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Abstract Retinal nerve fiber layer is the innermost layer of the retina, it is formed of the axons of ganglion cells. Attrition of nerve fibers in the anterior visual pathways is reflected directly in the nerve fiber layer of the retina. These retrograde degenerative changes are subtle but they can be seen with an ophthalmoscope and can be photographed with a fundus camera. In routine clinical practice identifying pathologic alterations in the RNFL ophthalmoscopically necessitates optimal viewing conditions, familiarity with the appearance of the normal RNFL, and a high index of suspicion. So, the importance of the new objective quantitative technologies for RNFL assessment which are the optical coherence tomography, the confocal scanning laser ophthalmoscopy, the scanning laser polarimetry and the retinal thickness analyzer had been proved. Retinal nerve fiber layer (RNFL) can be evaluated both structurally and functionally. This is helpful for early diagnosis and following up of the optic nerve diseases . For structural evaluation, RNFL can be evaluated by clinical examination of the optic disc, stereoscopic optic nerve photography, red-free monochromatic RNFL photograph as well as computer-based devices such as: optical coherence tomography, Confocal scanning laser ophthalmoscopy, and scanning laser polarimetry, that provide quantitative assessments of structural damage. For functional evaluation, RNFL can be evaluated by perimetry as well as electrophysiology; there are now many different methods for performing visual field testing including standard automated perimetry (SAP) as well as selective techniques including short wavelength automated perimetry (SWAP), frequency doubling technology (FDT) perimetry, high pass resolution perimetry (HRP) and motion perimetry. Glaucoma is a multi-factorial optic neuropathy characterized by Irreversible progressive loss of the retinal ganglion cells (RGCs) and thinning of the retinal nerve fiber layer (RNFL), leading to visual field loss and eventually, total loss of vision. 40% to 50% of the RNFL could be lost before visual field defects are detected by conventional perimetry. Thus, RNFL assessment had emerged as an important parameter for pre-perimetric diagnosis of glaucoma. Diabetic retinopathy (DR) is the fifth most common cause of blindness worldwide. In addition to typical retinopathies, neuro-visual impairments had been reported. Focal retinal nerve fiber layer loss in diabetic patients with preclinical DR was detected. In vitro studies had demonstrated that diabetes affects both retinal neurons and glial cells. Panretinal photocoagulation causes a sequential decrease in the peripapillary retinal nerve fiber layer (RNFL) thickness. Optic neuropathies are conditions that involve degeneration of the optic nerve, and can be hereditary or acquired. These neuropathies result in characteristic changes to the optic nerve head and the surrounding retinal nerve fiber layer as a result of direct and indirect damage to the retinal ganglion cells and their axons. Assessment of optic disc edema can be done by follow up the resolution of axonal swelling and thinning of the RNFL, which are essential aspects of optic atrophy. RNFL assessment appeared to be an important clue in the diagnosis of other disorders like neurodegenerative disorders including multiple sclerosis, Alzheimer’s and parkinson’s disease which show affection of the nerve fiber layer causing visual function affection. The majority of hereditary retinal dystrophies originate within the outer retinal layers. A secondary degeneration of t middle and inner retinal layers could be caused by a transsynaptic degeneration or by toxic products associated with the death of outer retinal structures. Middle and inner retinal layers in hereditary retinal dystrophies had gained more interest because some of the new potential therapeutic concepts such as transplantation of photoreceptors or pigment epithelium cells and visual prosthesis require functional second and third order retinal neurons . It was reported that clinically evident retinal nerve fiber layer thinning could be detected on fundus photography in various diseases of the outer retina. Some diseases had been thought to change RNFL, but studies had proved the opposite and that aided in the true understanding of these pathologies as in amblyopia in which RNFL assessment was insignificant. Evaluation the effect of LASIK on RNFL thickness measurements obtained with SLP, OCT, and HRT. Increased numbers of clinically visible optic nerve head drusen correlated with NFL thinning shown by OCT measurements and both visual field defects and NFL loss seen by red-free photography. Significant thinning of the RNFL occurs in HIV-positive patients without a history of CMV retinitis and with a history of low CD4 cell counts in comparison to the same group of patients with CD4 cell count increased above 100 and HIVnegative control subjects. RNFL thinning in Obstructive sleep apnea syndrome was correlated with the severity of this condition, as the disease becomes more severe, RNFL thinning is proportionally. |