Developmental anomalies of the optic disc

Optic nerve aplasia is a rare, very severe pathology, in which the optic nerve does not form at all and visual functions are absent due to delayed ingrowth of axons of the second neuron into the peduncle of the optic cup or due to premature closure of the embryonic fissure. At the same time, underdevelopment or absence of the ganglion layer of the retina is observed. Ophthalmoscopy reveals the absence of the optic nerve disc and retinal vessels at different bottoms. In place of the disc, an atrophic zone or a depression immersed in a pigment rim is determined. The process can be unilateral or bilateral.

Optic nerve hypoplasia is an underdevelopment of the optic nerve disc caused by incomplete differentiation of retinal ganglion cells and a decrease in the number of axons of the first neuron, with the formation of mesodermal and glial elements usually normal. Ophthalmoscopy reveals a decrease in the disc diameter to 1/3 of its size, monotonous pallor of the disc, narrow, sometimes filiform retinal vessels. Vision is poor, rarely 0.1 D.

Aplasia and hypoplasia are often combined with microphthalmos, nystagmus, strabismus and developmental defects of other organs.

Optic nerve colobomas are crater-like depressions of pale gray color, round or oval shape, usually with an uneven stepped bottom. Colobomas can be localized in the center or along the edge of the disk and combined with choroidal coloboma. With central localization of the coloboma, the vascular bundle of the disk shifts sharply and all the vessels exit along the edge of the coloboma, more often along the lower one. Visual functions depend on the size and location of the coloboma: if the coloboma formed in the projection zone of the papillomacular bundle (lower temporal quadrant), vision is poor; if the coloboma is small and located in the nasal half of the disk, vision is high, up to 1.0. The visual fields remain unchanged with small colobomas, and corresponding defects are revealed with large ones.

The optic nerve pits are small in diameter but deep (up to 4-5 mm) dark gray formations that are clearly visible under biomicroscopy. Under slit illumination, a beam of light, passing over the pit, "dives" into this depression, making a beak-shaped bend. The mechanism of pit formation is as follows. Normally, the retina breaks off at the edge of the disk and does not penetrate deep into the optic nerve tissue. However, with this pathology, a segment of the retina is embedded in the optic nerve and a pit is formed at this site. In other words, there is a rudiment of the retina at the bottom of the pit. The anomaly may not affect visual functions and be an accidental finding during examination of the patient. However, if the pit is localized in the temporal half of the disk, central serous chorioretinopathy and secondary dystrophic changes in the macula with a significant decrease in vision may develop. Central serous chorioretinopathy may manifest in adolescence or later in life. The anomaly is unilateral.

Inclined discs

This pathology is caused by the oblique course of the scleral canal of the optic nerve. During ophthalmoscopy, the optic nerve has an elongated oval shape, and from the temporal side, a scleral cone is visible, resembling a myopic one, and from the opposite side, a disk of saturated color, protruding above the level of the retina, with blurred borders. All the tissue of the disk is shifted towards the nose. The refraction of the eye is often hypermetropic with astigmatism. Visual functions with correction can be high. Differential diagnostics are carried out with neuritis and initial congestive disks. The anomaly is bilateral in most cases.

Optic disc pigmentation

Normally, there are no pigment-containing cells in the tissue of the optic nerve disc, and the disc has a characteristic yellow-pink color. Around the circumference of the disc, more on the temporal side, there may be a pigment accumulation in the form of a ring or semicircle. In pathological conditions, pigment formations are also detected in the tissue of the optic nerve. They look like pigment spots, dots, tracks, and arcuate stripes. A case of diffuse pigmentation of the disc, which was colored grayish-black, has been described. Such patients should be under dispensary observation.

Myelinated fibers

Myelin fibers are normally located in the retrobulbar, namely, intraorbital, section of the optic nerve, without penetrating into the eyeball. In developmental anomalies, some of the myelin fibers enter the eye, following the axons of the ganglion cells. In the fundus, they are determined as shiny milky-white fibers located along the edge of the disk. These fibers are usually described as "tongues of white flame" of varying degrees of expression and density. Sometimes they significantly cover the central vessels of the retina. Diagnostics is not difficult.

