• View in gallery

    Representative transverse ultrasonographic images of the common carotid artery of a 19-year-old female horse prior to (A) and immediately following (B) intra-arterial injection of ICG. Notice needle placement within the common carotid artery (arrow) in addition to transient extravascular hemorrhage (asterisk) caused by needle placement.

  • View in gallery

    Representative ASICGA images of the left eye of a 24-year-old female horse with a brown iris. These images obtained after ICG injection show filling of the radial iris arteries at 12 seconds after injection (arterial phase; A); initial filling of complex arterial vascular networks within the pupillary zone, terminal capillary loops, and radial iris veins at 14 seconds (capillary phase; B); and progressive filling of radial iris veins at 18 seconds (venous phase; C). A—Notice the radial iris artery (arrowhead). C—Notice the radial iris vein (arrow). Bar = 5 mm.

  • View in gallery

    Representative ASICGA images of the left eye of the same horse as in Figure 2 following intra-arterial (A) and IV (B) administration of ICG. Images depict the same point following dye administration (20 seconds). Notice the superior dye fluorescence, vascular detail, and image contrast following intra-arterial injection, compared with results following IV injection. Bar = 5 mm.

  • View in gallery

    Representative ASICGA (A) and ASSFA (B) images of the left eye of a 25-year-old female horse with a brown iris. Images were obtained 18 seconds after dye injection of both dyes. Notice the superior visibility of the iris vasculature with ICG versus SF. Visibility of the iridal vasculature with SF is limited to the smaller vessels located within the pupillary zone. Bar = 5 mm.

  • 1. Brooks DE. Fluorescein angiography in equine ophthalmology. Equine Vet Educ 2008;20:1618.

  • 2. Molleda JM, Cervantes I, Galan A, et al. Fluorangiographic study of the ocular fundus in normal horses. Vet Ophthalmol 2008;11:27.

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  • 4. Baggesen LH. Fluorescence angiography of the iris in diabetics and non-diabetics. Acta Ophthalmol (Copenh) 1969;47:449460.

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  • 6. Guex-Crosier Y, Durig J. Anterior segment indocyanine green angiography in anterior scleritis and episcleritis. Ophthalmology 2003;110:17561763.

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  • 9. Flower RW. Injection technique for indocyanine green and sodium fluorescein dye angiography of the eye. Invest Ophthalmol 1973;12:881895.

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  • 10. Yoshioka H, Kinouchi H, Nishiyama Y, et al. Advantage of microscope integrated for both indocyanine green and fluorescein videoangiography on aneurysmal surgery: case report. Neurol Med Chir (Tokyo) 2014;54:192195.

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  • 11. Kuroda K, Kinouchi H, Kanemaru K, et al. Intra-arterial injection fluorescein videoangiography in aneurysm surgery. Neurosurgery 2013;72(2 suppl operative):ons141-ons150.

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  • 14. Devoisselle J, Mordon S, Soulie S, et al. Fluorescence properties of indocyanin green/part 1: in vitro study with micelles and liposomes. In: Lakowicz J, Thompson J, eds. Advances in fluorescence sensing technology III. Bellingham, Calif: SPIE—The International Society for Optical Engineering 1997;530537.

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  • 15. Pitet G, Amalric P, Hygounenc O. Etude anlytique de la fluorescence des solutions de fluoresceinate de sodium. In: Amalric P, ed. Fluorescein angiography: proceedings of the international symposium on fluorescein angiography, albi 1969. Basel, Switzerland: Karger, 1971;811.

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  • 16. Maruyama Y, Kishi S, Kamei Y, et al. Infrared angiography of the anterior ocular segment. Surv Ophthalmol 1995;39:S40S48.

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  • 18. Simoens P, Muylle S, Lauwers H. Anatomy of the ocular arteries in the horse. Equine Vet J 1996;28:360367.

  • 19. Horie N, So G, Debata A, et al. Intra-arterial indocyanine green angiography in the management of spinal arteriovenous fistulae: technical case reports. Spine 2012;37:E264E267.

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  • 20. Yamamoto S, Kim P, Kurokawa R, et al. Selective intraarterial injection of ICG for fluorescence angiography as a guide to extirpate perimedullary arteriovenous fistulas. Acta Neurochir (Wien) 2012;154:457463.

