36 Congenital Fundus Abnormalities
36.1 Vascular Anomalies of the Optic Disc
36.1.1 Prepapillary Vascular Loops
First described by Liebrich in 1871, 1 these vascular abnormalities were originally thought to be remnants of an incompletely regressed hyaloid system. Most evidence now suggests this is not the case, but rather that they occur because of aberrant development of the retinal vascular system. 2 , 3 , 4 Despite the fact that some of these anomalies appear dark and venous, approximately 95% of prepapillary loops are arterial. 3
Clinically, the vessels present as loops that extend from the optic disc into the vitreous cavity and then back to the disc within Cloquet’s canal (Fig. 36-1). In contrast to a single hyaloid artery, each prepapillary loop has at least one ascending and one descending branch. Loops can assume a spiral or corkscrew shape (Fig. 36-1), have a figure-of-eight appearance (Fig. 36-2), or manifest with a simple hairpin-turn configuration. 3 Spontaneous movement or pulsations, coincident with the heartbeat, are seen in about one-half of the cases. Approximately 30% are encased by a white, glial-appearing sheath.
Arterial prepapillary loops average about 1.5 mm in height. 3 In contrast to a persistent hyaloid artery, arterial prepapillary loops achieve a maximum height of only about 5 mm and do not extend anteriorly to the posterior capsule of the lens. Bilaterality is present in 9 to 17% of cases, 4 and cilioretinal arteries have been noted in up to 75% of affected eyes. Consistent systematic associations have not been identified.
Histopathologically, a prepapillary arterial loop has been shown to contain intima but not an internal elastic lamina (Fig. 36-3). 5 The loop was demonstrated to lie beneath a loose connective tissue sheath continuous with the internal limiting membrane of the retina.
Mann 2 has suggested that prepapillary arterial loops arise at about the 100-mm stage (3.5–4 mo) of gestation. At this time, mesenchymal cells- the precursors of retinal capillary endothelial cells- inadvertently grow anteriorly into the supporting tissue of Bergmeister’s papilla overlying the optic nerve head. They then proceed back down onto the disc and on their course into the developing retina. Bergmeister’s papilla subsequently regresses, leaving the vascular abnormality within Cloquet’s canal.
The major complication associated with prepapillary arterial loops is retinal artery occlusion in the distribution of the area supplied by the loop (Fig. 36-4). 4 Reported in approximately 10% of cases of prepapillary loops described in the literature, the occlusion has been hypothesized to occur secondary to turbulent flow, which predisposes to endothelial damage and thrombus formation. Vitreous hemorrhage and hyphema have also been noted. 3 It is likely that vitreous hemorrhage occurs in conjunction with the development of posterior vitreous detachment.
The major complication associated with prepapillary arterial loops is retinal artery occlusion, likely due to a clot in the loop. Rarely, vitreous hemorrhage and hyphema can also be seen.
Congenital prepapillary venous loops are usually single vessels that extend 0.5 mm or less into the vitreous cavity (Fig. 36-5). Acquired prepapillary venous loops are often multiple (Fig. 36-6), seen in adults, and found in conjunction with retinal venous occlusion or diseases associated with retinal venous occlusion, such as glaucoma, papilledema, or meningioma of the optic nerve or sphenoid wing.
36.1.2 Persistent Hyaloid Artery
A persistent hyaloid artery presents clinically as a single vessel that travels from the optic disc, through Cloquet’s canal, and anteriorly to the posterior capsule of the lens. 4 The point of attachment to the posterior capsule, most often in a location inferonasal to the visual axis, is known as a Mittendorf’s dot (Fig. 36-7). Hyaloid artery remnants are seen in the eyes of premature infants in up to 95% of cases but are observed in only 3% of full-term infants. 6 The incidence in children and adults is less, but exact figures are lacking. Most commonly, a persistent hyaloid artery in a child is bloodless, but in rare instances it can contain blood and be associated with vitreous hemorrhage. 7 Ocular associations reported with persistent hyaloid artery include persistent hyperplastic primary vitreous (PHPV), coloboma of the optic disc, optic nerve hypoplasia, and posterior vitreous cysts. 4
36.1.3 Persistent Bergmeister’s Papilla
Although not a vascular abnormality in the strictest sense, Bergmeister’s papilla develops around the posterior aspect of the fetal hyaloid artery. It has been described very elegantly by Mann. 8 Between the first and the second months of gestation, a group of neuroectodermal cells within the optic cup at the superior end of the embryonic fissure differentiate into a structure known as the primitive epithelial papilla. This primitive epithelial papilla becomes the optic nerve head when axons from retinal ganglion cells pass through it at 7 to 8 weeks of gestation. At the end of the fourth month of gestation, neuroectodermal glial cells on the surface of the optic disc multiply rapidly and form a sheath around the hyaloid artery that extends anteriorly for approximately one-third the length of the vessel (Fig. 36-8). The sheath is maximally developed at about 5.5 months of gestation, following which atrophy occurs. The amount of regression determines, in part, the degree of physiologic cupping of the optic disc.
