- Email: [email protected]
Low vision rehabilitation for a target-shooting marksman with visual field loss and diplopia
Optometry (2008) 79, 235-240
Low vision rehabilitation for a target-shooting marksman with visual field loss and diplopia Richard Jamara, O.D.,a,b Walter Potaznick, O.D.,a and Ippolit Matjucha, M.D.c a
New England College of Optometry and bSouth Boston Community Health Center, Boston, Massachusetts; and cLahey Clinic, Peabody, Massachusetts. KEYWORDS Visual field; Nonarteritic anterior ischemic optic neuropathy; Shooting sports; Low vision rehabilitation
Abstract BACKGROUND: In the United States in 2006, there were 17.8 million hunters and 17.1 million target shooters. When these sportsmen suffer significant visual loss, it can have a devastating effect on their participation in the shooting sports. According to the National Rifle Association, there are no reliable data sources on the number of target shooters with visual impairment. This case report describes a retired, nationally ranked, competitive target shooter who suffered bilateral visual field loss secondary to nonarteritic anterior ischemic optic neuropathy and diplopia secondary to cerebral vascular accident. CASE REPORT: A retired 67-year-old white man was referred by a local optometrist to a neuroophthalmologist with a suspicious finding of disc pallor and a restriction of the visual field. Examination revealed right hypertropia and visual field defects: binocular superior altitudinal losses and inferior arcuate loss in his dominant, right eye. He had best-corrected distance acuity of 20/20 ⫺ 2 in the right eye and 20/25 ⫺ 2 in the left eye. Because of this, he received several adaptive rehabilitation devices to help him regain his shooting performance. These included a single-vision add for the pistol sight, yellow tint, low-power telescope, and patching. In this report, the fundamentals of eye care for competitive shooting are described with an emphasis on providing the best acuity for presbyopic patient prescriptions at nonstandard distances and the avoidance of diplopia. CONCLUSION: A visually impaired sportsman who participated in shooting sports at a high level was attempting to return to his previous shooting performance. This case report shows how sports vision and low vision rehabilitation techniques can improve the visual function of a competitive shooter. Optometry 2008;79:235-240
Case report A retired 67-year-old white man was referred by a local optometrist to a neuro-ophthalmologist with a suspicious finding of disc pallor and a restriction to the visual field. The differential diagnosis included glaucoma or some other type of optic neuropathy. At the time of referral, the patient had
Corresponding author: Richard Jamara, O.D., The New England College of Optometry, 424 Beacon Street, Boston, Massachusetts 02115. (For shooting vision inquiries, contact Walter Potaznick, O.D., at the same address; e-mail: [email protected].) E-mail: [email protected]
best-corrected distance acuity in the right eye (O.D.) of ⫹2.00 ⫺.50 ⫻ 25 20/20 ⫺ 2 and in the left eye (O.S.) of ⫹2.25 ⫺ 1.00 ⫻ 180 20/25 ⫺ 2. He had narrow angles, dry eyes, cataracts, and symptoms of poor contrast and glare. He also had vertical diplopia that had been corrected with a total of 5 prism diopters (D) (O.D. 2.5 base down and O.S. 2.5 base up) in his prescription. His motility was full, and the Amsler grid showed the O.D. missing lines inferiorly and metamorphopsic, and the O.S. missing lines superiorly and metamorphopsis. The visual fields showed a bilateral superior altitudinal hemianopia in both eyes with an arcuate inferior field defect in his shooting, dominant right eye (see Figure 1). His medical history included angina for 20 years,
1529-1839/08/$ -see front matter © 2008 American Optometric Association. All rights reserved. doi:10.1016/j.optm.2007.06.014
236
Optometry, Vol 79, No 5, May 2008
Figure 1
Visual field defects for each eye of the patient.
