The Hirschberg test is a basic eye exam which we use to determine if the eyes are properly aligned and to also look for strabismus (which is also called a squint). It’s a procedure in which we watch how light reflects off the eyes.
At places like Vasan Eye Care this test is a primary step in the evaluation of strabismus we perform at our clinic which also includes young children or individuals that may not be able to do more in depth eye alignment tests.
Hirschberg Test: Why Patients Hear About It
Many parents come to the clinic feeling anxious that their child’s eye looks turned in pictures, or they notice something seems off when their child is looking straight ahead. They may have heard that their child requires a Hirschberg test, or corneal light reflex test, to assess for squint or strabismus (crossed eyes) and often wonder what this test is all about, if it hurts, and really how much information this test provides about the alignment of the child’s eyes.
In this article, we will look at the Hirschberg test – what it is, how the test is performed, what a doctor actually sees with a normal eye and a strabismic eye, and how the test relates to the overall evaluation and treatment plan for a squinting (strabismic) child at a specialized eye hospital.
What Is the Hirschberg Test?
The Hirschberg test, referred to as the “Hirschberg Corneal Reflex Test” or “Corneal Light Reflex Test,” is a simple method to assess eye alignment by observing the location that a small light reflecting off of the clear front surface of the eye (the cornea) occurs. If the two eyes are properly aligned, the reflection of the light will be in the same (slightly nasal) position relative to the center of each pupil.
The position of the corneal light reflex will move in a predictable manner depending on which way the involved eye turns (in, out, up or down) when there’s strabismus present. By comparing this reflex in both the involved and unaffected eyes; the physician can get an estimate of the direction and approximate amount of misalignment. Therefore, the Hirschberg test is an objective and effective way to screen for strabismus without requiring any sort of response from the patient. This feature makes it very useful in infants, young children and patients who do not cooperate very well.
When Do Doctors Use the Hirschberg Test?
The Hirschberg test is commonly used by doctors to assess eyesight in children during regular eye exams, at squint clinics, and when strabismus is suspected but where traditional cover tests cannot provide satisfactory results. The test is particularly useful if a child is very young, has developmental delays, is shy, or is too ill to maintain steady alignment as would be required for other, more precise, alignment testing.
The Hirschberg test may be used as an approximate way to monitor changes in strabismus over time and to differentiate between a true squint and pseudo-squint due to facial features, such as a wide bridge of the nose. However, this test is just one element of an overall squint assessment, and must be supplemented by other tests such as the use of prisms, cover/uncover tests and refractions to help determine treatment options.
Hirschberg Test Steps:
Simple, Quick & Pain-Free Hirschberg Tests are easy and fast to perform. The tests usually take place in a dimly lit room so that the light reflex can easily be observed on the cornea of the eye being tested.
Common procedure includes:
- The patient is comfortably seated with his/her shoulders facing the physician and his/her head and eyes in primary position.
- The physician then holds a small penlight (or flashlight) at eye level and positions approximately 33-50 cm directly in front of the patient (typically about the midpoint of the patient’s nose).
- Depending on the situation and where the doctor has the patient look, this could mean sometimes looking at a small fixation target that is near to or around the light. With the patient’s gaze directed towards the light, the doctor has their eyes positioned directly behind it. The doctor can view both of the patient’s tiny white corneal reflections simultaneously.
Because there are no drops, no injections and no direct contact with the eye, children generally tolerate this very well. This can often be accomplished while the child is sitting on a parent’s lap.
Normal Demonstration of Hirschberg Test by Physicians
Both eyes’ corneal light reflex is positioned the same (on either side) in a straight, well-aligned eye and is slightly to the nose side of the pupil’s center. This slight nasal deviation represents normal anatomical relationships between the visual axis and the actual center of the cornea due to the angle formed by these lines.
The critical concept of symmetry is what constitutes normal eye alignment based on the results of the Hirschberg test. If both pupils demonstrate the reflexes relative to each other at corresponding relative positions, then the result indicates normal alignment, though there may still be extremely small misalignments which need additional tests to detect.
