•Anteriorly, retinal tears may form at the posterior border of VR separation.11

Pearl

The vitreous has no per se function in the fully developed eye. This explains why its removal has no adverse effect, except the increased risk of cataract formation, which is due to the higher oxygenation in the cavity. Nevertheless, detachment of the retina progresses faster in eyes devoid of the mechanical support of the gel.

26.1.3 Retinal Histology and Macroanatomy

The retina is the “film of vision”: it captures the incoming light, translates it into electric signals, and sends these toward the visual cortex. The retina has ten layers, except in the periphery and at the fovea; the outermost layer is the RPE, to which nine layers of the neuroretina12 attach. The inner half of the retina gets its nourishment from the retinal blood vasculature; the outer half is supplied by the choroidal vasculature. The latter fact explains the deleterious effects of RD.

•Thickness: The retina is thinnest in the periphery (~0.1 mm) and gets progressively thicker posteriorly, reaching 0.23 mm in the peripheral part of the macula.

•RPE: Extending from the optic disc to the ora serrata,13 this monolayer of some 120 million cells have a crucial role in maintaining retinal attachment (see Sect. 26.3). In the posterior pole the cells are narrow and tall, becoming thinner toward the periphery.

•ILM: Consisting mostly of the basal lamina of the Müller cells, this membrane of

type IV collagen gives the retina a smooth inner surface and a shiny light reflex in younger individuals. It is 0.5 μ thick in the periphery and ~1.5 μ centrally.14 It is missing over the optic disc and occasionally over the major blood vessels.15 This is the sole inelastic layer of the neuroretina, and its rigidity plays a role in several pathological conditions, serving as a rational for ILM removal.

–The ILM is transparent, remaining invisible during the operation – unless the surgeon holds the light pipe at a certain angle.16 The ILM is so thin

11The classical description of RD development (see Chap. 54).

12Also referred to as sensory retina. In a strict interpretation of the condition, RD is not a true detachment but an intraretinal separation (between the RPE and the neuroretina).

13Where it becomes contiguous with the pigmented ciliary epithelium and then the anterior layer of the iris epithelium.

14The human hair is 20–180 (average: 70) μ thick.

15As seen during ILM peeling: the border of the ILM removal typically follows the major vessels.

16This is where using a slit lamp for surgical viewing has a clear advantage.

that even OCT machines with the highest axial resolution17 are unable to delineate it.

For the VR surgeon, the important macroanatomical landmarks are the following:

•Ora serrata (“ora”). This is the endpoint of the retina with its ten layers; peripheral to the ora serrata, the retina becomes contiguous with the nonpigmented epithelium of the pars plana ciliaris. The ora is straddled by the vitreous base.

•Pars plana.18 It is the posterior section of the ciliary body, a ring ~4 mm wide in adults.

•Pars plicata.19 This part of the ciliary body, a 2 mm wide ring whose anterior border is at 1 mm posterior to the limbus, contains 60–70 ciliary processes.

• Macula.20 A horizontally oval area of 2.0 × 0.9 mm, whose center is located 3.4 mm temporal and 0.8 mm inferior from the margin at the midline of the optic disc. The macula is responsible for ~20° of the visual field.

•Fovea. The central depression inside the macula, with a diameter of 1.8 mm. The light reflex seen here is explained by its slanted architecture.21

–The fovea is inside the avascular zone, which is 0.5 mm in diameter.22

–Its epicenter is called the foveola, with a diameter of 0.35 mm. It has no cells except the outer segment of red and green cones.

–The fovea is surrounded by a 0.5 mm wide ring that is called the parafoveal area.

–The parafoveal ring is surrounded by another, 1.5 mm wide ring called perifoveal area.

•Optic disc. An oval area measuring 1.76 mm horizontally and 1.92 mm vertically; this is the entry point of the arterial system for the eye and the exit point for the veins and neurons. It is located nasally from the macula, 2.3 mm to the optical axis.

•Posterior pole. An area typically meant to be bordered by the vascular arcades.

17~8 μ at the time of this writing.

18Technically, it is not part of the retina, but is discussed here because this is the intended entry site for intravitreal surgery and injections.

19Also called corona ciliaris.

20The proper name is macula lutea. The name comes from its somewhat yellowish color due to the high carotenoid pigment (xanthophyll), which is missing in the fovea. In clinical practice, “macula” is often used when “fovea” would be the correct term.

21Clivus (slope).

22The avascular zone is the forbidden area for laser treatment. This is especially true at the fovea, where even minor iatrogenic injury can inflict maximal damage.