a quadruple coronary artery bypass graft 4 years previously, cerebrovascular accident 15 years previously, and non– insulin-dependent diabetes mellitus for 3 years. The neuroophthalmologist rendered a diagnosis of suspected bilateral, sequential nonarteritic anterior ischemic optic neuropathies and referred the patient for sports vision and vision rehabilitation evaluations. The patient reported that he had been a nationally ranked pistol, rifle, and shotgun (trap) competitor. His goals included returning to competing as a target pistol shooter and target and hunting rifle shooter and participating in trap-style shotgun sports. An overview of the type of shooting tasks listed with the visual requirements and our patient’s limitations are shown in Table 1 for target pistol, rifle marksman, rifle hunting, and trap shotgun shooting. These tasks were analyzed relative to his visual function and visual fields, and separate solutions were designed for his pistol and rifle shooting needs. The pistol shooting optics (Figure 2) and rifle shoot-
Table 1
ing optics (Figure 3) detail the visual function demands of the shooting activity. (More information about various types of firearms can be found at the USA Competitive Team Web site at http://www.usashooting.org/index.php.) The rehabilitation care included spectacles prescribed for a focal point aligned with the front target sight of his gun and the use of a full eye patch over his left eye to relieve the diplopia during shooting tasks. (However, to improve his function for activities of daily living he wore prism eyeglasses to eliminate his diplopia.)
Shooting tasks solutions For his pistol shooting, a ⫹1.25 D add was prescribed over the right eye to clear the front pistol sight in a single-vision lens. Included in the optical correction was a 35% yellow tint. Because of his head posture, prism lenses were not possible; therefore, full patching of the left eye was used to
Overview of shooting requirements and vision impairment
Task
Visual requirements
Treatments
Patient limitations
Pistol (Figure 4)
Maximum discernable BVA 20/25 up to 20/50 Largest field
Blur of front sight and vertical diplopia Arcuate field loss
Rifle (Figure 5)
Maximum discernable BVA 20/25 Largest field
Presbyopic correction for intermediate distance and patch of nondominant eye Field alignment with target using head, arm, and body position Best distance correction
Shotgun*
Binocularity Following moving target Time-limited target
Scope and low magnification Binocularity and best visual acuity at distance
Prescription needed for distance Field loss and telescope field of view Vertical diplopia Field loss superior Response time to following target
BVA ⫽ best visual acuity. * Information included for completeness but by mutual decision the authors decided not to pursue these treatments.
Jamara et al
Clinical Care
Figure 2 Pistol shooting optics. Eye to rear sight is 16 to 18 inches. Rear sight to front sight is 4 to 8 inches. Target is 25 feet.
avoid vertical diplopia. (His stance and head position were changed to best use his remaining visual field as shown in Figure 4.) The prescription for the right eye pistol shooting was ⫹3.25 ⫺ 0.50 ⫻ 25 (this is the single vision lens of his refraction plus the pistol sight add of ⫹1.25) with the yellow 35% for outdoor and bright indoor shooting. Using this optimal refractive correction for the dominant eye for the front sight post was helpful in minimizing the loss of definition caused by the reduced contrast sensitivity of optic nerve disease. An alternate therapy to assist this patient in reaching his goal would have been to utilize a Red Dot sight system, which would rely on the patient’s excellent distance vision. The Red Dot sight system uses a laser technology to place a laser beam image in alignment with the pistol and does not require the use of a pistol sight. However, the patient was not willing to change his class of competition as required to use this type of technology. For the patient’s rifle shooting, the use of a low-power, good-quality telescope sight, as seen in Figure 5, was found to increase his usable field of view and his performance in dim illumination. Because the Keplerian/terrestrial telescope has a smaller “floating” exit pupil that is harder for someone with field loss to locate, the lower power telescope provides a larger size exit pupil. The higher quality telescopes have multicoated surfaces to maximize the light transmission, decrease the reflective light loss, and reduce chromatic aberrations. Telescopic magnification was determined by an analysis of the visual task and the visual environment. The strategy is to provide the lowest power necessary to sight the target, which maximizes the field of view. This is based on the inverse relationship between magnification and field of view. In one survey, this strategy has shown moderate success for low vision patients and telescope use.1 Because the very long distance ranges typical for hunters in the western United States are not as common in the eastern states, using a good-quality, lowpowered, manual zoomed telescope (e.g., 1-4⫻) would be sufficient for this patient. The low-power telescope results in the largest exit pupil for ease of field location with maximum eye relief. Eye relief is the maximum distance from the rear of the scope to the eye itself, which allows a
237 full unvignetted view of the target. The longer the eye relief, the more comfortable the head position of the shooter and the lower the likelihood of being hit by the scope during high-power rifle recoil. The patient was educated to sight in his rifle telescope at all power settings and to set the scope at the power most appropriate for his hunting stand or target setup. He was advised to use the low power for the short range or dense woods shooting and the high power for the moderate range shooting. After rehabilitation of body and head positions along with optical devices, the patient achieved a score of 289 out of 300 during his first qualifying pistol shoot. This score was just 6 points below his performance before the onset of vision impairment. He also reported satisfactory performance on the rifle target range. To ensure safety while hunting, the patient planned to be accompanied by a normally sighted friend. For his shotgun shooting, the patient’s field loss was too limiting for the task, and he would be unable to follow the trajectory of the clay target for trap shooting after it reached a certain height. Also, the testing for trap shooting could not be done in the office, so no further testing for trap shooting was performed. The patient was satisfied with the solutions for his chief complaint for improving his pistol and rifle shooting.
