Fig. 8-7  Patient viewing ‘snowfield’ on computer monitor. Defects are noticed by the patient as smudges or fuzzy areas on screen.

patient must undergo a full visual field examination to establish a baseline against which future change can be measured. Therefore, in persons suspected of having visual field defects, screening programs and other fast strategies that reduce examination time at the expense of evaluating the critical sensitivity area within 5 dB of threshold are of questionable value.23 Screening tests are used most appropriately to diagnose pathology rather than to follow or quantitate the degree of damage in a patient known or suspected of having disease.

Other Static Testing Techniques

Single-stimulus level static testing was used commonly in some of the early computerized perimeters. Because the visual threshold slopes from the center to the periphery of vision, a single-stimu- lus intensity cannot be effective in testing a large area of the retina. This technique is useful only as a relatively crude screening method. A variety of innovative screening techniques has been developed to aid clinicians in obtaining the maximum amount of useful information in the minimum amount of time. A few of these bear mention for illustrative purposes.

Noisefield perimetry, also known as white-noise perimetry or

campimetry, is performed by having the patient observe a computer screen (Fig. 8-7) or home television set.28–30 The screen projects

a ‘noise’ pattern of small (roughly 1–4 mm), irregularly shaped dark and bright spots oscillating at 50 Hz. Patients with localized defects notice the defective region as a smudge or blank area on the screen. In simple terms, they detect the noise pattern in normal regions of the field, and its absence in the abnormal areas is perceivable. Detection takes only seconds in alert patients, but not all patients can cooperate fully with the test requirements. The information gained is useful mainly for screening.31–33 Optokinetic perimetry is a novel approach to visual field screening in which the patient is presented a series of cards with static stimuli arranged in a set pattern. While

maintaining steady fixation, the patient is asked how many spots she sees.34–36 Stimuli in defective areas of the field are not detected, and

by evaluating the points missed during the test, the examiner can gain a fairly clear idea of the nature and extent of the field loss.37–40

This method is very fast, taking perhaps only 30–50% of the total time needed for screening fields conventionally. These methods are used rarely, if at all, in clinical practice.

The Swedish Interactive Test Algorithm (SITA) was developed to address the issue of patient fatigue and discomfort during tedious full-threshold static automated perimetry examinations, which can require 30 minutes or more per eye. Long, boring examinations are stressful for patients; fatigue and a resultant lack of concentration can decrease test reliability. The SITA was developed to reduce testing time without reducing reliability or sensitivity. The basic approach is fairly straightforward, although the programming required to achieve these aims was very sophisticated. The SITA relies on a continually updated model of the patient’s predicted field, based on all of the information available on the patient, including, importantly, answers to test questions as the test itself progresses.17 The program is termed ‘interactive’ because it changes the questions it asks based on the patient’s responses, in real time. In addition to predicting the model of the patient’s field, the program assesses the certainty of its prediction at each test point. Testing is interrupted as soon as a predetermined level of certainty is reached. This is in contrast to standard testing algorithms in which testing follows a more rigid pattern, whether or not additional information will further refine the model.

The initial model of the patient’s field is based on a large databank of normal and glaucomatous fields, adjusted for age. As test points within the field undergo threshold evaluation, the model is updated. If, for example, the first few test points are characteristic of a generally depressed field, subsequent stimuli will be brighter than if the initial test points had suggested a normal field. An important feature of SITA is that it uses all of the available information as it refines its model.As more information is accumulated, the program develops a more accurate prediction of the final field, and can confirm its prediction with fewer additional test questions. During an initial evaluation, SITA used fewer test points in normal and glaucomatous fields. Because the interval between stimulus presentations is also adjusted, the actual testing time can be reduced by an even greater amount. In clinical tests, SITA standard examinations require less than half the time required to perform a full-threshold exam.41 Because of its combination of speed, accuracy, and patient acceptance, most centers and offices with SITA equipped perimeters use this as their basic testing strategy.

