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CHAPTER 3 HOW TO PERFORM PERIMETRY YOU CAN TRUST

INTRODUCTION

PERIMETRY – A SUBJECTIVE TEST

Perimetry is an elaborate test that depends, to a great In view of the relatively high occurrence of untrust- extent, on subjective factors such as the patient’s cooper- ™‘”–Š›˜‹•—ƒŽϐ‹‡Ž†•ǡ‹–‹•‡š–”‡‡Ž›‹’‘”–ƒ––‘ƒ‡ ation and comfort, as well as on using the correct patient sure that the time invested in perimetry is well spent, information and set-up. Due to this subjective compo- because poorly performed perimetric tests have hardly ‡–ǡ—–”—•–™‘”–Š›˜‹•—ƒŽϐ‹‡Ž†–‡•–•ƒ”‡ ‘‘ǤŠ‡ ƒ›†‹ƒ‰‘•–‹ ˜ƒŽ—‡Ǥ ––Š‡”‡ˆ‘”‡’ƒ›•–‘–ƒ‡–Š‡–‹‡ extent of untrustworthy results largely depends on how and care necessary to obtain trustworthy results by fol- well perimetry is performed in clinical practice and has lowing certain rules to avoid the most common pitfalls. been reported to range from 3% to 29% of all visual ϐ‹‡Ž†–‡•–•’‡”ˆ‘”‡†Ǥͽ-΁ 26 Chapter 3 | How to perform perimetry you can trust

PERIMETRY – NEED FOR A TEAM APPROACH

Š”‡‡‡›’Žƒ›‡”•ƒ”‡‹˜‘Ž˜‡†‹’‡”‹‡–”›ǣ–Š‡’ƒ–‹‡–ǡ FIG 3-1 shows how each member of the team can contrib- –Š‡‡šƒ‹‡”ƒ†–Š‡‡›‡†‘ –‘”ǤŽŽ–Š”‡‡•Š‘—Ž†™‘” ute. When this approach is successfully implemented, collaboratively to obtain optimal perimetric test results. perimetry can be performed in a positive atmosphere.

PERIMETRY REQUIRES A TEAM APPROACH

st te e E th xp f e r r PATIENT e A o du s s e ce s k c ro n p st P n q a g te ro e u t n e P v e e r i h r i d s o t t o d s v e f t p e m t y i o io t r u tr P d c m o o e r e r n i e f b t o l r m h v e a s h a ri r e a e t e o id n p s e u r b h p e c t h n g i r t o f o n e i o h s t i o u s a e t o u z w s u p r t k i d e a r e t e u s e e c g t t u t r c a n e a h v a q a m t h r v t e i i i s o p k r o t i e t s o o n b o e n m

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EXAMINER P ro g DOCTOR vid in e a rain A dequate t P llo to ro w n me v fo ecessary ti ide cus try n re on perime tio cog ecia nition and appr

l Perf wel orm perimetric test M Acc data ce ak uracy in entering an e no rform tes about patient pe

FIGURE 3-1 In perimetry, it is essential that doctors, examiners and patients have a positive attitude towards perimetry and that each member of the team contributes to achieving optimum results.

THE IMPORTANT ROLE OF THE DOCTOR

THE DOCTOR-PATIENT RELATIONSHIP

Patients who understand why perimetry is needed and and trust they establish with their patients, doctors are ‹–•‹’‘”–ƒ ‡–‘–Š‡‹”‡›‡ ƒ”‡ƒ”‡Ž‹‡Ž›–‘„‡‘”‡‘–‹- in the best position to convey the importance of perimetry vated to undergo a perimetric test. Due to the relationship to their patients. Introduction 27

THE DOCTOR-EXAMINER RELATIONSHIP

Eye doctors should also clearly convey the importance of this goal, the doctor must provide training and give feed- ’‡”‹‡–”› –‘ –Š‡ ˜‹•—ƒŽ ϐ‹‡Ž† ‡šƒ‹‡”• ™Š‘ ™‘” ™‹–Š „ƒ –‘–Š‡‡šƒ‹‡”•Ǥ –‹•ƒŽ•‘ ”— ‹ƒŽˆ‘”–Š‡†‘ –‘”–‘ them in the clinic. For example, the doctor is responsible Šƒ˜‡”‡ƒ•‘ƒ„Ž‡‡š’‡ –ƒ–‹‘•‹–‡”•‘ˆ–Š‡–‹‡”‡“—‹”‡† ˆ‘”‡•—”‹‰–Šƒ––Š‡˜‹•—ƒŽϐ‹‡Ž†‡šƒ‹‡”•—†‡”•–ƒ† to perform trustworthy perimetric tests. Doctors should the importance of trustworthy perimetric results to the ƒ””ƒ‰‡ˆ‘”–Š‡‹”˜‹•—ƒŽϐ‹‡Ž†‡šƒ‹‡”•–‘„‡ƒ„Ž‡–‘†‡†‹- Ž‹‹ ƒŽ†‡ ‹•‹‘Ǧƒ‹‰’”‘ ‡••ǤŠ‡˜‹•—ƒŽϐ‹‡Ž†‡šƒ‹- ƒ–‡–‹‡‡š Ž—•‹˜‡Ž›–‘’‡”ˆ‘”‹‰’‡”‹‡–”‹ –‡•–•ǤŠ‹• ‡”••Š‘—Ž†‘™–Šƒ––Š‡†‘ –‘”Šƒ•ƒ‰‡—‹‡‹–‡”‡•–‹ ‡ƒ•–Šƒ––Š‡›•Š‘—Ž†„‡ˆ”‡‡‘ˆ‘–Š‡”–ƒ••–Šƒ–‹‰Š– „—‹Ž†‹‰–Š‡‹”’‡”‹‡–”‹ ‘™Ž‡†‰‡ƒ†•‹ŽŽ•Ǥ‘™ƒ”†• reduce the examiner’s focus on the patient.

THE IMPORTANT ROLE OF THE VISUAL FIELD EXAMINER

Š‡˜‹•—ƒŽϐ‹‡Ž†‡šƒ‹‡”‹•‹ƒ—‹“—‡’‘•‹–‹‘–‘Šƒ˜‡ setting up the perimeter, they also directly oversee the ƒ‹’ƒ –‘–Š‡“—ƒŽ‹–›‘ˆ–Š‡’‡”‹‡–”‹ ”‡•—Ž–•‹–™‘ patient during the test. ways. Not only are examiners responsible for correctly

ROLE IN CORRECTLY SETTING UP THE PERIMETER

Š‡˜‹•—ƒŽϐ‹‡Ž†‡šƒ‹‡”‹•”‡•’‘•‹„Ž‡ˆ‘”‡–‡”‹‰ in performing this aspect of perimetry can significantly –Š‡ ‘””‡ –’ƒ–‹‡–‹ˆ‘”ƒ–‹‘‹–Š‡’‡”‹‡–‡”ǤŠ‹•‹• reduce the number of untrustworthy tests and inter- crucial because this information has a direct impact on ’”‡–ƒ–‹‘ ‡””‘”•Ǥ Š‡ ‡šƒ‹‡” ‹• ƒŽ•‘ ”‡•’‘•‹„Ž‡ ˆ‘” whether the results of the test can be trusted. Diligence ‡•—”‹‰–Šƒ–ƒƒ†‡“—ƒ–‡”‡ˆ”ƒ –‹˜‡Ž‡•‹•—•‡†Ǥ

THE EXAMINER-PATIENT RELATIONSHIP

 ”— ‹ƒŽ ”‘Ž‡ ‘ˆ –Š‡ ˜‹•—ƒŽ ϐ‹‡Ž† ‡šƒ‹‡” ‹• –‘ ‡•—”‡ patient. Additionally, the patient should be encouraged that the patients perform perimetry to the very best of –‘ ‘—‹ ƒ–‡–‘–Š‡‡šƒ‹‡”ƒ›†‹ˆϐ‹ —Ž–‹‡•‘”’”‘„- –Š‡‹” ƒ’ƒ ‹–›‡ƒ Š–‹‡–Š‡›–ƒ‡ƒ–‡•–Ǥ‘‰‹˜‡–Š‡‹”„‡•– lems encountered, and when a brief rest period would be performance, patients need to be comfortably positioned „‡‡ϐ‹ ‹ƒŽǤ ƒ––Š‡’‡”‹‡–‡”ǡ–Š‡›‡‡†–‘‘™™Šƒ–‹•‡š’‡ –‡†‘ˆ them, and they need to understand how to perform the Š‡”‡‹•‘”‡ǡŠ‘™‡˜‡”ǡ–‘–Š‡”‘Ž‡‘ˆƒ˜‹•—ƒŽϐ‹‡Ž†‡šƒ- test. A competent examiner will ensure that the patient ‹‡”Ǥ—–•–ƒ†‹‰‡šƒ‹‡”•™‹ŽŽŠƒ˜‡–ƒ‡’‡”‹‡–”‹  is not only correctly positioned, but also comfortable. tests themselves and will understand how the patient Similarly, a good examiner will convey what is expected ˆ‡‡Ž•†—”‹‰–Š‡–‡•–ǤŠ‹• ‘’ƒ••‹‘ƒ–‡ƒ’’”‘ƒ Š™‹ŽŽ of the patient and will give clear instructions on how to go a long way in ensuring patient cooperation and will ’‡”ˆ‘”–Š‡–‡•–ǤŠ‡‡šƒ‹‡” ƒƒŽ•‘’”‘˜‹†‡„”‹‡ˆ”‡•– allow the examiner to give genuine encouragement to the periods by pausing the test if this will be helpful to the patient when needed during the test. 28 Chapter 3 | How to perform perimetry you can trust