Discussion According to the National Sporting Goods Association Web site,2 in the United States in 2006 there were 17.8 million hunters and 17.1 million target shooters. When these sportsmen suffer significant visual loss it can have a devastating effect on their participation in the shooting sports. According to the National Rifle Association (NRA), there are no reliable data sources on the number of target shooters with visual impairment. However, as the population ages, and we have more people with vision impairment, there will be an increase in people with vision impairment who enjoy shooting sports. Blindness or low vision affects approximately 1 in 28 Americans older than age 40.3
Figure 3 Rifle shooting optics. Eye to rear sight is 4 to 6 inches. Rear sight to front sight is 22 to 26 inches. Target is 50 feet to 100 yards.
238
Optometry, Vol 79, No 5, May 2008
Figure 4 Photograph of red front sight for adaptive solution within the superimposed image of the patient’s visual field. The patient’s field loss is greater than the picture shows, but to demonstrate the surrounding environment to the reader the area outside the field loss was left visible. Note slightly blurred rear sight and target.
The patient presented with visual fields that were consistent with a bilateral, sequential nonarteritic anterior ischemic optic neuropathy (NAION). The right eye has extensive, superior-more-than-inferior arcuate losses, whereas the left eye has a classic superior altitudinal defect. The condition of NAION is the most common cause of acute optic neuropathy in persons older than the age of 50 years. Risk factors for NAION include age and small cup-to-disc ratio.4 Systemic diseases such as diabetes and hypertension increase risk. The incidence of NAION is estimated at 2.3 to 10.2 per
Figure 5
100,0005 with 1,500 to 6,000 new cases in the United States per year.6 Vision loss is sudden and can progress. The visual field defect is most often altitudinal but can manifest as an arcuate defect or a central scotoma. The cause is occlusion of the short posterior ciliary arteries. New treatments for NAION are being investigated.7-9 No treatments were recommended for this patient by the consulting neuro-ophthalmologist. The visual skills for shooting have specific requirements for central vision and visual fields. Sports vision performance has been identified as a special interest of
Rifle shooting telescopic sights and target view using low-power telescope and full-distance correction. (Rifle tilted 90° to facilitate photography.)
