Anomalies in the development of the optic disc

Aplasia of the optic nerve is a rare, very serious pathology in which the optic nerve is not formed at all and there are no visual functions due to delay in the growth of neuron axons into the leg of the eye cup or in connection with the premature closure of the embryonic cleft. At the same time, there is an underdevelopment or absence of the ganglionic layer of the retina. With ophthalmoscopy, there is no disc of the optic nerve and retinal vessels on a different day. At the site of the disc, an area of atrophy or a depression embedded in a pigment rim is determined. The process can be one-sided or two-way.

Hypoplasia of the optic nerve is an underdevelopment of the optic 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 diameter of the disc to 1/3 of its size, monotonic pallor of the disc, narrow, sometimes threadlike retinal vessels. Vision is low, rarely 0.1 D.

Aplasia and hypoplasia are often combined with microphthalmia, nystagmus, strabismus and defects in the development of other organs.

Colonies of the optic nerve - crater-like indentations of pale gray color, round or oval, usually with uneven stepped bottom. Colobolics can be localized in the center or along the edge of the disc and combined with the coloboma of the choroid. With the central localization of the colonies, the vascular bundle of the disc abruptly shifts and all the vessels emerge along the edge of the colobolics, often along the lower ones. The visual functions depend on the size and localization of the colobolics: if the coloboma was formed in the projection zone of the papillomacicular fascicle (low-temporal quadrant), vision is low; if the coloboma is small and is located in the nasal half of the disc, vision is high, up to 1.0. Fields of vision for small colobomas remain unchanged, at large identify the corresponding defects.

The dimples of the optic nerve are small in diameter, but significant in depth of formation (up to 4-5 mm) dark gray color, clearly visible with biomicroscopy. With a slit illumination, a ray of light, passing over a dimple, "dives" into this depression, making a beak-shaped bend. The mechanism of dimple formation is as follows. Normally, the retina terminates at the edge of the disc and not into the tissue of the optic nerve. Penetrates, with the same pathology segment of the retina is introduced into the optic nerve and a dimple is formed on this place. In other words, at the bottom of the dimple there is a rudimentary retina. Anomaly may not have an effect on visual functions and be an accidental finding in a patient's examination. However, when the dimple is localized in the temporal half of the disc, it is possible to develop central serous chorioretinopathy and secondary dystrophic changes in the macula with a significant decrease in vision. Central serous chorioretinopathy can manifest itself in adolescence or more mature age. The anomaly is one-sided.

Inclined discs

This pathology is due to the oblique course of the scleral canal of the optic nerve. With ophthalmoscopy, the optic nerve has an elongated oval shape, and from the temporal side there is a scleral cone resembling a myopic cone, and from the opposite side there is a disk of saturated color that stands above the retina level and has border edges. The entire tissue of the disc is shifted to the side of the nose. Refraction of the eye is more often hypermetropic with astigmatism. Visual functions with correction can be high. Differential diagnosis is performed with neuritis and initial stagnant discs. The anomaly is in most cases two-sided.

Pigmentation of the optic nerve

Normally, there is no pigment containing cells in the optic nerve disc tissue and the disc has a characteristic yellow-pink color. On the circumference of the disc, more from the temporal side, it is possible to accumulate a pigment in the form of a ring or semirings. In pathological conditions, pigmented lesions are also detected in the optic nerve tissue. They have the form of pigment spots, dots, paths, arched bands. A case of diffuse pigmentation of the disc, which was dyed grayish black, is described. Such patients should be under observation.

Myelin fibers

Myelin fibers are normally located in the retrobulbar, namely the intraorbital, optic nerve section, without penetrating the eyeball. With developmental anomalies, part of the myelin fibers enters the eye, following the course of the axons of the ganglion cells. On the fundus, they are defined as glistening milk-white colored fibers, located at the edge of the disc. Usually these fibers are described as "white flame tongues" of varying degrees of intensity and density. Sometimes they significantly cover the central vessels of the retina. Diagnosis is not difficult.

