Vision Corrections for the Older Adult PDF

CHAPTER 11 Vision Corrections for the Older Adult ROBERT J. LEE and ROD TAHRAN A ccording to AARP some 18 million older adults (defined as people older than 55 years) are currently in the workforce. A recent...

CHAPTER 11 Vision Corrections for the Older Adult ROBERT J. LEE and ROD TAHRAN A ccording to AARP some 18 million older adults (defined as people older than 55 years) are currently in the workforce. A recent questions should be asked about working dis- tance, field of view, and visual acuity require- ments based on each task and an explanation of AARP survey suggests that number will con- unfamiliar occupations or hobbies. tinue to grow.6 Currently 63.2 million older adults live in the United States, which repre- SPECTACLE PRESCRIPTION CHANGES sents 29% of the entire population.4 What are Because of normal age-related changes to the some of the visual challenges and opportunities ocular media, crystalline lens, and retina, eye care practitioners can expect when pre- changes in the spectacle lens power are often scribing spectacles for this patient population? necessary for older patients. An increase in dis- How can their visual well-being be better tance minus power caused by media changes served? such as cataracts or systemic changes from dia- betes can be unnerving to the patient, especially LIFESTYLE CHANGES if the prescription change is greater than 1.00 D. Millions of older, active Americans are trying Patient education and trial framing of the new new careers, launching new businesses, volun- prescription are beneficial to aid in adaptation teering, and returning to school.6 For eye care and visual comfort. Patients with unstable practitioners to prescribe effectively and learn blood glucose levels require a referral as well as more about their diverse visual needs, a lifestyle patient education on expected spectacle lens questionnaire may be useful. The lifestyle ques- changes until their glucose levels are stabilized. tionnaire should ask about each of these activi- An increase in plus add power is especially dif- ties along with details about sports and hobbies. ficult because near and intermediate working An ideal questionnaire has patients check off distances will both be reduced. The shortened activities they regularly participate in and rank working distances will also necessitate more the importance of these activities from “impor- positive fusional convergence by the patient. tant” to “very important.” Vision enhancement This demand is compounded by the higher add recommendations based on activities most power, which results in a more exophoric pos- important to the patient should be well received ture at near. Symptomatic patients may be made (Fig. 11-1). An area on the questionnaire that more comfortable by the decentration of the asks about the likes and dislikes of the patient’s multifocal segment inward to create a base in present eyewear can also provide valuable prism effect at near. The segment width should information to discuss features and benefits of be increased to compensate for the decentration lens materials, design, and treatments. Secondary effect. Consider a flat top 35 or 45 segment, 201 202 ROSENBLOOM & MORGAN’S VISION AND AGING Fig. 11-1 Sample lifestyle questionnaire. (Courtesy Southern California College of Optometry Eye Care Center.)  Chapter 11 Vision Corrections for the Older Adult 203 noting that the segment “ledge” will be more Abbe of 30. Trivex can also be surfaced down to apparent as the width of the segment increases. 1.0-mm center or edge thickness for dress lenses. These lenses are especially suited for LENS MATERIALS rimless and three-piece applications because of A thinner, lighter lens with good optical per- reduced distortion and stress at the drill holes formance is a goal of lens designers, eye care (Table 11-1). professionals, and patients. Are both comfort and good vision possible with today’s lens LENS DESIGNS materials? Polycarbonate has gained a U.S. The maturing patient with presbyopia typically market share of greater than 25% because of a already has a habitual vision correction. This relatively high index of refraction (n = 1.586), correction may take the form of store-bought low specific gravity (1.20 g/cm3), and superior reading glasses, lined multifocals, or progres- impact resistance compared with CR-39 resin sive addition lenses.2 These patients are experi- (n = 1.498) specific gravity (1.32 g/cm3).3 enced spectacle wearers and may have minimal Polycarbonate also offers good value to the or no complaints with their habitual multifocal patient with its inherent scratch-resistant lens design. How does the practitioner decide coating and ultraviolet (UV) blocking proper- what lens design is most appropriate for the ties (blocks 97% of UV radiation up to 400 nm). patient? Should the patient be kept in the same Lenses can be surfaced to 1.0 mm center or edge style lens as before? Certainly a well-adapted thickness, which reduces