Jamara et al
Clinical Care
the Sports Vision Section of the American Optometric Association. This patient’s decreased contrast sensitivity, loss of visual field, and vertical deviation significantly hindered his ability to sight through his telescope. Fitting the ⫹1.25 presbyopic (intermediate) add prescription for the patient’s dominant shooting eye was required. The low-power telescope and yellow filter were also used to improve performance. In 1988, Carkeet et al.10 examined the effects of target defocus using plus lenses on the accuracy of presbyopic and nonpresbyopic pistol shooters. The results showed the best shot groupings (how closely the impact points group) resulted from using adds of ⫹0.50 to ⫹0.75 over the distance prescriptions at the distance of the front sights. In 1995, Ishigaki et al.11 developed a laboratory setup that showed that experienced nonpresbyopic pistol shooters focused on the front sight, and they recommended correction to that point. The add selection in this case was guided by work from Gregg,12 suggesting that optimal visual performance is attained when using the lowest power add that clears the front sight. Using the lowest power add results in a blurred distance acuity closer to 20/50 that is well tolerated by shooters. The nonshooting eye in the normally sighted shooter would be corrected for distance, so a clear view of the target could be obtained for confirmation and recognition, but for our shooter the full patch was used to avoid diplopia. Most rifle hunters commonly use a telescopic sight in the range of 3 to 9 (zoom) times magnification. In this case, a zoom telescopic sight of 1 to 4 times magnification was suggested. In an actual hunting situation, this patient would attain optimal visual functioning by using the higher range of 4 times magnification to sight on his target, then decreasing the magnification to 1 to 1.5 times magnification for shooting. The selection of the lower-powered telescopic sight would maximize the hunter’s field of view, which is inversely proportional to the power of the scope. Rifle telescopic sights, like most multilens optical devices, have an eye relief factor based on the number of optical elements and the quality of the lens coatings. Eye relief is determined by how far from the telescopic sight you can view a nonvignette image in the scope. With a longer eye relief distance, the hunter is less likely to be hit by the scope after the rifle’s recoil. The hunter will also experience a more comfortable head and eye placement. This occurs as a result of the best total body position given the length and height of the stock relative to the position of the scope, the length of the shooter’s arm, and shoulder-to-eye measurement. The less the patient has to tilt the head, bend the neck, or stretch the arms, the more comfortable the shooter. The loss of target tracking of the clay target for the trap shooting after NAION with field loss and stroke with diplopia were not reversed with expanding or vertical prism for our patient. However, prism treatment for reduction of diplopia and increased peripheral awareness13,14 should be tried for patients with goals for skills of daily living including improved mobility. Optometric care for the normally sighted presbyopic pistol shooter would include providing excellent distance acuity, fitting appropriate protective eyewear, and using
239 specially designed eyewear. The presbyopic pistol shooter can also use an aperture that is a pinhole device of 1 mm to 2 mm positioned over the dominant sighting eye on the spectacles, which sharpens the front sight and improves depth of focus. Selection of eye dominance is a key step in training for competitive shooting. Also important is determining whether the physiological diplopia at the target plane that results from focusing on the front sight can be ignored or if the nonsighting eye should be occluded. The prescribing of the minimum add to clear the front sight for pistol shooters has been the standard management protocol.12,15,16 Several different options are available for people with disabilities who wish to enjoy shooting hobbies. The NRA has disabled shooting programs for people with disabilities as does the Paralyzed Veterans Association, which has a similar type of program called Trapshoot Circuit.17
Conclusions This case report shows how a combination of sports vision and visual rehabilitation techniques can improve the function of a competitive shooter with significant visual field loss and diplopia. With careful analysis of the visual impairment, the visual demands and safety18 issues for most of the shooting sports can be addressed successfully. As a result, avid sportsmen and women do not have to give up their lifelong passion for the shooting sports after significant visual impairment.
Acknowledgments The authors thank Dr. Elizabeth Hoppe, Catherine Berce, and Marek Jacisin.
References 1. Lowe JB, Rubinstein MP. Distance telescope: a survey of user success. Optom Vis Sci 2000;77(5):260-9. 2. NSGA. Available at: http://nsga.org/public/pages/index.cfm?pageid⫽ 149. National Sporting Goods Association, 2006. Last accessed March 27, 2008. 3. Congdon N, O’Colmain B, Klaver C, et al. Causes and prevalence of visual impairment among adults in the United States. Arch Ophthalmol 2004;122(4):477-85. 4. Jonas J, Xu L. Optic disc morphology in eyes after nonarteritic anterior ischemic optic neuropathy. Invest Ophthalmol Vis Sci 1993;34:2260-5. 5. Levin LA, Arnold AC. Neuro-ophthalmology. The practical guide. New York: Thieme Medical Publishers, 2005:194-97. 6. Dickersin K, Manhiemer E, Li T. Surgery for nonarteritic anterior ischemic optic neuropathy (Review). Cochrane Data Base of Systemic Reviews 2006;(1):1-10. 7. Fujikado T, Morimoto T, Matsushita K, et al. Effect of transcorneal electrical stimulation in patients with nonarteritic ischemic optic neuropathy or traumatic optic neuropathy. Jpn J Ophthalmol 2006; 50(3):266-73.
