m
Recent Posts
Connect with:
Monday / September 21.
HomemieyecareVisual Field Testing Is Pupil Dilation a Compromise?

Visual Field Testing Is Pupil Dilation a Compromise?

Pharmacological pupillary dilation and visual field testing are both crucial components of primary care eye examinations.1-6 With the push towards more streamlined appointment times, despite growing numbers of chronic eye diseases,7 some clinicians choose to dilate their patients prior to visual field testing in the interest of improving workflow.

While pharmacological pupil dilation is advantageous for the comprehensive stereoscopic assessment of the ocular media and posterior eye,2-6 it is accompanied by a myriad of undesirable changes in ocular function.8,9 With this in mind, are clinicians able to dilate patients prior to visual field testing without having to compromise on perimetric accuracy? This article aims to present the most up-to-date evidence addressing this controversial topic.

there are still no clear clinical guidelines for the timing of pupillary dilation in clinical practice

Figure 1. Schematic diagram depicting ocular changes associated with pharmacological pupil dilation.

CHANGES IN VISUAL FUNCTION ASSOCIATED WITH PUPIL DILATION

With its relatively good safety profile and short-lasting effects, tropicamide 0.5% is typically the pharmacological agent of choice for routine examinations requiring a dilated pupil.5,9 As a muscarinic antagonist, it binds to the M3 receptors of the iris sphincter and ciliary muscles, resulting in both mydriasis and cycloplegia.10 

The resultant increase in pupil size and reduction in accommodative function results in a constellation of ocular changes such as: an increase in aberrations,11,12 partial paralysis of accommodation,9 a decrease in depth of focus,13,14 and an increase in retinal illumination15 (Figure 1).

These changes in ocular structure have the potential to affect threshold sensitivities measured during visual field testing.

Currently, the recommendation is that visual field testing should be performed with consistent natural pupils greater than 3mm in diameter16 (a numerical upper limit in pupil size has not been defined). Although several studies have reported on the relationship between pharmacological dilation and visual field sensitivity,12,17-21 there are still no clear clinical guidelines for the timing of pupillary dilation in clinical practice.

DOES PUPIL DILATION AFFECT GLOBAL INDICES IN VISUAL FIELD RESULTS?

Mean deviation (MD) is a global index often used by clinicians to quantify the overall degree of sensitivity loss across the entire visual field.1 From a practical perspective, it may be used to stage the level of patients with glaucoma.22 Previous studies suggest there is a small but statistically significant reduction in the MD of normal subjects following pupil dilation using tropicamide with an average change between -0.83 to -1.15 dB.18,20 Interestingly, the effect of pupil dilation has been shown to be more pronounced in patients with existing visual field loss.21

A study by Mendivil in 199721 examined the effect of pupil dilation on a cohort of patients with existing primary open angle glaucoma. He found MD worsened following dilation with 10% phenylephrine by an average of -3.01 dB. The degree of worsening was proportional to the predilation MD whereby patients with greater pre-existing visual field defects were more significantly affected by pupil dilation compared to those with milder defects. It is not clear whether this finding was simply an epiphenomenon with more recent computer-based modelling of measurement variability in glaucomatous visual fields showing the degree of MD variability to also be greater in patients with more advanced visual field defects.23 

To put these numbers into perspective, the expected test-retest variability of MD is between 1.5 and 4 dB, depending on the integrity of the visual field.24 This suggests that while dilation may not cause a worsening of MD outside of expected test-retest variability in normal subjects or patients with early visual field loss, clinicians need to be careful in differentiating perimetric worsening associated with pupil dilation from true worsening, especially in patients with advanced visual field loss.

Current evidence relating to the effect of pupil dilation on other global indices, such as the pattern standard deviation (PSD), remain conflicting with some studies showing a worsening in PSD following dilation18 while others have found no significant change.25 The unknown impact of this may become important in glaucoma diagnosis as PSD tends to be used as a ‘cutoff ’ to determine whether a visual field defect is considered significant22 and variability here could confound the diagnostic process.

There have been no studies to date reporting the effect of dilation on the visual field index (VFI) which is a percentage-based metric that represents the functional integrity of the visual field.

IS THERE A LOCATION-DEPENDENT EFFECT?