Incomplete regression of Bergmeister’s papilla causes a persistent Bergmeister’s papilla, also known as an epipapillary veil. Clinically, the entity appears as a tuft of glial tissue that is most commonly located on the nasal aspect of the nerve head (Fig. 36-9). Absence of physiologic cupping can also be seen in affected eyes. The visual acuity is unaffected by the abnormality, and systemic associations are generally lacking.
36.1.4 Enlarged Vessels
Causes of enlarged vessels on the optic disc in children include arteriovenous malformations, retinal capillary hemangiomas (von Hippel’s tumors), and retinoblastoma. Because the latter two conditions are most appropriately classified as tumors, they are not addressed in this section (see ¦Chapter 27¦). Choroidal melanoma has also been associated with enlarged vessels on the optic disc, 9 but the tumor is rare in children.
Arteriovenous malformations in the retina can be mild, moderate, or severe, and thus have been correspondingly classified by Archer et al 10 as grade I, II, and III abnormalities. They are predominantly unilateral. Grade I arteriovenous communications, the mildest variants, have also been noted as a subgroup of congenital macrovessels. 11 A congenital macrovessel is a single enlarged retinal vessel, usually a vein, that traverses both sides of the horizontal raphe (Fig. 36-10). Most of these vessels are associated with arteriovenous communications, although some may be subtle. Cysts in the central fovea have been seen in association with congenital retinal macrovessels, but they may be transient and appear to affect the visual acuity only minimally.
Grades II and III arteriovenous communications have also been called racemose angiomas or racemose hemangiomas. The grade II variant is moderate and usually associated with normal vision (Fig. 36-11), whereas in the grade III type the vision can be severely reduced due to replacement of optic nerve tissue by enlarged vessels (Fig. 36-12). 12 , 13
Both grades II and III arteriovenous communications can be associated with arteriovenous communications in the face, scalp, mandible, and central nervous system. The eponym Wyburn-Mason’s syndrome has been applied to retinal arteriovenous communications associated with similar systemic abnormalities. 14 Rundles and Falls 15 found that among 34 cases of congenital retinal arteriovenous malformations reported through 1951,18 (53%) had associated central nervous system and/or dermatologic involvement.
Over 50% of congenital retinal arteriovenous malformations have the Wyburn-Mason’s syndrome, retinal arteriovenous malformations in conjunction with malformations of the mandible, maxilla, cerebrum, brainstem, and/or spinal cord. Malformations in the cerebrum typically are deep and follow the optic tracts.
The lesions in the central nervous system are typically midline or unilateral on the same side as the ocular lesion, and tend to follow the optic tract. Because the optic tract is deep within the cerebrum, the arteriovenous anastomoses are rarely accessible surgically.
36.2 Colobomatous and Other Excavated Defects of the Optic Disc
36.2.1 Congenital Pit of the Optic Disc
Found in approximately 1 per 11,000 patients, 16 a congenital pit of the optic nerve head appears as a localized depression typically measuring from one to several diopters in depth. It can be yellow-white, gray, or black in color (Fig. 36-13). The defect generally ranges in size from 0.25 to 0.40 disc diameters. More than 50% are located on the temporal side of the disc, and approximately one-third are located centrally (Fig. 36-14).
Peripapillary retinal pigment epithelial disturbances are seen in 95% of eyes with optic pits that are not located centrally (Fig. 36-13a,b). 17 In unilateral cases, the optic nerve head with the pit is larger than the normal fellow nerve head in 85% of patients. Most pits are single, but about 5% of affected eyes have more than one pit on the optic disc. Occasionally, the optic pits are located within the peripapillary region of the disc. Cilioretinal arteries are frequently associated with optic pits.