What Doctors See in Strabismus on Hirschberg Test
When an eye is improperly aligned (strabismus), the light reflex of the deviated eye will move in the opposite way from the direction toward which the eye has been turned. The doctor can use this data to calculate how much angle deviation the eye deviates. The physician will record the amount of shift, as well as its direction.
Common patterns of misalignment in one or both eyes consist of:
Esotropia (the eye is turned inwards) – The light reflex will appear laterally (towards the ear) on the cornea of the affected eye.
Exotropia (the eye is deviated outwards) – The light reflex will appear nasally (towards the nose) on the deviating eye.
Hypertropia – Occurs when one eye appears above the other; therefore, the reflex will move downward on the cornea of the higher eye.
Hypotropia – Is evidenced by one eye appearing lower than the other; in this instance, the reflex will appear higher on the cornea of the lower eye.
An examiner can make a rough estimate of the size of a deviation by judging how far out of the centre of the pupil, the reflex is displaced.
How Much Misalignment Can Hirschberg Test Estimate?
The Hirschberg test provides a rough estimate of the squint angle. Various other simple treasured-based methods can be used in clinical practice to estimate it as well. Many sources within clinical education reference that a 1 mm displacement of the light reflex from the centre of the pupil approximately corresponds to 7 degrees or approximately 15 prism diopters of strabismus.
Larger angles of squint, often between 30 and 45 degrees or more, can occur as an indicator of large displacement of the reflex from the pupil border to the limbus. Since these estimates are approximations, physicians verify them with prism cover test(s) or other quantitative methods prior to making treatment or surgical decisions for squint eyes.
Hirschberg Test Procedure in Children, Adults and New App‑Based Methods
Infants and small children tend not to cooperate with long evaluations, and cannot accurately read eye charts, so the Hirschberg test is very useful for them. Adults who are ill or confused may also benefit from the Hirschberg test, since they often will not be able to participate in an extensive series of alignment tests.
The Hirschberg test procedure has undergone recent technological advances with the advent of photographs and smartphones that facilitate corneal reflex pictures and software, thereby enabling a more accurate measurement of misalignment. A number of app-based tools are currently under investigation as potential screening tools in rural areas where eye care providers are not readily available; however, these tools supplement rather than replace a full examination for strabismus.
Is Hirschberg Test Enough to Plan Treatment?
Although the Hirschberg test serves as an excellent initial screening tool for determining squint eye treatment, it is not typically sufficient in and of itself to determine what treatment to provide through a more detailed squint-eye assessment. The test provides a general estimate of how far away from true alignment the eyes are but does not indicate any other associated conditions that may require an understanding of refractive error, binocular vision, amblyopia (lazy eye), or of any potential underlying nerve or muscle problems.
When complete diagnostic information is gathered, a physician may confirm their findings through additional measures such as o Cover and cover-uncover tests o Measuring prisms (prism bar) o Refraction (checking lens power) o Assessing ocular movements and binocularity This comprehensive summary will ultimately help the medical professional determine whether or not the patient requires glasses, patching or training, medication or surgery, including specialized strabismus treatment for both adults and children.
Is the cause of strabismus brain-based?
Strabismus (often referred to as squinting or crossed eye condition) occurs when there is a misalignment of the eyes (or they do not work together) and may arise from several different parts of the visual system. For patients with refractive error, strabismus may be due mainly to refractive errors and an imbalance between their woeful focusing systems. For other patients, strabismus may occur due to muscle problems, issues with the nerves supplying those muscles or in the brain centers that coordinate eye movements.
Squint associated with a neurological condition affecting the brain, including stroke, head injury, or other specific neurological disorders, can cause squint in children; however, there are also children who will have no brain disease but still develop squint as a result of problems with binocular fusion, uncorrected visual problems, etc. Thus, early diagnosis and appropriate squint treatment are important in preventing vision loss; therefore, it is essential to have an assessment when using the Hirschberg test.
