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Home , Foveola, Pars plicata

26 Journal of Ophthalmic Photography Vol. 2, No. 1 August 1979

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Fundus photography and fluorescein angiography

Anatomy

An integral part of the optical system transparent layer (), the center of blood supply to the outer layers of the in photography is the subject . which forms the anterior pole. The points and extends from the optic nerve The condition of the intra-ocular media of junction between the cornea and posteriorly to the anteriorly. therefore is an important factor to the are called the corneo-scleral limbus. The The ciliary body is an intermediate, image quality of the resultant picture, and posterior pole is located at the posterior ring-shaped structure that lies between since the eye does play such an important curvature of the eyeball, while the equator the and the . This body is di- role, it is desirable that the ophthalmic is the imaginary line which lies mid-way vided into two parts, the uveal and epi- photographer become familiar with its between the anterior and posterior poles thelial portions (Figure 9). The ciliary structures. and is about 16 mm posterior to the cor- muscle is located in the uveal portion of Only a small portion of the eyeball is neo-scleral limbus. the ciliary body and controls the ability of seen, the major part of it resting in the The middle layer the to change its powers of refraction. . The average eye measures 24 mm in When the muscle is at rest (Figure 10), the diameter along the antero-posterior axial The is made up of the choroid, zonular fibers (which extend from the diameter, with a normal range of 22 to 27 ciliary body and iris. The choroid is a ciliary body and attach to the lens) are mm (Newell and Ernst, 1974). The eyeball highly vascular layer which forms the taut, and the lens is at its narrowest; is surrounded by fatty and connective tissue and is controlled by six muscles which arise from the orbit. The optic nerve forms the connecting link from the eyeball to the brain, along which images are transmitted to the brain in the form of electrical impulses. The is made up of three chambers, the anterior and pos- terior chambers and the vitreous cavity (Figure 8), and consists of three main layers, the outer layer (sclera), middle layer (uvea) and the inner layer (retina). The outer layer The sclera is a tough layer of tissue which makes up the entire posterior por- tion of the eye and is avascular, but is covered by a thin membrane (bulbar ), which does have fine blood vessels passing through it. The anterior portion of the sclera consists of a central, Don Wong, RBP and fluorescein angiography 27

conversely, when the is are known as the . cells firmly attached to Bruchs mem- tensed, the zonules become slack, en- The iris is a thin, flexible curtain lo- brane of the choroid. It is the pigment abling the elastic properties of the lens to cated in the eye anterior to the ciliary epithelium which gives the fund us a increase its thickness, and in that manner, body, in the center of which is an opening granular appearance. The more complex its power of refraction. () which expands and contracts to part of the retina is the inner layer, or The epithelial portion of the ciliary control the amount of light entering the sensory retina. The sensory retina is di- body faces the vitreous cavity and consists eye. vided into nine substrata (Figure 10). of the and . The Topography of the retina pars plicata is formed by numerous folds The inner layer () which range in number The retina is the innermost layer of The portion of the optic nerve that is between 60 and 70. The zonular fibers the eye and is the layer on which the vi- seen ophthalmoscopically is the arise from the areas between the ciliary sual image is formed, then transmitted to (Figure 11), which measures about 1.5 mm processes and extend toward the lens the brain via the optic nerve. The retina in diameter. Normally, the optic disc is where they attach to the lens capsule. The is divided into two main parts; the outer uniform in color, with fairly well defined points at which the pars plana meet the layer is the retinal pigment epithelial margins. The major vessels providing retina have a scalloped appearance and layer and is made up of a single layer of circulation to the retina are the central retinal artery and the central retinal vein. These vessels bifurcate at the surface of the disc and branch nasally and tempo- rally both superiorly and inferiorly. The nasal vessels arch in a fairly direct, straight fashion, whereas the temporal branches curve from the disc superiorly and inferiorly forming arches that are referred to as superior and inferior tem- poral arcades. Outlined within these temporal ar- cades is the central retina, in the center of which is seen a dark, oval-shaped reflex. This dark ring, which represents a thicker layer of pigment cells than its surrounds, is the . In the center of this ring is a brighter reflex area, the . The foveola is the point; of central fixa- tion. Often, the ophthalmic photographer

