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Abstract
Wet ARMD is one of most common causes of CNV which causes irreversible visual loss in people over 50 years old. Other causes of CNV include high myopia, choroidal rupture, angioid srteaks, inflammatory disease as multifocal choroiditis ,iatrogenic after LASER photocoagulation and may be idiopathic.
The pathology of CNV involves the events that happen in any disease causing break through Bruch’s membrane that permits new vessels from choriocapillaris to invade subRPE or subretinal spaces producing RPE detachment or subretinal exudates and hemorrhage which end by scar formation with marked affection of V/A, central scotoma and metamorphopsia.
OCT is investigative tool that produces high resolution cross-sectional images of the retina analogous to B scan U/S which utilizes sound waves. OCT uses light from superluminscent diode with resolution of 10µm.
OCT permits simultaneous viewing of the position of the ocular structure which is being scanned as well as its transverse cross-section .
OCT image can be acquired extremely rapid. OCT measurement beam is in the infrared range so patient discomfort during the examination is minimized. The rapid acquisition time of OCT images permits many to be acquired on different cross-sectional planes in the anterior segment or the fundus.
OCT images contain quantitative information on dimensions of intraocular structures and have the potential to stage disease progression or response to therapy.
OCT can confirm the conversion, differentiation and identification of subtle changes that could have never been documented previously.
High resolution OCT will lead to better discrimination between retinal layers and perhaps the ability to examine cellular morphology and retinal mapping.
OCT help the ophthalmologist to diagnose CNV if there’s a drusen or mild macular edema in old patient with metamorphopsia. OCT also can differentiate CNV from other causes of metamorphopsia as juxtafoveal telangiectasia &can also differentiate fibrovascular PED from serous PED with monitoring of occult CNV .
OCT can’t replace FFA in diagnosis and follow up of CNV, however OCT may have a role as screening tool to prioritize FFA requests.
In treating a patient with wet ARMD there’s a need for doing OCT and FFA at base line as the OCT doesn’t delineate the exact extent of a CNV nor the composition of the lesion, therefore fluorescein is very important as a guide for treatment ,whether it is PDT ,thermal laser or anti-VEGF injection.
OCT has helpful role in selection of cases eligible for surgical removal of CNV as it determines the relation of CNV to RPE, if the CNV membrane reaches above the RPE (typeII) it is eligible for submacular surgery. OCT can also be used to follow up patients after different surgical procedures for CNV as submacular surgery, macular translocation and RPE transplantation.
OCT has a very helpful role in following up the patients after treatment of CNV by PDT, anti-VEGF or TTT by measuring retinal thickness and confirm the presence of intraretinal, subretinal fluid ,cystoid macular edema or RPE detachment which appears in FFA as active leakage. If it shows recurrence or persistence FFA is a must to help determining spot size and treatment parameters in retreatment of PDT. If there’s a plan to use a therapy other than PDT such as anti -VEGF there’s no need to do FFA in follow up just an OCT is enough. So in following up a patient who is getting anti-VEGF injection; OCT is done 6 weeks after the injection. If the lesion looks the same , or still some leakage was present so there’s a need for reinjection . FFA will be done for these patients every 6 ms ;only to make sure that the treatment is having same effect.
OCT can diagnose the complication occuring after treatment of CNV by bivacizumab as RPE tear.