Optic disc drusen

Drusen are observed in one or, more often, in both eyes and are light yellow formations of a round shape, resembling sago grains. They can be single and superficial, then they are easy to diagnose, but sometimes drusen are located deep in the tissue and the entire disc is as if stuffed. In such cases, the disc has blurred or scalloped borders, protrudes, physiological excavation is absent, as a result of which diagnosis is difficult and differential diagnosis is required, in which direct biomicroscopy with the use of filters helps. In particularly difficult cases, fluorescent angiography is performed, which notes focal hyperfluorescence of the disc according to the drusen zones. Eye functions may not be impaired, but with a large number of drusen, the boundaries of the visual field are narrowed. It should be noted that age-related changes in disc tissue in such eyes occur early. The pathology is based on a violation of metabolic processes with the formation of colloidal substances - mucopolysaccharides.

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The "morning glow" symptom

The ophthalmoscopic picture is characterized by a raised mushroom-shaped optic disc, around which there is an unevenly pigmented raised ridge of altered choroidal and retinal tissue. Visual functions are variable.

Double (split) optic disc

The anomaly is extremely rare. In all the described cases, the process was unilateral. Two disks may only touch ("thin waist") or almost merge ("wide waist"). Each disk has its own vascular system with abnormal variations. One disk may be close to normal in size and appearance, and the other is significantly smaller, or both are small (hypoplasia). The division of the optic nerve concerns not only its visible part - the disk, but also the intracranial sections. Vision is usually poor (within hundredths).

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Enlarged discs (megalopapilla)

Congenital pathology, often bilateral. Normally, the diameter of the optic nerve disc varies from 1.2 to 1.9 mm, on average 1.5-1.6 mm. In this pathology, an increase in the disc diameter to 2.2-2.5 mm is observed regardless of the refraction of the eye. Ophthalmoscopy reveals a characteristic picture: large discs of a rich gray-pink color significantly protrude above the level of the retina, the edges of the disc are shaded, "combed", the surrounding retina has radial striation. The vessels seem to slide off the disc, making a characteristic bend. The arteriovenous ratio is unchanged, but increased tortuosity of the veins is often noted. In some cases, an anomaly in the branching of vessels on the disc is revealed - a scattered type of division, whereas normally it is dichotomous. The process is based on excessive proliferation of glial tissue - glial hyperplasia. This may be a consequence of insufficient reverse development of the embryonic processes of optic nerve head formation.

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Pseudo-stagnant discs

This pathology is a type of megalopapilla. The picture revealed by ophthalmoscopy resembles that of congestive discs. Enlarged discs protrude above the level of the retina, have a rich gray-pink color and blurred borders, but, unlike congestive discs, there are no hemorrhages or other extravasates. The ophthalmoscopic picture is stable throughout the patient's life.

Pseudoneuritis

This is also a type of optic nerve gliosis, but the degree of glial tissue development is even lower than in pseudostagnation. The picture observed during ophthalmoscopy resembles that of optic neuritis: saturated disc coloration, blurred borders, prominence, but unlike neuritis, there is no exudative effusion or hemorrhage. The ophthalmoscopic picture is also stable throughout life. Biomicroscopy of the disc using filters plays an important role in differential diagnostics. Visual functions remain high (0.4-0.8). Peripheral vision is unchanged or an increase in the blind spot is detected.

Anomalies in the development of the optic nerve vessels

Various variants of anomalies of the arterial and venous systems of the optic nerve are described: spiral and loop-shaped course of vessels with the formation of arteriovenous and venovenous anastomoses, entanglement of the optic nerve with vessels.

Prepapillary membranes

Translucent films are formed above the optic nerve disk, sometimes associated with the remnants of the vitreous artery. The degree of membrane density may vary. With pronounced compaction, the optic nerve disk is not clearly visible. Differential diagnostics are performed with exudative effusion in the posterior layers of the vitreous body.