Lecture 4_ Retinal imaging modalities.pdf

DEPT. OF OPTOMETRY, UCC OPT 526: Ocular imaging & biometry Retinal & choroidal imaging Learning Outcomes By the end of this lecture, students should be able to; Describe various imaging procedures for the retina and choroid Interpret chorioretinal pathologies from images ...

DEPT. OF OPTOMETRY, UCC OPT 526: Ocular imaging & biometry Retinal & choroidal imaging Learning Outcomes By the end of this lecture, students should be able to; Describe various imaging procedures for the retina and choroid Interpret chorioretinal pathologies from images  Colour fundus Ocular photography biometry  Specially modified cameras may be used to acquire photographs of the ocular fundus  These cameras employ the same optical principles as the indirect ophthalmoscopy except that the condensing lens is fixed within the camera housing  A flash illumination source is required for photographic exposure  Colour fundus Ocular photography biometry  Similar to indirect ophthalmoscope, there is illumination source to project light onto retina through the pupils  A condensing lens and mirrors are used to direct light into the pupils  The illumination system also includes a flash lamp for photography (a beam splitter allows the flash light to follow the same path was the illumination system)  Optical filters are positioned along the pathway of the illumination system to allow for light of different wavelengths  When the fundus is illuminated, an aerial image of the fundus is formed by the camera’s objective lens  Colour fundus Ocular photography biometry  The viewing system consist of the camera which initially was a single lens film but now employs digital camera  The camera lens focuses image from the condensing lens to the photographic film  A fixation pointer is placed in the illumination pathway at a point conjugate with the patient’s fundus  An illuminated fundus will show an aerial image which is picked up by the camera’s objective lens  The objective lens then focuses on the image formed by the condensing lens and project this onto the photographic film  Colour fundus Ocular photography biometry  Non-mydriatic cameras  These cameras permit fundus photography without having to dilate the pupils of the patient  These cameras use infrared light which minimises pupillary constrict from visible light source  Fundus cameras are typically described by their optical field of view:  Earlier models had 20 deg & 30 deg  Current generations have > 50 deg – wide field cameras & > 100 deg – ultra field cameras  Colour fundus photography Fluorescein Angiography (FA):  Fluorescein angiography is an indispensable procedure that can be used to investigate the integrity of the retinal vasculature in retinochoroidal pathologies Indications: FA is indicated in all the following conditions: macular degeneration, central serous chorioretinopathy, cystoid macular oedema, ischemic optic neuropathy, malignant choroidal melanoma, diabetic retinopathy, retinal tumours, retinal vascular occlusions, rubeosis, subretinal neovascular membranes and unexplained vision loss  Colour fundus photography Fluorescein Angiography (FA): Stages of test:  Fluorescein angiograms progress through five phases: pre-arterial (choroidal flush), arterial, arteriovenous, venous and late recirculation  The process begins with injection of sodium fluorescein dye into the antecubital vein & the dye reaches the posterior pole via the short posterior ciliary arteries, then spreads anteriorly to the ora serrata  Choroidal filling begins 10-20 seconds after injection, and is first visible as a patchy and lobular pattern  Because the choroidal vascular system is fenestrated, fluorescein freely enters the extravascular spaces and appears as a generalized hyperfluorescence  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Stages 1 (choroidal flush):  Choroidal flush appears as mottled fluorescence of the choriocapillaris, due to variable blockage by the retinal pigment epithelium  Choroidal fluorescence is normally absent in the macular area due to the presence of xanthophyll and lipofuscin pigments that absorb the cobalt blue exciting light  Delayed choroidal filling time happens in ocular ischemic syndrome (OIS)  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Stages 2 (arterial phase):  The arterial phase begins 1-2 sec (11-18 seconds after injection) after choroidal filling, and is usually over within seconds of the first appearance of fluorescein dye  In a normal angiogram, branches fill simultaneously. Any delay in the filling of the arterial tree is abnormal and requires investigation  Arteries are bright, but the veins remain dark  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Stages 3 (arteriovenous phase):  In the arteriovenous phase, dye spreads to the pre-capillary arterioles, the capillaries and the postcapillary venules, resulting in a laminar flow pattern with a railroad track appearance in the filling venules  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Stages 4 (venous phase):  Venous filling occurs in two phases: laminar and complete  In the laminar venous phase, a flow pattern in which the blood closest to the vessel wall fluoresces is observed along with a bright outline of fluorescence along the walls of the vessel and a dark line centrally in larger venules (This occurs due to the rapid flow of plasma along the vessel walls and the high density of erythrocytes in the central lumen)  Laminar flow in the veins – the walls of the Venous phase, showing focal hyperfluorescence in the veins are bright while the center of the vein is temporal perifoveal region due to dilatation and leakage still dark from perifoveal capillaries, and filling followed by staining of microaneurysms  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Stages 4 (venous phase):  As more blood converges on the larger venules from smaller tributaries, complete venous filling occurs until the lumen completely fills with dye  The filling process usually takes 45-60 seconds.  