HOW TO PERFORM VISUAL FIELD TESTING

SETTING UP THE PERIMETER

Perimetry should be performed in a distraction-free ”‘‘ǡ‘’ƒ“—‡ —”–ƒ‹•ƒ”‘—†–Š‡’‡”‹‡–‡”ƒ†‡ƒ”—ˆˆ• environment, to enable the patient to concentrate on offer a cost-effective alternative. the perimetric test (FIG 3-2).Š‡”‘‘•Š‘—Ž†„‡“—‹‡–ǡ with no activity distracting the patient, and should be at Š‡’‡”‹‡–‡”‹•ƒ—–‘ƒ–‹ ƒŽŽ› ƒŽ‹„”ƒ–‡†‡ƒ Š–‹‡‹–‹• ƒ ‘ˆ‘”–ƒ„Ž‡”‘‘–‡’‡”ƒ–—”‡ǤŠ‡ —’‘Žƒ•Š‘—Ž†„‡ –—”‡†‘Ǥ –‹•‹’‘”–ƒ–ˆ‘”–Š‡ ƒŽ‹„”ƒ–‹‘–‘–ƒ‡’Žƒ ‡ ‡’– Ž‡ƒƒ†ˆ”‡‡‘ˆ†—•–ƒ†’ƒ”–‹ Ž‡•Ǥ††‹–‹‘ƒŽŽ›ǡ–Š‡ in the same lighting conditions as those used during peri- room should be dimly lit, to prevent stray light from in- ‡–”‹ –‡•–‹‰ǤƒŽ‹„”ƒ–‹‘ ƒ–ƒ‡—’–‘–™‘‹—–‡•ƒ† ϐŽ—‡ ‹‰–Š‡’‡”‹‡–”‹ ”‡•—Ž–Ǥ†‹Ž›ǦŽ‹–‡˜‹”‘‡– •Š‘—Ž†„‡’‡”ˆ‘”‡†’”‹‘”–‘–‡•–‹‰’ƒ–‹‡–•ǤŠ—•ǡ–Š‡ is essential when a cupola perimeter, such as the Octopus perimeter should be turned on prior to the patient visit. 900 is used, but is also helpful for non-cupola perimeters. Ideally, patient data (date of birth, refraction, etc.) are Ideally, perimetry should be performed in a room dedi- entered before the patient enters the room. If an electronic cated solely to this purpose. However, if the layout of the medical record system is in use, it will automatically pop- clinical practice does not offer a stand-alone perimetry ulate the information to the perimeter.

PERIMETER SET UP Light Heat Noise Cold

FIGURE 3-2 A perimeter should be set up in a distraction-free, dimly-lit environment. How to perform visual field testing 29

PLACING AN ADEQUATE TRIAL LENS

Š‡ –”‹ƒŽ Ž‡• ƒŽ —Žƒ–‘” ‹• Š‡Ž’ˆ—Ž ‹ †‡–‡”‹‹‰ –Š‡ than one trial lens is used, the spherical correction should ƒ†‡“—ƒ–‡•’Š‡”‹ ƒŽƒ† ›Ž‹†”‹ ƒŽ–”‹ƒŽŽ‡•‡•ǡ„ƒ•‡†‘ be placed closest to the patient’s eye. Special attention the patient’s current refraction and age. It is vital to en- should be given to the orientation of cylindrical lenses, sure that the patient’s refractive data is up-to-date and it which should be oriented in the angle of the astigmatism ‹•„‡•–’”ƒ –‹ ‡–‘†‡–‡”‹‡–Š‹•’”‹‘”–‘‡ƒ Š–‡•–ǤŠ‡ (FIG 3-3). correct trial lens should be put into the trial lens holder ’”‹‘” –‘ •‡ƒ–‹‰ –Š‡ ’ƒ–‹‡–Ǥ ”‹ƒŽ Ž‡•‡• ™‹–Š ƒ ƒ””‘™ ‘ ‘ϐ‹”–Šƒ–ƒ†‡“—ƒ–‡”‡ˆ”ƒ –‹‘‹•—•‡†ǡ–Š‡‡šƒ‹‡” metal rim should be used, to prevent the rim of the •Š‘—Ž†’‘•‹–‹‘–Š‡’ƒ–‹‡–ƒ†ƒ•™Š‡–Š‡”–Š‡ϐ‹šƒ–‹‘ –”‹ƒŽŽ‡•ˆ”‘„Ž‘ ‹‰–Š‡’ƒ–‹‡–ǯ•ϐ‹‡Ž†‘ˆ˜‹‡™Ǥ ˆ‘”‡ target is clearly visible.

PLACEMENT OF CYLINDRICAL TRIAL LENSES

30°

180° 0°

150° 30°

120° 60° 90°

FIGURE 3-3 Placement of a cylindrical lens for a patient with a cylindrical correction of 30°, seen from the examiner’s perspective.

INSTRUCTING THE PATIENT

Due to the subjective components involved in perimetry, 3-4ȌǤ – ƒ„‡Š‡Ž’ˆ—Žˆ‘”‡šƒ‹‡”•–‘–ƒ‡ƒ’‡”‹‡–”› careful patient instruction is fundamental to achieving test themselves, in order to gain a better understanding trustworthy results. Patients will be able to cooperate of what patients are experiencing. more effectively and produce more consistent results if they understand what is expected of them and why the –‹•ˆ—†ƒ‡–ƒŽ–‘‡•—”‡–Šƒ––Š‡’ƒ–‹‡–•‘™–Šƒ– test is being performed. they are not expected to see all stimuli and that some- –‹‡•‘•–‹—Ž‹ƒ”‡’”‡•‡–‡†ǤŠ‹•™‹ŽŽŠ‡Ž’–‘”‡†— ‡ Š‡˜‹•—ƒŽϐ‹‡Ž†‡šƒ‹‡”•Š‘—Ž†–Š‡”‡ˆ‘”‡–ƒ‡–Š‡–‹‡ some of the potential anxiety experienced by patients, to explain the aim of the test, what the patient should ex- ™Š‘•Š‘—Ž†ƒŽ•‘‘™–Šƒ––Š‡› ƒ’ƒ—•‡–Š‡–‡•–‹ˆ–Š‡› pect to see, and what the patient is expected to do (FIG ‡š’‡”‹‡ ‡ˆƒ–‹‰—‡‘”Šƒ˜‡“—‡•–‹‘•Ǥ 30 Chapter 3 | How to perform perimetry you can trust

STEP-BY-STEP PATIENT INSTRUCTIONS

1. Perimetry tests your central and peripheral vision.

2. Be relatively still once positioned.

3. Always look straight ahead at the fixation target. Do not look around the bowl for stimuli.

4. Press the response button whenever you see the stimulus. a. The stimulus is a flash of light. b. Only one stimulus is presented at a time. c. The stimulus might appear anywhere. d. Some stimuli are very bright, some are very dim, and sometimes no stimulus is presented. e. You are not expected to see all stimuli. f. Do not worry about making mistakes.

5. Blink regularly to avoid discomfort. a. Don’t worry about missing a point, the device does not measure while you blink.

6. If you feel uncomfortable or are getting tired a. Close your eye for a moment, the test will automatically stop. b. The test will resume once you open your eye.

7. If you have a question a. Keep the response button pressed; this will pause the test.

FIGURE 3-4 Proper instructions to the patient are essential for the patient to understand their task and consequently to perform perimetry well. The sequence of instructions listed in this Figure can be used. How to perform visual field testing 31

SETTING UP AND POSITIONING THE PATIENT

”—•–™‘”–Š› ƒ† ƒ —”ƒ–‡ ’‡”‹‡–”‹  ”‡•—Ž–• ƒ”‡ ‘”‡ tient is correctly positioned and that the non-tested eye Ž‹‡Ž› –‘ „‡ ‘„–ƒ‹‡† ™Š‡ –Š‡ ’ƒ–‹‡– ‹• ‘ˆ‘”–ƒ„Ž‡ ‹• ‘˜‡”‡†ǤŠ‡‘’–‹—™ƒ›•–‘‡•—”‡’ƒ–‹‡– ‘ˆ‘”– during the test. It is also important to ensure that the pa- and correct alignment will be discussed in this section.

CORRECT EYE PATCH POSITION

Before fully positioning the patient, the eye not being test- for the tested eye. If an adhesive eye patch is used, it is ed should be covered with an eye patch that allows the ‹’‘”–ƒ––‘ƒ‡•—”‡–Šƒ–‹–ƒ†Š‡”‡•™‡ŽŽƒŽŽƒ”‘—† ’ƒ–‹‡––‘„Ž‹ˆ”‡‡Ž› (FIG 3-5). If the eye patch is main- the eye. All eye patches should be translucent, to avoid tained in place with a cord, it is important to ensure that ƒ†ƒ’–ƒ–‹‘–‘–Š‡†ƒ”„›–Š‡—–‡•–‡†‡›‡ǡ™Š‹ Š™‘—Ž† –Š‡ ‘”††‘‡•‘–‘„•–”— ––Š‡’ƒ–‹‡–ǯ•ϐ‹‡Ž†‘ˆ˜‹‡™ ƒŽ–‡”–Š‡”‡•—Ž–•‘ˆ•—„•‡“—‡––‡•–‹‰‘ˆ–Šƒ–‡›‡Ǥ΂

EYE-PATCH POSITION

CORRECT INCORRECT Unobstructed view of test eye Cord obstructs view of test eye

FIGURE 3-5 An eye patch should cover the eye that is not being tested. It should be positioned so as to not obstruct the patient’s vision in the tested eye.