240 8. Jonas J, Spandau U, Harder B, et al. Intravitreal triamcinolone acetonide for treatment of acute nonarteritic anterior ischemic optic neuropathy. Graefe’s Arch Clin Ex Ophthalmol 2007;245:749-50. 9. Ramunni A, Giancipoli G, Guerriero S, et al. LDL-apheresis accelerates the recovery of nonarteritic acute anterior ischemic optic neuropathy. Therapeutic Apheresis and Dialysis 2005;9(1):53-8. 10. Carkeet A, Chan P, Brown B. Vision in competitive pistol shooters: effects of distance defocus on performance. clinical and experimental optometry. 1988;71(2):60-5. 11. Ishigaki H, Edagawa H, Miyao M. On the focal distance of the eye during sighting in pistol shooting. Percept Mot Skills 1995;81(1):191-4. 12. Gregg J. The sportsman’s eye. New York: Winchester Press, 1971:134-9.
Optometry, Vol 79, No 5, May 2008 13. Cohen JM. An overview of enhancement techniques for peripheral field loss. J Am Optom Assoc 1993;64(1):60-70. 14. Leigh R, Zee D. The neurology of eye movements. New York: Oxford University Press, 2006:581-3. 15. Gregg J. How to prescribe for hunters and marksmen. J Am Optom Assoc 1980;51(7):675-81. 16. Breedlove HW. Prescribing for marksmen and hunters. Optometry Clinics 1993;3:77-90. 17. Paralyzed Veterans of America, 2008. Available at: http://www.pva.org/ site/PageServer?pagename⫽sports_shoot. Last accessed March 27, 2008. 18. Federal Aid Project W-1045. Texas Hunting Accidents Analysis. 2004.
Low vision rehabilitation for a target-shooting marksman with visual field loss and diplopia Richard Jamara, O.D.,a,b Walter Potaznick, O.D.,a and Ippolit Matjucha, M.D.c a
New England College of Optometry and bSouth Boston Community Health Center, Boston, Massachusetts; and cLahey Clinic, Peabody, Massachusetts. KEYWORDS Visual field; Nonarteritic anterior ischemic optic neuropathy; Shooting sports; Low vision rehabilitation
Abstract BACKGROUND: In the United States in 2006, there were 17.8 million hunters and 17.1 million target shooters. When these sportsmen suffer significant visual loss, it can have a devastating effect on their participation in the shooting sports. According to the National Rifle Association, there are no reliable data sources on the number of target shooters with visual impairment. This case report describes a retired, nationally ranked, competitive target shooter who suffered bilateral visual field loss secondary to nonarteritic anterior ischemic optic neuropathy and diplopia secondary to cerebral vascular accident. CASE REPORT: A retired 67-year-old white man was referred by a local optometrist to a neuroophthalmologist with a suspicious finding of disc pallor and a restriction of the visual field. Examination revealed right hypertropia and visual field defects: binocular superior altitudinal losses and inferior arcuate loss in his dominant, right eye. He had best-corrected distance acuity of 20/20 ⫺ 2 in the right eye and 20/25 ⫺ 2 in the left eye. Because of this, he received several adaptive rehabilitation devices to help him regain his shooting performance. These included a single-vision add for the pistol sight, yellow tint, low-power telescope, and patching. In this report, the fundamentals of eye care for competitive shooting are described with an emphasis on providing the best acuity for presbyopic patient prescriptions at nonstandard distances and the avoidance of diplopia. CONCLUSION: A visually impaired sportsman who participated in shooting sports at a high level was attempting to return to his previous shooting performance. This case report shows how sports vision and low vision rehabilitation techniques can improve the visual function of a competitive shooter. Optometry 2008;79:235-240
Case report A retired 67-year-old white man was referred by a local optometrist to a neuro-ophthalmologist with a suspicious finding of disc pallor and a restriction to the visual field. The differential diagnosis included glaucoma or some other type of optic neuropathy. At the time of referral, the patient had
Corresponding author: Richard Jamara, O.D., The New England College of Optometry, 424 Beacon Street, Boston, Massachusetts 02115. (For shooting vision inquiries, contact Walter Potaznick, O.D., at the same address; e-mail: [email protected].) E-mail: [email protected]
best-corrected distance acuity in the right eye (O.D.) of ⫹2.00 ⫺.50 ⫻ 25 20/20 ⫺ 2 and in the left eye (O.S.) of ⫹2.25 ⫺ 1.00 ⫻ 180 20/25 ⫺ 2. He had narrow angles, dry eyes, cataracts, and symptoms of poor contrast and glare. He also had vertical diplopia that had been corrected with a total of 5 prism diopters (D) (O.D. 2.5 base down and O.S. 2.5 base up) in his prescription. His motility was full, and the Amsler grid showed the O.D. missing lines inferiorly and metamorphopsic, and the O.S. missing lines superiorly and metamorphopsis. The visual fields showed a bilateral superior altitudinal hemianopia in both eyes with an arcuate inferior field defect in his shooting, dominant right eye (see Figure 1). His medical history included angina for 20 years,
1529-1839/08/$ -see front matter © 2008 American Optometric Association. All rights reserved. doi:10.1016/j.optm.2007.06.014
236
Optometry, Vol 79, No 5, May 2008
Figure 1
Visual field defects for each eye of the patient.