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Comparison of angiographic dyes and injection techniques for ocular anterior segment angiography in horses

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  • 1 Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.
  • | 2 Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.
  • | 3 Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.

Abstract

OBJECTIVE To assess and compare 2 injection techniques for conducting ocular anterior segment indocyanine green angiography (ASICGA) and sodium fluorescein (SF) angiography in horses.

ANIMALS 3 healthy adult female horses (age range, 19 to 25 years).

PROCEDURES Horses were sedated, jugular catheters were placed, and manual restraint was used to ensure proper positioning for the angiography procedure. Two injection techniques (IV and intra-arterial) were performed for each horse 1 week apart. Intravenous injections of 0.25% indocyanine green (ICG; 50 mg) and 10% SF (10 mg/kg) were administered via the jugular catheter. Intra-arterial injections of ICG (1 mg) and SF (1 mg/kg) were administered into the common carotid artery with ultrasound guidance. Angiography was performed by use of an adaptor system comprised of a modified digital single-lens reflex camera, camera adaptor, and lens. Imaging was performed at a rate of 3 images/s for 60 seconds immediately following ICG injection, then at 2, 3, 4, and 5 minutes after injection. The SF was injected 5 minutes thereafter.

RESULTS ASICGA allowed visual identification of the arterial, capillary, and venous phases of angiography. Intra-arterial administration provided superior dye fluorescence, sharper contrast, and faster dye passage than IV administration. Visibility of the iris vasculature was limited with SF, and extravasation of SF was noted. No clinically important adverse events were detected.

CONCLUSIONS AND CLINICAL RELEVANCE ASICGA images were obtainable with both injection techniques; however, visibility of the iris vasculature was better with intra-arterial administration of ICG. The ASICGA technique may serve as a viable ocular imaging modality for horses.

Abstract

OBJECTIVE To assess and compare 2 injection techniques for conducting ocular anterior segment indocyanine green angiography (ASICGA) and sodium fluorescein (SF) angiography in horses.

ANIMALS 3 healthy adult female horses (age range, 19 to 25 years).

PROCEDURES Horses were sedated, jugular catheters were placed, and manual restraint was used to ensure proper positioning for the angiography procedure. Two injection techniques (IV and intra-arterial) were performed for each horse 1 week apart. Intravenous injections of 0.25% indocyanine green (ICG; 50 mg) and 10% SF (10 mg/kg) were administered via the jugular catheter. Intra-arterial injections of ICG (1 mg) and SF (1 mg/kg) were administered into the common carotid artery with ultrasound guidance. Angiography was performed by use of an adaptor system comprised of a modified digital single-lens reflex camera, camera adaptor, and lens. Imaging was performed at a rate of 3 images/s for 60 seconds immediately following ICG injection, then at 2, 3, 4, and 5 minutes after injection. The SF was injected 5 minutes thereafter.

RESULTS ASICGA allowed visual identification of the arterial, capillary, and venous phases of angiography. Intra-arterial administration provided superior dye fluorescence, sharper contrast, and faster dye passage than IV administration. Visibility of the iris vasculature was limited with SF, and extravasation of SF was noted. No clinically important adverse events were detected.

CONCLUSIONS AND CLINICAL RELEVANCE ASICGA images were obtainable with both injection techniques; however, visibility of the iris vasculature was better with intra-arterial administration of ICG. The ASICGA technique may serve as a viable ocular imaging modality for horses.

Ocular angiography is a time-contrast imaging technique that allows direct visual inspection of the ocular vasculature, assessment of tissue perfusion, and determination of the integrity of the blood-ocular barriers. This technique can be further classified as anterior segment angiography, which can be used to evaluate the iris, and posterior segment angiography, which can be used to evaluate the retinal and choroidal vasculature.

For horses, descriptions of ocular angiographic techniques have not been widely reported and have solely focused on the posterior segment involving SF.1–3 This paucity of information is believed to relate to the cumbersome and often expensive imaging equipment required and the lack of additional clinically important information it provides.1 To the authors’ knowledge, no reports exist of anterior segment angiography in horses.

