Functional and Structural Evaluation of Retrobulbar Glaucomateus Damage

Glaucoma represents a group of neurodegenerative diseases characterized by structural damage to the optic nerve and the slow, progressive death of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) is traditionally considered to be the most important risk factor for glaucoma, and treatment options for the disease have hitherto been limited to its reduction. However, visual field loss and RGC death continue to occur in patients with well controlled IOPs (Chidlow et al, 2007). Currently, increased IOP has been excluded from the definition of glaucoma, considered a major risk factor, and glaucoma has been defined as an optic neuropathy. Though we have effective medical and surgical therapies at hand, progressive visual loss is still a prevalent symptom in glaucoma cases. Evidence today proves that glaucomatous damage proceeds from RGCs to the brain (Weinreb, 2007). The ophthalmologist is fully aware that he/she is dealing with the whole visual system –not just the globe, in many neuro-ophthalmic disorders, knowing a defect in the visual field can be due to much pathology from the globe to cortex. Today, we should take areas beyond the retina and optic nerve into consideration in glaucoma follow ups as well. If we recall the anatomy, it is as follows: the retina, optic nerves, optic chiasm, optic tracts, lateral geniculate nuclei (LGN), other brainstem primary visual nuclei (superior colliculus, pretectum), hypothalamic nuclei, pulvinar and accessory optic system, geniculostriate (optic) radiations, striate cortex, visual association areas, and related interhemispheric connections constitute the primary visual sensory system in humans. The optic nerve consists of four segments: intraocular (1 mm in length), intraorbital (about 25 to 30 mm), intracanalicular (about 9 to 10 mm), and intracranial (about 16 mm). Thus, the entire length of the optic nerve from the globe to the optic chiasm is about 5 to 6 cm. Behind the laminar cribrosa, the optic nerve abruptly increases in diameter from 3 mm to 4 mm in midorbit and to 5 mm intracranially. The optic chiasm derives from the merging of the two optic nerves and sits 10.7 ± 2.4 mm above the dorsum of the sella turcica. Occasionally, the intracranial optic nerves are shorter, and the chiasm may lie directly above the sella in a position that is called "prefixed." More commonly, the optic chiasm is positioned 10 to 12 mm above the insertion of the diaphragma sellae onto the dorsum. The significance of this region arises from the fact that lateral fibers originating from the temporal side of the globe directly pass it, while medial fibers originating from the nasal side cross over to the opposite hemisphere (Figure 1). As the retinofugal fibers pass through