Figure 10—The mechanism of . A—When the ciliary muscle is at rest, the zonular fibers are will encounter the terms "macula," "ma- taut, and the lens is at its narrowest, B—When the ciliary muscle is tensed, the zonular fibers become slack, cular area" or "macular dark spot" when enabling the elastic properties of the lens to increase the lens thickness, and thus, its power of refraction. receiving instructions for photography. 28 Journal of Ophthalmic Photography Vol 2, No. 1 August 1979

systems produce pictures with an angle of view of about 30°. This enables the pho- tographer to obtain pictures of the "pos- terior pole" to include the entire disc (including the nasal rim); the central retinal arteries and central retinal veins; the central retina; both superior and in- ferior arcades; and about a full disc-di- ameter temporal to the fovea] area. Any other view outside of these boundaries, therefore, constitutes equatorial and/or peripheral fundus photography. Since a 30° view photograph shows only a portion of the fundus, a number of overlapping "survey" photographs are required (Fig- ure 13) if you want to show any wide- spread changes in the fundus.

The lens The front surface of the lens is sit- uated immediately behind the iris at the level of the papillary area and is adjacent to the . On clinical exami- nation the lens appears to he totally clear. However, under high magnification and slit-beam illumination, one can see that this is not so. The lens is a symmetrical, convex structure encased in an elastic Figure 11—Regions of the retina. capsule and held in place by very fine zonular fibers. Controlled by the ciliary muscle, these fibers tense or relax, as was These terms are synonomous with fovea In order to obtain proper orientation described earlier, which allows the lens to and to know whether a given photograph centralis and merely reflect anatomical vs. change its shape. This changing of the is of the right (OD) eye or left (OS) eye, histologic terminology. The histologic lens shape in the anterior-posterior di- definition of the central retina (macula) consider the foveola as the central point mension is known as accommodation of the central retina. The optic disc is al- is a 6 mm diameter zone radiating out- (Stein and Slatt, 1971) and is a trait which wards from the foveola nasally to the optic ways nasal to the foveola and the foveola diminishes with age. disc, and temporally to an equal distance, is always inferior to an imaginary hori- as well as superiorly and inferiorly to the zontal line drawn through the center of The vitreous body temporal arcades. the optic disc (Figure 12). Most camera The vitreous body is a transparent, gel-like tissue which fills the vitreous cavity and which is in firm contact with the retina. It is attached firmly to the ciliary body and retina at the ora serrata anteriorly, as well as to the margins of the disc posteriorly. Abnormalities of the eyeball In the normal (emmotropic) eye, parallel rays of light are brought to a focus on the retina due to a combination of factors, namely, the axial length of the globe in respect to the combined refrac- tive powers of the cornea, lens and other intra-ocular media. Each element pos- sesses its own refractive power, the cornea being an average of 43 diopters, the lens 17 diopters and the total refractive power

Figure 12—Orientation of right fundus (OD) and left fundus (OS ). The optic disc is always positioned nasally to about 58 diopters. If the eyeball is ab- the foveola, and the foveota is always slightly inferior to a horizontal line drawn through the center of the optic normally short (hyperopic) or abnormally disc. long (myopic) in its axial length, the cor- relation of the refractive power of the eye, Don Wong, RBP Fundus photography and fluorescein angiography 29

Figure 13—A number of overlapping (survey) photographs are required to provide full documentation of the retina with the standard fundus camera. It is not possible to obtain pictures of the retina beyond the equator without utilizing special clinical examination techniques.

the accommodative ability of the lens and lens suffers defects in only these two Factors in image formation the length of the eye, will not permit planes, the condition is referred to as and quality proper focusing of parallel rays of light on "regular" astigmatism; however, if more In the healthy, normal state, all of the the retina. Thus, in the physiologically than two planes are involved, the condi- intra-ocular media are essentially trans- hyperopic eye, the rays of light come to a tion is known as "irregular" astigmatism. parent. Any alteration in this normal state focus at some point behind the retina, Astigmatism in the eye can also be the will effect the quality of photography. The whereas in the myopic eye the rays are result of differences in the curvature of ophthalmic photographer should become brought to a focus somewhere in front of the cornea in the horizontal and vertical familiar with the factors of dilatation and the retina. These conditions are com- planes. The greater the differential in alterations in the antra-ocular media in pensated for with corrective lenses; simi- these curvatures, the more severe the order to know the best approach to take larly, the photographer must choose the condition in the eye. In hyperopic astig- for optimum photographic results. appropriate diopter lens for fundus pho- matism, the focal points will he some- tography. where behind the retina, and in myopic Dilatation Astigmatism occurs in an eye in astigmatism, the focal points will be which the refractive powers are not the somewhere in front of the retina. It is ob- The must be well dilated for same in all meridians, and thus will not vious then, that unless correction for photography. The greater the degree of permit the proper resolution of an image astigmatism is undertaken in fundus dilatation, the better the photographic on the retina. Therefore, if there is a dif- photography, it is possible that parts of results, since more light is allowed to enter ferential in resolving power of the lens the image will suffer. If an astigmatic the eye. Since the iris is the involuntary between the horizontal and vertical correction control is available on the diaphragm mechanism of the eye, the planes, that difference respresents the camera, its use will assist in yielding op- pupils constrict by contraction of the iris degree of astigmatism in the lens. If the timum photographic results. sphincter muscle when a bright light 30 Journal of Ophthalmic Photography Vol. 2, No. 1 August 1979

