Documenta Ophthalmologica 6 3 : 3 2 1 - 3 2 4 (1986) �9 Martinus Ni]hoff/Dr W. Junk Publishers, Dordrecht - Printed in the Netherlands

E f f e c t o f p u p i l l a r y d i l a t a t i o n i n f l a s h V E R t e s t i n g

HAROLD SKALKA and JANE HOLMAN

Department of Ophthalmology, Eye Foundation Hostpital, University of Alabama at Birmingham, 1720 University Boulevard, Birmingham, AL 35233, USA

Abstract. Light flash transient visual evoked response (VER) testing is often a part of the perioperative evaluation of eyes with opaque media, and pupillary size in these pa- tients may not be knowable or may be inadvisable to alter. We therefore evaluated transient light flash VER responses before and after pupillary dilation in normal controls and in patients with media opacities to evaluate the effects of pupil size on the ampli- tude and latency of the recorded VER. Monocular testing was performed bilaterally with a Grass PS-22 photostimulator at the $1 and $16 settings, with monopolar record- ings 1 cm above the inion. One hundred twenty-eight 200-msec samplings were recorded and averaged on a Nicolet CA-1000 clinical averager. Latencies were often shorter with the stronger light stimulus, but pupiUary dilation did not produce a clear trend toward shorter latencies. Overall, pupillary dilatation did not significantly increase recorded ampli- tudes, nor did iris color appear to be a factor. These results suggest that, under our testing conditions, pupiltary dilatation is not necessary for obtaining reliable transient flash VER recordings.

Light flash transient visual evoked response (VER) testing is often useful in the preoperative or postoperative evaluation o f traumatized eyes or eyes with opaque media from other causes (e.g. cataracts, corneal opacities). Pupillary dilatation may not always be possible (e.g. corneal laceration, pos- terior synechiae), desirable (e.g. subluxated lens with narrowed anterior chamber angle), or determinable (e.g. hyphema or opaque cornea). I t is

therefore important to know whether pupillary dilatation has a significant effect on the amplitude and latency of flash-evoked transient VER recor-

dings. We performed transient light flash VER testing before and after pupillary

dilatation in normal controls and in comparably-aged patients with significant media opacities and evaluated amplitude and latency of the P10o wave. Monocular testing was performed bilaterally before and after 1% tropicamide dilatation, at the $1 and $16 settings of the Grass PS-22 photost imulator (intensity ratio 1:16), with the stimulating lamp placed four feet from the subject in subdued room lighting. The stimulation frequency was 1 Hz. Mono- polar recordings were obtained from a Beckmann cup electrode placed in the midline 1 cm above the inion, with the reference electrode placed over the ipsilateral mastoid. Resistance was less than 5,000 ohms in all cases. For each

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Table 1. Voltage and latency averages in control eyes, before and after pupillary di- latation

Undilated Dilated Sz $16 $1 Sl6 voltage latency voltage latency voltage latency voltage latency (t~V) (msec)

OD 9.9 110.5 10.0 107.4 9.9 110.1 10.2 109.7 OS 8.5 109.5 9.6 108.7 8.3 106.6 9.6 109.2

Table 2. Voltage and latency averages in opaque media eyes ~ , before and after pupiltary dilatation

Undilated Dilated S 1 $1~ S~ S~ uV msec vV msec ~V msec ~zV msec

2.5 132.7 5.7 139.4 3.1 120.6 5.5 130.0

~N=8

test 128 samplings were recorded for 200msec and were averaged on a Nicolet CA-1000 averager. The amplitude (preceding trough to peak) and time to peak of the P10o wave (latency) were determined.

Our normal controls consisted of six young (ages 28-42) volunteers free of ocular disease. Pathology in the opaque media group (eight eyes of six patients, ages 20-48) included dense cataracts, large corneal leu- komas, vitreous hemorrhage, and proliferative diabetic retinopathy with preretinal hemorrhages. Totally opaque corneas were excluded, as pupil- lary size could not be adequately evaluated in such patients. All undilated pupils were ~< 4.5 mm in diameter and all pupils were/> 7 mm in diameter for dilated testing.

In both groups dilatation often produced some shortening of latency, which on average was greater in eyes with opaque media. In the control eyes, dilatation did not produce any overall change in recorded voltage (Table 1). In the opaque media eyes dilatation produced a slight increase in voltage with the $1 stimulus, but did not augment the undilated $16 response (Table 2). Undilated or dilated, all tested eyes produced clearly recordable responses with the $16 flash, and the recorded waveforms were generally similar in appearance for the eye tested (Figure 1). All but one eye yielded responses to the $1 flash. This eye had the most dense vitreous opacity - visually totally opaque, allowing visualization only of the retrolental vitreous surface. Karpe and Wulflng (1969), evaluating ERG amplitudes with varying pupil size, likewise found that maximal b-waves could be obtained regardless of pupil- lary size if the stimulating light was sufficiently intense.

It would appear that the $16 Grass photostimulator setting provides a sufficiently bright flash for transient VER testing in eyes with opaque media, although the possibility of opaque media dense enough to compromise

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Figure 1. $1~ flash VER recordings of eye with vitreous hemorrhage (visual acuity of hand movements). Undilated response above, dilated response below. Upward deflection positive. Similarity of waveforms may be seen, although in this eye dilatation did increase voltage from 7.4 ~V to 8.9 taV.

this stimulus cannot be excluded; certainly, standard ERG testing may be unreliable in eyes with extremely dense media, requiring bright flash ERG testing for reliable recordings.

Pupillary dilatation would not appear to be necessary for reliable transient flash VER testing when S16 Grass photostimulation is used four feet from the subject's eye. We found no apparent effect of iris color on amplitude change with dilatation. If it has any effect, the iris probably contributes in a small way to the ganzfeld effect produced by the media opacities and is

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unlikely to block such a strong stimulus in any effective way. Indeed, Rubin and Dawson (1978) described successful flash VER testing in eyes with corneal or lens opacities by means of transsceral stimulation through the lid via a light pipe.

We conclude that reliable transient flash VER resting may be performed in the clinical setting without undue consideration of pupillary size if the stimulus is sufficiently intense, and that the $16 setting of the Grass PS-22 photostimulator placed four feet from the subject's eye provides an adequate stimulus for such testing.

References

Karpe G and Wulfing B (1969) Importance of pupil size in clinical ERG. Acta Oph- thalmol Supp 70:53-61

Rubin ML and Dawson WW (1978) The transsceral VER: Prediction of postoperative acuity. Invest Ophthalmol Vis Sci 17:71-74