Role of Dedicated Eye Hospitals and Eye Treatments
In a specialist centre for eyes, the Hirschberg test forms part of a structured work-up for strabismus and is not taken as a single definitive diagnostic test. Examination of the patient is completed at the slit lamp; refraction is completed; as well as cover test and ocular motility; and if necessary, on imaging procedures, i.e. retinoscopy or ultrasound, are completed, allowing the medical team to develop step by step treatment options for squinted eyes or other conditions of the eye.
Depending on the person, it is possible that glasses and close observation could be sufficient; however, for other individuals, there are options such as prisms, patching, orthoptic exercises and eye muscle surgery, particularly when treating an adult with a large-angle squint or a child with a large degree of deviation from normal. Regular follow-ups will also aid in identifying any change in alignment and making the necessary treatment adjustments.
Strabismus and Eye Alignment Care at Vasan Eye Care
Many families come to Vasan Eye Care because they have seen one eye drifting while taking photographs or their child’s teacher or pediatrician has referred to a potential squint. A typical visit to the Vasan centre would begin by completing an initial, complete visual assessment, refraction and outside eye evaluation before completing a few simple, fun-to-do child friendly alignment tests, including the Hirschberg test and cover tests.
Using the findings above, a team will be able to recommend what type of treatment/management will be best to correct misalignment at that moment in time (eg, observation, spectacles, vision therapy, medical treatment or surgical management). This means that as all these different types of eye treatment options will be available to patients from one location, patients can receive uninterrupted ongoing care starting with their initial assessment till the end of their treatment and continuing with their long‑term post treatment follow up for proper eye alignment and overall eye health.
FAQs on Hirschberg Test and Strabismus
In individuals with strabismus, the corneal light reflex will be shifted from the center of pupils between both eyes. The direction of deviation of the eyes will determine where the light reflex is displaced. For example, the corneal light reflex will be seen closer to the ear in an eye with an inward turn (esotropia) and closer to the nose in an outward-turning eye (exotropia). The greater the degree the corneal light reflex is displaced from the center of the pupil, the larger the approximate angle of the strabismus is likely to be.
A number of different tests may be carried out to diagnose strabismus, with the simplest screening test being the Hirschberg test. Other more detailed testing will typically include cover and cover/uncover tests, prism measurements, refraction and evaluation of binocular vision to fully define the type and size of the deviation. The physician will choose a combination of these tests based on the patient’s age, ability to cooperate with the testing, and the suspected cause of the squint.
There are different origins for strabismus, including the muscles in the eye, the nerves that connect these muscles, the part of the brain that coordinates eye movement, and what you see. Some types of squint may be caused by neurological disorders but many types in children are caused by problems with the fitting of the eye or by not being able to see fully from both eyes instead of a serious brain condition. Since there are multiple sources for strabismus, a thorough eye exam must be completed to fully understand the cause and formulate a treatment plan for the strabismus.
The Hirschberg corneal reflex test is a quick way to screen for strabismus by shining a small light at the eyes and observing where the light reflects on each cornea. If the reflections are centred and symmetrical, alignment is likely normal; if they are centered in one eye, it suggests the presence, direction and approximate size of strabismus.
Because it is objective, non‑invasive and easy to perform with just a penlight, it is widely used in paediatric eye care and squint clinics as an initial assessment tool.
References
- Hirschberg test – Wikipedia
https://en.wikipedia.org/wiki/Hirschberg_test - Strabismus – StatPearls (NCBI Bookshelf)
https://www.ncbi.nlm.nih.gov/books/NBK560782/ - Hirschberg Test (Corneal Reflex Test) – Smart Optometry Academy
https://smartoptometryacademy.com/hirschberg-test-all-you-need-to-know/ - Hirschberg – ABCD Vision Screening
https://www.abcd-vision.org/vision-screening/Hirschberg.html