Beyond the Manual: A Homemade SHIMP Approach Using Infrared Goggles

The head impulse test has revolutionized the clinical evaluation of vestibular function, and the introduction of the SHIMP paradigm has further expanded the understanding of vestibulo-ocular reflex dynamics.

The head impulse test has revolutionized the clinical evaluation of vestibular function, and the introduction of the SHIMP paradigm has further expanded the understanding of vestibulo-ocular reflex dynamics. However, access to dedicated vHIT systems may not always be available in every clinical setting.

In this interview, Dr. Vincenzo Marcelli discusses the concept of infrared clinical SHIMP (IR-cSHIMP), a simplified approach that allows clinicians to observe anti-compensatory saccades using commonly available infrared goggles. The discussion explores the physiological principles behind the method, its clinical applications, and how creative use of existing tools can expand vestibular diagnostics beyond traditional device-based testing.

AudiologyOnline: Dr. Marcelli, could you briefly explain what the head impulse test represents in vestibular diagnostics?

Dr. Vincenzo Marcelli: Since its introduction in the late 1980s, the head impulse test (HIT) has represented a turning point in the clinical evaluation of semicircular canal function. The bedside clinical HIT (cHIT) is a simple, fast, and powerful maneuver that can identify unilateral or bilateral vestibular hypofunction at the patient’s bedside. The subsequent advent of the video head impulse test (vHIT) refined this tool by adding objective quantification of the vestibulo-ocular reflex (VOR), including gain values, compensatory early and late refixation saccades, side-to-side asymmetry and, above all, the apparent gain which, measured after the first early saccade, indicates whether the patient’s gaze returned completely or only partially to the target.

This transition from qualitative to quantitative testing marked the beginning of a new era in vestibular diagnostics. More recently, the suppression head impulse paradigm (SHIMP) has further enriched this approach. Unlike the classical HIT, in which patients fixate on an earth-fixed target, SHIMP requires fixation on a head-fixed target, typically a laser dot projected from the goggles. This paradigm reveals anti-compensatory saccades, providing information about residual vestibular function and about the dynamic interaction between vestibular and visual inputs.

AudiologyOnline: How does the SHIMP paradigm differ from the classical HIT approach?

Dr. Vincenzo Marcelli: In healthy subjects, during a high-frequency head impulse, a properly functioning VOR is not suppressed during the first 100 ms and is able to keep the gaze fixed in space. Consequently, at the end of the impulse, the subject must perform a wide and rapid eye movement in the same direction as head rotation, namely an anti-compensatory saccade. In subjects with reduced dynamic VOR gain, the VOR generates slow-phase eye movements that are insufficient, or only partially capable, of moving the eyes away from the head-fixed target. As VOR gain decreases or becomes absent, progressively smaller refixation saccades occur and eventually no anti-compensatory saccades are observed.

AudiologyOnline: Why did you feel the need to develop a simplified SHIMP approach such as IR-cSHIMP?

Dr. Vincenzo Marcelli: SHIMP has proven particularly valuable in detecting subtle differences between compensated and uncompensated vestibular lesions. However, its application requires specific vHIT equipment that incorporates laser projection and sophisticated eye-tracking systems. This requirement limits its widespread adoption, especially in clinics with constrained resources or in emergency and outpatient settings.

This limitation prompted us to ask whether SHIMP could be adapted, simplified, and reintroduced into the clinical arena using tools that are already available in most practices. Our answer was the infrared clinical SHIMP (IR-cSHIMP), an adaptation of infrared video-oculoscopy (IR-VOS) that allows direct visualization of anti-compensatory saccades during head impulses. This “homemade shimmy” represents a creative and practical solution— an example of going beyond the manual.

AudiologyOnline: Your article introduces the concept of IR-cSHIMP. What inspired this idea?

Dr. Vincenzo Marcelli: The broader message of IR-cSHIMP is one of creativity and resourcefulness. By repurposing existing equipment, clinicians can overcome technological barriers and provide patients with faster access to meaningful vestibular assessment. This approach exemplifies how innovation often arises not from new devices, but from reimagining the potential of familiar tools. A solid knowledge of vestibular physiology enables clinicians to creatively use almost any instrument, beyond what the manual prescribes, transforming ordinary equipment into an innovative diagnostic resource.

AudiologyOnline: What equipment is required to perform IR-cSHIMP in daily practice?