CORRECT PATIENT POSITION

Š‡’ƒ–‹‡–•Š‘—Ž†„‡•‡ƒ–‡†‹ƒ ‘ˆ‘”–ƒ„Ž‡’‘•‹–‹‘ patient is comfortable. Different Octopus models offer that can be easily maintained throughout the test. A †‹ˆˆ‡”‡– –›’‡• ‘ˆ ’‘•‹–‹‘‹‰ǣ –Š‡  –‘’—• ͻͲͲ ‘ˆˆ‡”• ƒ Š‡‹‰Š–Ǧƒ†Œ—•–ƒ„Ž‡ Šƒ‹”™‹–Šƒ„ƒ ”‡•–ƒ†ǡ‹ˆƒ˜ƒ‹Žƒ„Ž‡ǡ straight-upright patient position and the Octopus 600 ƒ””‡•–••Š‘—Ž†–Š‡”‡ˆ‘”‡„‡—•‡†ǤŠ‡’‡”‹‡–‡”•Š‘—Ž† offers a forward-leaning position. be placed on a height-adjustable table to ensure that the 32 Chapter 3 | How to perform perimetry you can trust

STRAIGHT-UPRIGHT POSITION

FIGURE 3-6 This drawing illustrates the correct straight-upright patient position recommended for the Octopus 900 and older Octopus models.

For the Octopus 900 and all older Octopus models, the pa- his or her chin on the chinrest and forehead on the head- –‹‡–•Š‘—Ž†•‹–ƒ• Ž‘•‡ƒ•’‘••‹„Ž‡–‘–Š‡†‡˜‹ ‡ǤŠ‡–Š‡ rest (FIG 3-6). It is important to ensure that the patient height of the table should be adjusted until the patient’s maintains direct contact with the device throughout ˆ‘”‡Š‡ƒ†–‘— Š‡•–Š‡Š‡ƒ†”‡•–ǤŠ‡’ƒ–‹‡–•Š‘—Ž†’Žƒ ‡ testing.

FORWARD-LEANING POSITION

1. PREPARATION 2. FINAL POSITION

Headrest 20cm/8 inches

FIGURE 3-7 This drawing illustrates the correct forward-leaning patient position recommended for the Octopus 600.

For the Octopus 600, the patient is positioned in a for- headrest, to allow enough space to lean forward. By ward-leaning and downward-gazing position (FIG 3-7). inclining from this position, the patient is automatically Š‡ ‘””‡ –’‘•‹–‹‘‹•‘„–ƒ‹‡†„›ϐ‹”•–•‡ƒ–‹‰–Š‡’ƒ- ’‘•‹–‹‘‡†ƒ––Š‡ ‘””‡ –Š‡‹‰Š–ǤŠ‡’ƒ–‹‡–ǯ•Š‡ƒ†Ž‡ƒ• tient in an upright position at a distance of approximately ‹ˆ—ŽŽ›‘–‘–Š‡Š‡ƒ†”‡•–ǡ’”‘˜‹†‹‰•–ƒ„Ž‡ϐ‹šƒ–‹‘. 20cm/8 inches, with the eyes at the upper level of the How to perform visual field testing 33

CORRECT EYE POSITION

Once the patient is correctly positioned in the device, it lens. However, the lens should not touch the eyelashes, is important to ensure that the eye is also correctly po- ƒŽŽ‘™‹‰–Š‡’ƒ–‹‡––‘„Ž‹ˆ”‡‡Ž›ƒ†ƒ˜‘‹†‹‰–Š‡Ž‡• sitioned. Overall, the eye should be well-aligned with the „‡‹‰•‡ƒ”‡†™‹–Šƒ‡Ǧ—’. ϐ‹šƒ–‹‘–ƒ”‰‡–ƒ†•Š‘—Ž†„‡”‡Žƒ–‹˜‡Ž› Ž‘•‡–‘–Š‡–”‹ƒŽ

CORRECT PUPIL POSITION

CORRECT INCORRECT Central pupil position Off-center pupil position

FIGURE 3-8 The left-hand panel shows an eye in the video monitor that is correctly positioned, with the cross-hair target locat- ed within the boundaries of the pupil. The right-hand panel shows an eye that is incorrectly positioned, with the cross-hair target located outside the boundaries of the pupil.

Š‡ –‘’—•’‡”‹‡–‡”•’”‘˜‹†‡ƒ˜‹†‡‘‘‹–‘”•‘–Šƒ– ‘‹–‘”Ǥ Š‡ ’ƒ–‹‡– ‹• ‘””‡ –Ž› ’‘•‹–‹‘‡† ™Š‡ –Š‡ the examiner can see the patient’s eye. When the patient cross-hair target is within the boundaries of the pupil Ž‘‘••–”ƒ‹‰Š–ƒ––Š‡ϐ‹šƒ–‹‘–ƒ”‰‡–ǡ–Š‡’—’‹Ž•Š‘—Ž†„‡ (FIG 3-8). Š‡ ’‘•‹–‹‘ ‘ˆ –Š‡ ’—’‹Ž ƒ „‡ ƒ†Œ—•–‡† „› aligned with the cross-hair target provided on the video changing the position of the chinrest.

CORRECT TRIAL LENS POSITION

CORRECT INCORRECT CORRECT INCORRECT Trial lens close to eye Trial lens too far away Central pupil position Off-center pupil position

FIGURE 3-9 The patient’s eye should be positioned in the center of the trial lens and as close as possible without touching it.

It is important for the patient’s eye to be as close as pos- patient is positioned too far away from the trial lens (FIG sible to the trial lens, in order to avoid the typical “ring” 3-9). Š‡‡›‡Žƒ•Š‡••Š‘—Ž†‘––‘— Š–Š‡Ž‡•ǡŠ‘™‡˜‡”Ǥ defect (i.e., trial lens rim artifact) that occurs when the 34 Chapter 3 | How to perform perimetry you can trust

Š‡ƒ˜‹•—ƒŽϐ‹‡Ž†–‡•–ƒ••‡••‡•„‘–Š–Š‡ ‡–”ƒŽƒ†–Š‡ ‹‘”†‡”–‘ƒ˜‘‹†–”‹ƒŽŽ‡•”‹ƒ”–‹ˆƒ –•ǤŽ•‘ǡ˜‹•—ƒŽϐ‹–‡•• ’‡”‹’Š‡”ƒŽ˜‹•—ƒŽϐ‹‡Ž†•ǡ‹–™‹ŽŽ„‡‡ ‡••ƒ”›–‘”‡‘˜‡–Š‡ to drive is assessed binocularly (both eyes open). In this trial lens for the part of the test that covers the periphery, case, no trial lens should be used.

CORRECT FIXATION

– ‹• ‡••‡–‹ƒŽ ˆ‘” ’ƒ–‹‡–• –‘ ƒ‹–ƒ‹ •–‡ƒ†› ϐ‹šƒ–‹‘ target is not recommended for the G, M, N and D patterns –Š”‘—‰Š‘—––Š‡–‡•–ǤŠ‡ –‘’—•’‡”‹‡–‡”•‘ˆˆ‡”–Š”‡‡ (see Chapter 5) and for any pattern where the foveal †‹ˆˆ‡”‡–ϐ‹šƒ–‹‘–ƒ”‰‡–• (FIG 3-10) –‘’”‘‘–‡•–‡ƒ†›ϐ‹š- threshold function is turned on. ation in as many patients as possible. Most patients will „‡ ƒ„Ž‡ –‘ ƒ‹–ƒ‹ ϐ‹šƒ–‹‘ —•‹‰ –Š‡ •–ƒ†ƒ”† ”‘•• ‹ƒŽŽ›ǡ•‘‡’ƒ–‹‡–•™‹–Š•‡˜‡”‡˜‹•—ƒŽϐ‹‡Ž†Ž‘••‹–Š‡ ƒ”ϐ‹šƒ–‹‘–ƒ”‰‡–Ǥ ˆ’ƒ–‹‡–•Šƒ˜‡†‹ˆϐ‹ —Ž–›—†‡”- macula region may not be able to see the standard cross •–ƒ†‹‰ ™Š‡”‡ –‘ Ž‘‘ ™Š‡ –Š‡ ”‘•• ƒ” ϐ‹šƒ–‹‘ ƒ”ϐ‹šƒ–‹‘–ƒ”‰‡–Ǥ –Š‡•‡’ƒ–‹‡–•ǡ–Š‡—•‡‘ˆ–Š‡Žƒ”‰‡” –ƒ”‰‡– ‹• —•‡†ǡ –Š‡ ‡–”ƒŽ ’‘‹– ϐ‹šƒ–‹‘ –ƒ”‰‡– ƒ „‡ ring target is recommended, to provide an estimate of the used, provided that the test pattern does not test the Ž‘ ƒ–‹‘‘ˆ–Š‡ϐ‹šƒ–‹‘–ƒ”‰‡–Ǥ ‡–”ƒŽ’‘‹–Ǥ ‘”–Š‹•”‡ƒ•‘ǡ–Š‡ ‡–”ƒŽ’‘‹–ϐ‹šƒ–‹‘

FIXATION TARGETS

CROSS MARK CENTRAL POINT RING Standard Alternative For patients with severe (do not use on test patterns visual field loss in the with central locations) macula

10° 10°

FIGURE 3-10 Octopus perimeters offer 3 different fixation targets. The cross mark target is the default target. The central point target can be used in test patterns that do not test the central point. The ring target is recommended for patients with fixation issues due to severe visual field loss in the macula. How to perform visual field testing 35

