Congenital anomalies of the optic nerve

The optic nerve is the nerve responsible for sending visual information from the eye to the brain.

Congenital optic nerve anomalies include a heterogenous group of entities with specific ophthalmoscopic characteristics and some of them have frequent systemic associations. A correct and early diagnosis allows for the necessary complementary tests to be requested and for appropriate monitoring and treatment of patients. 

From a clinical point of view, there is a series of general characteristics or symptoms shared by these anomalies. Congenital optic nerve anomalies can be asymptomatic or produce symptoms. The majority of patients affected usually have poor vision during infancy. Refractive errors (prescriptions) are the norm and in the some cases cause serous retinal detachment.

In cases where both eyes are affected, patients may have nystagmus (uncontrolled eye movement) and in cases where one eye is affected they may have strabismus. 

Some congenital optic nerve anomalies are associated with central nervous system malformations while others may be accompanied by systemic malformations, which is why a good differential diagnosis is required.

The origin of eye malformations and optic nerve anomalies in particular is complex and includes environmental and genetic factors. The environmental causes may be related to teratogenic factors like chemical, biological (infections) or physical agents that alter the development of the eye during pregnancy. A multifactoral type where a combination of genetic and environmental factors leads to a malformation is deemed to be the most common cause of congenital eye anomalies. 

The genetic causes may have a risk of repeating themselves in the children of affected patients. This is why the identification of malformations is highly important for the management of families of affected patients. 

• Papillary aplasia

It is an extraordinarily rare anomaly, normally unilateral (affecting one eye), characterised by the lack of nerve fibres, ganglion cells and central veins in the retina. 

The visual acuity of affected patients is that they "cannot perceive light" (they cannot see out the affected eye). 

• Papillary hypoplasia 

It is a bilateral anomaly in 70% of cases and is most common among men. In these cases, the optical papilla is smaller than normal. In addition, a double ring consisting of a white-yellow halo with a pigmented border surrounding the papilla is a characteristic sign. 

The visual acuity of these patients varies and high refractive errors are common, especially astigmatism. 

Hypoplasia of the optic nerve may be associated with different eye malformations like microophthalmos, blepharophimosis, oculomotor palsy. Furthermore, it can also be associated with systemic malformations and central nervous system malformations like septo-optic dysplasia, atrophy or agenesis of the corpus callosum, third ventricle dysplasia and hypopituitarism.

• Tilted disk syndrome (oblique optic disk)

It is a non-hereditary bilateral anomaly that affects 1-2% of the population.

In these cases, the papilla appears oval-shaped. This papillary configuration is accompanied by a situs inversus of the retinal veins. 

It's important to bear in mind that the oblique papillae will cause visual field defects. 

• Papillary coloboma 

This congenital anomaly has a very low incidence rate among the general population. It is bilateral in 50% of cases. The majority of cases are sporadic or of autosomal dominant inheritance.

Visual acuity is usually quite low (depending on the size of the lesion and integrity of papillomacular bundle) and it is difficult to predict based on the appearance of the optic disk. 

• Morning Glory disk anomaly

It is normally sporadic and unilateral. It is more common in women. Visual acuity is usually below 0.1, although there may be patients with better vision. It is commonly associated with a myopic astigmatism. 

This anomaly gets the name "morning glory" as its ophthalmoscopic image is similar to the "ipomoea purpurea" or common morning glory flower. 

• Peripapillary staphyloma

It is a primary scleral anomaly. It is normally unilateral. The papilla is normal and a it is in a deep fundus excavation. Visual acuity is normally very limited. This anomaly is not usually accompanied by other types of malformations. 

• Persistent myelinated fibres 

The anomalous presence of these myelinated fibres is usually a benign and stable clinical entity. It is a bilateral phenomenon in 17-20% of cases (although in an asymmetrical shape). They appear as white patches with feathery edges that hide the retinal veins. 

Visual acuity is usually normal, and the visual field can change in relation to the myelinated patches. 

• Papillary drusen

Peripapillary drusen are grainy yellowish-white deposits. TThey are found in 0.2-2% of the population. In seventy to eighty percent of cases it is a bilateral anomaly. The majority are asymptomatic, although there are some patients with sudden short-term visual loss that eases by itself. Papillary drusen can present associated vascular anomalies, which is why their study and a correct ophthalmological diagnosis are important. 

As they are congenital bodies, they cannot be prevented per se. However, it's important to highlight the need for a correct early diagnosis. Nowadays, genetic studies are perfomed on affected patients and families.

With some congenital optic nerve anomalies frequent systemic associations occur. A correct, early diagnosis means we can request the necessary complementary tests and carry out monitoring or provide appropriate treatment for these patients. For example, concerning symptoms of hypoplasia of the optic nerve, the presence of septo-optic dysplasia must be ruled out by performing a MRI of the patient's brain, and if required, replacement therapy with growth hormones.