In humans, anterior segment angiography has been a valuable imaging technique for identifying various sight-threatening conditions.4–7 This technique is considered more sensitive than slit-lamp biomicroscopy in the identification of iris abnormalities.8 Given that anterior segment diseases such as anterior uveitis are common in horses, we sought to determine the feasibility of conducting anterior segment angiography in horses, assessing the usefulness of ICG versus SF for this purpose. Because of the larger total blood volume in horses, compared with that in small animal species, we also sought to evaluate the diagnostic usefulness of anterior segment angiography using a targeted route of dye administration (intra-arterial) versus a more conventional route (IV). We anticipated that intra-arterial administration would allow for a substantial reduction in the amount of dye required relative to IV administration, thereby allowing a considerable reduction in the cost associated with this imaging modality in horses.

Materials and Methods

Animals

Three female horses (2 Standardbreds and 1 Morgan cross) owned by Tufts University for teaching and research purposes were used in the study. Median age was 24 years (range, 19 to 25 years), and median body weight was 480 kg (range, 430 to 520 kg). Iris pigmentation was heavy (dark brown) in all eyes imaged. One horse was known to have a solitary ruptured corpora nigra cyst in the anterior segment of each eye.

Sample size for the study had been determined by assuming a difference of at least 20 seconds in perfusion times between the routes of dye administration (IV vs intra-arterial) and a power of 0.90, α value of 0.05, and SD of 2. The study protocol was approved by the Institutional Animal Care and Use Committee of the Cummings School of Veterinary Medicine at Tufts University and conformed to the statement of the Association for Research in Vision and Ophthalmology regarding use of animals in vision research.

Procedure

Several days prior to angiography, all horses received a complete ocular examination by a board-certified veterinary ophthalmologist (CGP) and were deemed free of clinically relevant ocular disease. This examination included fluorescein staining,a slit-lamp biomicroscopy,b rebound tonometry,c and direct ophthalmoscopy.d

On the days of angiography, all horses were sedated by IV administration of detomidine hydrochloridee (0.01 mg/kg), and gentle manual restraint, in addition to a head stand,f was used to ensure proper positioning of the head and bulbus oculi (globe). The right or left jugular vein (chosen as the same side of the eye to be imaged) was cannulated with a 14-gauge catheter in a sterile fashion. Choice of eye to be imaged was chosen at random by means of sequential randomization (coin toss). An eyelid speculum was used to aid in retraction of the eyelids, and the globe was regularly irrigatedg every 30 to 60 seconds.

Two routes of dye administration were assessed to image the same eye in each horse, with a 1-week washout period provided between administration sessions. Intravenous dye administration was performed first via the jugular catheter. To perform anterior segment angiography via this route, a standard dose (50 mg) of 0.25% ICGh was administered first, followed by 10% SFi at a dose of 10 mg/kg. The ICG dose had been extrapolated from human medicine (data not shown) with the intent of obtaining a final blood concentration that would provide maximum fluorescence of ICG (0.03 mg/mL).9 The SF dose was chosen on the basis of prior research involving posterior segment angiography in horses.2

Five minutes was allowed to elapse between completion of the ASICGA procedure and injection of SF. Intra-arterial administration of both ICG and SF into the common carotid artery was performed with ultrasound guidance. Briefly, a 10-MHz microconvex probej was placed in the jugular furrow caudal to the ramus of the mandible to identify the common carotid artery in transverse view (Figure 1). A 20-gauge, 3.5-in spinal needlek was then inserted into the common carotid artery with ultrasound guidance to visually monitor injection of the dye. For the purpose of angiography via this route, a 1-mg dose (0.4 mL) of 0.25% ICG was administered first, followed by 10% SF (1 mg/kg; approx 4 mL). The amount of dye administered intra-arterially was calculated (data not shown) on the basis of data from human medicine involving a similar route of injection.10,11

Figure 1—
Figure 1—

Representative transverse ultrasonographic images of the common carotid artery of a 19-year-old female horse prior to (A) and immediately following (B) intra-arterial injection of ICG. Notice needle placement within the common carotid artery (arrow) in addition to transient extravascular hemorrhage (asterisk) caused by needle placement.