Approximately 40% of eyes with a congenital pit of the optic disc have an associated or previous serous retinal detachment of the sensory retina (Fig. 36-15). 17 , 18 , 19 Retinal detachment is seen more commonly with larger, temporally located pits and usually involves the macula. Splitting of the retinal layers, or macular retinoschisis, has also been described in eyes with congenital optic pits and retinal detachment. 20 Centrally located pits have not been associated with retinal detachment and/or retinoschisis. The subretinal fluid rarely extends beyond the posterior pole and, in most cases, can be seen extending to the optic disc in the vicinity of the optic pit. Cystic changes within the detached retina are found in two-thirds of cases, and a macular hole develops in about 25%. In contrast to most lamellar macular holes, in which absence of the inner retinal layers is observed, the macular holes noted in conjunction with optic pits tend to involve the outer retina, giving the appearance that the internal limiting membrane is intact.
The age of onset of the retinal detachment is variable, with a mean age of approximately 30 years. 17 We have observed retinal detachment developing in children as young as 6 years, as well as in patients in their 80s.
Approximately 40% of eyes with a congenital pit of the optic nerve head have, or will have, an associated serous retinal detachment/retinoschisis.
Uncertainty exists as to the origin of the subretinal fluid seen in conjunction with congenital optic pits. Approximately 20% of collie dogs have either a congenital pit of the optic disc or optic nerve coloboma, and histopathologic evidence in the collie dog model suggests the subretinal fluid originates from the vitreous cavity. 18 Other possible origins of the subretinal fluid or retinoschisis fluid include cerebrospinal fluid from the subarachnoid space, leakage from choroidal vessels, and leakage from small vessels located at the base of the optic pit (Fig. 36-16). 17
Evidence suggests that in the majority of instances, the presence of an associated retinal detachment in the posterior pole is visually disabling. Although the amount of subretinal fluid can wax and wane spontaneously, a Wills Eye Hospital report noted that, among 20 such untreated eyes followed for at least 1 year, the visual acuity was 20/100 or worse in 55%. 19 When the vision is decreased due to serous macular retinal detachment and/or retinoschisis, laser photocoagulation in the peripapillary region has been advocated to induce reattachment of the retina to the underlying retinal pigment epithelium and subsequent resorption of the subretinal fluid (Fig. 36-17). The laser should not involve the nerve fiber layer of the retina, but should extend into flattened retina both superiorly and inferiorly to the subretinal fluid/retinoschisis extending from the disc. This allows the retina to tack down to the retinal pigment epithelium from the edges. Laser therapy applied to an area greater than 120 degrees should be performed with caution and is compatible with 20/20 vision. Nonetheless, temporal peripapillary laser photocoagulation of 180 degrees or greater has been shown to cause counting fingers vision, likely due to loss of nerve fibers to the central fovea and/or damage to the ciliary vascular supply to the prelaminar optic nerve head (personal communication, Dr. Michael Klein, MD). Laser photocoagulation is successful in reattaching the retina in about 50% of cases, although it may have to be repeated at 2 to 4 months. The subretinal fluid may be present for a prolonged period of time without severely damaging the photoreceptors. We have noted vision to improve to 20/25 when a serous retinal detachment resolves at 9 months after the development of subretinal fluid. Rarely, subretinal choroidal neovascularization can develop at the edge of the laser photocoagulation.
With cases of severe vision loss that do not respond to laser photocoagulation, the possibility of repeat peripapillary laser photocoagulation in conjunction with either an injection of long-acting gas into the vitreous cavity or a pars plana vitrectomy and a gas/fluid exchange can be considered. 21 , 22 Overall, approximately 80% of eyes with a serous retinal detachment that does not resolve with laser therapy alone demonstrate resolution of the retinal detachment after laser therapy in conjunction with gas tamponade. Thus, approximately 90% of all serous retinal detachments associated with congenital optic pits can be flattened with interventions.
Peripapillary laser photocoagulation causes resolution of subretinal fluid in 50% of eyes with a congenital pit of the optic disc and an associated serous retinal detachment.