Difference Between Internal and External Ophthalmoplegia

The key difference between internal and external ophthalmoplegia is that the internal ophthalmoplegia is due to damage to the medial longitudinal fasciculus whereas external ophthalmoplegia is predominantly secondary to damage to the medial longitudinal fasciculus. Therefore, this difference in the pathological basis of the disease causation is the key difference between internal and external ophthalmoplegia.

Both internal and external ophthalmoplegia are eye conditions that have a neurological basis. Further, both are ocular disease conditions.

1. Overview and Key Difference
2. What is Internal Ophthalmoplegia
3. What is External Ophthalmoplegia
4. Side by Side Comparison – Internal vs External Ophthalmoplegia in Tabular Form
5. Summary

What is Internal Ophthalmoplegia?

Internal ophthalmoplegia is due to damage to the medial longitudinal fasciculus. If the lesion is on the right side fasciculus, the right eye will not be able to adduct during the attempted lateral gaze, and the left eye will develop nystagmus. When these manifestations are present bilaterally that is more likely to be due to multiple sclerosis.

What is External Ophthalmoplegia?

The paralysis of 3^rd, 4^th and 6^th cranial nerves at the optical apex or inside the cavernous sinus impairs the movements of the eyeball. This is known as external ophthalmoplegia. Furthermore, if the lesion is at the level of the optical apex, it is more likely to be a metastatic deposit that impinges on the nerves passing alongside.

On the other hand, if the damage to the nerves are within the cavernous sinus, it is most often secondary to cavernous sinus thrombosis or a meningioma.

What is the Difference Between Internal and External Ophthalmoplegia?

External ophthalmoplegia is the paralysis of 3rd, 4th and 6th cranial nerves at the optical apex or inside the cavernous sinus that impairs the movements of the eyeball. Internal ophthalmoplegia, on the other hand, is due to damage to the medial longitudinal fasciculus where the patient develops nystagmus on the contralateral eye when attempting lateral gaze to the opposite side of the lesion. In external ophthalmoplegia, the damage is at the level of the optical apex or inside the cavernous sinus. However, in internal ophthalmoplegia, it is the medial longitudinal fasciculus that is damaged.

Furthermore, looking at on the causative side, cavernous sinus thrombosis, metastatic deposits at the level of optical apex and meningiomas are the main causes of external ophthalmoplegia. In contrast, multiple sclerosis is the main cause of internal ophthalmoplegia. In this condition, the contralateral eye shows nystagmus, and the Ipsilateral eye finds difficult to adduct during the attempted lateral gaze to the opposite side of the lesion.

Summary – Internal vs External Ophthalmoplegia

Both internal and external ophthalmoplegia are eye conditions that have a neurological basis. In internal ophthalmoplegia 3^rd, 4^th and 6^th cranial nerves are damaged. But in external ophthalmoplegia, the problem is in the medial longitudinal fasciculus. This is the main difference between internal and external ophthalmoplegia conditions.