While global indices are useful to quickly and quantitatively assess progression of visual fields, it is also important for clinicians to consider the effect of pupil dilation on the individual threshold sensitivities across the visual field that are used to derive these global metrics. This is also relevant when doing event and trend analysis on visual fields in diseases like glaucoma, as individual or clusters of points are examined for sensitivity change.

It has been hypothesised that there is an eccentricity-dependent effect whereby peripheral locations are thought to be more affected by dilation compared to central locations.21 A study by Mendivil21 examining the effect of dilation in patients with established primary open angle glaucoma divided the 30-2 test grid into three ring-like zones, each spanning 10˚. They found the innermost zone (10˚) only showed an average change of 0.74 dB while the outermost zone (30˚) showed a significantly higher average change of 6.35 dB. This was concordant with the findings of a study examining the effect of dilation on the size of kinetic visual fields in young normal subjects, which found a reduction in isopter area following dilation.17 Interestingly, in patients with retinitis pigmentosa, the isopter area is unaffected by dilation.26

WHAT’S NEW IN THE LITERATURE?

More recently, the research team at the Centre for Eye Health (CFEH) located at the University of New South Wales, Sydney, conducted a research study examining the effect of pupil dilation in normal subjects.27 In addition to looking at global indices, the team performed a pointwise analysis and showed that pupil dilation results in localised sensitivity changes that fall outside of expected intra-observer variability. Furthermore, CFEH found that the area of the visual field affected varied significantly between subjects with no systematic pattern of change identified using a pattern recognition analysis software.

THE VERDICT

Based on CFEH’s recent findings, the effect of pupillary dilation on visual field testing varies considerably between individuals. The effects of pupil dilation are difficult to predict and have the potential to confound visual field interpretation at an individual level. As such, further work is required to identify the factors driving these changes and to help clinicians identify patients who may be more predisposed to changes in perimetric sensitivity associated with pupil dilation. In the meantime, clinicians should try to maintain a consistent pupil size for testing where possible, particularly in patients with existing visual field loss for the purposes of valid progression analysis.

Henrietta Wang BOptom (Hons.), BSc, FAAO graduated from the University of New South Wales in 2016. She is a Fellow of the American Academy of Optometry. During her undergraduate degree, she received numerous clinical and academic awards, including a research scholarship for her work in the Retinal Networks Laboratory. She is a staff optometrist at the Centre for Eye Health, with clinical interests in retinal disease and advanced imaging modalities. Her research interests are also in the areas of retinal disease and optimizing clinical psychophysical procedures. 

References 

  1. Phu J, Khuu SK, Yapp M, et al. The value of visual field testing in the era of advanced imaging: clinical and psychophysical perspectives. Clinical & experimental optometry. 2017;100(4):313-32.
  2. Pollack AL, Brodie SE. Diagnostic yield of the routine dilated fundus examination. Ophthalmology. 1998;105(2):382-6.
  3. Taylor H, Binder S, Das T. ICO Guidelines for Diabetic Eye Care: International Council of Ophthalmology

2017 [Available from: http://www.icoph.org/downloads/ICOGuidelinesforDiabeticEyeCare.pdf.

