Understanding Ophthalmic Examination for Squint Diagnosis
Apr 24, 2023
Do you often struggle preparing for Squint workup? Does Ophthalmic examination for squint diagnosis gives you jitters. Not anymore!
This detailed article will help you understand Squint workup like never before. So, let’s get started. This is the very important topic of Ophthalmology Subject in NEET PG exam preparation.
History-taking can be very elaborate.
The time of deviation. Whether the deviation is constant or intermittent. Whether the patient has Diplopia (any double vision or gaze). Any typical head posture. Whether the patient is using specks (since when and which number) – gives an idea about the refractory status. Old photographs are compared with the present ones.
Head posture. Ocular alignment (if it is normal or there is a squint). Ocular movements: All types of ocular movements should be seen.
Ductions: Single-eye movements.
Versions: Both eyes moving together.
All 9 gazes for far and near.
Vergence: It is when 2 eyes moves in opposite directions (Convergence and Divergence).
The convergence is checked by the RAF rule i.e., by finding out the near point of convergence. Ask the patient to look at box or ruler and then bring the ruler near to the patient so the point where the patient sees the double is the near point of convergence. Whenever the patient sees the blurred, it is the near point of accommodation. The normal value for the near point of convergence is 10cm.
Visual acuity – to check the vision in the patient.
Refraction – to see if this vision can be corrected to 6/6.
Detailed anterior segment examination as any opaque media or bleeding can lead to squint. Check for Ptosis. Pupils particularly should be properly checked.
Posterior segment examination
Any problem in fovea or central retina can cause squint. Check for Phobial fixation – if it is Phobial fixation or Paraphobial fixation. Foveal fixation – The star from the direct of the ophthalmoscope is projected and the patient is asked to look at it. If star projected is falling within 2° of fovea, then it is central fixation but if it is 2-5° away then it is parafoveal fixation.
Check for any pathology
To check whether there is squint present or not
Two tests are performed for squint.
It is the manifest test for squint. Cover the normal eye and the movement of the uncovered eye is seen.
The movement is always opposite to the type of squint. Exotropia:On covering, the eye goes in and the movement is in.
Esotropia – the movement is out.
Hypertropia – the movement is down.
Whenever it has to take the phobial fixation, it will move in the opposite direction. Primary deviation is the deviation of squinted eye. Secondary deviation is the deviation of normal eye behind the cover. If the cover test is normal, then the Uncover test is done.
The movement of the covered eye is seen while uncovering it. This test is done to check Phorias (Latent squint). It is seen due to breaking of the fusion reflex, therefore it is manifested. If there is no Latent squint, there will be no movement. Esophoria – the movement is out. In the normal eye, there is no movement. The movement will always be opposite to the squint.
If the cover test or the uncover test is positive, then the next step is to check the amount of squint.
The amount of squint is denoted either in degrees or prism dioptre and the prism dioptre is almost the double of the degrees.
To know the amount of squint
Show the torch light in front of the eye, the location of the reflex is found.
If the patient has a reflex that is more toward the pupillary border, squint is around 18-20°. If the reflex is between the limbus and the papillary border, squint is around 35°. If the reflex is at the limbus, squint is 45°.
And this test is known as Hirschberg test
This test tells the amount of squint. If the eye is outward, the reflex is going inwards. Corneal reflections are usually symmetrical in the absence of a squint. In Esodeviation, the reflex falls on the temporal cornea. Roughly 1mm of displacement is around 7° of squint which is around 14-15 prism dioptre. Prism Dioptre is either written as PD or ∆D.
This test only tells about the presence of a squint. This test is helpful to check for squint in infants. It can be done in bigger children as well. The light is shown to the eye. If one reflex is brighter than the other, then the brighter one will be squinted. A brighter reflex means there is a squint. The dull reflex is normal.
Prism Cover Test (PCT)
The same cover test is done and the movement of the eye is seen. The prism of different strengths is placed. Prism Bar is the different prisms on the same scale. At what Prism Dioptre, there is no movement in the cover test that will be the exact amount of squint.
How to place the prism?
The prism has an apex and a base. The base is always opposite to the direction of the squint. If the base is opposite it means the patient has Esotropia and base out prism is placed to check the amount of squint.
If the patient is in Exotropia, the base is put in and the amount of squint is checked.
Prism Reflection Test
The right eye deviates inward on doing Hirchberg test it is seen that light reflex is at centre but in the affected eye light reflex is at pupillary border or out because the eye is deviated inwards. When the eye is in, put the base out prism in front of squinted eye and keep observing the behaviour of normal eye. Now observe at what prism strength, both eyes corneal reflex is at the centre.
Krimsky test is the test where the same prism is put in front of the normal eye and is checked. If the reflex is out, the eye is in so the prism base should be out. In the normal eye, the two reflexes are at the center.
It is a differential image method.
It tells the amount of squint and the angle of squint.