edge thickness and bifocal wearer may subjectively be free of visual weight. Because of an Abbe value of 30, color complaints. As previously mentioned, a lifestyle fringes caused by lateral chromatic aberration questionnaire and additional questions may can sometimes be seen by patients, especially uncover visual needs that the patient never when viewing off the lens optical center. considered. Consider the vision requirements Although chromatic aberration can be expected of diverse hobbies and interests such as a home and is a factor with all high-index materials, it workshop, piloting a plane, playing billiards, can be distracting for the patient. A reduction in surfing the Internet, painting at an easel, and contrast and peripheral acuity is a function of playing the piano. They all have something in the prismatic effect and the nu value of the lens common: the need for clear, comfortable, inter- material.18 To minimize these unwanted effects, mediate vision. Although reduced amplitudes polycarbonate should be limited to corrections of accommodation as presbyopia increases are less than 4 D. inevitable, the loss of intermediate vision ranges A lens material called Trivex (Younger can be maintained by prescribing trifocals or Optics, Torrance, Calif.) is a viable alternative to progressive addition lenses (PALs). polycarbonate. Marketed under the Trilogy Restrictions with vertical and lateral head or name, it combines the best attributes of thermo- eye movements may limit the patient’s ability plastics (polycarbonate) and thermosets (CR- to use a trifocal or PAL effectively, especially for 39). The Abbe value is similar to CR-39 with a extended periods of reading. The trifocal design specific gravity less than polycarbonate. Trivex lowers the near segment in the lens because of is a mid-index lens (n = 1.53) and has a specific the position of the intermediate segment. The gravity of 1.11 g/cm3. Its Abbe value of 43 to 46 progressive lens wearer may also be affected (depending on the manufacturer) rivals CR-39’s because the full add power is also lower in the TABLE 11-1 Comparison of Lens Materials n Abbe Specific Gravity (g/cm3) Edge Thickness* CR-39 1.498 58 1.32 4.50 mm Polycarbonate 1.586 30 1.20 3.13 mm Trivex 1.530 45 1.11 3.36 mm *-4.00 D sphere prescription, 50 mm round lens. CR-39: 2.0 mm center thickness. Polycarbonate and Trivex: 1.0 mm center thickness. 204 ROSENBLOOM & MORGAN’S VISION AND AGING Fitting Height Comparison 25 22 22 22 20 20 18 17 18 18 18 18 18 18 18 16 17 17 17 15 Minimum fitting height 10 5 0 ax a t II 3 e e o i k p n c rt XS M e pt pac e d i t 1 Wid Wid c ol Min ook ise da To atio a ni fo e l c o l lif la er c m c e m a ic F ut on K da v an om v So a P Co Pro um Hoy LX ir P x A O ra or O x P x C ssi l O S ya m t a r a ak C G l u u re So A ik o ya Ho Sha Pen g d ss si ril aril og Te Ko Es Va Se Ho e ie V Pr s Z ck Ea to on n s si de Vi Ro Fig. 11-2 Progressive lens fitting height comparison. lens. A vertical head movement is necessary to access the near reading zone of the PAL. Consider a short-corridor progressive addition 1 mm lens for these patients. The progression of plus 75 mm 5 mm power for near is reached faster because the corridor length is shorter. By reaching the full add power sooner, vertical excursions of the head and eyes are reduced (Fig. 11-2). Trifocal wearers may be satisfied with their current lens style: three defined areas of stable, 14 mm clear vision. The intermediate power of a tri- focal is typically 50% of the add power. Trifocals are also offered with intermediate powers of Fig. 11-3 4 × 35 trifocal. The vertical intermediate height is twice the height of traditional flat top trifo- 40% and 70% of the add power. For those cals. (Courtesy Vision Ease, Ramsey, Minn.) patients desiring a larger vertical field of view through their intermediate segments, consider the 14 × 35 trifocal. Also consider an occupa- tional trifocal; the vertical height of the inter- wearer with a “hard” design PAL. Hard designs mediate segment is 14 mm—twice the height of have their unwanted peripheral astigmatism in a conventional trifocal (Fig. 11-3). concentrated areas below the 180 line of the Progressive addition lenses (PALs) have lens, mainly on either side of the progressive come a long way since the Varilux 1 was intro- corridor. Patients accustomed to viewing through duced in 1959 and should be considered for all a lined segment were thought to adapt to the mature patients. Progressive lenses are espe- hard design’s defined corridor and near zone. cially appropriate for add powers greater than For older patients desiring to wear PALs, +1.75 D because these patients benefit from the today’s “soft” designs have their advantages. intermediate working distance afforded by a Unwanted astigmatism is spread over larger PAL. Patients who have tried the older genera- areas of the lens, including above the 180 line of tion progressives did not have the benefit of the lens. This results in a smoother transition today’s