Crossed polarising filters to measure relative afferent pupillary defects: reproducibility, correlation with neutral density filters and use in central retinal vein occlusion

Diagnostic Value of Point-of-Care Ultrasound-Guided Assessment of Relative Afferent Pupillary Defect in Adult Ocular Trauma Patients Presenting to the Emergency Department: A Prospective Cohort Study

OBJECTIVES

Early diagnosis of relative afferent pupillary defects (RAPDs) in patients with ocular trauma is crucial for timely management and improved outcomes. However, clinical examination can be challenging for patients with periorbital ecchymosis. This study aimed to compare the diagnostic accuracy of point-of-care ultrasound (POCUS) and clinical examination by emergency physicians for detecting RAPD in adult ocular trauma patients and to evaluate the proportion of RAPD in patients with ocular trauma who presented to the ED.

METHODS

This prospective cohort study was conducted at an academic emergency department in South India. Adult ocular trauma patients were assessed for RAPD using clinical examinations by emergency physicians and POCUS. The diagnostic accuracies of both methods were compared, with the ophthalmologist's final diagnosis serving as the gold standard. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated for both techniques.

RESULTS

A total of 376 patients (median age, 35 years) were included in this study. RAPD was identified in 14.63% of the patients. The sensitivity and specificity of POCUS in detecting RAPD were 92.73% and 99.38%, respectively, which were higher than those of clinical examination, with a sensitivity of 81.82% and specificity of 99.07%. The PPV and NPV of the clinical examination were 93.75% and 96.95%, respectively, whereas the PPV and NPV of POCUS were 96.23% and 98.76%, respectively. POCUS accurately diagnosed RAPD in patients with periorbital ecchymosis.

CONCLUSION

POCUS-guided RAPD assessment proves to be a better diagnostic adjunct compared to clinical examination in patients with ocular trauma presenting to the emergency department.

Pupil assessment in optic nerve disorders

BACKGROUND

The normal pupillary constriction to light is an involuntary reflex that can be easily elicited and observed without specialized equipment or discomfort to the patient. Attenuation of this reflex in optic nerve disorders was first described 120 years ago. Since then, pupil examination has become a routine part of the assessment of optic nerve disease.

CLINICAL TECHNIQUES

The original cover/uncover test compares pupillomotor drive in the two eyes, but requires two working pupils and is relatively insensitive. The swinging flashlight test is now the standard clinical tool to detect pupillomotor asymmetry. It requires only one working pupil, is easily quantified, and has high sensitivity in experienced hands, but interpretation of the results needs care. Measurement of the pupil cycle time is the only clinical test that does not rely on comparison with the fellow eye, but it can only be measured in mild to moderate optic nerve dysfunction, is more time consuming, and less sensitive.

LABORATORY TECHNIQUES

Infrared video pupillography allows recordings to be made of the pupil responses to full-field or perimetric light stimulation under tightly controlled conditions with a high degree of accuracy. Frustratingly, there is a wide range in reflex gain in normal subjects limiting its usefulness unless comparison is made with the fellow eye or stimulation of unaffected adjacent areas of the visual field.

CORRELATION WITH OTHER TESTS

In general, pupillomotor deficit shows good correlation with visual field deficit. However, some diseases of the optic nerve are associated with relative sparing either of pupil function or visual function implying that pupil tests and psychophysical tests may assess function in different subpopulations of optic nerve fibres. Less is known of the relationship between pupil measurements and electrodiagnostic tests.

USES IN CLINICAL PRACTICE

Pupil assessment is invaluable when distinguishing functional from organic visual loss. Its usefulness in distinguishing between different causes of optic neuropathy and as a prognostic sign is gradually emerging.

Quantifying relative afferent pupillary defects using a Sbisa bar

AIM

To compare the Sbisa bar (Bagolini filter bar) with neutral density filters (NDF) in quantifying relative afferent pupillary defects (RAPD).

METHODS

11 patients with a RAPD were graded and a neutral density filter bar was used to quantify the RAPD. This was repeated using the Sbisa bar. The Sbisa bar (Bagolini filter bar) is used by orthoptists to quantify density of suppression in amblyopia and is of a similar construct to NDFs. Before this clinical part of the study the luminance for each filter was measured, which enabled a direct comparison to be made.