Dr. Vincenzo Marcelli:

Equipment

The IR-cSHIMP requires only two components:

1. Infrared video-oculoscopy goggles, commonly used to observe spontaneous and positional nystagmus in darkness.
2. A central LED light placed inside the goggle frame, serving as a head-fixed target for the patient.

No additional sensors or recording systems are necessary.

Procedure

Patients are seated comfortably and asked to fixate on the LED light. The examiner, standing in front of or behind the patient, delivers small-amplitude, high-acceleration head impulses in both the horizontal and vertical planes, in accordance with standard HIT methodology and clinician observes the eye movements directly on the IR monitor.

Sample

We tested the method on healthy controls, patients with unilateral vestibulopathy and patients with bilateral vestibulopathy. For validation, all participants also underwent vHIT and vSHIMP, which served as the gold standard. Head impulses were delivered in horizontal and vertical planes, allowing us to compare IR-cSHIMP observations with quantitative instrument-based results.

AudiologyOnline: What did your observations show in healthy subjects and in vestibular patients?

Dr. Vincenzo Marcelli:

Results

The IR-cSHIMP yielded consistent and clinically relevant results.

1. Healthy subjects: Anti-compensatory saccades were observed in all horizontal impulses and in 93% of vertical impulses. This demonstrates the robustness of the technique in detecting normal physiology.
2. Unilateral vestibulopathy: In these patients, IR-cSHIMP reliably demonstrated the absence or asymmetry of saccades, which matched the side and extent of the lesion as confirmed by vHIT/ vSHIMP.
3. Bilateral vestibulopathy: In almost all cases, IR-cSHIMP revealed a complete absence of anti-compensatory saccades, in line with instrumental findings.

The method showed a few false positives, particularly in vertical trials where eye movement detection is intrinsically more challenging. However, crucially, there were no false negatives. Whenever vestibular hypofunction was present, IR-cSHIMP did not fail to identify it.

AudiologyOnline: What are the main advantages and limitations of this approach?

Dr. Vincenzo Marcelli:

Clinical value

IR-cSHIMP is not intended to replace vHIT or vSHIMP. Instead, it offers a complementary, pragmatic tool that extends the diagnostic reach of clinicians. Its advantages are several:

1. Accessibility: Most clinics already have IR goggles; no additional investment is required.
2. Rapidity: The technique can be learned quickly, with a learning curve comparable to the classical cHIT.
3. Educational impact: Eye movements are displayed in real time, providing a valuable teaching aid for residents, medical students, and even for patient education.
4. Versatility: The test can be used in outpatient clinics, at the bedside, or in emergency settings where rapid vestibular assessment is essential.

Limitations

Naturally, IR-cSHIMP does not provide quantitative VOR gain or latency/amplitude measurements. Its sensitivity for vertical canals is slightly lower, and it cannot replace the precision of vHIT recordings. Yet, as a screening tool, its value lies in rapid, reliable, and inexpensive detection of vestibular dysfunction. Obviously, without additional costs, the test can also be performed using a videonystagmographic system, which provides objective data that clearly require standardization, such as ocular velocity during head rotation and the characteristics of the saccade generated after the impulse.

AudiologyOnline: How could this method contribute to clinical education and future vestibular research?

Dr. Vincenzo Marcelli: Further validation is needed in larger, multicenter cohorts, particularly in acute vestibular syndrome where rapid decision-making is crucial. Integration of IR-cSHIMP into telemedicine frameworks could be explored, allowing remote observation of eye movements. In teaching hospitals, it may serve as an intermediate step between bedside cHIT and full vHIT training, giving students a clearer view of vestibular physiology.

Moreover, simple technological refinements (such as improved LED placement or portable IR goggles) could enhance the sensitivity and portability of the method.

AudiologyOnline: What message would you like clinicians to take from this “beyond the manual” approach?

Dr. Vincenzo Marcelli: The IR-cSHIMP illustrates how clinical ingenuity can expand diagnostic horizons. By adapting infrared goggles with a fixation LED, we obtained a test that is simple, reliable, and clinically meaningful. While it does not replace vHIT/vSHIMP, it provides a valuable complement; particularly in settings where resources are limited or rapid assessment is required.

This method is more than a technical shortcut. It embodies a philosophy: that clinicians can go beyond the manual, transforming everyday tools into powerful diagnostic allies. It reminds us that true mastery of the subject allows freedom from the constraints of the manual, enabling creativity in adapting any available instrument for clinical innovation. In this sense, the IR-cSHIMP is not just a clinical test; it is a homemade shimmy, a small innovation with the potential to make a big difference in patient care.

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