It also helps in telling the grades of binocular single vision that the patient has. It can help to improve those grades without an optic axis but only if the patient is within 8 years of age. It can also help in the convergence axis.
Hirschberg test tells the amount of squint.
Bruckner test tells about the presence of squint.
The prism has an apex and a base. The base is always opposite to the direction of the squint.
Krimsky test is when the prism is put in front of the normal eye.
These are done to catch the small degrees of Phorias. They are differential image tests. The tests are based on the Diplopia principle – the Diplopia of the patient is artificially created.
It is done for the far vision of up to 6m of distance. It is red-colored with a series of plane or convex lenses. The patient is shown a spot of light and the lens is put in front of the eye. From the right eye, a line of light is seen and from the left eye, a spot of light is seen. The line of light will be vertical as the rod is placed horizontally and from normal eye a spot of light is seen. As the inference depends upon how the patient responds hence it is an subjective test. Now the 2 images is created, one is in line and other is spot so the different images are created hence called as differential image test. These 2 different images can not diffuse causing diplopia. The patient is asked what does he/she see? Orthophoria – if the patient is normal, he sees line of the light and the spot of light is crossing the line of light. It is done to check the latent squint. Exophoria – if the patient says that the line of light is left to the spot of light. Crossed diplopia is seen. Esophoria – if the line of light is on the right side towards the same side and the spot of light is on the left then it is uncrossed diplopia.
It is done for near vision. In a Maddox wing, the right eye will only see the arrows and the left will only see the numbers. The red arrow is for the vertical and white arrow is for the horizontal. The patient is asked to what numbers the white and red arrows are pointing. Esophoria – If the patient says that the white arrow is on the right side. (Same side, uncrossed). Exophoria – if the white arrow is on the left side. (Crossed)
Left Hyperphoria – vertical squints have crossed Diplopia. If the red arrow is pointed at upper numbers/upwards that means the right eye is hypo but it is known as Left Hyperphoria.
Right Hyperphoria – if the red arrow is pointed at lower numbers (the right eye is up), it is Right Hyperphoria.
Intorsion and Extorsion can also be checked
Double Maddox Rod
The Maddox rod is vertically put on both eyes, the patient sees horizontal lines. If there is Torsion, both lines should be seen parallel. If one line is tilted, the movement of the corrective lens is done in cyclotorsion or incyclotorsion till both lines become parallel. The amount of correction needed in the lens to make the two lines parallel is known as Double Maddox Rod. It helps to catch the torsion and the amount of torsion. It is very helpful to assess the superior oblique Bell’s palsy. It does not differentiate between Phorias and Tropias.
Hess Screen/Lees screen
It is based on the Haploscopic principle.
This test is done in inconcomitant squints.
This is based on phobial projections.
This test if performed with each eye fixating in turn. The patient is seated 50cm away from the screen. The patient wears red (right side) and green goggles (left side). The eye which has to be tested should have green glass in front of it. Red acts as fixator and green is indicator. Red light is projected on the lens and the patient is asked to locate the red light. The chart has an electronically operated board with small red lights. The patient is asked to place green light in each of the points on a red light as illuminated. Next, the goggles are changed. The green is not in front of the right eye.
In the Hess chart, each square is 5°. The inward green square is 15°and the outer purple square is 30°. In the chart, the Right Lateral Rectus is underaction and because of that, the Left Medial Rectus is in overaction. The affected eye looks smaller as the Lateral Rectus is underaction. Also, the central fixation should be checked if it is correct or not.
In this, instead of the red-green goggles, the image is reflected on the mirror according to that the patient put markers. Alternate illuminations occur and the mirror is in between. Both the eyes are tested like this.
Maddox rod is done for far vision.
Maddox wing is done for near vision.
Double Maddox rod does not differentiate between Phorias and Topias.
Hess screen and Lees screen tests are based on the Haploscopic principle.
In maddox rod test, if the rod is place vertically then the patient sees horizontal line of light and the spot of light in normal eye. It is done for vertical squints. If the line passes through then it is normal. But if the light is passing below than that means that the right eye is up showing right hyperphoria. If the line of light is above that means that the right eye is below showing left hyperphoria.
This test is done to check for near point accommodation and near point convergence in child to check when she sees double
When the muscle is pulled, the reflex from the trigeminal ganglion (afferent) through the Ciliary ganglion goes to the motor nucleus of the Vagus nerve (efferent), and efferent nerve can cause cardiac depression.
For squint surgery, Retrobulbar anesthesia is given so that it blocks the ciliary ganglion and helps to suppress the reflex.
Retrobulbar anesthesia is given to block the Ciliary ganglia and suppress the reflex.
Q. If you are operating the child with a squint and the child starts developing Bradycardia. What should be your next step?
Ans: The surgery should be immediately stopped.
Q. Where is the injection given in Retrobulbar anesthesia?
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