Citation: American Journal of Veterinary Research 79, 5; 10.2460/ajvr.79.5.562

Angiographic images were obtained with a dSLR camera imaging system, which consisted of a modified (full-spectrum) dSLR camera,l dSLR camera adaptor, and camera lens,m as described elsewhere.12 Images were obtained immediately following bolus administration of each dye at a rate of 3 images/s for a period of 60 seconds. Images were then obtained at 2, 3, 4, and 5 minutes following dye injection. For ASICGA purposes, appropriate excitationn and barriero filters were inserted within the illumination and optical pathways of the adaptor, respectively, and camera settings included a shutter speed of 1/100, an effective aperture of f/8, and an International Organization for Standardization setting of 6,400, as described elsewhere.12 Similarly, for ASSFA purposes, appropriate excitationp and barrierq filters were inserted into the adaptor, and camera settings included a shutter speed of 1/30, an effective aperture of f/8, and an International Standards Organization setting of 800, as described elsewhere.13

Measurements

Angiographic measurements included times to onset of the arterial, capillary, and venous phases as well as durations of the arterial and capillary phases. All such measurements were performed in duplicate, and means of each measurement pair were calculated by 1 investigator (CGP) on the completion of the study. Angiographic techniques were compared through subjective characterization of each dye's capacity to provide clear visibility of the iris vasculature and the degree of dye extravasation. Furthermore, routes of administration for each dye were compared through subjective assessment of image quality and contrast, dye fluorescence, and dye passage. For comparative purposes, all images were converted to black and white by use of a black-and-white adjustment tool (entire image) with image-editing software.r

Statistical analysis

Times to onset of the arterial, capillary, and venous phases of angiography for ICG were compared between routes of administration (IV vs intra-arterial) by use of the Wilcoxon signed rank test with the aid of statistical software.s Comparisons between routes of administration for SF were limited to the time of onset of the arterial phase. Data are reported as median and range. Values of P < 0.05 were considered significant.

Results

Animals

The left eye was imaged in 2 horses, and the right eye was imaged in the remaining horse. No adverse effects were identified following IV or intra-arterial administration of ICG or SF.

Procedures

For the purpose of intra-arterial dye administration, identification and temporary catheterization of the common carotid artery were readily performed with ultrasound guidance. Procedure duration ranged from 90 to 120 seconds once adequate sedation was obtained. Ultrasonographic examination of the common carotid artery following dye administration and needle removal revealed no important changes or abnormalities. Extravascular hemorrhage was evident following needle removal in all 3 horses; however, this change was considered mild, and no worsening over time was observed (Figure 1).

ASICGA

Performance of ASICGA provided visibility of the iris vasculature and its hemodynamics (arterial, capillary, and venous phases of angiography) in all 3 imaged eyes, regardless of dye administration route. Although vascular patterns appeared comparable between routes, significant differences were identified in times to onset of each vascular phase (Table 1).

Table 1—

Median (range) time to onset of the arterial, capillary, and venous phases of anterior segment angiography and median (range) duration of arterial and capillary phases following ICG administration in 1 eye of each of 3 adult female horses.

 ICGSF
Route, by phaseOnset (s)Duration (s)Onset (s)
Arterial
 IV38 (33–39)*3 (2–4)47 (44–50)
 Intra-arterial9 (8–11)3 (2–4)10 (12–14)
Capillary
 IV41 (35–44)*1 (1–2)
 Intra-arterial12 (11–13)1 (1–2)
Venous
 IV42 (36–44)*
 Intra-arterial13 (12–14)

Within a column, value differs significantly (P < 0.05) from that for intra-arterial administration for the same phase.

Within a row, value differs significantly (P < 0.05) between ICG and SF.

— = Not calculated.

The arterial phase began following ICG injection when initial filling of the radial iris arteries was noted. Median time to onset of the arterial phase following IV dye administration (38 seconds) was significantly longer than that following intra-arterial dye administration (9 seconds; Table 1). The arterial phase persisted for a median of 3 seconds, regardless of dye administration route. No fluorescence of the major arterial circle was evident in any imaged eye. Centripetal filling of radial iris arteries toward the pupillary edge differed among eyes, often appearing as a segmental pattern with initial filling occurring within the dorsal and ventral regions of the iris (Figure 2). Radial iris arteries appeared slightly tortuous, often bifurcating as they approached the pupillary edge, forming complex vascular networks within the pupillary zone.