advanced technology. Past strategies from distance to near, making adaptation easier. suggested fitting an established multifocal Studies have shown that more than 90% of  Chapter 11 Vision Corrections for the Older Adult 205 lined multifocal wearers successfully adapt 55- to 64-year-olds, which surged 78% to to PALs 1,14 approximately 2.9 million.9 Computer use has obviously become commonplace in the lives VARIABLE FOCUS LENS of many older adults. However, the visual Patients who are effectively emmetropic at dis- demands of using a computer are different from tance may only wear single-vision reading the demands of reading printed text (Box 11-1). glasses. The practitioner often has to address Variable focus lenses position the lens power the complaint of “blurry vision when I look up at the correct height and distance for a com- with my readers.” Another scenario is the lined puter monitor. These lenses virtually eliminate multifocal wearer who reports blurred vision the awkward head posture required of tradi- and neck and shoulder discomfort after surfing tional bifocal wearers. Because the lens pro- the Internet for several hours. Yet another vides only near and intermediate vision, the scenario is the PAL wearer who works on the unwanted astigmatism can be distributed to computer and desires a wider intermediate a more peripheral part of the lens, thereby field of view. Could the lens design be con- increasing the field of view. tributing to these patients’ complaints? Variable focus lenses should not be restricted Variable focus lenses are an all-purpose lens to only computer use and reading. They are a for vision tasks in the near to intermediate viable option for eye care practitioners as well. range. Because of its design, the lens has Entrance tests are easier to observe with variable unwanted astigmatism like a progressive. focus lenses, including the cover test, motility, However, because the lens has only interme- and external adnexa. The phoropter is in clear diate and near power, the unwanted astigma- focus along with the patient’s chart (Table 11-2). tism can be moved farther out in the lens periphery, away from the patient’s field of view. This results in wider intermediate and near BOX 11-1 zones compared with a traditional progressive Issues Causing Vision Problems lens (Fig. 11-4). Although these lenses are not for Computer Users designed for driving, the reduction in plus power from the bottom of the lens toward the The monitor is higher and farther away compared top allows acceptable distance vision up to 6 to with printed text. The monitor is self-illuminated. 10 feet. This lens design can address the com- The text viewed on the monitor has poor contrast plaint of blur through single-vision lenses when compared with printed text. looking up from reading. Traditional bifocals do not provide clear vision According to Liz Kelleher, content develop- unless the user leans forward and elevates the chin to ment manager for AARP Services, Nielsen/ view through the bifocal segment. Traditional trifocals and progressive lenses NetRatings found that in 2002 the fastest intermediate viewing zones are narrow, necessitating growing population for broadband Internet lateral head movement. access in the United States was composed of Fig. 11-4 Variable focus versus progressive lens viewing zones. 206 ROSENBLOOM & MORGAN’S VISION AND AGING TABLE 11-2 Examples of Variable Focus Lenses Brand Name Description AO TruVision Technica CR-39, small distance window above the fitting cross Sola Access CR-39 and polycarbonate, power shifts of 0.75 D and 1.25 D Sola Continuum Spectralite and polycarbonate, power shift of 1.00 D Essilor Interview CR-39, power shift of 0.80 D Prio’s Prio CR-39, with four power shifts: 0.75 D, 1.25 D, 1.75 D, and 2.25 D Prio Browser CR-39, with two power shifts: 1.00 D and 1.50 D Rodenstock Cosmolit Office CR-39, power shifts of 1.00 D and 1.75 D Zeiss Gradal RD CR-39, lab increases distance power by 0.50 D and reduces add power by 0.50 D LENS APPEARANCE, PERFORMANCE, BOX 11-2 AND WEIGHT Items to Consider When Selecting Frames Patient adaptation and comfort may further be hindered by the physical appearance and Select a frame that is approximately the same width weight of a new prescription. Weight is perhaps as the patient’s face. The top of the frame should be no higher than the the biggest consideration in choosing frame and top of the patient’s eyebrows. lens materials for the older patient. When lens The patient’s eyes should be centered or appear in weight is a factor, both Trivex and polycar- the top third of the frame. bonate are available in aspheric designs in flat top and progressives. These lenses can be sur- faced to 1.0 mm thickness, further reducing weight. The older patient has the same concerns of lens appearance relating to their eyewear as any patient would. The three tips listed in Box 11-2 can be given to patients when selecting frames. To minimize the temporal and nasal thick- ness of the finished