DIY# Optokinetic Nystagmus (OKN) Drum

▶ Demonstration of OKN is needed in some ophthalmic situations.
▶ Name at least five ophthalmic uses of the OKN drum?
▶ The answer will be shared here weekly (one use per week)- stay tuned! :)

■ Uses
A. Vision-related uses (Afferent): -
1. Vision assessment
In preverbal children and patients with developmental or intellectual disabilities.
A response to a standard OKN drum implies visual acuity equivalent to finger counting at 3-5 feet.
Can be assessed binocularly and monocularly.
The presence of OKN indicates at least gross vision in one eye (binocular testing).
Primarily a qualitative test of vision, though quantitative estimation is possible by varying the testing distance and stripe width.
In patients with horizontal nystagmus, the drum is oriented horizontally to elicit vertical OKN.

2. Functional (non-organic) visual loss e.g. Malingering, hysteria (conversion syndrome)
The OKN drum is suitable if the vision is very poor (HM, PL, NPL).
If the patient claims to see nothing while the eyes move with the drum, a functional component has been established.
It is possible for malingerers to purposely minimize or prevent the response by looking around or focusing past the drum.

B. Motility-related uses (Efferent): -
1. Convergence retraction nystagmus that seen in Dorsal midbrain syndrome (Parinaud's Syndrome)
Having the patient follow a downward- rotating OKN drum, you will notice defective upward saccadic movement, associated convergence (from contraction of both medial rectus muscles overpowering the lateral rectus muscles), and globe retraction ((from co-contraction of inferior and superior rectus muscles)
Convergence retraction nystagmus is highly localizing (dorsal midbrain lesion) and, although not actually a form of nystagmus, is often listed with nystagmus.
   • Convergence Retraction Nystagmus (Parinaud...  
   • Dorsal midbrain syndrome, Parinaud syndrome  

2. INO: The OKN drum can be used to evaluate suspected subclinical internuclear ophthalmoplegia. In INO, the medial rectus (responsible for adduction) on the affected side shows slower response compared to the MR on the healthy side. For example, in right INO, rotate the drum to the patient’s left side and observe adduction of the right eye (right MR). Then rotate the drum to the patient’s right side and observe adduction of the left eye. A diagnosis of right INO is supported if the right eye’s adduction is slower than that of the left eye (Asymmetry of adduction).

3. ...to be continued:)

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Requirements:-
■ Plastic cylindrical lidded container
■ A fidget spinner
■ Printed black-and-white striped A4 paper (x2)- the width of the stripe in the video is 1.5cm
■ Black cardboard paper (e.g., Canson paper A4)
■ Black marker (for the handle of the OKN drum)
■ Adhesive materials (all-purpose adhesive,e.g., UHU - cyanoacrylate glue- double-sided paper plaster tape)
■ Sharp scissors (curved and straight)
■ A coin slightly larger than the central disk of the spinner
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Method:-
As shown in the video. The most important point is to ensure that the central circular hole is larger than the central disk of the spinner. Also, make sure not to spill glue around the central disk of the spinner, as this will interfere with the spinner mechanism. Best of luck!:)
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Be creative ◕‿◕ Be curious ◕‿◕ Be courageous
Gh.Z :)