The future of visual field testing

The current generation of computerized perimeters allows placement of stimuli of varying sizes, intensities, and colors into backgrounds of varying intensities, and they accurately chart the patient’s responses.42 This flexibility facilitates design of an almost infinite number of testing protocols. Recent improvements have involved both hardware and software. A wide variety of test and interpretation protocols are in use, and more are being developed continually. Most commercially available protocols have been standardized against groups of normal patients. A few disease-specific protocols

have been standardized against groups of patients with the target condition.4,43–47 Although these programs do not fully replace care-

ful interpretation by a trained observer, they certainly help to guide us toward more consistent evaluation of visual field information.

Differential light sensitivity is a rather primitive retinal function. Quigley and Green found that up to 50% of retinal nerve fibers may be lost before a diagnostic glaucomatous visual field defect is detected by manual kinetic measurement.48 Computerized static perimetry with statistical analysis of the results is more sensitive,49

but some amount of nerve fiber loss precedes even computerized field loss in most cases.50 These lost nerve fibers assist in other visual functions that may be more sophisticated than simple differential light sensitivity. One of the more intriguing ways that this has been investigated is with blue-on-yellow, or short wavelength, automated perimetry (SWAP). A series of studies has indicated that the short wavelength-sensitive (blue) system may be more sensitive to early glaucoma.51–53 The test is similar to conventional perimetry except blue stimuli are projected on a yellow background to isolate the short wavelength-sensitive system. The results of these studies have been quite interesting. In one study, Johnson and co-workers54 tested 38 ocular hypertensive patients and 62 normal controls with conventional white-on-white (w/w) perimetry and subsequently with SWAP.  All 38 ocular hypertensive patients had normal w/w perimetry at the time the study began. Nine of these eyes had a defect detected by SWAP at the beginning of the study. Five years later, 5 of the 9 eyes that initially showed a SWAP defect but were normal by w/w perimetry had developed w/w visual field loss. The w/w defects were in the same locations of the visual field as the SWAP defects, but the SWAP defects were larger. No eye that was initially normal on SWAP testing developed w/w field loss during the period of study.  Thus SWAP perimetry was very sensitive (100%) for early glaucoma; its specificity (using w/w defects as the standard) was 55% (5/9) at 5 years, but this may rise with longer follow-up.

Other studies have generated similar findings. The general pattern is that SWAP defects, although similar in location and shape, appear earlier and are larger than subsequent w/w defects.55–58 This method is not entirely without cost, however. Short wavelength, automated perimetry takes longer than equivalent w/w perimetry, and increased patient fatigue and decreased dynamic range may contribute to significantly higher fluctuation values. Newer com-

binations of SWAP and more interactive programs that shorten test time will make SWAP testing more acceptable to patients.59,60

The increased testing time and fluctuation have limited the use of SWAP in routine clinical settings. It is employed most frequently to help confirm the diagnosis, or detect subtle progression in a patient with early disease.

In addition to perimetric techniques, there are a host of other psychophysical methods of detecting and following glaucomatous damage. Some of these are discussed in Chapter 11.

Combined static and kinetic perimetry

Combined static and kinetic perimetry uses the speed of kinetic perimetry and the sensitivity of static testing. It is used routinely in manual perimetry, and rarely with automated perimeters. Generally, the peripheral field and scotomata are defined by kinetic methods, and the central field is examined by static perimetry. With manual perimetry, a threshold stimulus is chosen for testing the central field. This stimulus is chosen by a variety of methods, but commonly it is the weakest stimulus visible at the point either 15° above or 15° below the horizontal meridian 25° temporal to fixation.

Aulhorn and Harms,3 Armaly,61–63 Drance and Anderson,24 and Rock and co-workers64 suggested methods using this approach to rapidly detect and define scotomata. The threshold stimulus is used to kinetically define the central field and any scotomata demonstrated by the static presentations. Static stimuli are presented at various locations for no more than 1 second. Hesitant or absent patient response indicates a potential defect, which then can be more completely analyzed by kinetic perimetry using varying stimulus sizes and intensities (Fig. 8-8).