strikes it. Therefore, in order that retinal a program of medication to control glau- this patient, though the chart indicated examinations and fundus photography coma must be instructed by their doctors completely normal and clear intra-ocular may be performed, eye drops are utilized to alter this program at the time of the media. When the patient was directed to temporarily neutralize the functioning fundus photography appointment in hack into the examining room and was of these muscles. These drugs are gener- order to allow the dilating drops to func- re-examined with a slit-lamp microscope ally divided into two major groups, myd- tion. Any glaucoma patient who has taken by the doctor, disturbances of the epi- riatics and cycloplegics. Both act as dila- his medication on the day on which pho- thelial layers of the cornea were discov- tors, hut mydriatic drops act only on the tography is scheduled generally cannot be ered. These disturbances were not noted iris muscle, whereas cycloplegic drops act photographed because the dilating drops on the initial examination. Tracing the on both the iris and ciliary body muscu- will not he effective. In some instances, patients route through the office, each lature. One recommended protocol for photography can be attempted through a apparatus was carefully examined, and dilatation of the pupil is the use of poorly dilated or an undilated pupil in an finally, a close inspection of the footplate quick-acting drops such as Mydriacyl 1% effort to get some information. In these of a tonographer disclosed a small, un- in combination with Neosynephrine in cases, it is acknowledged that the results usual spur which caused the disturbances. viscous solution. The following is one will usually be compromised. This plate was immediately removed and. recommended order of application: sent out for repair. The patient was re- Alterations in the intra-ocular 1) One drop of Mydrialcyl 1%. scheduled for photography. 2) Mydriacyl 1 media % followed 1-2 minutes A contact lens examination of the eye later by a drop of 10% Neosyne- Cornea. Changes in the clarity of the requires the use of a viscous contact lens phrine. cornea may he encountered that will be lubricant applied over the cornea leaving 3) Repeat the dosage six times for the disruptive to image formation. These a residual film which obstructs visibility. next 15 minutes. changes include drying of the tear film This lubricant generally cannot be satis- The average time required for satisfac- layer that normally covers the cornea, or factorily washed off to enable good image tory dilatation is in the order of 30 to 60 excessive tearing. These conditions are of resolution, and therefore, this type of ex- minutes. The diabetic patient often pre- a transient nature and may occur at any amination should not be scheduled im- sents a problem in achieving adequate y time during the photographic session. In mediatel prior to fun dus photography. dilatation and may require a considerably the event that the patient is capable of If the physician must perform a contact longer period of time to be prepared for maintaining a fixed gaze for a consider- lens examination in order to arrive at a photography. Some patients will not di- able length of time without blinking, in- clinical diagnosis and if photography must late well no matter how many doses they struct him to blink just prior to exposure also be done, allow some time to pass be- are given, thus making photography dif- in order to restore the tear film layer. If fore proceeding with the photography. In ficult. the patient tears due to sensitivity of light, these photographs, image quality will Precautions. Generally speaking, ancil- rest periods should be given in order to suffer, and fine details may he lost. lary health personnel may perform within dry off the excess moisture over the cor- In the presence of mild corneal the framework of programs established by nea. Photographs done through a dry edema where the cornea, being excessively the physician and may administer medi- cornea will appear out-of-focus, whereas hydrated, swells and loses transparency, cations if done under direct supervision. those taken through excessive moisture the application of a small amount of The application of dilating drops is gen- may have flare or specular highlights. glycerol by a doctor will temporarily erally performed by ancillary health per- A number of eye testing and exami- dehydrate the cornea, long enough for sonnel according to guidelines established nation procedures such as applanation photography to be satisfactorily per- by the physician for that office. It would tonometry, indentation tonography or formed. Other corneal pathology, eg., be unwise for ancillary health personnel contact lens examination require a direct central opacifications, will probably be too to apply dilating drops to an unknown application of an instrument to the cor- disruptive to the quality of image resolu- patient, since the act of dilating a pupil nea. It is recommended that all important tion to warrant serious photographic may provoke an attack of acute angle- photographic and angiographic work he consideration. closure glaucoma. In the event this does scheduled before these procedures in Lens. By definition, any decrease in the occur, a physician should he notified im- order to avoid the possibility of obtaining transparent quality of the lens is a cata- mediately in order to initiate corrective pictures with poorly resolved images. ract, and how disruptive these changes are steps. Generally, tonometry or tonography do is determined by two factors. The more Patients being referred to the labo- not cause problems in this regard, since important of these factors is the location ratory for fundus photography or angi- the corneal tissues are not affected. of the changes within the lens; the second ography from an ophthalmologists office However I can cite a personal experience factor is the density of the opacities. The have already been screened by a doctor, in which this was the case. photographer may encounter other terms and therefore may be dilated by the lab- A patient, in the course of a visit to used to describe these changes, eg., "lens oratory staff, following the established an ophthalmologist, was examined by the opacities" or "lenticular changes." It is protocol. It is imperative that special in- physician and then routed through the possible to obtain very satisfactory re- structions sent along with the patient by office for several test procedures before sults, despite the presence of lens changes, his doctor be noted and adhered to arriving in the photography laboratory for by manipulating the camera so that the strictly. If any questions do occur, the an angiogram. Upon initiating photogra- image-forming rays pass through clear doctor should be consulted before any phy, it was discovered that a critically lens material. This, of course, requires action is taken. Patients who are kept on resolved image could not be obtained on patient cooperation and precise camera Don Wong, RBP Fundus photography and fluorescein angiography 31