MONITORING THE PATIENT DURING THE EXAMINATION

‘‡•—”‡‰‘‘†’ƒ–‹‡– ‘‘’‡”ƒ–‹‘ƒ†–”—•–™‘”–Š› •’‘•‡‡˜‡‹ˆ–Š‡”‡‹•‘•–‹—Ž—•ǡ‘”—•–‡ƒ†›ϐ‹šƒ–‹‘Ȍǡ results, it is essential to monitor patients throughout the the test should be interrupted and the patient should be examination and not leave them unattended and unmon- reinstructed. If the results seem compromised, it is rec- itored. During the test, it is helpful to encourage patients ommended to start a new test and discard the compro- by telling them that they are doing well and by letting mised one. It is important to note, however, that patients –Š‡‘™Š‘™— Š‘ˆ–Š‡–‡•––Š‡›Šƒ˜‡ƒŽ”‡ƒ†› ‘- with impaired vision often do not respond due to their ’Ž‡–‡†ǤŠ‹•™‹ŽŽŠ‡Ž’–Š‡–‘”‡ƒ‹ƒ––‡–‹˜‡ƒ†ƒ›”‡- condition and not because they answer unreliably. †— ‡ƒš‹‡–‹‡•–Šƒ–‹‰Š–‡‰ƒ–‹˜‡Ž›‹ϐŽ—‡ ‡–Š‡”‡•—Ž–•Ǥ If a patient shows inconsistent behavior, the examiner ƒ”–‹ —Žƒ”ƒ––‡–‹‘•Š‘—Ž†„‡’ƒ‹††—”‹‰–Š‡ϐ‹”•–‹- •Š‘—Ž†ƒ‡ƒ‘–‡‘ˆ–Š‹•‘–Š‡‡šƒ‹ƒ–‹‘ϐ‹Ž‡ǡ–‘ ‘- ute of the test, to ensure that patients have understood —‹ ƒ–‡–Š‹•‹ˆ‘”ƒ–‹‘–‘–Š‡ Ž‹‹ ‹ƒǤŠ‡‘™Ž‡†‰‡ what they are expected to do during the test. If a patient –Šƒ––Š‡–‡•–Šƒ•”‡†— ‡†”‡Ž‹ƒ„‹Ž‹–›ƒ›‹ϐŽ—‡ ‡–Š‡ shows an unusual response (e.g., no response at all, a re- interpretation of the test.

USE OF FIXATION CONTROL

‘••‘ˆϐ‹šƒ–‹‘‹•ƒ’”‹ƒ”›”‡ƒ•‘ˆ‘”—”‡Ž‹ƒ„Ž‡˜‹•—ƒŽ Control mechanisms active. However, since some patients ϐ‹‡Ž†”‡•—Ž–•ǤŠ‡”‡ˆ‘”‡ǡƒŽŽ —””‡– –‘’—•†‡˜‹ ‡•Šƒ˜‡ ‹‰Š–‘–„‡ƒ„Ž‡–‘ƒ‹–ƒ‹•–‡ƒ†›ϐ‹šƒ–‹‘ˆ‘”’ƒ–Š‘Ž‘‰- ƒ„—‹Ž–Ǧ‹ ‹šƒ–‹‘‘–”‘Žˆ‘”•–ƒ–‹ –‡•–‹‰–Šƒ– ƒ–”ƒ  ical reasons (i.e., reduced central vision, unsteady pupil or –Š‡’ƒ–‹‡–ǯ•’—’‹Žƒ–ƒŽŽ–‹‡•ƒ†’”‡˜‡–ϐ‹šƒ–‹‘‡””‘”•Ǥ nystagmus), individual mechanisms within Fixation Con- With Fixation Control, the test is stopped automatically if –”‘Ž ƒ„‡–—”‡†‘ˆˆ‹†‹˜‹†—ƒŽŽ›ǡ–‘ƒ‡’ƒ–‹‡––‡•–‹‰ –Š‡’ƒ–‹‡–Ž‘•‡•ϐ‹šƒ–‹‘ȋ†—‡–‘„Ž‹‹‰ǡ•‡ƒ” Š‹‰ˆ‘” possible. If it is necessary to turn off some mechanisms, stimuli or head movements) and automatically restarted ƒ”‡ˆ—Ž’ƒ–‹‡–‘‹–‘”‹‰‹•‡›ƒ†‹–‹•‰‘‘†’”ƒ –‹ ‡–‘ ‘ ‡’”‘’‡”ϐ‹šƒ–‹‘‹•”‡‰ƒ‹‡†Ǥ‹••‡†•–‹—Ž‹ƒ”‡ƒ—- ƒ‡ƒ‘–‡‹–Š‡’ƒ–‹‡–ϐ‹Ž‡ƒ„‘—––Š‡’ƒ–‹‡–ǯ•ƒ„‹Ž‹–›–‘ –‘ƒ–‹ ƒŽŽ›”‡’‡ƒ–‡†Žƒ–‡”†—”‹‰–Š‡–‡•–Ǥ ˆϐ‹šƒ–‹‘Ž‘•• ƒ‹–ƒ‹ϐ‹šƒ–‹‘ǤŠ‡ Ž‹‹ ‹ƒ•Š‘—Ž†–Š‡‹–‡”’”‡––Š‡ occurs for more than just a few seconds, a warning results in the light of this information and should consider message will alert the examiner to properly reposition that the test might have reduced reliability. and reinstruct the patient. FIG 3-11 provides more information about the different Fixation Control consists of several separate control control mechanisms of Octopus Fixation Control. Note mechanisms, as outlined in FIG 3-11, which can be turned –Šƒ––Š‡ ‘ϐ‹‰—”ƒ–‹‘†‡’‡†•‘–Š‡ –‘’—•‘†‡ŽǤ ‘ƒ†‘ˆˆǤ –‹•”‡ ‘‡†‡†–‘‡‡’‡ƒ Š‘ˆ–Š‡ ‹šƒ–‹‘ 36 Chapter 3 | How to perform perimetry you can trust

FIXATION CONTROL PREVENTS FIXATION LOSSES

BLINK CONTROL Prevents fixation loss due to blinking.

• Detects eye closure due to blinking or falling asleep RUNNING PAUSED • Testing occurs only if the patient’s eye is open • Allows the patient to blink normally • Prevents dry eyes • Increases patient comfort

• Ensures that no stimuli are missed due to blinking

CONTACT CONTROL Prevents loss of contact with the perimeter. RUNNING PAUSED • Detects contact with the headrest or chinrest • Testing occurs only if the head is in contact with the device • Ensures that the head remains close enough to the device to minimize lens rim artifact

PUPIL POSITION CONTROL Prevents fixation losses due to incorrect pupil position.

RUNNING PAUSED • Detects off-centered pupils due to incorrect fixation or head movement • Testing occurs only if the pupil is correctly centered • Ensures correct gaze direction

DART CONTROL Prevents fixation loss due to rapid eye movement.

RUNNING PAUSED • Detects rapid eye movement when the patient is searching for stimuli • Testing occurs only if the pupil is steadily fixating • Ensures correct gaze direction

AUTOMATED EYE TRACKING (AET) Automatically adjusts the patient’s eye position.

RUNNING ADJUSTING POSITION • Moves the headrest and chinrest to keep the eye in the center of the trial lens • Maintains optimum position even if the patient is moving around slightly • Reduces trial lens rim artifacts due to off-centered eye position

FIGURE 3-11 Fixation control prevents fixation losses by automatically pausing the test during blinks, loss of contact with the device, off-centered pupils and rapid eye movements. The test is automatically restarted once optimum conditions are achieved. Further, Automated Eye Tracking automatically centers the pupil. Note that not all mechanisms are available on the different Octopus perimeter models. Common pitfalls to avoid 37

COMMON PITFALLS TO AVOID

Š‡”‡ƒ”‡ƒ›ˆƒ –‘”•–Šƒ– ƒŽ‡ƒ†–‘˜‹•—ƒŽϐ‹‡Ž†–‡•–• ‹–Š‡•‡–Ǧ—’’”‘ ‡†—”‡ǡƒ†‡š–‡”ƒŽ‘„•–”— –‹‘•„Ž‘ - that cannot be trusted. By paying attention to and man- ing the stimuli from reaching the retina, are all commonly aging these factors, a well-trained examiner will have a ‘ —””‹‰•‘—” ‡•‘ˆ—–”—•–™‘”–Š›˜‹•—ƒŽϐ‹‡Ž†”‡•—Ž–•Ǥ •—„•–ƒ–‹ƒŽ’‘•‹–‹˜‡‹ϐŽ—‡ ‡‘–Š‡“—ƒŽ‹–›‘ˆ–Š‡˜‹•—ƒŽ Many of these pitfalls can be avoided by paying close at- ϐ‹‡Ž† ”‡•—Ž–• ƒ† ‘ –Š‡ •—„•‡“—‡– Ž‹‹ ƒŽ †‡ ‹•‹‘•Ǥ tention to the set-up procedure, by observing the patient Š‡”‡ˆ‘”‡ǡ–Š‹••‡ –‹‘‹•†‡†‹ ƒ–‡†–‘–Š‡‘•– ‘‘ ƒ”‡ˆ—ŽŽ›†—”‹‰–‡•–‹‰ǡƒ†„›ƒ‹‰ƒ†Œ—•–‡–•‘” pitfalls in perimetry and provides guidance on how to repeating instructions if necessary, which is the focus of avoid them. this section. Chapters 7 and 8 provide information on Š‘™–‘†‡–‡ –˜‹•—ƒŽϐ‹‡Ž†”‡•—Ž–•–Šƒ– ƒ‘–„‡–”—•–‡† ƒ–‹‡–„‡Šƒ˜‹‘”ȋ‹Ǥ‡ǤǡŽƒ ‘ˆ’ƒ–‹‡– ‘‘’‡”ƒ–‹‘Ȍǡ‡””‘”• after the test is completed.

