Evaluation of the Relationship Between Periodontal Disease Severity and Retinal Layer Thickness in Patients With Diabetic Retinopathy Using Optical Coherence Tomography

Optical Coherence Tomography (OCT) Measurement

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A macular thickness map (ETDRS = Early Treatment Diabetic Retinopathy Study) is examined using OCT, with the center at the fovea centralis. According to the ETDRS map, the central 1 mm represents the fovea, the surrounding 3 mm area represents the inner retinal layers, and the outermost 6 mm area represents the outer retinal layers.

Optical Coherence Tomography Angiography (OCTA) Measurement

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OCTA is a non-invasive technique that allows the evaluation of microvascular changes at the capillary level and imaging of the retinal plexuses layer by layer.

Retinal Layer Thickness

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Definition: Retinal thickness is the distance between the internal limiting membrane (ILM) and the retinal pigment epithelium (RPE), measured by optical coherence tomography (OCT). ETDRS Mapping: The macular region is divided into nine sectors based on the ETDRS grid: Central subfield: A 1 mm diameter circle centered on the fovea. Inner ring (parafoveal region): 1-3 mm diameter, divided into superior, inferior, nasal, and temporal quadrants. Outer ring (perifoveal region): 3-6 mm diameter, also divided into four quadrants.

Choroidal Thickness (CSI Reference)

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Definition: The choroid is the vascular layer beneath the RPE. Choroidal thickness is the perpendicular distance from Bruch's membrane to the choroid-sclera interface (CSI). Measurement: Typically obtained with enhanced depth imaging OCT (EDI-OCT), mapped according to the ETDRS grid.

Ganglion Cell Layer (GCL) Thickness

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Definition: The GCL is composed of the cell bodies of retinal ganglion cells, located between the inner plexiform layer and the retinal nerve fiber layer. Measurement: OCT can quantify GCL alone or GCL + inner plexiform layer (GCL+IPL), usually reported using the ETDRS 9-sector mapping.

Retinal Nerve Fiber Layer (RNFL) Thickness

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Definition: The RNFL consists of the unmyelinated axons of ganglion cells, located at the innermost surface of the retina. Measurement: Often assessed in the peripapillary region or in the macular area using ETDRS mapping.

Choroid-Sclera Interface (CSI)

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Definition: The CSI is the outer anatomical boundary of the choroid where it transitions into the sclera. Role in Thickness Measurement: Serves as the lower reference point for choroidal thickness measurements (Bruch's membrane to CSI), which can be mapped according to the ETDRS grid.

Superficial Retinal Layers

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Definition: The inner portion of the retina, located closer to the vitreous side. Typically associated with the superficial capillary plexus. These layers are among the first affected in diseases such as glaucoma, optic neuropathies, and ischemic retinopathies.

Deep Retinal Layers

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Definition: The middle and outer portions of the retina, located closer to the photoreceptors. Associated with the deep capillary plexus. Clinical relevance: Important changes are observed here in conditions such as macular edema, diabetic retinopathy, and age-related macular degeneration.

Foveal Avascular Zone (FAZ)

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Definition: A circular area at the center of the fovea devoid of retinal capillary vessels. Location: In the central fovea, approximately 500-600 micrometers in diameter. Characteristics: Contains the highest density of photoreceptors (especially cones). Avascular nature means nutrition is supplied via diffusion from the choroid. Responsible for the highest visual acuity. Clinical relevance: FAZ size, measurable by OCT angiography (OCTA), is an important biomarker in diabetic retinopathy, retinal vein occlusion, and macular ischemia.