a quadruple coronary artery bypass graft 4 years previously, cerebrovascular accident 15 years previously, and non– insulin-dependent diabetes mellitus for 3 years. The neuroophthalmologist rendered a diagnosis of suspected bilateral, sequential nonarteritic anterior ischemic optic neuropathies and referred the patient for sports vision and vision rehabilitation evaluations. The patient reported that he had been a nationally ranked pistol, rifle, and shotgun (trap) competitor. His goals included returning to competing as a target pistol shooter and target and hunting rifle shooter and participating in trap-style shotgun sports. An overview of the type of shooting tasks listed with the visual requirements and our patient’s limitations are shown in Table 1 for target pistol, rifle marksman, rifle hunting, and trap shotgun shooting. These tasks were analyzed relative to his visual function and visual fields, and separate solutions were designed for his pistol and rifle shooting needs. The pistol shooting optics (Figure 2) and rifle shoot-
Table 1
ing optics (Figure 3) detail the visual function demands of the shooting activity. (More information about various types of firearms can be found at the USA Competitive Team Web site at http://www.usashooting.org/index.php.) The rehabilitation care included spectacles prescribed for a focal point aligned with the front target sight of his gun and the use of a full eye patch over his left eye to relieve the diplopia during shooting tasks. (However, to improve his function for activities of daily living he wore prism eyeglasses to eliminate his diplopia.)
Shooting tasks solutions For his pistol shooting, a ⫹1.25 D add was prescribed over the right eye to clear the front pistol sight in a single-vision lens. Included in the optical correction was a 35% yellow tint. Because of his head posture, prism lenses were not possible; therefore, full patching of the left eye was used to
Overview of shooting requirements and vision impairment
Task
Visual requirements
Treatments
Patient limitations
Pistol (Figure 4)
Maximum discernable BVA 20/25 up to 20/50 Largest field
Blur of front sight and vertical diplopia Arcuate field loss
Rifle (Figure 5)
Maximum discernable BVA 20/25 Largest field
Presbyopic correction for intermediate distance and patch of nondominant eye Field alignment with target using head, arm, and body position Best distance correction
Shotgun*
Binocularity Following moving target Time-limited target
Scope and low magnification Binocularity and best visual acuity at distance
Prescription needed for distance Field loss and telescope field of view Vertical diplopia Field loss superior Response time to following target
BVA ⫽ best visual acuity. * Information included for completeness but by mutual decision the authors decided not to pursue these treatments.
Jamara et al
Clinical Care
Figure 2 Pistol shooting optics. Eye to rear sight is 16 to 18 inches. Rear sight to front sight is 4 to 8 inches. Target is 25 feet.