With automated perimetry, the central field is examined in the standard static fashion, and one or two peripheral isopters are

examined to avoid missing defects that do not involve the central field.65–67 The peripheral field can be examined by static-

threshold perimetry,but this is a time-consuming and tedious process. Full-threshold testing of the periphery costs a great deal in terms of patient fatigue and satisfaction for relatively little gain, and is therefore performed rarely. Static twoor three-zone screening tests are a reasonable compromise that allow the examiner to de-emphasize, but not ignore, the periphery.

REFERENCES

 1. Harrington DO, Drake MV:The visual fields: a textbook and atlas of clinical perimetry, 6th edn, St Louis, Mosby, 1990.

 2. Hoskins HD Jr, Migliazzo C: Development of a visual field screening test using a Humphrey visual field analyzer, Doc Ophthalmol Proc Series 42:85, 1985.

 3. Aulhorn E, Harms H:Visual perimetry. In: Jameson D, Hurvich LM, editors: Handbook of sensory physiology, vol 7, NewYork, Springer-Verlag, 1972.

 4. Zulauf M: Normal visual fields measured with Octopus program G1. I. Differential light sensitivity at individual test locations, Graefes Arch Clin Exp Ophthalmol 232:509, 1994.

 5. Zulauf M, LeBlanc RP, Flammer J: Normal visual fields measured with Octopus program G1. II. Global visual field indices, Graefes Arch Clin Exp Ophthalmol 232:516, 1994.

 6. Gandolfo E, et al: Effects of random presentation on kinetic threshold, Doc Ophthalmol Proc Series 42:539, 1985.

 7. Hudson C,Wild JM, O’Neill EC: Fatigue effects during a single session of automated static threshold perimetry, Invest OphthalmolVis Sci 35:268, 1994.

 8. Wild JM, et al: Long-term follow-up of baseline learning and fatigue effects in the automated perimetry of glaucoma and ocular hypertensive patients,Acta Ophthalmol Scand Suppl 69:210, 1991.

 9. Araujo ML, Feuer WJ,Anderson DR: Evaluation

of baseline-related suprathreshold testing for quick determination of visual field nonprogression,Arch Ophthalmol 111:365, 1993.

10.Flanagan JG,Wild JM,Trope GE: Evaluation of FASTPAC, a new strategy for threshold estimation with the Humphrey Field Analyzer, in a glaucomatous population, Ophthalmology 100:949, 1991.

11.Vivell PM, Lachenmayr BJ, Zimmermann P: [Comparative study of various perimetry strategies], Fortschr Ophthalmol 88:819, 1991.

12.Zeyen TG, Zulauf M, Caprioli J: Priority of test locations for automated perimetry in glaucoma, Ophthalmology 100:518, 1993.

13.Fingeret M: Clinical alternative for reducing the time needed to perform automated threshold perimetry,

J Am Optom Assoc 66:699, 1995.

14.Nordmann JP, et al: Static threshold visual field in glaucoma with the Fastpac algorithm of the

Humphrey Field Analyzer: is the gain in examination time offset by any loss of information? Eur J Ophthalmol 4:105, 1994.

15.Schaumberger M, Schäfer B, Lachenmayr BJ: Glaucomatous visual fields: FASTPAC versus full threshold strategy of the Humphrey Field Analyzer, Invest OphthalmolVis Sci 36:1390, 1995.

16.Young IM, et al: Comparison between Fastpac and conventional Humphrey perimetry,Aust N Z J Ophthalmol 22:95, 1994.

17.Bengtsson B, Heijl A, Olsson J: Evaluation of a new threshold visual field strategy, SITA, in normal

subjects. Swedish Interactive Thresholding Algorithm, Acta Ophthalmol Scand 76:165, 1998.

18.Turpin A, et al: Properties of perimetric threshold estimates from full threshold, ZEST, and SITA-like strategies, as determined by computer simulation, Invest OphthalmolVis Sci 44:4787, 2003.

19.Budenz DL, et al: Sensitivity and specificity of the Swedish interactive threshold algorithm for glaucomatous visual field defects, Ophthalmology 109:1052, 2002.

20.Sekhar GC, et al: Sensitivity of Swedish interactive threshold algorithm compared with standard full threshold algorithm in Humphrey visual field testing, Ophthalmology 107:1303, 2000.