INCONSISTENT PATIENT BEHAVIOR

LEARNING OR PRACTICE EFFECT

Š‡–ƒ‹‰–Š‡‹”ϐ‹”•––‡•–•ǡ’ƒ–‹‡–•‘ˆ–‡†‘‘–ˆ—ŽŽ›—†‡”- While learning and practice effects most often occur stand the nature of the test and hesitate to press the button ˆ‘”’ƒ–‹‡–•–ƒ‹‰–Š‡‹”ϐ‹”•–˜‹•—ƒŽϐ‹‡Ž†‡šƒ‹ƒ–‹‘ǡ ™Š‡•‡‡‹‰ˆƒ‹–•–‹—Ž‹‡ƒ”–Š‡•‡•‹–‹˜‹–›–Š”‡•Š‘Ž†ǤŠ‹• they can also occur when switching from one perimeter –”ƒ•Žƒ–‡•‹–‘˜‹•—ƒŽϐ‹‡Ž†”‡•—Ž–•–Šƒ–ƒ”‡™‘”•‡–Šƒ–Š‡’ƒ- to another, due to small differences in the design (see –‹‡–ǯ•–”—‡˜‹•—ƒŽϐ‹‡Ž†ǡƒ•‹ŽŽ—•–”ƒ–‡†‹ FIG 3-12. •—„•‡“—‡– Chapter 12). –‡•–‹‰ǡ–Š‡’ƒ–‹‡–•–Š‡’‡”ˆ‘”„‡––‡”ƒ†–Š‡‹”˜‹•—ƒŽϐ‹‡Ž† results resemble their true visual function more closely.

EXAMPLE OF A LEARNING EFFECT

LEARNING EFFECT NO LEARNING EFFECT

1st Test 2nd Test 3rd Test 4th Test 5th Test

FIGURE 3-12 Example of a patient with normal vision with a strong learning or practice effect from the first to third visual field tests. The fourth and fifth tests represent the true visual field of the patient. 38 Chapter 3 | How to perform perimetry you can trust

While learning or practice effects cannot always be ƒŽ•‘Š‡Ž’ˆ—ŽǤ ˆƒ’ƒ–‹‡–†‘‡•‘–—†‡”•–ƒ†–Š‡–ƒ•‘ˆ ’”‡˜‡–‡†ǡ–Š‡‹”ˆ”‡“—‡ › ƒ„‡”‡†— ‡†„› ƒ”‡ˆ—Ž’ƒ- performing perimetry, the patient will often be hesitant tient instruction and observation. Running a practice test †—”‹‰–Š‡ϐ‹”•–’ƒ”–‘ˆ–Š‡–‡•–ǡ‘”™‹ŽŽ‘–’”‡••–Š‡”‡- prior to real testing is a good procedure if time allows. sponse button at all. If this is observed, it is recommended ƒ”‡ˆ—Ž‘„•‡”˜ƒ–‹‘†—”‹‰–Š‡ϐ‹”•–‹—–‡‘ˆ–Š‡–‡•–‹• to interrupt the test and reinstruct the patient.

FATIGUE EFFECT

‹•—ƒŽϐ‹‡Ž†–‡•–•”‡“—‹”‡ƒŽ‡”–‡••ƒ†ƒ––‡–‹‘ǤŠ‡ ˜‹•‡†–‘„Ž‹”‡‰—Žƒ”Ž›–‘ƒ˜‘‹††”›‡›‡•ƒ††‹• ‘ˆ‘”–ǡ patients become tired, their attention level may decrease ‰‹˜‡–Šƒ– ‹šƒ–‹‘‘–”‘Ž‹•ƒ –‹˜‡Ǥ”–‹ϐ‹ ‹ƒŽ–‡ƒ”†”‘’• and their answers may become less consistent, resulting prior to the test may also reduce fatigue effects due to ‹ƒ˜‹•—ƒŽϐ‹‡Ž†–Šƒ–‹•™‘”•‡–Šƒ–Š‡’ƒ–‹‡–ǯ•–”—‡˜‹•—ƒŽ dry eyes. Additionally, patients should be encouraged to ϐ‹‡Ž† (FIG 3-13).΃-ͽͽ –ƒ‡„”‹‡ˆ”‡•–•ǡ„› Ž‘•‹‰–Š‡‹”‡›‡•–‘”‡Žƒšǡ‹ˆ–Š‡›ˆ‡‡Ž that they are getting tired. Usually, this adds only a few ‘”‡†— ‡ˆƒ–‹‰—‡‡ˆˆ‡ –•ˆ‘”’ƒ–‹‡–•™Š‘Šƒ˜‡†‹ˆϐ‹ —Ž–› •‡ ‘†•–‘–Š‡–‡•–†—”ƒ–‹‘ǡ„—–•‹‰‹ϐ‹ ƒ–Ž›‹’”‘˜‡• concentrating for long periods of time, it may be appro- the reliability of the results. Furthermore, using a beep- priate to use tests that are shorter in duration, despite ing sound upon each stimulus presentation may help the –Š‡ƒ••‘ ‹ƒ–‡†Ž‘••‘ˆƒ —”ƒ ›ǤŠ‹•ƒ›‰‡‡”ƒ–‡‘”‡ patients to concentrate better on the test. BOX 3A pro- ‡ƒ‹‰ˆ—Ž˜‹•—ƒŽϐ‹‡Ž†”‡•—Ž–•„›”‡†— ‹‰–Š‡—”‡Ž‹ƒ„‹Ž- vides more information about the advantages and disad- ity due to the fatigue effect. Individual differences exist in vantages of this option. Š‘™“—‹ Ž›’ƒ–‹‡–•‡š’‡”‹‡ ‡ˆƒ–‹‰—‡ǡƒ†–Š‹••Š‘—Ž† be considered when selecting a test. Sometimes fatigue is noticeable as drooping eyelids. In such cases, it is best to actively interrupt the test for a while ‘ˆ—”–Š‡””‡†— ‡ˆƒ–‹‰—‡‡ˆˆ‡ –•ǡ’ƒ–‹‡–••Š‘—Ž†„‡ƒ†- and to allow the patient to rest before continuing testing.

INFLUENCE OF FATIGUE EFFECT ON VISUAL FIELD

NO FATIGUE EFFECT FATIGUE EFFECT 9:30 am 9:45 am

FIGURE 3-13 Example of a patient tested on the same day and eye within 15 minutes. Note the significant worsening of the visual field in the second test, due to fatigue. Common pitfalls to avoid 39

LOSS OF FIXATION

ˆƒ’ƒ–‹‡–†‘‡•‘– ‘•‹•–‡–Ž›ϐ‹šƒ–‡‘–Š‡ ‡–”ƒŽ–ƒ”- Š‡ –‘’—• ‹šƒ–‹‘‘–”‘Ž•Š‘—Ž†„‡‡ƒ„Ž‡†™Š‡- get, the test will lose its reference point and it will not be ‡˜‡”’‘••‹„Ž‡ǡ–‘ƒ˜‘‹†—”‡Ž‹ƒ„Ž‡˜‹•—ƒŽϐ‹‡Ž†•†—‡–‘ϐ‹šƒ- ’‘••‹„Ž‡–‘‹†‡–‹ˆ›–Š‡Ž‘ ƒ–‹‘‘ˆƒ„‘”ƒŽ˜‹•—ƒŽϐ‹‡Ž† tion losses. It should only be turned to a lower setting or points (FIG 3-14).Š‹•‹• ƒŽŽ‡†ϐ‹šƒ–‹‘Ž‘••ƒ†‹•‘‡‘ˆ completely turned off if a patient is not able to maintain –Š‡‘•– ‘‘•‘—” ‡•‘ˆ—”‡Ž‹ƒ„Ž‡ϐ‹‡Ž†•Ǥͽ; –‘ —”• •–‡ƒ†› ϐ‹šƒ–‹‘ǡ ˆ‘” ’ƒ–Š‘Ž‘‰‹ ƒŽ ”‡ƒ•‘• ȋ‹Ǥ‡Ǥǡ ”‡†— ‡† especially if the patient is insecure about his or her per- central vision, unsteady pupil or nystagmus). Direct ob- ˆ‘”ƒ ‡ƒ†•–ƒ”–•Ž‘‘‹‰ƒ”‘—†ǡ•‡ƒ” Š‹‰ˆ‘”•–‹—Ž‹Ǥ •‡”˜ƒ–‹‘‘ˆ–Š‡’ƒ–‹‡–ǯ•ϐ‹šƒ–‹‘„‡Šƒ˜‹‘”‡ƒ”Ž›‹–Š‡ ‘ƒ˜‘‹†ϐ‹šƒ–‹‘Ž‘••‡•ǡ‹–‹•–Š‡”‡ˆ‘”‡ ”— ‹ƒŽ–‘‡š’Žƒ‹ test can also be helpful in this regard. carefully to the patient that it is perfectly normal not to be able to see all of the stimuli.

INFLUENCE OF LOSS OF FIXATION ON VISUAL FIELD

CORRECT FIXATION LOSS OF FIXATION Real defect is detected Real defect is missed and/or artifactual defect is identified

Do you see? Do you see?