avoid vertical diplopia. (His stance and head position were changed to best use his remaining visual field as shown in Figure 4.) The prescription for the right eye pistol shooting was ⫹3.25 ⫺ 0.50 ⫻ 25 (this is the single vision lens of his refraction plus the pistol sight add of ⫹1.25) with the yellow 35% for outdoor and bright indoor shooting. Using this optimal refractive correction for the dominant eye for the front sight post was helpful in minimizing the loss of definition caused by the reduced contrast sensitivity of optic nerve disease. An alternate therapy to assist this patient in reaching his goal would have been to utilize a Red Dot sight system, which would rely on the patient’s excellent distance vision. The Red Dot sight system uses a laser technology to place a laser beam image in alignment with the pistol and does not require the use of a pistol sight. However, the patient was not willing to change his class of competition as required to use this type of technology. For the patient’s rifle shooting, the use of a low-power, good-quality telescope sight, as seen in Figure 5, was found to increase his usable field of view and his performance in dim illumination. Because the Keplerian/terrestrial telescope has a smaller “floating” exit pupil that is harder for someone with field loss to locate, the lower power telescope provides a larger size exit pupil. The higher quality telescopes have multicoated surfaces to maximize the light transmission, decrease the reflective light loss, and reduce chromatic aberrations. Telescopic magnification was determined by an analysis of the visual task and the visual environment. The strategy is to provide the lowest power necessary to sight the target, which maximizes the field of view. This is based on the inverse relationship between magnification and field of view. In one survey, this strategy has shown moderate success for low vision patients and telescope use.1 Because the very long distance ranges typical for hunters in the western United States are not as common in the eastern states, using a good-quality, lowpowered, manual zoomed telescope (e.g., 1-4⫻) would be sufficient for this patient. The low-power telescope results in the largest exit pupil for ease of field location with maximum eye relief. Eye relief is the maximum distance from the rear of the scope to the eye itself, which allows a
237 full unvignetted view of the target. The longer the eye relief, the more comfortable the head position of the shooter and the lower the likelihood of being hit by the scope during high-power rifle recoil. The patient was educated to sight in his rifle telescope at all power settings and to set the scope at the power most appropriate for his hunting stand or target setup. He was advised to use the low power for the short range or dense woods shooting and the high power for the moderate range shooting. After rehabilitation of body and head positions along with optical devices, the patient achieved a score of 289 out of 300 during his first qualifying pistol shoot. This score was just 6 points below his performance before the onset of vision impairment. He also reported satisfactory performance on the rifle target range. To ensure safety while hunting, the patient planned to be accompanied by a normally sighted friend. For his shotgun shooting, the patient’s field loss was too limiting for the task, and he would be unable to follow the trajectory of the clay target for trap shooting after it reached a certain height. Also, the testing for trap shooting could not be done in the office, so no further testing for trap shooting was performed. The patient was satisfied with the solutions for his chief complaint for improving his pistol and rifle shooting.
Discussion According to the National Sporting Goods Association Web site,2 in the United States in 2006 there were 17.8 million hunters and 17.1 million target shooters. When these sportsmen suffer significant visual loss it can have a devastating effect on their participation in the shooting sports. According to the National Rifle Association (NRA), there are no reliable data sources on the number of target shooters with visual impairment. However, as the population ages, and we have more people with vision impairment, there will be an increase in people with vision impairment who enjoy shooting sports. Blindness or low vision affects approximately 1 in 28 Americans older than age 40.3
Figure 3 Rifle shooting optics. Eye to rear sight is 4 to 6 inches. Rear sight to front sight is 22 to 26 inches. Target is 50 feet to 100 yards.
238
Optometry, Vol 79, No 5, May 2008
Figure 4 Photograph of red front sight for adaptive solution within the superimposed image of the patient’s visual field. The patient’s field loss is greater than the picture shows, but to demonstrate the surrounding environment to the reader the area outside the field loss was left visible. Note slightly blurred rear sight and target.
The patient presented with visual fields that were consistent with a bilateral, sequential nonarteritic anterior ischemic optic neuropathy (NAION). The right eye has extensive, superior-more-than-inferior arcuate losses, whereas the left eye has a classic superior altitudinal defect. The condition of NAION is the most common cause of acute optic neuropathy in persons older than the age of 50 years. Risk factors for NAION include age and small cup-to-disc ratio.4 Systemic diseases such as diabetes and hypertension increase risk. The incidence of NAION is estimated at 2.3 to 10.2 per
Figure 5
100,0005 with 1,500 to 6,000 new cases in the United States per year.6 Vision loss is sudden and can progress. The visual field defect is most often altitudinal but can manifest as an arcuate defect or a central scotoma. The cause is occlusion of the short posterior ciliary arteries. New treatments for NAION are being investigated.7-9 No treatments were recommended for this patient by the consulting neuro-ophthalmologist. The visual skills for shooting have specific requirements for central vision and visual fields. Sports vision performance has been identified as a special interest of
Rifle shooting telescopic sights and target view using low-power telescope and full-distance correction. (Rifle tilted 90° to facilitate photography.)
