The retina is the innermost layer of the eye, including the photoreceptor cells and neurons (retinal ganglion cells(RGC)). The retina is a very thin layer that covers about 75% of the area of the eye. Any disorder in the functioning of the retina and its blood vessels has an adverse effect on vision and in some cases causes serious damage and blindness. Ophthalmologists of Tehran-Iran Noor Eye Hospital do their best to quickly and accurately diagnose retinal diseases, using advanced and new techniques.
Retinal Blood Vessels Tests
To perform this test, a contrast agent, such as fluorescein dye, or the like, is injected into a vein in the arm or hand of the patient. Images of the posterior pole were taken by the Micron III rodent fundus camera. This test is used to assess retinal and choroidinal blood flow. Fluorescein dye is best for studying the retinal blood vessels while indocyanine green (ICG) is often better for studying the deeper choroidal blood vessel layer and deeper parts. Fluorosine angiography is most commonly used for the diagnosis of diabetic retinopathy, vascular occlusive diseases such as retinal arterial occlusion and wet macular degeneration evaluation. The ICG is also used to assess blood flow in patients with age-related macular degeneration. Both types of these substances have very few side effects and can be used safely.
Common Complications of the Use of Contrast Materials
- Fluorescein: This substance may cause jaundice in the skin or eyes and orange urine for about 24 hours after injection. It should not make you worried, since these complications resolve spontaneously.
- ICG: In some patients, they may rarely have allergic reactions. Additionally, ICG use in patients with hypersensitivity to iodine is prohibited.
2. HRA Angiography: Using this technique increases the accuracy of fluorescein and ICG angiographies and offers different imaging modes for angiography, so that single images or image sequences can be acquired and stored.
3. OCT: This new technique is known as Optical Coherence Tomography. An ophthalmologist uses OCT to achieve high-resolution tomography maps of retina layers and other valuable information. It is therefore used to diagnose and follow up many retinal diseases such as macular holes, macular edema, macular degeneration, diabetic retinopathy, and glaucoma. Since a light source is applied in this technique, there is no need to contact with the eye and it is performed within a few seconds.
4. Electroretinography (ERG) : the assessment of retinal potentials by Flash, Pattern, and M.F methods is the feature of ERG system that is applied in Iran-Tehran Noor Eye Hospital. These facilities help to diagnose many retinal diseases. This test assesses the overall electrical response of the retina to a visual stimulus by measuring the retinal potential difference between the two electrodes. One of them is placed slightly underneath the lower eyelid on the cornea and is in contact with it, and the other electrode, which is neutral, is placed on the skin around the eyes. For patients' convenience, anesthetic drops are used and in some cases, for example, when the patient is a child, general anesthesia is used. This test is used to detect retinal disorders such as cone dystrophy or retinitis pigmentosa (RP).
5. Electrooculography (EOG): One of the most important tests for electrophysiology is Electrooculography (EOG). This test is applied to assess the pharmacological effects and pathological changes. It is typically used to evaluate the retinal pigment epithelium and photoreceptors; rod and cone cells. In general, there is a potential difference of 6 milliliters between the cornea and the retina. This potential difference is measurable by placing electrodes on the skin and on both sides of the eye.
Method of Performing EOG Testing:
For performing this test, the patient was asked to keep his eye steady on a light-emitting object; the light will be so distorted that the axis of the eye diverges 30 degrees from its horizontal direction. The potential difference between the two electrodes is amplified and recorded on the device. This test is especially valuable for examining patients who are suspected of having a disorder in the retinal pigment epithelium, such as retinitis pigmentosa (RP). Performing these tests with high precision is now possible at Tehran-Iran Noor Eye Hospital.