Ocular Motility Photography
Gary E. Miller, CRA, OCT-C
Geisinger Medical Center
Illustrations by Diane Latranyi
The term ocular motility refers to the study of the twelve extraocular muscles and their impact on eye movement. Each eye has six muscles, four rectus and two oblique, which, when functioning properly, allow the eyes to work together in a wide range of gaze.
Muscles of the Right Eye
Patients are usually tested for eye position and movement during a routine eye examination. To observe the action of all twelve muscles, the patient is asked to look in the 9 diagnostic positions of gaze. The patient follows a target to various points of gaze while the physician closely monitors their eye movements. Any noted limitation or misalignment of the eyes could indicate muscle weakness or paralysis and warrant further investigation.
9 Diagnostic Positions of Gaze
Normal alignment on forward gaze
Deviation on upward gaze
Ocular motility photographs may be requested in order to document any improper muscle action. These images can be used to reinforce the physician's clinical impression, for medical-legal reasons or as a starting point prior to muscle surgery. Patients with strabismus and those diagnosed with cranial nerve palsies are good candidates for motility documentation.
Strabismus is a generic term used to describe any misalignment of the eyes often due to an imbalance of the extraocular muscles. This misalignment may develop at any age and occur in any direction. However, strabismus can be especially harmful to the development of vision in young children. If not diagnosed and treated early, visual acuity could be irreversibly damaged.
"V" Pattern Esotropia
Pre-operative Motility Series
Post-operative Motility Series
Cranial Nerve Palsies
Because the brain controls eye movement through a series of cranial nerves, observing ocular movements can often give clues to help diagnose central nervous system disorders. The III, IV and VI cranial nerves are used to control the extraocular muscles, thereby controlling eye movement. If any of these cranial nerves are compromised, ocular motility photographs will document the affected muscles limited movement.
Left IV Nerve Palsy
Equipment and Technique
Despite the overwhelming popularity of digital photography, motility images can be captured using either a film or digital camera. Although getting the end result may differ between the two modalities, the camera techniques for capturing the images are the same. The equipment list and method for making composites are different, but the techniques for acquiring the images remain the same.
Equipment for film imaging:
- 35mm SLR camera
- 105mm lens
- Flash unit (camera mounted) or studio strobe
- 100 ISO film
Equipment for digital imaging:
- Digital SLR camera
- 85mm lens
- 105mm (full chip)
- Flash unit (camera mounted) or studio strobe
When using a 35mm film camera and a 105mm lens, set the lens to a ratio of 1:4. This is the typical magnification used to photograph both eyes simultaneously. With a digital SLR, the exact magnification will be dependant on the size of the image sensor. For a digital camera with less than a full sensor, your lens should be set to a ratio of around 1:5. Full sensor cameras can be set at 1:4. There can be a slight variance in the exact ratio, but once chosen, the ratio should remain same for all patients on that particular camera. This will ensure images of the patient shot today will have the same magnification when they come back, whether it be in three months or in 3 years.
Focusing with either system can be accomplished by moving forward and back from the subject (rocker focusing). While looking through the viewfinder, the photographer needs to sure the subject properly aligned in the frame. The camera should be positioned squarely in front of the subject and the eyes should be parallel in the viewfinder. Replacing the ‘generic' focusing screen with a grid focusing screen will help keep things straight.
Grid Focusing Screen
Once the subject is in focus and properly positioned in the frame, direct the patient to look in the 9 diagnostic gazes and photograph each one. Having a target for the patient to fixate on will help them focus their gaze in the proper direction. The nine gazes are: straight ahead, left, right, straight up, up and to the left, up and to the right, straight down, down and to the left, down and to the right. To get an unobstructed view of the eyes in the downgaze positions, have the patient or better yet, a helper, elevate the patient's upper lids.
Uniform picture quality is very important, so always be aware of composition throughout the series. Patient head movement should be kept to a minimum. Instruct them to keep their head straight and use only their eyes to follow the target. A chin and headrest may be used to position the patient while doing the series. When photographing children, having them sit on their parents lap may be helpful. Movement can be minimized by having the parent gently hold the child's head in the forward position.
9 Gaze Composite
Once a 9 gaze series is completed, a composite image showing all nine views is often requested. How you create this image depends on the equipment at your disposal.
Since digital photography is by far the most popular method of image capture, any of the popular image management software, such as Adobe Photoshop, can create a nine gaze composite. While these programs will differ slightly in the step by step process, creating a digital composite is usually a ‘copy and paste' process. Some programs will allow you to create a ‘template' that can be opened every time you need to create the composite image. If you are use a digital retinal imaging system, you may be able to import your images into the program and create a 9 up.
With a film based camera, the easiest way to produce a composite image is to use negative film for the original photography, then re-photographing the prints. After photographing the 9 diagnostic gazes, have the lab make 2" x 3" prints from the negatives. The prints can then be placed in their proper order into a nine sectioned, plastic file page. Then simply make a photographic copy of the entire page with a digital camera and you will have created a composite image.
A flat bed scanner can also be used to create a composite image. Lay the 9 print images into position, then create a pre-scan image using your scanning software. If the initial scan is of good quality, crop the image to size and make your final scan.
Regardless of which option works best in your situation, once completed, your new composite image can now saved as a digital file, emailed or printed in hard copy form.