21.Anderson AJ, Johnson CA:Anatomy of a supergroup: does a criterion of normal perimetric performance

generate a supernormal population? Invest OphthalmolVis Sci 44:5043, 2003.

22.Johnson CA, et al: Structure and function evaluation (SAFE): I. criteria for glaucomatous visual field loss using standard automated perimetry (SAP) and short wavelength automated perimetry (SWAP),Am J Ophthalmol 134:177, 2002.

23.Gloor BP, Simitrakos SA, Rabineau PA: Long-term follow-up of glaucomatous fields by computerized (Octopus) perimetry. In: Krieglstein GK, editor:

Glaucoma update III, Berlin, Springer-Verlag, 1987.

24.Drance SM,Anderson DR:Automatic perimetry in glaucoma: a practical guide, NewYork, Grune & Stratton, 1985.

25.Hong C, et al: Detection of glaucomatous visual field defect using a screening program of Humphrey Field Analyzer, Korean J Ophthalmol 4:23, 1990.

26.Marraffa M, et al: Comparison of different screening methods for the detection of visual field defect in early glaucoma, Int Ophthalmol 13:43, 1989.

27.Sponsel WE, et al: Prevent Blindness America visual field screening study.The Prevent Blindness America Glaucoma Advisory Committee,Am J Ophthalmol 120:699, 1995.

28.Aulhorn E, Kost G: [White noise field campimetry: a new form of perimetric examination], Klin Mbl Augenheilk 192:284, 1988.

29.Shirato S,Adachi M, Hara T: Subjective detection of visual field defects using home TV set, Jpn J Ophthalmol 35:273, 1991.

30.Schiefer U, Stercken-Sorrenti G: [A new white-noise campimeter], Klin Mbl Augenheilk 202:60, 1993.

31.Adachi M, Shirato S:The usefulness of the noise-field

test as a screening method for visual field defects, Jpn J Ophthalmol 38:392, 1994.

32.Kolb M, et al: Scotoma perception in white-noise- field campimetry and postchiasmal visual pathway lesions, Ger J Ophthalmol 4:228, 1995.

33.Hettesheimer H, et al: [White-noise field campimetry in HIV patients], Ophthalmologe 96:437, 1999.

34.Clark BJ,Timms C, Franks WA: Oculokinetic perimetry for the assessment of visual fields,Arch Dis Child 65:432, 1990.

35.Damato BE, et al:  The detection of glaucomatous visual field defects by oculo-kinetic perimetry: which points are best for screening, Eye 3:727, 1989.

36.Damato BE, et al:  A hand-held OKP chart for the screening of glaucoma: preliminary evaluation, Eye 4:632, 1990.

37.Felius J, et al: Oculokinetic perimetry compared with standard perimetric threshold testing, Int Ophthalmol 16:221, 1992.

38.Greve M, Chisholm IA: Comparison of the oculokinetic perimetry glaucoma screener with two types of visual field analyzer, Can J Ophthalmol 28:201, 1993.

39.Vernon SA, Quigley HA: Improving the sensitivity of the OKP visual field screening test with the use of neutral density filters, Eye 8:406, 1994.

40.Wishart PK: Oculokinetic perimetry compared with Humphrey visual field analysis in the detection of glaucomatous visual field loss, Eye 7:113, 1993.

41.Bengtsson B, Heijl A: Inter-subject variability and normal limits of the SITA Standard, SITA Fast, and the Humphrey Full Threshold computerized perimetry strategies, SITA STATPAC,Acta Ophthalmol Scand 77:125, 1999.

42.Delgado MF, and others;American Academy of Ophthalmology. Ophthalmic Technology Assessment Committee 2001–2002 Glaucoma Panel:Automated perimetry: a report by the American Academy of Ophthalmology, Ophthalmology 109:2362, 2002.

43.Asman P, Heijl A: Glaucoma hemifield test: automated visual field evaluation,Arch Ophthalmol 110:812, 1992.