Figure 2—
Figure 2—

Representative ASICGA images of the left eye of a 24-year-old female horse with a brown iris. These images obtained after ICG injection show filling of the radial iris arteries at 12 seconds after injection (arterial phase; A); initial filling of complex arterial vascular networks within the pupillary zone, terminal capillary loops, and radial iris veins at 14 seconds (capillary phase; B); and progressive filling of radial iris veins at 18 seconds (venous phase; C). A—Notice the radial iris artery (arrowhead). C—Notice the radial iris vein (arrow). Bar = 5 mm.

Citation: American Journal of Veterinary Research 79, 5; 10.2460/ajvr.79.5.562

Median time to onset of the capillary phase following IV dye administration (41 seconds) was significantly longer than that following intra-arterial dye administration (12 seconds). This phase persisted for a median of 1 second, regardless of administration route (Table 1).

Median time to onset of the venous phase following IV dye administration (42 seconds) was also significantly longer than that following intra-arterial dye administration (13 seconds). This phase was characterized by centrifugal dye movement within slightly tortuous radial veins, many of which appeared subjectively smaller than their neighboring arteries (Figure 2).

Subjective comparisons between dye administration routes indicated that intra-arterial administration of ICG yielded images with superior dye fluorescence, vascular detail, and image contrast, compared with those achieved via IV administration (Figure 3).

Figure 3—
Figure 3—

Representative ASICGA images of the left eye of the same horse as in Figure 2 following intra-arterial (A) and IV (B) administration of ICG. Images depict the same point following dye administration (20 seconds). Notice the superior dye fluorescence, vascular detail, and image contrast following intra-arterial injection, compared with results following IV injection. Bar = 5 mm.

Citation: American Journal of Veterinary Research 79, 5; 10.2460/ajvr.79.5.562

ASSFA

Performance of ASSFA failed to provide clear visibility of the iris vasculature in the 3 imaged eyes, regardless of dye administration route. Median time to onset of SF fluorescence following IV dye administration (47 seconds) was significantly longer than that following intra-arterial dye administration (10 seconds). In 2 horses, different degrees of the iridal vasculature within the pupillary zone became visible following intra-arterial injection of SF (Figure 4). Extravasation of SF during the latter measurement points was visible within the iris stroma of 1 eye and within the aqueous humor of 2 eyes following dye administration.

Figure 4—
Figure 4—

Representative ASICGA (A) and ASSFA (B) images of the left eye of a 25-year-old female horse with a brown iris. Images were obtained 18 seconds after dye injection of both dyes. Notice the superior visibility of the iris vasculature with ICG versus SF. Visibility of the iridal vasculature with SF is limited to the smaller vessels located within the pupillary zone. Bar = 5 mm.

Citation: American Journal of Veterinary Research 79, 5; 10.2460/ajvr.79.5.562

ASICGA versus ASSFA

Subjective comparisons between angiographic dyes (ICG vs SF) for conducting anterior segment angiography revealed that ICG, regardless of administration route, provided superior visibility of the iris vasculature.

Discussion

Results of the study reported here provided insights into the potential diagnostic usefulness for horses of anterior segment angiography via 2 dye administration routes. Anterior segment diseases such as uveitis (eg, equine recurrent uveitis) and keratitis (eg, ulcerative, fungal, or immune-mediated disease) are common in horses. Information generated via anterior segment angiography may aid diagnosis early in the disease process through the detection of new vessel formation, blood-aqueous barrier disruption, or perfusion abnormalities. Additionally, such information could help clinicians more accurately monitor disease progression and assess response to various treatments (eg, cyclosporine implantation). This could allow for more efficient and effective treatment and translate into greater long-term success rates for many sight-threatening conditions affecting horses.

Use of ICG provided visibility of the normal iridal vasculature, with no dye extravasation, in heavily pigmented equine eyes. Fluorescence of ICG was enhanced when this dye was administered intra-arterially (vs IV), yielding images of superior quality. Fluorescence of SF, regardless of administration route, was largely masked by iridal pigmentation, and dye extravasation was observed.