Jamara et al
Clinical Care
the Sports Vision Section of the American Optometric Association. This patient’s decreased contrast sensitivity, loss of visual field, and vertical deviation significantly hindered his ability to sight through his telescope. Fitting the ⫹1.25 presbyopic (intermediate) add prescription for the patient’s dominant shooting eye was required. The low-power telescope and yellow filter were also used to improve performance. In 1988, Carkeet et al.10 examined the effects of target defocus using plus lenses on the accuracy of presbyopic and nonpresbyopic pistol shooters. The results showed the best shot groupings (how closely the impact points group) resulted from using adds of ⫹0.50 to ⫹0.75 over the distance prescriptions at the distance of the front sights. In 1995, Ishigaki et al.11 developed a laboratory setup that showed that experienced nonpresbyopic pistol shooters focused on the front sight, and they recommended correction to that point. The add selection in this case was guided by work from Gregg,12 suggesting that optimal visual performance is attained when using the lowest power add that clears the front sight. Using the lowest power add results in a blurred distance acuity closer to 20/50 that is well tolerated by shooters. The nonshooting eye in the normally sighted shooter would be corrected for distance, so a clear view of the target could be obtained for confirmation and recognition, but for our shooter the full patch was used to avoid diplopia. Most rifle hunters commonly use a telescopic sight in the range of 3 to 9 (zoom) times magnification. In this case, a zoom telescopic sight of 1 to 4 times magnification was suggested. In an actual hunting situation, this patient would attain optimal visual functioning by using the higher range of 4 times magnification to sight on his target, then decreasing the magnification to 1 to 1.5 times magnification for shooting. The selection of the lower-powered telescopic sight would maximize the hunter’s field of view, which is inversely proportional to the power of the scope. Rifle telescopic sights, like most multilens optical devices, have an eye relief factor based on the number of optical elements and the quality of the lens coatings. Eye relief is determined by how far from the telescopic sight you can view a nonvignette image in the scope. With a longer eye relief distance, the hunter is less likely to be hit by the scope after the rifle’s recoil. The hunter will also experience a more comfortable head and eye placement. This occurs as a result of the best total body position given the length and height of the stock relative to the position of the scope, the length of the shooter’s arm, and shoulder-to-eye measurement. The less the patient has to tilt the head, bend the neck, or stretch the arms, the more comfortable the shooter. The loss of target tracking of the clay target for the trap shooting after NAION with field loss and stroke with diplopia were not reversed with expanding or vertical prism for our patient. However, prism treatment for reduction of diplopia and increased peripheral awareness13,14 should be tried for patients with goals for skills of daily living including improved mobility. Optometric care for the normally sighted presbyopic pistol shooter would include providing excellent distance acuity, fitting appropriate protective eyewear, and using
239 specially designed eyewear. The presbyopic pistol shooter can also use an aperture that is a pinhole device of 1 mm to 2 mm positioned over the dominant sighting eye on the spectacles, which sharpens the front sight and improves depth of focus. Selection of eye dominance is a key step in training for competitive shooting. Also important is determining whether the physiological diplopia at the target plane that results from focusing on the front sight can be ignored or if the nonsighting eye should be occluded. The prescribing of the minimum add to clear the front sight for pistol shooters has been the standard management protocol.12,15,16 Several different options are available for people with disabilities who wish to enjoy shooting hobbies. The NRA has disabled shooting programs for people with disabilities as does the Paralyzed Veterans Association, which has a similar type of program called Trapshoot Circuit.17
Conclusions This case report shows how a combination of sports vision and visual rehabilitation techniques can improve the function of a competitive shooter with significant visual field loss and diplopia. With careful analysis of the visual impairment, the visual demands and safety18 issues for most of the shooting sports can be addressed successfully. As a result, avid sportsmen and women do not have to give up their lifelong passion for the shooting sports after significant visual impairment.
Acknowledgments The authors thank Dr. Elizabeth Hoppe, Catherine Berce, and Marek Jacisin.
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