Patient Fixation Fixation Loss of Fixation Target Fixation & Patient Target Fixation

FIGURE 3-14 If there is a loss of fixation, visual field defects will not be in their exact location, but will either be shifted together with the fixation or masked. In the above example, loss of fixation took place during the entire test. In practice, loss of fixation is typically brief, resulting in more random defect patterns.

ADVANTAGES AND DISADVANTAGES OF USING SOUNDS UPON STIMULUS BOX 3A PRESENTATION

A beeping sound upon stimulus presentation may be helpful for some patients, to maintain their atten- tion during the perimetric test, because it provides them with a steady rhythm to follow. Additionally, it ’”‘˜‹†‡•”‡ƒ••—”ƒ ‡–‘–Š‡’ƒ–‹‡––Šƒ––Š‡–‡•–‹•”—‹‰ƒ†‡˜‡”›–Š‹‰‹•™‘”‹‰‘”ƒŽŽ›Ǥ However, the beeping sound may also encourage patients to press the response button even though –Š‡› ƒ‘–•‡‡ƒ•–‹—Ž—•ǤŠ‹•ƒ›‹ ”‡ƒ•‡ˆƒŽ•‡ƒ•™‡”•ǡ”‡•—Ž–‹‰‹—”‡Ž‹ƒ„Ž‡˜‹•—ƒŽϐ‹‡Ž†•Ǥ  addition, if more than one perimeter is in a room, the beeping sound of neighboring machines may be distracting. By default, it is thus recommended to turn the beeping sound off and to only use it for selected patients –Šƒ–Šƒ˜‡†‹ˆϐ‹ —Ž–‹‡•™‹–Šƒ‹–ƒ‹‹‰ ‘ ‡–”ƒ–‹‘–Š”‘—‰Š‘—––Š‡–‡•–Ǥ 40 Chapter 3 | How to perform perimetry you can trust

LACK OF PATIENT ATTENTION

‹•—ƒŽˆ‹‡Ž†–‡•–•”‡“—‹”‡–Š‡’ƒ–‹‡–ǯ•ˆ—ŽŽƒ––‡–‹‘Ǥ ‘‘–Š‹‰ ƒ† ‡ ‘—”ƒ‰‹‰ ™‘”†• ˆ”‘ –Š‡ ˜‹•—ƒŽ ϐ‹‡Ž† ‹•–”ƒ –‹‘• •— Š ƒ• ‘‹•‡ ƒ ‡‰ƒ–‹˜‡Ž› ‹ϐŽ—‡ ‡ –Š‡ technician can strongly reduce these anxieties and in- patient’s test performance. In addition, some patients crease the reliability of the results. Distractions should ‡š’‡”‹‡ ‡ ƒš‹‡–› ™Š‡ ’‡”ˆ‘”‹‰ ˜‹•—ƒŽ ϐ‹‡Ž† –‡•–•ǡ also be reduced to a minimum. If the clinic layout does due to fear that they are not performing well, or anxiety not offer a stand-alone perimetry room, light-dimming about the outcome. curtains around the perimeter and ear muffs can offer a cost-effective alternative.

TRIGGER-HAPPY PATIENTS

Some patients, consciously or unconsciously, want to answers carefully during the examination. If a patient ’‘•‹–‹˜‡Ž›‹ϐŽ—‡ ‡–Š‡”‡•—Ž–‘ˆ–Š‡˜‹•—ƒŽϐ‹‡Ž†–‡•–ȋ‡Ǥ‰Ǥǡ responds to more than one false positive stimulus during ‹ˆ–Š‡‹”ƒ„‹Ž‹–›–‘†”‹˜‡‹•ƒ–•–ƒ‡ǡ‘”‹ˆ–Š‡›ˆ‡ƒ”ƒ„ƒ††‹ƒ‰- the test, it will be helpful to interrupt the test immediately ‘•‹•ȌǤŠ‡•‡’ƒ–‹‡–•ƒ›„‡–”‹‰‰‡”ǦŠƒ’’›ǡ’”‡••‹‰ and reinstruct the patient, in order to avoid an unreliable the response button even if they do not see a stimulus. result. Note that a beeping sound upon stimulus presen- False positive trials where no stimuli are presented are tation may encourage trigger-happy patients to press the used to detect trigger-happy patients (for more details, response button and it is thus recommended not to use see Chapter 7). It is important to watch for false positive –Š‹•ǡ‡š ‡’–‹•’‡ ‹ϐ‹ •‹–—ƒ–‹‘•Ǥ

MISTAKES IN THE SET-UP PROCEDURE

ACCURATE ENTRY OF PATIENT INFORMATION

Patient data, such as date of birth and refraction, need to measured sensitivities is compared to the data for an be entered in the perimeter. It is important to ensure that average normal person of the same age, rather than an this information is accurate. For example, if the wrong average normal person who is younger or older. FIG 3-15 date of birth is entered, most representations of the ‹ŽŽ—•–”ƒ–‡•–Š‡‹ϐŽ—‡ ‡‘ˆ‹ ‘””‡ –’ƒ–‹‡–ƒ‰‡‘–Š‡ ˜‹•—ƒŽ ϐ‹‡Ž† –‡•– ™‹ŽŽ „‡ ‹ƒ —”ƒ–‡ǡ „‡ ƒ—•‡ ‡ƒ Š •‡– ‘ˆ ’ƒ–‹‡–ǯ•˜‹•—ƒŽϐ‹‡Ž†Ǥ

INADEQUATE CORRECTION OF REFRACTIVE ERROR

ƒ†‡“—ƒ–‡ ‘””‡ –‹‘‘ˆ”‡ˆ”ƒ –‹˜‡‡””‘” ƒŽ‡ƒ†–‘ ”‡ˆ”ƒ –‹‘ˆ‘”ƒ’ƒ–‹‡–Ǥ‘ƒ˜‘‹†–Š‹•ǡ‹–‹•”‡ ‘‡†‡† a blurring of the stimulus. If the patient does not have a –‘ Š‡ –Š‡”‡ˆ”ƒ –‹‘‘–Š‡•ƒ‡†ƒ›ƒ•–Š‡’‡”‹‡–”‹  •Šƒ”’‹ƒ‰‡‘ˆ–Š‡•–‹—Ž—•ǡ–Š‡˜‹•—ƒŽϐ‹‡Ž†”‡•—Ž–•™‹ŽŽ –‡•–Ǥ ˜‡ ‹ˆ –Š‡ ’ƒ–‹‡–ǯ• ”‡ˆ”ƒ –‹‘ Šƒ• „‡‡ Š‡ ‡† „‡™‘”•‡–Šƒ–Š‡’ƒ–‹‡–ǯ•–”—‡˜‹•—ƒŽϐ‹‡Ž†Ǥ††‹–‹‘ƒŽŽ›ǡ previously, it is possible that it may have changed since ƒŽ‡•™‹–Š–‘‘— Š’Ž—•’‘™‡” ƒŽ‡ƒ†–‘ƒƒ”–‹ϐ‹ ‹ƒŽŽ› then, especially among older patients. ‡Žƒ”‰‡†˜‹•—ƒŽϐ‹‡Ž†ǡ™Š‹Ž‡ƒŽ‡•™‹–Š–‘‘— Š‹—• power will have the opposite effect. Š‡•‡ ‘†•‘—” ‡‘ˆ‡””‘”‹•–Š‡‹ ‘””‡ – Š‘‹ ‡‘ˆ–”‹ƒŽ lens. It is important to consult the user manual for the Š‡ϐ‹”•–•‘—” ‡‘ˆ‡””‘”‹•–Šƒ––Š‡’ƒ–‹‡–Šƒ•„‡‡‹- respective perimeter, as the choice of trial lens depends correctly refracted, or that the examiner uses the wrong ‘–Š‡’‡”‹‡–‡”‘†‡ŽǤŠ‡’ƒ”ƒ‰”ƒ’Š•„‡Ž‘™†‡• ”‹„‡ Common pitfalls to avoid 41

INFLUENCE OF INCORRECT PATIENT AGE ON VISUAL FIELD RESULTS

ABCCORRECT AGE INCORRECT AGE INCORRECT AGE 58 years Too old: 88 years Too young: 18 years

FIGURE 3-15 If the date of birth of a 58-year-old patient (A) is incorrectly entered, so that the patient’s age is 88 in the perimeter, the results will be artificially good (B). If the same patient is entered as an 18-year-old patient, the results will be artificially bad (C).

the choice of trial lens for the current Octopus models ‘•ƒ˜‡–‹‡ƒ†ƒ˜‘‹†‹•–ƒ‡•ǡ‹–‹•”‡ ‘‡†‡†–‘ƒŽ- 900 and 600. ways use the built-in trial lens calculator to determine the ”‡“—‹”‡†”‡ˆ”ƒ –‹˜‡Ž‡•ǤŠ‡–”‹ƒŽŽ‡• ƒŽ —Žƒ–‘”ƒŽ™ƒ›• Patients need their far-distance correction for relaxed uses the patient’s actual best far-distance correction. It vision. Depending on age, an added near-distance correc- then automatically calculates the necessary age-dependent tion for presbyopia is also needed, because perimeters near-distance correction. It determines and recommends –‡•–ƒ–‡ƒ”†‹•–ƒ ‡•Ǥ –‹•‹’‘”–ƒ––‘—•‡–Š‡ƒ†‡“—ƒ–‡ the trial lens with the lowest possible power, in order to correction for presbyopia proposed by the perimeter’s ‹‹‹œ‡–Š‡”‹•‘ˆƒ”–‹ˆƒ –•Ǥ BOX 3B presents the under- manufacturer, and not the patient’s reading glass pre- lying assumptions of the trial lens calculator. scription. Special attention should be given to noting the sign (plus or minus) of the correction. If a minus lens is –‹•„‡•–’”ƒ –‹ ‡–‘ƒ•‡ƒ Š’ƒ–‹‡–’”‹‘”–‘•–ƒ”–‹‰–Š‡ employed when a plus lens should have been used, the –‡•–™Š‡–Š‡”–Š‡› ƒ•‡‡–Š‡ϐ‹šƒ–‹‘–ƒ”‰‡–•Šƒ”’Ž›ƒ†ǡ patient’s vision may become blurry. ‹ˆ‡ ‡••ƒ”›ǡƒ†Œ—•––Š‡”‡ˆ”ƒ –‹‘•‘ƒ•–‘ƒ˜‘‹†‹ƒ†‡“—ƒ–‡ correction of the refractive error.