The superior diagnostic usefulness of ICG versus SF for anterior segment angiography was likely related to its different metabolic and spectral properties. Indocyanine green is a large (775 Da) tricarbocyanine molecule that, following injection, has a rapid and high (98%) binding affinity for lipoproteins and major plasma proteins.14 Conversely, SF is a small (376 Da) molecule that binds up to 60% to 80% of plasma proteins.15 The high protein-binding affinity of ICG is considered its most important quality and accounts for its high vasculature retention. Furthermore, unlike SF which absorbs and emits light within the visible spectrum, ICG has absorption and emission characteristics within the near-infrared spectrum. At these longer wavelengths, 90% of light is transmitted through melanin-laden structures, thereby increasing the fluorescence quantum yield and tissue penetration.16 Angiographic findings of the present study were comparable to those reported for dogs12 and healthy humans,8 in which poor transmission of SF was found in heavily pigmented eyes, in addition to dye extravasation.

Vascular patterns observed by means of ASICGA in the present study were consistent with those in previous studies17,18 in which the anterior segment of equine eyes was examined via corrosion casting and histologic techniques. Those studies showed that the major blood supply to the iris in horses is provided by a complete major arterial circle. This anatomic structure is formed by the terminal branches of the medial and lateral long posterior ciliary arteries, in addition to the dorsal and ventral anterior ciliary arteries. Histologic examination has also revealed a thick, often pigmented, adventitia surrounding the major arterial circle, which is described as being located beneath the last ciliary process deep within the iris base.17 In the present study, no major arterial circle was visible, and we believe its location within the iris base, in addition to its thick and often pigmented adventitia, likely accounted for this. Initial dye fluorescence characterizing the onset of the arterial phase was evidenced by centripetal filling of numerous slightly coiled arteries. When the dye reached the pupillary zone, numerous anastomoses were visible leading to the formation of complex vascular networks.

Controversy exists regarding whether a minor arterial circle exists in equine eyes. Results of the present study were most consistent with a report18 that complex vascular networks are present within the pupillary zone. No true minor arterial circle was identified in the present study. Similar to findings reported for other species,12,13 the capillary phase was shortlived, with rapid transition into the venous phase, as indicated by progressive centrifugal filling of radial veins. Subjectively, radial veins appeared of larger caliber than their neighboring arteries. Despite previous histologic observations of numerous pigment-laden cells surrounding radial veins,17 visibility of these vessels was not hindered in the present study.

In addition to assessing the usefulness of ICG and SF for conducting anterior segment angiography in horses in the present study, we also sought to evaluate different routes of dye administration. Results indicated that a small amount of dye, particularly ICG, administered intra-arterially could yield angiographic images that subjectively provided more detail and contrast, in addition to superior dye fluorescence, than the more conventional IV route. In humans, intra-arterial dye administration is becoming increasingly more common, particularly as an aid during vasculature or spinal surgery.10,11,19,20 However, little information exists regarding its usefulness for performing ocular angiography.

Use of the conventional IV route for dye injection, especially in a large animal species such as horses, has inherent challenges. Following IV bolus injection, the dye is diluted within the cardiopulmonary circulation prior to reaching the ocular vasculature, causing a decrease in the fluorescent contrast provided by the dye. In humans, this effective dilutional factor has been calculated to be on the order of 600-fold.9 Because of the larger total blood volume in horses, a greater amount of dye is required to obtain sufficient blood concentrations in horses, thereby allowing adequate dye fluorescence to occur. This greater amount of dye is associated with certain adverse effects (eg, toxic effects). In humans, adverse effects are characterized as mild (for 20% SF and 0.15% ICG), moderate (for 1.6% SF and 0.2% ICG), and severe (for 0.05% SF and 0.05% ICG) and are generally believed to be linked to the amount of dye administered.21,22 Targeted routes of dye administration not only allow for considerable smaller doses to be used and fewer toxic effects, but as demonstrated in the present study, intra-arterial administration allowed for enhanced visibility of the iris vasculature through superior dye fluorescence and image contrast relative to that achieved with IV administration. Additionally, considerable dose reductions in the clinical setting should result in lower costs for horse owners, which could ultimately translate into an increased likelihood of these angiographic techniques being performed routinely.