lens, select a frame in which the frame PD (box system “A” measurement added to the distance between lenses) equals the patient’s pupillary distance. This will reduce the need for decentration of the optical centers of the lenses, reducing weight and lens edge thickness. If the correction exceeds 4.00 D, recommend Fig. 11-5 Blended 28-mm bifocal. Note the 2-mm a higher index aspheric lens to reduce the lens blended annular ring. (Courtesy Sola International, center or edge thickness. The cosmetic improve- San Diego, Calif.) ment is especially apparent with hyperopic corrections. The surface curves of aspheric lenses flatten toward the periphery of the lens. Complaints of flat top segments being too This flattening reduces the sagittal depth of the visible can be helped by prescribing round, lens, allowing the lens to be fit closer to the blended, or curved top bifocal designs. A slight eye. Reducing this vertex distance reduces the hint of tint in a skin-enhancing color such as magnified image of the hyperopic eye. Because pink or beige renders the segment almost of the geometry of the lens, decentering the invisible. Be aware that the blended segment optical center to induce prism is not recom- has an annular ring of blur of 2 mm sur- mended. Prescribed prism, however, can still be rounding the segment (Fig. 11-5). This blur area ground. may be disconcerting to some patients.  Chapter 11 Vision Corrections for the Older Adult 207 Field of view through the segment can be rule, which is equal to the add power (F) multi- expanded by increasing the segment width, plied by the distance (in centimeters) the seg- decreasing the vertex distance, and increasing ment optical center is from the segment top. pantoscopic tilt. A dedicated pair of glasses Executive bifocals in which the segment optical available for any prolonged task in which sharp center is located on the segment line have zero vision and a larger field of view are required image jump. Round and Ultex segments6a with may be beneficial to the patient. Suggest single- lower optical center locations have the greatest vision reading or variable focus lenses for tradi- amount of image jump. As shown in Figure tional progressive lens wearers who enjoy 11-6, this is a base-down prismatic effect, reading in bed or a recliner. resulting in a scotoma as the eye traverses the The well-adapted multifocal wearer will not segment top. typically have complaints adapting to their lined multifocal lens design. Potential adapta- TINTS AND COATINGS tion problems may occur, however, when As the eye ages the amount of useful light attempting to increase field of view or cosmesis reaching the retina may be attenuated by fluores- by changing segment styles. Image jump is the cence and increased scatter. Morgan10 reported prismatic effect produced when the wearer is that light levels reaching the retina of a healthy not viewing through the optical center of the 60-year-old are approximately one third of the segment. The jump is most bothersome at the light reaching the retina of a 20-year-old. Thus top of the segment where the distance from the older patients require more light to achieve segment optical center is greatest. Patients often the retinal illumination of younger patients. perceive image jump as a shift or altered posi- Kelleher9 also found that visual performance in tion of the image as their line of site passes from the home is significantly worse compared with the distance portion of the lens to the reading the clinical setting because of insufficient segment, or vice versa. The amount of image lighting. Light transmission is reduced to 92.06% jump is independent of the distance prescrip- viewing through clear CR-39 resin, 91.4% tion. This prism effect is calculated by Prentice’s through clear crown glass, and 89.4% through clear polycarbonate. This reduction in light transmission is caused by inherent surface reflections found in all lens materials. As the index of refraction increases, so does the surface reflection. Prescribing an antireflective coating (ARC) can increase light transmission up to 99% by reducing these spectacle lens surface reflections (Table 11-3). Other strategies to reduce reflections are changing the pantoscopic tilt or face form of the spectacles. Often this Fig. 11-6 Image jump. The base-down prism effect adjustment moves the reflection to a peripheral causes a scotoma. The letter U is in the scotoma, lens area away from the visual axis. Patients resulting in the word “MAD” being read. (Reprinted with myopia sometimes are bothered by the from Fannin TE, Grosvenor T: Clinical optics, ed 2, presence of myopic rings—multiple reflections Newton, MA, 1996, Butterworth-Heinemann.) within the lens of the roughened, semiopaque TABLE 11-3 Light Transmission Lens Material Index of Refraction Without ARC (%) Including Multilayer ARC (%) CR-39 1.50 92.06 99.1 Glass 1.52 91.4 99.2 Polycarbonate 1.59 89.4 99.0 High-index plastic 1.60 89.4 99 Super-high-index plastic 1.67 87.8 98.2 208 