RATIONALE USED IN THE DESIGN OF THE TRIAL LENS CALCULATOR BOX 3B

DETERMINATION OF APPROPRIATE SPHERICAL LENS he current Octopus perimeter models 600 and 900 present stimuli at a distance of 30 cm (11.8 inches) ˆ”‘–Š‡‡›‡ǤŠ‹• ‘””‡•’‘†•–‘ƒƒ’’”‘š‹ƒ–‡”‡ˆ”ƒ –‹‘‘ˆΪ͵Ǥʹͷ†‹‘’–‡”•ȋȌǡƒ• ƒŽ —Žƒ–‡†—•‹‰ –Š‡ˆ‘ŽŽ‘™‹‰ˆ‘”—Žƒǣ

Power (D) = 1/stimulus distance (m) = 1/0.3 = 3.33

o enable the patient to focus at this distance, the patient’s far-distance refraction values are needed. ‡’‡†‹‰‘–Š‡’ƒ–‹‡–ǯ•”‡ˆ”ƒ –‹‘ǡ†‹ˆˆ‡”‡–• ‡ƒ”‹‘•‘ —”ǣ 42 Chapter 3 | How to perform perimetry you can trust

Normally sighted patients: Young emmetropic patients can accommodate at 30cm, so they do not need an additional trial lens. With increasing age, patients gradually lose their ability to accommodate their eyes (i.e., to change their Ž‡•’‘™‡”Ȍ–‘‘„Œ‡ –•’”‡•‡–‡†ƒ–‡ƒ”†‹•–ƒ ‡•Ǥ‘ˆƒ ‹Ž‹–ƒ–‡‡ƒ”‘’–‹ ƒŽ ‘””‡ –‹‘ǡƒ††‹–‹‘ƒŽ†‹‘’- ters (D) of refractive power are needed depending of the age of the patient (see table below).

Hyperopic and presbyopic patients: H›’‡”‘’‹ ’ƒ–‹‡–ƒ›Šƒ˜‡†‹ˆϐ‹ —Ž–›–‘ˆ‘ —•ƒ–͵Ͳ Ǥ ‘”–Š‡•‡’ƒ–‹‡–•ǡƒ–”‹ƒŽŽ‡•‹•‡‡†‡†ǡ ‘””‡- sponding to their refraction (R). As with emmetropic patients who are older, additional diopters (D) are needed to support their near optical correction (presbyopia) (see table below).

Myopic patients: Near sighted patients of up to -3 D do not necessarily need corrective lenses, as they can focus at 30 Ǥƒ–‹‡–•™‹–Š•–”‘‰›‘’‹ƒȋ‰”‡ƒ–‡”–ŠƒǦ͵Ȍ™‹ŽŽŠƒ˜‡†‹ˆϐ‹ —Ž–›ˆ‘ —•‹‰ƒ–͵Ͳ ƒ†‡‡† additional correction. For refractive values above -3 D, add 3.25 D to the refractive value (e.g., for R = -4 D; use a -0.75 D lens). As for presbyopic and emmetropic patients, with increasing age, near optical ‘””‡ –‹‘‹•‘”‡†‹ˆϐ‹ —Ž–ƒ†ƒ††‹–‹‘ƒŽ†‹‘’–‡”•ƒ”‡‡‡†‡†Ǥ

Corrections in the cupola perimeter of Octopus 900 C—’‘Žƒ’‡”‹‡–‡”•ƒŽŽ‘™ˆ‘”ˆ—ŽŽǦϐ‹‡Ž†’‡”‹’Š‡”ƒŽ–‡•–‹‰–Šƒ–‡š–‡†•„‡›‘†–Š‡”ƒ‰‡‘ˆƒ–”‹ƒŽŽ‡•Ǥ Š‡”‡ˆ‘”‡ǡƒŽŽŽ‡•‡•ƒ†–Š‡Ž‡•Š‘Ž†‡”—•–„‡”‡‘˜ƒ„Ž‡–‘ƒŽŽ‘™ˆ‘”’‡”‹’Š‡”ƒŽ–‡•–‹‰Ǥ‘–”‹ƒŽŽ‡• •Š‘—Ž†„‡—•‡†ˆ‘”–‡•–‹‰„‡›‘†͵Ͳι‡ ‡–”‹ ‹–›ǤŠ‡ –‘’—•ͻͲͲŠƒ•ƒ„—‹Ž–Ǧ‹–”‹ƒŽŽ‡• ƒŽ —Žƒ–‘” –‘†‡–‡”‹‡™Š‹ Š–”‹ƒŽŽ‡••Š‘—Ž†„‡—•‡†ǤŠ‡ˆ‘ŽŽ‘™‹‰Ž‘‘Ǧ—’–ƒ„Ž‡•Š‘™•–Š‡‘—–’—–•‘ˆ–Š‡ Octopus trial lens calculator.

Age Hyperopic Emmetropic Myopic R > 0 D R = 0 D R = -0.5 D R = -1 D R = -1.5 D R = -2 D R = -2.5 D R = -3 D R < -3 D < 30 R No lens No lens No lens No lens No lens No lens No lens Ϊ͵Ǥʹͷ 30 – 39 ΪͳǤͲ Ϊͳ ΪͲǤͷ No lens No lens No lens No lens No lens Ϊ͵Ǥʹͷ 40 – 44 ΪͳǤͷ ΪͳǤͷ ΪͳǤͲ ΪͲǤͷ No lens No lens No lens No lens Ϊ͵Ǥʹͷ 45 – 49 ΪʹǤͲ ΪʹǤͲ ΪͳǤͷ ΪͳǤͲ ΪͲǤͷ No lens No lens No lens Ϊ͵Ǥʹͷ 50 – 54 ΪʹǤͷ ΪʹǤͷ ΪʹǤͲ ΪͳǤͷ ΪͳǤͲ ΪͲǤͷ No lens No lens Ϊ͵Ǥʹͷ 55 -59 Ϊ͵ǤͲ Ϊ͵ǤͲ ΪʹǤͷ ΪʹǤͲ ΪͳǤͷ ΪͳǤͲ ΪͲǤͷ No lens Ϊ͵Ǥʹͷ >= 60 Ϊ͵Ǥʹͷ Ϊ͵Ǥʹͷ ΪʹǤ͹ͷ ΪʹǤʹͷ ΪͳǤ͹ͷ ΪͳǤʹͷ ΪͲǤ͹ͷ No lens Ϊ͵Ǥʹͷ

Correction in the central field perimeter of the Octopus 600 ‘”†‡”–‘•‹’Ž‹ˆ›–Š‡ Ž‹‹ ƒŽ™‘”ϐŽ‘™ǡ–Š‡ –‘’—•͸ͲͲ’‡”‹‡–‡”Šƒ•ƒ„—‹Ž–Ǧ‹Ϊ͵ǤʹͷŽ‡•–Šƒ– ‘˜‡”•–Š‡ ‡–”ƒŽ͵Ͳι‘ˆ–Š‡˜‹•—ƒŽϐ‹‡Ž†ǤŽŽ’ƒ–‹‡–•ǡ‹””‡•’‡ –‹˜‡‘ˆƒ‰‡ǡ–Š‡”‡ˆ‘”‡”‡ ‡‹˜‡–Š‡ƒš‹— correction for presbyopia. Only their actual refraction (R) is needed. If younger patients are over-cor- ”‡ –‡†ǡ–Š‡›ƒ”‡ƒ„Ž‡–‘ ‘’‡•ƒ–‡„›”‡Žƒš‹‰–Š‡‹”Ž‡•™‹–Š‘—–‡‰ƒ–‹˜‡‡ˆˆ‡ –‘–Š‡‹”˜‹•—ƒŽϐ‹‡Ž†Ǥ

DETERMINATION OF APPROPRIATE CYLINDER LENS

Cylinder Correction (Octopus 900) A cylinder correction can be discarded when the prescription is 0.25 D or less, because it does not alter –Š‡”‡•—Ž–‘ˆ–Š‡˜‹•—ƒŽϐ‹‡Ž†–‡•–Ǥ ‘” ›Ž‹†‡”•ˆ”‘ͲǤͷ–‘ͳǡ–Š‡•’Š‡”‹ ƒŽ‡“—‹˜ƒŽ‡–‹•—•‡†ƒ† ƒ††‡†–‘–Š‡•’Š‡”‹ ƒŽŽ‡•‡‡†‡†ˆ‘”‡ƒ Š’ƒ–‹‡–ǤŠ‡•’Š‡”‹ ƒŽ‡“—‹˜ƒŽ‡–‹• ƒŽ —Žƒ–‡†—•‹‰–Š‡ ˆ‘ŽŽ‘™‹‰ˆ‘”—Žƒǣ

