They advocate that neuro degeneration is an early component of DM, and may occur alongside diabetic retinopathy, but the preferential thinning of two quadrants only still needs to be explained.16 In a similar study conducted on Type-1 diabetic patients without retinopathy, RNFL thickness was measured with help of scanning laser polarimetry
and it was observed that the superior quadrant showed thinning, as compared to normative data base.17 These two studies have shown that irrespective of presence of retinopathy, the superior quadrants show RNFL thinning in Type-1 diabetic patients, irrespective of age, and the neurodegeneration may precede the development of diabetic retinopathy vascular component.
Various methods are being used to assess and image the RNFL, including fundus photography, scanning laser polarimetry
, Heidelberger retinal tomography(HRT) and optical coherence tomography (OCT).4 The OCT is a modern non-invasive imaging device which measures the peripapillary RNFL thickness in all quadrants in non-contact manner.5 The latest spectral domain optical coherence tomography (SD-OCT) provides high axial scanning resolution (2.00 dioptre, amblyopia, retinal and optic disc diseases, corneal disorders, strabismus, glaucoma, ocular hypertension and a previous history of ophthalmic surgery, both intraocular and refractive surgeries or ocular trauma were excluded.
The thinning of the RNFL can be measured by different imaging techniques, such as scanning laser polarimetry
(SLP), scanning laser tomography (SLT), and optical coherence tomography (OCT) .
Recent studies, implementing contemporary imaging modalities such as scanning laser polarimetry
(SLP) and/or optical coherence tomography (OCT), reported that transient IOP spikes during LASIK have no impact on peripapillary retinal nerve fiber layer (RNFL) thickness [4, 5].
Prevalence of split nerve fiber layer bundles in healthy eyes imaged with scanning laser polarimetry
(13-14) Another objective method to assess the RNFL is through scanning laser polarimetry
. The GDxVCC is a scanning laser polarimeter that measures RNFL thickness using polarized light.
The recent technological leap in automated, non-invasive, objective quantification of the structural parameters of the ONH coupled with visualisation and analysis of the retinal nerve fibre layer (RNFL) and ganglion cell layer (GCL) using techniques such as optical coherence tomography (OCT), scanning laser polarimetry
(SLP) and confocal scanning laser ophthalmoscopy (cSLO) combined with studies suggesting that overreliance on SAP in early glaucoma may lead to underestimation of the amount of glaucomatous damage, has led to renewed interest in the structure-function relationship in glaucoma.
They also include extensive articles on the basic principles and interpretation of imaging modalities such as flourescein angiography, indocyanine green angiography, optical coherence tomography, optical coherence tomographic ophthalmology, ultrasound, scanning laser tomography, scanning laser polarimetry
, the retinal thickness analyzer, adaptive optics ophthalmoscopy, and imaging of ocular blood flow.
However, when RNFL-T is measured by enhanced corneal compensation algorithms of scanning laser polarimetry
, CCT has significant relation with RNFL-T.
The red-free imaging of the optic disc is as valuable in differentiating between normal and glaucomatous patients as the OCT (optical coherence tomography), the SLP (scanning laser polarimetry
), and the CSLO (confocal scanning laser ophthalmoscope) [21-24].