Although advantageous, intra-arterial dye administration has potential adverse effects. Use of ICG and SF via an intra-arterial route is not mentioned within the FDA-approval documentation.23,24 Compared with IV dye administration, intra-arterial administration requires some additional time, requires additional (ultrasonographic) equipment and expertise, and runs the risk of piercing an artery. In the present study, the process of identifying and temporarily catheterizing the common carotid artery was considered straightforward, adding minimal additional time to the angiographic procedure. Mild extravascular hemorrhage around the common carotid artery was noted in all 3 horses following intra-arterial dye injection.

Limitations of the present study primarily involved the small number of horses and eyes imaged. Results achieved in the 3 healthy horses suggested that both ASICGA and ASSFA were without important adverse effects when performed via the 2 investigated routes of administration. However, a larger sample size would be necessary to further evaluate the safety of anterior segment angiography, particularly via a targeted intra-arterial route. Additionally, although ICG appeared superior to SF in its ability to provide visibility of the iridal vasculature, only ophthalmoscopically normal horses were imaged. It remains unknown whether similar results could be expected in horses with ophthalmic disease involving alterations within the iridal vasculature.

Acknowledgments

Supported by the Companion Animal Fund of the Cummings School of Veterinary Medicine, Tufts University.

Presented in abstract form at the 47th Annual Conference of the American College of Veterinary Ophthalmologists, Monterey, Calif, October 2016.

ABBREVIATIONS

ASICGA

Anterior segment indocyanine green angiography

ASSFA

Anterior segment sodium fluorescein angiography

dSLR

Digital single-lens reflex

ICG

Indocyanine green

SF

Sodium fluorescein

Footnotes

a.

Ful-Glo, Akorn Inc, Lake Forest, Ill.

b.

Kowa SL-15 portable slit-lamp biomicroscope, Kowa Co, Tokyo, Japan.

c.

TonoVet, iCare, Vantaa, Finland.

d.

Welch Allyn direct ophthalmoscope, Welch Allyn distributors, Skaneateles Falls, NY.

e.

Dormosedan, Zoetis Inc, Kalamazoo, Mich.

f.

Hoofjack headstand, Swissvet Veterinary Products, Knoxville, Tenn.

g.

Balanced salt solution, Alcon Laboratories Inc, Fort Worth, Tex.

h.

IC-Green, Akorn Inc, Lake Forest, Ill.

i.

AK-Fluor, Akorn Inc, Lake Forest, Ill.

j.

GE Logiq e, GE Medical Systems, Milwaukee, Wis.

k.

BD Medial Technology, Franklin Lakes, NJ.

l.

Canon 6D, Canon, Tokyo, Japan.

m.

Canon EF-S (60 mm f/2.8 macro lens), Canon, Tokyo, Japan.

n.

769/41 nm Bright Line, Semrock, Rochester, NY.

o.

832/37 nm BrightLine, Semrock, Rochester, NY.

p.

MF479/40 nm, Thorlabs Inc, Newton, NJ.

q.

MF525/39 nm, Thorlabs Inc, Newton, NJ.

r.

Adobe CS6, Adobe Systems Inc, San Jose, Calif.

s.

SAS, version 9.2, SAS Institute Inc, Cary, NC.

References

  • 1. Brooks DE. Fluorescein angiography in equine ophthalmology. Equine Vet Educ 2008;20:1618.

  • 2. Molleda JM, Cervantes I, Galan A, et al. Fluorangiographic study of the ocular fundus in normal horses. Vet Ophthalmol 2008;11:27.

  • 3. Pachten A, Niedermaier G, Wollanke B, et al. Fluorescein angiography in a horse with optic nerve atrophy. Pferdeheilkunde 2009;25:554558.

    • Search Google Scholar
    • Export Citation
  • 4. Baggesen LH. Fluorescence angiography of the iris in diabetics and non-diabetics. Acta Ophthalmol (Copenh) 1969;47:449460.

  • 5. Bandello F, Brancato R, Lattanzio R, et al. Biomicroscopy and fluorescein angiography of pigmented iris tumors. A retrospective study on 44 cases. Int Ophthalmol 1994;18:6170.

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Contributor Notes

Dr. Pirie's present address is Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824.

Address correspondence to Dr. Pirie (piriechr@cvm.msu.edu).