ROSENBLOOM & MORGAN’S VISION AND AGING lens bevel (Fig. 11-7). A light tint may also lenses. This improves comfort and reduces provide a solution to multiple reflection com- fatigue while viewing a computer monitor. plaints. Pink tints have traditionally been used Avoid prescribing a single-layer ARC because to reduce the glare from fluorescent lights. The it is optimal for only one particular wavelength, pink tint serves to reduce some of the blue light and resulting reflections will be strongly colored. emitted from the fluorescent lights. This Modern ARCs are multilayer coatings reflecting decreases brightness and fluorescence within little, if any, light at any wavelength. A sec- the eye. ondary benefit of ARCs is enhanced cosmetic appearance of the eyes. ARCs minimize lens ANTIREFLECTIVE COATINGS reflections that hide the eyes, in turn making The use of ARCs can reduce glare from an eye contact easier to establish when communi- oncoming car’s headlights, thereby improving cating with other people. The ocular surface of night vision (Fig. 11-8). The glare from car head- a sunglass lens may act as a mirror, often lights behind the driver can also be reduced resulting in patients complaining that they see a with ARCs. Swanson16 reported that disability reflection of their own eyes. Sunglass lenses glare during driving at night can be so burden- should have a backside ARC to reduce these some that many older drivers voluntarily stop annoying reflections. driving during evening hours. ARCs can also reduce annoying surface reflection from sur- GLARE rounding objects reflecting on the spectacle Two types of glare exist: discomfort glare and disabling, or veiling, glare. Discomfort glare has been reported to typically start at approxi- mately 3000 lumens (Table 11-4).17 The response of the unprotected eye to low levels of glare is a squint. This glare can occur in any weather, including overcast days. Glare from higher luminance sources causes pupil constriction, eye closure, and head turnaway from the offending source. Disabling glare occurs at 10,000 lumens and causes lower contrast. An example of direct dis- abling glare is looking toward a sunset or auto- Fig. 11-7 Myopic rings caused by internal reflection. mobile headlights at night. Reflective disabling Fig. 11-8 Glare reduction while driving at night with antireflective coatings. (Reprinted from Giammanco F: Vision care product news, Essilor Product News 2002.)  Chapter 11 Vision Corrections for the Older Adult 209 TABLE 11-4 of the lens having the most photochromic com- Illumination of Typical Environments pounds present. In-mass technology also had the limitation of lenses not being truly clear Environment Illumination (lumens) indoors because of excessive photochromic dye. Indoor, with artificial light 400 Transitions Optical developed and commer- Sunny day, in the shade 1000-14,000 (optimal lighting) cially introduced Imbibition or Trans-Bonding Sunny day, on the grass 3500 (comfort limit) photochromic technology. With Imbibition, Concrete highway 6000-8000 photochromic compounds are driven into the Beach or ski slopes 10,000-12,000 High-altitude snowfield >12,000 lens surface. The compounds become perma- nently imbedded to a depth of 150 to 200 microns. The photochromic compounds cannot glare occurs when light is reflected off an object be scratched or peeled off and do not exhibit the (e.g., a windshield) on a sunny day. The glare is bull’s-eye or raccoon effect. The Trans-Bonding intense enough to overwhelm the eye with process makes it possible to offer photochromic light, masking what is behind the glare. It can technology in desirable lightweight, impact have a drastic effect on vision and create dan- resistant, and durable materials such as poly- gerous situations when driving. Two or more carbonate and Trivex. glare sources in the field of vision have also Plastic photochromic lenses, such as Transi- been shown to be additive.17 Increased light tions, automatically darken and lighten in scatter within the lens is largely responsible for response to varying degrees of UV exposure. the clinical complaint of glare experienced by Visual comfort and function are maintained, the older driver. ranging from virtually clear indoors, to semi- dark under cloudly or overcast conditions, to PHOTOCHROMIC LENSES sunglass dark under direct high illumination. The first commercially available ophthalmic Night vision has been shown to be affected photochromic lenses appeared in the late 1960s. by an individual’s previous exposure to sun- The best-known photochromic glass products light during the day.17 Visual acuity, contrast, were Photogray Extra, Photobrown Extra, and and overall sensitivity can be reduced up to Photosun developed by Corning Glass Works. 