had between 1,000–2,000 hours of useful life and were less energy efficient, radiating a noticeable amount of heat. Being made of solid-state components, LEDs are less susceptible to external shock, unlike the more fragile incandescent bulbs, which is useful when the devices are carried in bags and pockets.
Some product ranges now incorporate a surface- mounted LED that is soldered directly onto a circuit board. With no leads or surrounding ‘packaging’ that comes with a standard LED, weight and bulk are further reduced. The surface-mounted LED gives off almost no heat and has low voltage and low current requirements. Surface-mounted LEDs have an extended life span estimated at 100,000 hours. Some products that incorporate surface-mounted LEDs will use a step-up converter to ensure consistent illumination over time so when the voltage drops near the end of battery life, the light dims quickly, giving the user clear indication when to replace the batteries.
Integral illumination is an essential feature for many users with low vision; attention should, therefore, be given to the position of the LED within the design. To maximise field of view, many users hold their device close to the eye, so it is important to have the light source concealed from view to avoid causing a glare source while at the same time ensuring that the LED is not in a location where it is obscured by hands or fingers when in use. An ideal light source should create even illumination across the entire field of view. To achieve this, one or two product lines house the LED within a collimator (see Figure 3: Clip-in collimators provide even illumination, or may be used to alter the colour temperature).
There have been few studies that have considered the benefits of different correlated colour temperatures (CCT) in low vision devices and there is no evidence to suggest that there is an improved reading performance using one specific colour temperature over another.6 Anecdotally, however, low vision practitioners are aware there are undoubtedly subjective preferences between users, therefore, it is important to offer all colour temperature options where possible. Manufacturers offer alternative colour temperatures in their more popular ranges of hand or stand devices. Most commonly used colours include 2,700K (orange), 4,500K (warm yellow-white) and 6,000K (cool white). Products offering a range of colour temperatures are available as either separate devices or one single device offering filters that are simply clipped over the LED (see Figure 3).
Although the use of a LED/surface-mounted LED adds little weight to the device, the batteries most certainly do. Smaller batteries are often more difficult for elderly patients to hold and change and ideally they should be readily available as many elderly or infirm patients are less likely to travel far or shop on the Internet for replacements. The battery compartment should be simple to open and close and be robust enough to withstand heavy handling. Insertion and removal of batteries should be intuitive as many patients may not be able to see well enough and will ‘feel’ their way around when trying to open the casing. All too often a design is let down by ignoring these important features when marketing a device with a visually impaired user in mind. If a patient is unable to change the batteries, the device will end up unused and abandoned in a kitchen drawer.
Within any low vision service, hand magnifiers continue to be the most popular choice of aid, being readily available and familiar. Most patients will still benefit from the additional practical advice from practitioners to get the most out of the aid such as improving their field of view by reducing the lens-eye working distance (see Figure 4: To improve the filed of view, the patient should be encouraged to reduce the eye-lens working distance).
Hand magnifiers offer the most flexibility, both within the home and when out and can be used with either distance or near spectacles. For specific tasks, the use of a double-ended clamp provides a ‘hands-free’ option (see Figure 5: Patient using a hand magnifier and a flexible double end clamp to create a hands free position) or a sturdy reading stand with a variety of tilting positions offers an improvement on reading posture, and may also help those struggling to achieve shorter working distances (see Figure 6: The use of a reading stand can create a more comfortable reading posture). Illuminated stand magnifiers can be useful when filling forms or completing crosswords (see Figure 7: An illuminated stand magnifier being used with a pen – useful for form filling or puzzles).
A fixed lens-object working distance gives a more stable image, useful for those who struggle to keep a steady hand, especially when using lenses in the higher power range. Popular designs include stand magnifiers, which have a good sturdy handle to house the batteries. Weight is less of an issue as the device is placed directly over the object. Visual tracking is aided in some designs with the incorporation of an additional reading line, which can be moved out of view when not required.
Larger diameter lenses that have a longer focal length may be used for writing and some designs are shaped to assist a comfortable hand position. Double lens systems also have the benefits of increasing magnification and maintaining a larger field of view. These lens systems are not to be confused with telescopes where lenses are separated by a defined distance based upon their focal lengths.
With having a fixed lens-object distance the vergence of the overall system is fixed. If the lens-object distance is set within the focal length of the lens or lens system, then the emergent vergence entering the patient’s eye will be slightly divergent. This means that the patient will need to either accommodate to focus the image on the retina or use a reading addition. If the lens is placed at its focal length from the object then the emergent vergence of the overall system is now parallel; the patient will not require additional accommodation and will need to wear a distance correction, if they have one. The majority of manufacturers set the lens-object distance of stand magnifier designs within the focal length, so that a +2.50D reading addition (or +2.50D of accommodation) is needed. So it is important to remind patients to keep hold of their old reading glasses for use with some devices. However, there are several stand designs that have a lens set close to the focal length; practitioners need to be aware of the differences so that they may advise their patients accordingly on the best spectacle correction to use in conjunction with the aid.
There are a few products that have created a removable stand for a hand magnifier offering conversion to a stand magnifier when needed; this provides even more flexibility with little additional cost. For example, the hand magnifier may incorporate foldaway metal legs that can be used to create a tilted stand for a comfortable viewing experience. Alternative designs offer an additional stand as an attachment into which the hand magnifier may be placed or inserted.
Flat field magnifiers
The term ‘flat field’ refers to a range of aids where the lens is placed directly onto the reading material or object in view and the image created has the same field of view regardless of the eye-lens working distance. As such, there is no change in the field of view by moving in closer to the lens compared to using a hand or stand magnifier. These devices offer the user an improvement on posture when in use and provide a binocular view. Although this type of aid is only available in the lower powers, several designs are available from the popular ‘dome’ magnifiers, to those that have successfully incorporated additional illumination.
It seems only fair to the patient to offer referral to a low vision clinic where the expense of prescribing may be borne by the local authority or hospital trust. However, it may be that due to the demands of a restricted budget, patients may not necessarily be offered the best option that meets their needs. In recent years, an increasing number of optometrists and dispensing opticians are investing in a range of magnification equipment for both hobbyists and visually impaired patients to differentiate themselves from other optical practices. In offering an alternative range of equipment that some hospital budgets may not stretch to, their visually impaired patients may prefer to opt for a personal purchase of a device that may be more suited to their needs.
Using a device of any nature is always a compromise to the previous experience of being able to read a book on a lap. But for many it can be a lifeline. Many practitioners are still concerned that optical magnifiers can be expensive and yet that additional enhancement on vision may be priceless for the patient. Either way, the value of optical magnification is personal to the patient and ideally should be offered in addition to spectacle correction. It is a challenge that faces those practitioners, who still believe that the only method of correction they can provide is spectacle-based rather than consider the needs of their patients who have probably already tried using a magnifier anyway without the guidance of an expert.
About the author
Jane Macnaughton FCOptom, Prof Cert LV, is currently an associate trainer for Associated Optical Ltd, specialist optometrist at the Leicester Royal Infirmary, and runs a private low vision practice at the Nuffield Health Leicester Hospital. She has lectured widely in the practice of low vision from undergraduate to post graduate level and is the author of Eye Essentials: Low Vision Assessment (2005).
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- Wolffsohn J, Palmer E, Rubinstein R et al (2012) Effect of light-emitting diode colour temperature on magnifier reading performance of the visually impaired. Clinical and Experimental Optometry 95: 510-514