technique. The resultant photograph may Another type of vitreous opacifica- If it is necessary to study the retinal cir- not be sharp throughout the entire picture tion is asteroid hyalosis. This opacifica- culation of an eye with asteroid hyalosis, area, since part of the illuminating beam tion appears as a suspension of calcium there should be no hesitation to perform may be passing through some of the opa- soap particles that are bound within the the procedure, even though the view of cities. This is not important, if the area of vitreous gel. These particles obscure ret- the fundus may seem to be almost com- primary interest is rendered sharply on inal details and are recorded with ordi- pletely obliterated. film. Central lens opacities (Figure 14A) nary white-light fundus photography, but will be bothersome for posterior polar are not seen in the fluorescein angiogram. views in that the photographer cannot obtain a single photograph in which the image of important landmarks or pa- thology is well-resolved. In these cases, a montage of photographs should be made to provide a complete photographic rec-. ord. The quality of peripheral fundus photographs will suffer if there are corti- 14A cal peripheral opacities (Figure 14B), and good results may be obtained only if there is clear lens material between the opaci- ties for the image-forming rays to pass through. No attempt at fundus photog- raphy should he made if one is able to visualize a cataract grossly by penlight or by ambient room illumination. Once the cataract has been surgically removed, and a clear optical pathway to the retina has been restored, and excellent pictures may usually he obtained. Vitreous. Hemorrhage into the vitreous body is probably the most common change that the photographer will en- counter, and often the photography must be postponed until the vitreous becomes clear enough for good image resolution. It would be helpful, under these circum- stances for the physician to be familiar 14B with the capabilities of the photographic system to recognize when the photogra- pher will not be able to produce pictures of diagnostic value. Often the doctor will find it difficult to correlate the view that he is able to get through his indirect ophthalmoscope to the poor image quality of the resultant picture due to a vitreous hemorrhage. The illumination of the in- direct ophthalmoscope is brighter than that of the photographic system, and is therefore capable of penetrating through the hemorrhage to a greater degree than the light of the fundus camera.

Figure 14A—Central lens opacity. Photographs taken through central ens opacities (" bubbles at about 12:00 and 6:00 oclock near the specular highlights) do not clearly delineate important landmarks or pathology. 14B—Cortical peripheral opacities obstruct image-forming rays in peripheral fundus photography.