50% from the sun’s sustained bleaching of the With the introduction, proliferation, and accept- retinal photochemical rhodopsin. A 2- or 3-hour ance of plastic lenses, market share of glass exposure to sunlight delays the initial phase of lenses has declined to 5%. Plastic photochromic dark adaptation as much as 10 minutes. After lenses were introduced in the early 1990s. Early 10 daily exposures, visual acuity and contrast plastic photochromic lenses were not recom- discrimination show a 50% elevated threshold. mended for older adults because the lenses To maintain night vision, contrast discrimination, never became clear. A slight reduction of light and visual acuity, lenses with 20% transmission transmission occurred when worn indoors and or less should be worn when participating in at night. This presented a potential problem for activities of 2 hours or longer in bright sunlight. older eyes after dark. With new photochromic These can be fixed-tint or photochromic lenses. technology, modern plastic photochromics are virtually clear indoors and at night. These POLARIZED LENSES lenses are indicated for nearly all older patients Fixed-tint and photochromic lenses attenuate because of their ability to adjust to varying light glare, but polarized lenses eliminate glare from levels. Photochromic lenses block up to 100% of reflected surfaces. Delamination issues in the UVA and UVB. past have been addressed by suspending the There are two methods of incorporating pho- polarizing film within the lens mold. The film tochromic technology in the lens material. The then becomes an integral part of the finished earlier “in-mass” method mixed photochromic lens. Polarized lenses should be prescribed for compounds into the lens monomer. The limita- any patient who spends time out of doors and tions of this technique led to “bull’s-eye” or desires visual comfort and clarity. They are “raccoon” effects for high plus or high minus available in virtually any lens material and lenses, respectively, because of the thickest part multifocal lens design. A more compelling 210 ROSENBLOOM & MORGAN’S VISION AND AGING Fig. 11-10 Clip-on sun lens. Fig. 11-9 Glare as a causative factor in auto- The mechanism of damage from UV radiation mobile accidents. (Courtesy Younger Optics, (UVR) is photochemical and thermal. The pho- www.youngeroptics.com/news/mur3.html.) tochemical mechanism is primarily in the UVC and UVB wavelengths. As UVA is approached, the thermal mechanism is involved. Pitts11 reported that UVR risk factors include aphakia, reason to prescribe polarized lenses to the older pseudophakia, cataracts, photosensitizing drug patient is driving safety. In 1999 a 100-car pile- use, and sun exposure more than 8 hours daily up on Highway 10 near San Bernardino, Calif., as well as vocations or avocations rich in UVR was attributed to drivers who simply could not such as arc welding, electronic chip assembly, see ahead of them because of intense sun glare snow skiing, or mountain climbing. The phakic (Fig. 11-9).12 Morgan,10 among others, reported retina is more sensitive to UVR at 325 nm by a that older adults are more sensitive to glare factor of 2.5. Strategies to control UVR exposure than are younger patients. This is indicated by include wearing ophthalmic lenses with UVA- an increase in reaction and redetection time in and UVB-blocking properties such as polycar- the presence of a glare source. Karr8 reported bonate and Trivex. For maximal protection that although they are involved in fewer these lenses should be larger and worn close accidents than younger people because they to the eyes. Although UV-absorbing soft and drive less often, individuals older than 65 years gas-permeable contact lenses and intraocular are the most likely to die in car accidents lenses protect the cornea, lens, and retina according to the National Highway Traffic against UVR, UV-blocking ophthalmic spec- Safety Administration. tacle lenses are necessary to protect the eyelids and surrounding skin. Rosenthal et al13 found PROTECTING THE EYE FROM GLARE that wearing a hat with a 4-inch brim in sun- AND ULTRAVIOLET RADIATION light reduced ocular exposure to UVR by Ocular changes from aging and various patho- approximately 50%. logical conditions can make the eyes hypersen- For the patients who would rather not have a sitive to what normal eyes see as moderate dedicated pair of sunglasses, alternatives do glare. This glare is often disabling glare, generally exist. Clip-on sunglasses are popular because of within the eye because of blue light scatter. the convenience of not having to carry two Patients may report hazy vision and loss of pairs of glasses. They are most beneficial when contrast. Prolonged adaptation time and photo- polarized lenses are dispensed. Clip-on sun- phobia often occur. Glare and loss of contrast glasses are attached to the frame with traditional may arise from developing cataracts, aphakia clips or sturdy magnets. The magnets provide a or pseudophakia, diabetic retinopathy, albinism, strong point of attachment but do add minimal retinitis pigmentosa, and aniridia. Patients additional weight to the clip (Fig. 11-10). An should visually test the lenses to ensure they can additional option is a pair of over-the-counter