Druises of the optic disc

Druses are noted in one or, more often, in two eyes and are light yellow formations of round shape resembling sago grains. They can be single and superficial, then they are easy to diagnose, but sometimes druses are located deep in the tissue and the whole disk is like stuffing. In such cases, the disk has smeared or scalloped borders, it does not exist, there is no physiological excavation, therefore the diagnosis is difficult and differential diagnostics is required, in which direct biomicroscopy with the use of filters helps. In particularly difficult cases, fluorescent angiography is performed, at which focal hyperfluorescence of the disk is noted, respectively, in the Druze zones. The eye's functions may not be disturbed, but with a large number of drusen narrowing the field of view. It should be noted that age changes in the tissue of the disc in these eyes come early. At the heart of the pathology is the violation of metabolic processes with the formation of colloidal substances - mucopolysaccharides.

[1], [2], [3], [4], [5]

Symptom of "morning light"

The ophthalmoscopic picture is characterized by an elevated mushroom-shaped disk of the optic nerve, around which there is an unevenly pigmented raised shaft of altered tissues of the choroid and retina. The visual functions are variable.

Double (divided) disc of optic nerve

Anomaly is extremely rare. In all the cases described, the process was one-sided. Two discs can only touch ("thin waist") or almost merge ("wide waist"). Each disc has its own vascular system with abnormal variations. One disc in size and appearance may approach normal, and another - much smaller or both small (hypoplasia). Separation of the optic nerve concerns not only its visible part - the disc, but also the intracranial divisions. Vision, as a rule, is low (within hundredths).

[6], [7], [8], [9], [10], [11], [12]

Enlarged disks (megalopapilla)

Congenital pathology, more often bilateral. Normally, the diameter of the optic disc varies from 1.2 to 1.9 mm, an average of 1.5 to 1.6 mm. With this pathology, the diameter of the disc is increased to 2.2-2.5 mm irrespective of the refraction of the eye. With ophthalmoscopy, a characteristic pattern is observed: large disks of saturated gray-pink color significantly prevail over the retina, the edges of the disc are stitched, "combed", the surrounding retina has a radial striation. Vessels as though slide from the disk, making a characteristic bend. The arteriovenous ratio is not changed, but often there is an increased tortuosity of the veins. In a number of cases, anomalous branching of the vessels on the disk is revealed-a loose type of division, whereas in normality it is dichotomous. The process is based on excessive growth of glial tissue - glial hyperplasia. Perhaps, this is the consequence of insufficient reverse development of embryonic processes of the formation of the optic disc.

[13], [14], [15], [16], [17], [18], [19], [20]

Pseudo-discs

This pathology is a kind of megalopapilla. The picture revealed during ophthalmoscopy resembles that with stagnant discs. Enlarged disks are pronounced above the level of the retina, have a rich gray-pink color and borders, but unlike stagnant discs there are no hemorrhages and other extravasates. Ophthalmoscopic picture is stable throughout the life of the patient.

Pseudo nystrites

It is also a kind of gliosis of the optic nerve, but the degree of development of glial tissue is even lower than with pseudosthenes. The picture observed in ophthalmoscopy resembles that in optical neuritis: saturated color of the disc, stitched borders, prominence, but unlike neuritis, exudative effusion and hemorrhages do not. Ophthalmoscopic picture is also stable throughout life. In differential diagnostics, an important role is played by biomicroscopy of a disk using filters. The visual functions are kept high (0.4-0.8). Peripheral vision is unchanged or an increase in the blind spot is detected.

Vascular anomalies of the optic nerve

Various variants of anomalies in the arterial and venous optic nerve systems are described: a spiral and loop-like course of vessels with the formation of arterio-venous and veno-venous anastomoses, and optic nerve vessels with vessels.

Prepapillary membranes

Semi-transparent films are formed above the optic nerve disc, sometimes associated with the remains of the artery of the vitreous. The degree of density of the membrane can be different. With pronounced compaction, the optic nerve disc is not clearly visible. Differential diagnosis is carried out with exudative effusion into the posterior layers of the vitreous.