  1. The College of Optometrists. The routine eye examination 2017 [Available from: guidance.college-optometrists.org/guidance-contents/knowledge-skills-and-performance-domain/the-routine-eye-examination/#open:66.
  2. Whitmer L. To see or not to see: routine pupillary dilation. Journal of the American Optometric Association. 1989;60(7):496-500.
  3. Jampel HD, Singh K, Lin SC, et al. Assessment of visual function in glaucoma: a report by the American Academy of Ophthalmology. Ophthalmology. 2011;118(5):986-1002.
  4. Foreman J, Xie J, Keel S, et al. Prevalence and Causes of Unilateral Vision Impairment and Unilateral Blindness in Australia: The National Eye Health Survey. JAMA Ophthalmology. 2018;136(3):240-8.
  5. Y, Zhao K, Jin Y, et al. Changes of higher order aberration with various pupil sizes in the myopic eye. Journal of refractive surgery (Thorofare, NJ : 1995). 2003;19(2 Suppl):S270-4.
  6. Pollack SL, Hunt JS, Polse KA. Dose-response effects of tropicamide HCl. American journal of optometry and physiological optics. 1981;58(5):361-6.
  7. National Center for Biotechnology Information. Tropicamide: PubChem Database; [Available from: pubchem.ncbi.nlm.nih.gov/compound/Tropicamide.
  8. Kim JH, Lim T, Kim MJ, Tchah H. Changes of higher-order aberrations with the use of various mydriatics. Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians (Optometrists). 2009;29(6):602-5.
  9. Lin H-Z, Chen C-C, Lee Y-C. Effect of pharmacologic pupil dilation with tropicamide and phenylephrine on wavefront measurements. Taiwan Journal of Ophthalmology. 2013;3(2):62-6.
  10. Yi F, Iskander DR, Collins MJ. Estimation of the depth of focus from wavefront measurements. Journal of vision. 2010;10(4):3.1-9.
  11. Marcos S, Moreno E, Navarro R. The depth-of-field of the human eye from objective and subjective measurements. Vision Research. 1999;39(12):2039-49.
  12. Franssen L, Tabernero J, Coppens JE, van den Berg TJTP. Pupil Size and Retinal Straylight in the Normal Eye. Investigative Ophthalmology & Visual Science. 2007;48(5):2375-82.
  13. Racette LF, M.; Bebie, H.; Hollo, G.; Johnson, C.; Matsumoto, C.;. External obstructions blocking stimuli from reaching the retina. In: AG H-S, editor. Visual Field Digest: A guide to perimetry and the Octopus perimeter. 6th ed. Koniz, Switzerland: Haag-Striet AG; 2016. p. 44.
  14. Hirasawa K, Shoji N, Kobashi C, Yamanashi A. Effects of mydriasis and miosis on kinetic perimetry findings in normal participants. Graefe’s archive for clinical and experimental ophthalmology = Albrecht von Graefes Archiv fur klinische und experimentelle Ophthalmologie. 2015;253(8):1341-6.
  15. Kudrna GR, Stanley MA, Remington LA. Pupillary dilation and its effects on automated perimetry results. Journal of the American Optometric Association. 1995;66(11):675-80.
  16. Levine L. Effective degree of mydriasis with phenylephrine and tropicamide. American journal of optometry and physiological optics. 1976;53(12):774-85.
  17. Lindenmuth KA, Skuta GL, Rabbani R, et al. Effects of pupillary dilation on automated perimetry in normal patients. Ophthalmology. 1990;97(3):367-70.
  18. Mendivil A. Influence of a dilated pupil on the visual field in glaucoma. Journal of glaucoma. 1997;6(4):217-20.
  19. Mills RP, Budenz DL, Lee PP, et al. Categorizing the stage of glaucoma from pre-diagnosis to end-stage disease. American journal of ophthalmology. 2006;141(1):24-30.
  20. Russell RA, Garway-Heath DF, Crabb DP. New insights into measurement variability in glaucomatous visual fields from computer modelling. PLoS One. 2013;8(12):e83595.
  21. Wall M, Doyle CK, Zamba KD, et al. The Repeatability of Mean Defect with Size III and Size V Standard Automated Perimetry. Investigative Ophthalmology & Visual Science. 2013;54(2):1345-51.
  22. Suram V, Chadaram, B., Kathuri, P.R. Changes in the visual fields before and after pupillary dilation. International Journal of Pharmaceutical and Medical Research 2015;3(1):24-8.
  23. Lam BL, Fishman GA, Anderson RJ, et al. Effect of Mydriasis on Visual Field Area in Retinitis Pigmentosa. Ophthalmology. 1992;99(11):1724-7.
  24. Wang H, Phu J, Qiu K, et al. Pharmacological pupil dilation causes significant sensitivity changes that are pupil change-dependent but not eccentricity-dependent. Investigative Ophthalmology & Visual Science. 2018;59(9):1267-.

DECLARATION

DISCLAIMER : THIS WEBSITE IS INTENDED FOR USE BY HEALTHCARE PROFESSIONALS ONLY.
By agreeing & continuing, you are declaring that you are a registered Healthcare professional with an appropriate registration. In order to view some areas of this website you will need to register and login.
If you are not a Healthcare professional do not continue.