distinguish traffic color signals before driving.5 sunglasses. Up to 52% of people with corrected  Chapter 11 Vision Corrections for the Older Adult 211 STRAP BRIDGE - SOFT PVC mm 6036 Medium - 30.5mm 6037 Large - 36.8mm Fig. 11-12 One-piece strap bridge. (Courtesy of Sadler Optical Tools and Findings, South Attleboro, Mass.) skin. Consider titanium and titanium alloy Fig. 11-11 Plano sunglasses that fit over prescrip- frames that offer corrosion resistance as well as tion spectacles. (Courtesy of Live Eyewear, San Luis high tensile strength, durability, and light Obispo, Calif.) weight. Plastic frames that offer light weight include polyamide and copolyamide materials. vision are reported as not electing to purchase These are a blend of nylons with reduced prescription sunglasses, photochromic lenses, weight and flexibility. Optyl is another good clips, or plano sunglasses. Polarized sunglasses choice because of its light weight (30% lighter that quickly slip over prescription eyewear are than zylonite) and hypoallergenic properties. an extremely popular option for prescription A round eyewire is the ideal frame shape to eyeglass wearers (Fig. 11-11). minimize weight. When minimal weight is desired, frame shapes that depart from a round FRAME CONSIDERATIONS or oval increase the weight of the lens. Steer FOR OLDER ADULTS patients away from goggle shapes, which add As people age, the fatty tissue between the nose unwanted lens mass at the frame’s inferior nasal and the nose pads thins, resulting in less cush- corner. A strap bridge is a one-piece nose pad ioning for glasses. This can result in pressure that acts like a saddle bridge of a zylonite frame. sores on the bridge of the nose. A temporary These can often be retrofitted to a metal frame, solution is to remove the glasses to relieve the increasing the weight-bearing area of the frame pressure. This may be a poor solution for and minimizing pressure points (Fig. 11-12). patients who depend on glasses. Larger nose pads may be helpful because the larger surface PRESCRIBING STRATEGIES FOR of the pads distributes the weight over a larger PATIENTS WITH ANISOMETROPIA surface area. Silicone pads can also be used to Anisometropia has been defined as “a condi- minimize frame slippage. Nylon suspension or tion of unequal refractive state for the two eyes, drill mount frames offer minimal weight while one eye requiring a different lens correction almost disappearing on the face, especially with than the other.”7 These patients can present with the addition of an antireflective coating. Nickel anisometropia as a consequence of unilateral is a common material used as the base material intraocular lens or refractive surgery proce- for metal frames. Patients who are bothered by dures, asymmetrical refractive error shifts from allergies and cannot wear costume jewelry or cataract progression, or blood glucose shifts in need to use hypoallergenic makeup may also be unstable diabetic patients. They may be symp- sensitive to nickel. This sensitivity can be seen tomatic because of vertical prism being induced by examining the inside of the frame’s temple. when they view below the distance optical cen- A patient’s skin oils or perspiration may cor- ters of their glasses. This typically occurs when rode the electroplating, exposing the under- the patient reads through multifocal segments. lying nickel. Look for roughened, dry, irritated Often a Fresnel prism is of diagnostic value areas where the temples make contact with the to determine the subjective amount of vertical 212 ROSENBLOOM & MORGAN’S VISION AND AGING prism to alleviate symptoms. These “press-on” tracting because of its striated appearance. They plastic membranes are applied to the ocular should also be instructed how to apply the side of the bifocal segment (Fig. 11-13). The top prism if they are inadvertently removed during of the prism should coincide with the segment routine cleaning of the lenses (Fig. 11-14). top. Patients should be made aware that the Optometrists have several prescribing Fresnel prism will reduce acuity by approxi- options to address the vertical prism imbalance: mately one line and can be cosmetically dis- (1) separate pairs of glasses for distance and reading, (2) prescribe dissimilar bifocal seg- ments to neutralize the vertical prism induced by the distance correction, or (3) prescribe slab- off or reverse slab-off lenses. The advantage of prescribing distance and near glasses is that the optometrist can control the vertical optical center height of both pairs of lenses. As long as the patient views through the optical centers, no prism effect is induced. As a rule the optical centers of the reading glasses should be low- ered 5 to 10 mm compared with the distance optical centers. The disadvantage, however, is the inconvenience of juggling two pairs of glasses. PRESCRIBING DISSIMILAR BIFOCAL SEGMENTS Fig. 11-13 Diagnostic Fresnel prism. The prism A vertical difference in location of the segment should be placed