The maximum concentration of fluorescein within the choroid and retina occurs 20-25 seconds after injection (this is the peak phase & the optimal time to see the foveal avascular zone)  Shortly after, the dye begins to recirculate Venous phase, showing focal hyperfluorescence in the and a gradual & progressive reduction in temporal perifoveal region due to dilatation and leakage fluorescence is observed as the kidneys from perifoveal capillaries, and filling followed by staining remove dye from the bloodstream of microaneurysms  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Stages 5 (late recirculation phase):  The late recirculation phase takes about 7- 20 minutes  By this time, arteries and veins are virtually devoid of fluorescein, and choroidal flush is barely perceptible  Photos taken at this time help identify late leakage of fluorescein, accumulation of intraretinal dye and staining of tissues with fluorescein  Things that are going to leak or pool will have done so already Late recirculation phase of the fluorescein angiogram of the right eye showing venous type of laminar flow in the superotemporal branch retinal vein (hypofluorescent blood in the central lumen  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Interpretation:  Monitor the time it takes for the dye to travel from the arm to the eye, as well as filling times for the major retinal vascular branches  Next, identify areas of hypofluorescence or hyperfluorescence, and evaluate any change over the course of the study  As always, study the results to make sure they are consistent with your tentative diagnosis  To interpret fluorescein angiography, measure the extent to which an area hypofluoresces or hyper-fluoresces relative to the normal background fluorescein pattern  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Blocking of Interpretation: choroidal hyperfluorescen  Hypofluorescence ce from subretinal blood.  There are 2 major types of hypofluorescence: You know it’s  Blocking : Blood or other opacities block the subretinal fluorescence. Blockage of the retinal because the retinal vessels fluorescence can happen due to preretinal or are overlying the vitreous hemorrhage. Blockage of the dark area choroidal fluorescence can happen due to nevi or melanomas, Stargardt’s disease (lipofuscin blocking choroidal flush leading to a “dark choroid”), or subretinal blood.  Filling defect – lack of retinal perfusion due to capillary dropout, retinal artery occlusion Nonperfusion and other causes. from diabetic capillary dropout  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Interpretation:  Hypofluorescence  Defects that show hypofluorescence can fall into two categories: those that occur due to blockage, and those that happen because of impaired vascular filling  The best way to differentiate is to compare the angiogram with the ophthalmoscopic appearance of the retina  If the hypofluorescent area corresponds to a visible structure, then the hypofluorescence is likely due to blockage  If nothing is visible ophthalmoscopically, then non-perfusion of the area probably causes the hypofluorescence  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Interpretation: Hyperfluorescence: There are 4 types of hyperfluorescence (brightness) in FA: 1. Leakage: A breakdown of the blood-retinal barrier causes leakage  Hyperfluorescence progressively enlarges with fuzzy borders. The dye permeates out of leaky, incompetent blood vessels in the setting of neovascularization, retinal vasculitis, vascular malformations, tumors, or disc edema (dye leaks from prepapillary capillaries)  It’s extravascular and most commonly appears late in the angiogram after blood vessels have emptied Petaloid leakage from cystoid macular available dye edem  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Interpretation: Hyperfluorescence: There are 4 types of hyperfluorescence (brightness) in FA: 2. Pooling: Hyperfluorescence progressively enlarges to fill the fluid cavity and then becomes fixed in size. Usually the dye fills a cavity like the subretinal space or sub-RPE space (in a PED). Pooling from a serous pigment epithelial detachment  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Interpretation: Hyperfluorescence: There are 4 types of hyperfluorescence (brightness) in FA: 3. Staining:  Late hyperfluorescence due to accumulation of fluorescein dye.  The hyperfluorescence gradually gets brighter, but the size stays the same. Usually a mild amount of fluorescence is seen, but it is never very bright. The optic disc always stains. Additionally, drusen and fibrosis will stain. Late staining of acute posterior multifocal placoid pigment epitheliopathy (APMPPE) lesions  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Interpretation: Hyperfluorescence: There are 4 types of hyperfluorescence (brightness) in FA: 4. Window defect:  Defect in the RPE allows transillumination of the choroidal hyperfluorescence. Remains static in size and brightness and becomes fluorescent with the choroidal phase before the arteries even fill in the early frames Window defect from geographic atrophy in AMD  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Interpretation: Hyperfluorescence  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Interpretation: Hyperfluorescence  When reading an angiogram, differentiate between leakage & staining. Staining occurs when fluorescein binds with tissue during its transit through the retina and choroid. Structures that frequently exhibit staining are the sclera, a healthy optic nerve, drusen and glial scars)  Lesions that produce retinal edema demonstrate late hyperfluorescence from the gradual accumulation of dye in extracellular spaces. Because of its architecture, retinal edema is commonly pronounced in the macular area. Macular edema may appear as a diffuse hyperfluorescence, or it may be cystic  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Interpretation: Hyperfluorescence  In cystoid macular edema, foveal capillaries leak fluid into the cystic spaces of the outer plexiform layer. It usually occurs secondary to other ocular or systemic conditions, and is mostly associated with cataract surgery with vitreous displacement. On angiography, this shows up as a classic petaloid (flower-like) pattern of hyperfluorescence  Colour fundus Ocular photography biometry Fluorescein Angiography (FA): Interpretation: Hyperfluorescence  A case of choroidal neovascularization  Colour fundus Ocular photography biometry Fluorescein Angiography (FA):  Risks and Side Effects  Nausea and emesis are the most frequently reported reactions. These  Patients with known hypersensitivity mild reactions tend to occur in 5% of to fluorescein dye should undergo cases or less fluorescein angiography only when vital  More severe reactions such as syncope, thrombophlebitis, fever, nerve palsy and  Although there are no confirmed necrosis of local tissue are reported in toxicity reactions in an unborn child, less than 1% of cases many doctors try to avoid this test in pregnant women.11 Many doctors  The incidence of death following the also tell nursing mothers not to injection of fluorescein dye is 1 in breast-feed for 24-48 hours after the 220,000 procedure  In some cases, orally administered  The most common reaction, which fluorescein may be administered as an happens in nearly all patients, is alternative temporary yellowing of the skin and References: 1. Reed, K. (2001). Fluorescein angiography refresher course. Review of optometry.