RESULTS

In the analysis of patients with RAPD a high correlation was found when comparing the Sbisa and NDF bars r = 0.95. This was statistically significant (p = <0.001). Correlation was also high when the luminance values for the filters were substituted for the clinical readings (r = 0.92; p=<0.001).

CONCLUSION

The Sbisa bar is a comparable instrument to the NDF bar in measuring RAPD. Its availability in the clinical situation makes it a practical choice.

Quantification of relative afferent pupillary defects induced by posterior sub-Tenon's, peribulbar, and retrobulbar anaesthetics

AIMS

The effect of local anaesthetics on optic nerve function can be investigated by quantifying the relative afferent pupillary defect (RAPD).

METHODS

The study compared the depth of induced RAPD following posterior sub-Tenon's, retrobulbar, and peribulbar local anaesthetics using crossed polarising filters before cataract surgery (time 1 = 5 minutes), immediately after surgery (time 2 = 42 minutes (av)), and once again on the ward (time 3 = 107 minutes (av)).

RESULTS

All patients developed a RAPD. There was no significant difference in the depth of RAPD between the groups at any one time period. The peribulbar group had a significantly steeper decay in RAPD from time 1 to time 2 (p = 0.014). This effect was reduced when the shorter operation time for this group was entered as a cofactor (p = 0.063). By time 3 the RAPDs for all groups had decayed similarly so that no differences could be detected.

CONCLUSION

All three anaesthetic methods caused a similar level of disruption to optic nerve conduction immediately following administration and at the time of day case discharge.

Portable pupillography of the swinging flashlight test to detect afferent pupillary defects

OBJECTIVE

To investigate the ability of a portable, personal computer-driven, pupillometer to record the pupillary response curve during the swinging flashlight test. Also, to determine whether these response curves can be used to identify and quantify relative asymmetry in the pupillary light reflex between eyes in healthy volunteers with simulated afferent pupil defects (APDs) and patients with optic neuropathies.

DESIGN

Comparative, observational case series and instrument validation.

PARTICIPANTS

Healthy volunteers with no known ocular disease and patients (n = 20) with various optic neuropathies noted to have relative APDs on examination.

METHODS

Pupillary response curves of the right eye were recorded with a portable, electronic, infrared pupillometer from healthy volunteers (with and without simulated APDs) and patients with APDs while the light stimulus alternated between eyes, simulating the swinging flashlight test. Simulated APDs in healthy volunteers were created with increasingly dense neutral density filters in front of the left eye.

MAIN OUTCOME MEASURES

Differences in constriction amplitude, latency, and constriction velocity of the pupillary response with right eye stimulation versus left eye stimulation in both groups of subjects.

RESULTS

A significant correlation between neutral density filter strength and intereye differences was seen for all measurement parameters in volunteers with simulated APDs. Depending on the measurement parameter and stimulus intensity, simulated APDs of 0.6 log units or more could be distinguished from normal responses. Clinically graded true APDs had intereye differences similar to simulated APDs of the same density. Those with real and simulated APDs of 0.9 log units or more could be distinguished from healthy volunteers with 80% sensitivity and 92% specificity. Responses from those with real and simulated small APDs of 0.3 to 0.6 log units could not be distinguished reliably.

CONCLUSIONS

Portable, personal-computer driven, electronic, infrared pupillography can record the swinging flashlight test accurately and identify large afferent pupillary defects. An affordable, portable, reliable device for identifying relative APDs would be useful in the identification and follow-up of patients with neurogenic vision loss.

Electroretinography of central retinal vein occlusion under scotopic and photopic conditions: what to measure?

INTRODUCTION

In the management of cases of central retinal vein occlusion it is important to identify those patients who will develop the complication of iris neovascularisation. Electroretinography is of proven use in this role but there is some confusion about which parameters to measure and at what stimulus intensities.

METHODS

A variety of ERG parameters in scotopic and photopic conditions were tested by ROC analysis for the prediction of the development of this complication in 39 patients with CRVO.

RESULTS

The results indicated that a single flash and measurement of the b/a ratio under photopic conditions is as effective in this aim as measuring multiple parameters.

CONCLUSION

A simplified and shortened protocol could be used in the examination of this condition thereby making the application of ERG more practical in the clinical setting.