with a base-down prism orienta- tion on the lens, with the most plus or least minus optical centers exists between dissimilar bifocal vertical power. (Courtesy 3M Health Care, St. Paul, segments. This difference in vertical location Minn.) induces a prism effect equal in power but oppo- site in base direction compared with the prism induced by the distance correction (Fig. 11-15). The segment that has its optical center farthest from the segment top induces base-up prism because of the segment. The base-up prism neu- tralizes the base-down prism caused by the distance correction. For example, consider a prescription of OD −5.00 DS and OS −2.00 DS. If the patient reads 10 mm below the distance Fig. 11-15 Dissimilar bifocal segments. The segment with its optical center farthest from the segment top is prescribed for the most minus lens. (Reprinted Fig. 11-14 Fresnel prism application. (Courtesy 3M from Fannin TE, Grosvenor T: Clinical optics, ed 2, Health Care, St. Paul, Minn.) Newton, MA, 1996, Butterworth-Heinemann.)  Chapter 11 Vision Corrections for the Older Adult 213 optical centers the vertical prism effect OD is prism or the most plus or least minus power in 5 prism diopters base down. The OS prism the vertical meridian. Reverse slab-off lenses effect is 2 prism diopters base down. Prescribe can be inventoried by the laboratory as semi- the flat top bifocal for the lower minus left eye finished lenses. The optometrist can realize and the round 22 bifocal for the more minus both reduced cost and faster delivery times right eye. In theory this works very well opti- compared with individually produced slab-off cally. Patient education is crucial because lenses. cosmesis will be an obvious concern. SLAB-OFF REFERENCES Slab-off lenses are indicated when the vertical 1. Borish IM, Hitzeman SA, Brookman KE: Double prism imbalance is 1.5 prism diopters or masked study of progressive addition lenses, J Am Optom Assoc 51:933-43, 1980. greater. A slab-off lens is made by bicentric 2. Boroyan HJ, Cho MH, Fuller BC, et al: Lined grinding. This procedure results in the removal multifocal wearers prefer progressive addition of base-down prism in the lower portion of the lenses, J Am Optom Assoc 66:296-300, 1995. lens. Note this prism removal does not change 3. Bruneni JL: Poly goes global, Eyecare Business the refractive power of the lens below the slab- April 2001: 64-7. off line. Because slab-off removes base-down 4. Bruneni JL: Going grey, Eyecare Business prism, it should be prescribed for the lens that December 2002:32-7. induces the most base-down prism from 5. Defranco LM: Spectacle lens options for light- viewing below the distance optical center. Thus sensitive patients, Refractive Eyecare for it should be placed on the lens having the least Ophthalmologists November/December 1998, plus or most minus power in the vertical 2:22-6. 6. Duka W, Nicholson T: Retirees rocking old roles, meridian. Bicentric grinding results in a hori- AARP Bulletin December 2002, pp. 1-2. zontal line across the entire width of the lens. 6a. Fannin TE, Grosvenor T: Clinical optics, Boston, The line is best concealed when the line coin- 1996, Butterworth-Heinemann, pp. 229-30. cides with the segment top of a straight top 7. Hofstetter HW, Griffin JR, Berman MS, et al: bifocal (Fig. 11-16). Dictionary of visual science and related clinical A high degree of skill is necessary to grind terms, Boston, 2000, Butterworth-Heinemann, plastic slab-off lenses. Precast or molded, semi- pp 26-7. finished reverse slab-off lenses are now avail- 8. Karr A: States find ways to aid older drivers, AARP able. These lenses have base-down prism in the Bulletin, www.aarp.org/bulletin/yourlife/Articles/ segment rather than removing base down a2001-06-26, accessed October 2003. prism by bicentric grinding. This lens is placed 9. Kelleher L: Breaking the stereotype of older adults online, AARP, www.aarp.org/olderwiserwired/ on the lens that induces the least base-down Articles/a2003-02-20, accessed October 2003. 10. Morgan MW: Normal age-related vision changes. In Rosenbloom A, Morgan M, editors: Vision and aging, Boston, 1993, Butterworth- Heinemann, pp 184, 189. 11. Pitts DG: Ocular effects of radiant energy. In Pitts DG, Kleinstein RN, editors: Environmental SLAB-OFF LINE vision: interactions of the eye, vision and the envi- ronment, Stoneham, MA, 1993, Butterworth- Heinemann, p 161. 12. Rips JD: Driving and sun glare—a lethal combi- nation, LensTalk April 2000. 13. Rosenthal FS, Phoon C, Bakalian AE, et al: The ocular dose of ultraviolet radiation to outdoor Fig. 11-16 Reverse slab-off lens. Prescribe reverse workers, Invest Ophthalmol Vis Sci 29:649, 1988. slab-off for the lens with the least minus vertical lens 14. Spaulding DH: Patient preference for a progres- power. (Reprinted from Fannin TE, Grosvenor T: sive addition multifocal lens (Varilux2) vs. a Clinical optics, ed 2, Newton, MA, 1996, Butterworth- standard multifocal lens design (ST-25), J Am Heinemann.) Optom Assoc 52:789-94, 1981.