Knobby Eye Syndrome

ABSTRACT

Introduction: A spherical globe is traditionally assumed, but this study employed magnetic resonance imaging (MRI) to demonstrate frequent occurrence of non-spherical staphylomata in strabismic patients.

Methods: High-resolution, surface coil MRI was obtained in multiple image planes in 21 highly myopic subjects (36 eyes) and compared with 17 normal controls (33 eyes). Images were analyzed for axial length, aspect ratio of eye shape, and deflection of muscle paths.

Results: All but two high myopes had strabismus. While myopic globes were generally spherical in 10 myopic eyes including both orthotropic subjects, 15 globes exhibited diffuse posterior staphylomata, 16 equatorial staphylomata, and 4 both posterior and equatorial staphylomata. Equatorial scleral ectasias were positioned to contact and elongate paths of horizontal rectus muscles in some gaze positions. Axial length in myopes averaged 28.8 ± 3.8 (SD) mm and did not differ significantly between regular vs. irregular staphylomata. Globe aspect ratios in the coronal, axial, and sagittal planes were significantly greater than normal in myopes (P < 0.005), but correlated significantly with axial length only in the axial and sagittal planes (P < 0.03). While myopes with irregular staphylomata were older at 57 ± 11 years than subjects with spherical globes at 24 ± 8 years (P < 0.0005), other clinical features were similar.

Conclusion: Irregular equatorial or posterior staphylomata are common in strabismic axial high myopes, acting, like “cams” affixed to the normally spherical globe so that they may have no mechanical effect until rotating eccentrically against muscles. After rotational contact, staphylomata would nonlinearly increase muscle tension with further duction. Imaging may be clinically informative about this “knobby eye syndrome.”

KEYWORDS:

• Magnetic resonance imaging
• myopia
• staphyloma
• strabismus

Declaration of interest

The author reports no conflict of interest.

FDA disclosure

MRI surface coils used in imaging are not FDA approved for this purpose.

Additional information

Funding

U.S. Public Health Service, National Institutes of Health, National Eye Institute grant EY008313, and an Unrestricted Grant from Research to Prevent Blindness.