Spherical equivalent = ½ * cylinder correction

Š‹•ˆ‘”—Žƒ‹•ƒƒ’’”‘š‹ƒ–‹‘–Šƒ–ƒ†‡“—ƒ–‡Ž› ‘””‡ –•ˆ‘”•ƒŽŽ ›Ž‹†‡”•ǡ„—–†‘‡•‘–•—ˆϐ‹ ‹‡–Ž› correct for cylinders larger than 1 D. For cylinders larger than 1 D, a cylindrical correction is needed. Remember to get the cylinder axis oriented to the proper angle on the lens holder. (For the special case of the Octopus 600 refer to the user manual). Common pitfalls to avoid 43

EXTERNAL OBSTRUCTIONS BLOCKING STIMULI FROM REACHING THE RETINA

LENS RIM ARTIFACTS

ˆ–Š‡‡†‰‡‘ˆ–Š‡–”‹ƒŽŽ‡•„Ž‘ •–Š‡’ƒ–‹‡–ǯ•˜‹‡™ȋFIG so that the eye is as close as possible to the trial lens with- 3-16Ȍǡ –Š‡ ˜‹•—ƒŽ ϐ‹‡Ž† ”‡•—Ž–• ™‹ŽŽ „‡ ƒ†˜‡”•‡Ž› ƒˆˆ‡ –‡† out touching it, and aligned in the center of the trial lens ƒ†™‹ŽŽ•Š‘™ƒ„•‘Ž—–‡†‡ˆ‡ –•ƒ––Š‡‡†‰‡•Ǥ‘ƒ˜‘‹† Š‘Ž†‡”ǤŠ‡ –‘’—•ͻͲͲ’”‘˜‹†‡•ƒ‡ƒ•—”‡‡–ˆ— - trial lens rim artifacts, the patient should be positioned tion to warn if the lens is too far from the eye.

INFLUENCE OF LENS RIM ARTIFACTS ON VISUAL FIELD RESULTS

A) B)

NO ARTIFACT LENS RIM ARTIFACT

FIGURE 3-16 If the patient is correctly positioned close to the trial lens (A), rim artifacts do not appear within 30° of the field of view. If the patient is too far away from the trial lens (B), the edge of the visual field shows the rim of the lens.

FACIAL STRUCTURE OF THE PATIENT

It is important to observe the physiognomy (facial struc- ”‘‘’›Ž‹†•ȋ’–‘•‹•Ȍƒ††”‘‘’›Ž‹†•‹ȋ†‡”ƒ–‘ ŠƒŽƒ•‹•Ȍ ture) of the patient. A prominent nose, a heavy brow or long ‹‰Š–ƒŽ•‘‘„•–”— ––Š‡’ƒ–‹‡–•ǯ—’’‡”ϐ‹‡Ž†‘ˆ˜‹‡™ (FIG ‡›‡Žƒ•Š‡• ƒƒŽ–‡”–Š‡ϐ‹‡Ž†‘ˆ˜‹‡™ǡŽ‡ƒ†‹‰–‘‹•‹–‡”- 3-17).‘ƒ˜‘‹†ƒ”–‹ˆƒ –• ƒ—•‡†„›’–‘•‹•ǡ–ƒ’‡ ƒ„‡—•‡† ’”‡–ƒ–‹‘‘ˆ–Š‡˜‹•—ƒŽϐ‹‡Ž†”‡•—Ž–•Ǥ ˆ–Š‡”‡‹•ƒ’”‘‹‡– –‘Ž‹ˆ––Š‡‡›‡Ž‹†Ǥƒ”‡•Š‘—Ž†„‡–ƒ‡–‘Ž‡ƒ˜‡‡‘—‰Š facial structure, it is recommended to turn or tilt the ˆ”‡‡†‘–‘ƒŽŽ‘™„Ž‹‹‰Ǥ ’ƒ–‹‡–ǯ•Š‡ƒ†–‘–Š‡•‹†‡•Ž‹‰Š–Ž›ǡ™‹–Š‘—–Ž‘•‹‰ϐ‹šƒ–‹‘Ǥ

DIRTY CONTACT LENS

Since very high corrections can lead to peripheral dis- lenses are used, they must be inspected before the test. tortions, it is advisable for a patient with very high cor- Dirty contact lenses reduce the amount of light entering rections to wear contact lenses. Patients with moderate –Š‡‡›‡ǡ”‡•—Ž–‹‰‹ƒ†‹ˆˆ—•‡†‡ˆ‡ –ǤŠ‹•™‹ŽŽƒŽ•‘ƒ’’‡ƒ” myopia may also leave their contact lenses in. If contact in the Defect Curve as a downward shift of the entire curve. 44 Chapter 3 | How to perform perimetry you can trust

PUPIL SIZE

Š‡ƒ‘—–‘ˆŽ‹‰Š–‡–‡”‹‰–Š‡‡›‡‹• ‘–”‘ŽŽ‡†„›–Š‡ ‘„•‡”˜‡†ǤŠ‡•‡ƒ”–‹ˆƒ –•ƒ›•‹—Žƒ–‡‰Žƒ— ‘ƒ–‘—• diameter of the pupil. As a rule, the pupil must have a ˜‹•—ƒŽϐ‹‡Ž††‡ˆ‡ –•Ǥ‘ƒ˜‘‹†–Š‹•ǡ’ƒ–‹‡–•™‹–Šƒ’—’‹Ž diameter of at least 3 mm for the results of the test to size of less than 3 mm, as measured in a dimly-lit room, be trustworthy. Small pupils decrease the amount of may be dilated before the perimetric examination. Highly incident light on the retina and result in a uniform de- ƒ”–‹ϐ‹ ‹ƒŽŽ›†‹Žƒ–‡†’—’‹Ž•ƒ›ǡŠ‘™‡˜‡”ǡ‘ ƒ•‹‘ƒŽŽ›Ž‡ƒ† ’”‡••‹‘ ‘ˆ –Š‡ ˜‹•—ƒŽ ϐ‹‡Ž† ȋFIG 3-18ȌǤͽͿ,ͽ΀  ”‡ƒ•‹‰ –‘‹Ž†’‡”‹’Š‡”ƒŽ˜‹•—ƒŽϐ‹‡Ž††‹•–‘”–‹‘•Ǥ diffraction around the margin of the pupil may also be

INFLUENCE OF FACIAL STRUCTURE ON VISUAL FIELD

A) PTOSIS

B) PTOSIS WITH LID TAPED UP

FIGURE 3-17 Ptosis (droopy lid) results in external superior obstruction of the visual field that is not related to any pathology of the eye (A). Patients with severe ptosis or dermatochalasis should therefore be tested with the lid taped up (B), in order to assess the visual field without the effect of ptosis, as seen in the example below.

INFLUENCE OF SMALL PUPIL SIZE ON VISUAL FIELD

SMALL PUPIL SIZE NORMAL PUPIL SIZE

Light Source

FIGURE 3-18 If a patient’s pupil is too small, the overall sensitivity to light will be reduced, resulting in a visual field with diffuse defect. References 45

CLINICAL RELEVANCE OF UNTRUSTWORTHY VISUAL FIELDS

Obtaining reliable results is important in order to interpret Š‡•‡ ‘†‘•–ˆ”‡“—‡– ƒ—•‡‘ˆ—”‡Ž‹ƒ„Ž‡˜‹•—ƒŽϐ‹‡Ž†• –Š‡˜‹•—ƒŽϐ‹‡Ž†• ‘””‡ –Ž›Ǥ”‡Ž‹ƒ„Ž‡˜‹•—ƒŽϐ‹‡Ž†•—ˆ‘”- was false positive errors, which accounted for 18% of all –—ƒ–‡Ž›‘ —””‡Žƒ–‹˜‡Ž›ˆ”‡“—‡–Ž›‹ Ž‹‹ ƒŽ’”ƒ –‹ ‡Ǥ  —”‡Ž‹ƒ„Ž‡˜‹•—ƒŽϐ‹‡Ž†•Ǥ;ˆƒŽŽ–Š‡˜‹•—ƒŽϐ‹‡Ž†Š‡‹ϐ‹‡Ž†• more controlled conditions such as the large Ocular Hy- ‹ Ž—†‡†‹–Š‡ ǡͲǤͶΨŠƒ†”‹ƒ”–‹ˆƒ –•ǡͽ;™Š‹Ž‡ ’‡”–‡•‹‘”‡ƒ–‡––—†›ȋ Ȍǡϐ‹šƒ–‹‘Ž‘••‡•™‡”‡ superior and inferior depressions due to facial features –Š‡‘•–ˆ”‡“—‡–Ž›‘„•‡”˜‡† ƒ—•‡‘ˆ—”‡Ž‹ƒ„Ž‡˜‹•—ƒŽ ƒ ‘—–‡†ˆ‘”‘Ž›ͲǤʹΨ‘ˆƒŽŽŠ‡‹ϐ‹‡Ž†•Ǥ Ž‡•• ‘–”‘ŽŽ‡† ϐ‹‡Ž†•ǡƒ ‘—–‹‰ˆ‘”͹ͲΨ‘ˆƒŽŽ—”‡Ž‹ƒ„Ž‡˜‹•—ƒŽϐ‹‡Ž†•Ǥ; ‘†‹–‹‘•ǡ–Š‡•‡—„‡”•ƒ›„‡•‹‰‹ϐ‹ ƒ–Ž›Š‹‰Š‡”Ǥ

REFERENCES

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