44.Funkhouser A, et al:A comparison of five methods for estimating general glaucomatous visual field depression, Graefes Arch Clin Exp Ophthalmol 230:101, 1992.

45.Kaufmann H, Flammer J, Rutishauser C: Evaluation of visual fields by ophthalmologists and by OCTOSMART program, Ophthalmologica 201:104, 1990.

46.Morgan RK, Feuer WJ,Anderson DR: Statpac 2 glaucoma change probability,Arch Ophthalmol 109:1690, 1991.

47.Smith SD, Katz J, Quigley HA:Analysis of progressive change in automated visual fields in glaucoma, Invest OphthalmolVis Sci 37:1419, 1996.

48.Quigley HA, Green WR:The histology of human glaucoma cupping and nerve damage: clinicopathologic correlation in 21 eyes, Ophthalmology 10:1803, 1979.

49.Katz J, et al:Automated perimetry detects visual field loss before manual Goldmann perimetry, Ophthalmology 102:21, 1995.

50.Sommer A, et al: Clinically detectable nerve fiber atrophy precedes the onset of glaucomatous field loss, Arch Ophthalmol 109:77, 1991.

51.Bielik M, et al: PERG and spectral sensitivity in ocular hypertensive and chronic open-angle glaucoma patients, Graefes Arch Clin Exp Ophthalmol 229:401, 1991.

52.Heron G,Adams AJ, Husted R: Foveal and nonfoveal measures of short wavelength sensitive pathways in glaucoma and ocular hypertension, Ophthalmic Physiol Opt 7:403, 1987.

53.Heron G,Adams AJ, Husted R: Central visual fields for short wavelength sensitive pathways in glaucoma and ocular hypertension, Invest OphthalmolVis Sci 29:64, 1988.

54.Johnson CA, et al: Progression of early glaucomatous visual field loss as detected by blue-on-yellow and standard white-on-white automated perimetry, Arch Ophthalmol 111:651, 1993.

55.Felius J, et al: Functional characteristics of blue-on- yellow perimetric thresholds in glaucoma, Invest OphthalmolVis Sci 36:1665, 1995.

56.Johnson CA, et al: Blue-on-yellow perimetry can predict the development of glaucomatous visual field loss,Arch Ophthalmol 111:645, 1993.

57.Johnson CA, et al: Short-wavelength automated perimetry in low-, medium-, and high-risk ocular hypertensive eyes: initial baseline results,Arch Ophthalmol 113:70, 1995.

58.Sample PA,Weinreb RN: Color perimetry for assessment of primary open-angle glaucoma, Invest OphthalmolVis Sci 31:1869, 1990.

59.Bengtsson B:A new rapid threshold algorithm for short-wavelength automated perimetry, Invest OphthalmolVis Sci 44:1388, 2003.

60.Bengtsson B, Heijl A: Diagnostic sensitivity of fast blue-yellow and standard automated perimetry in early glaucoma: a comparison between different test programs, Ophthalmology 113:1092, 2006.

61.Armaly MF: Ocular pressure and visual fields: a tenyear follow-up study,Arch Ophthalmol 81:25, 1969.

62.Armaly MF: Selective perimetry for glaucomatous defects in ocular hypertension,Arch Ophthalmol 87:518, 1972.

63.Armaly MF:Visual field defects in early open-angle glaucoma,Trans Am Ophthalmol Soc 69:147, 1971.

64.Rock WJ, Drance SM, Morgan RW:Visual field screening in glaucoma: an evaluation of the Armaly technique for screening glaucomatous visual fields, Arch Ophthalmol 89:218, 1973.

65.Ballon BJ, et al: Peripheral visual field testing in glaucoma by automated kinetic perimetry with the Humphrey Field Analyzer,Arch Ophthalmol 110:1730, 1992.

66.Miller KN, Shields MB, Ollie AR:Automated kinetic perimetry with two peripheral isopters in glaucoma, Arch Ophthalmol 107:1316, 1989.

67.Stewart WC, Shields MB, Ollie AR: Peripheral visual field testing by automated kinetic perimetry in glaucoma,Arch Ophthalmol 106:202, 1988.