**2. Classification of macular holes and OCT**

Evolution of macular hole and *clinical appearance* of the different stages of its development has been described by Gass [4, 5]. The earliest stage is an impending hole, characterized by a yellow spot (stage 1a) or a yellow ring (stage 1b) at the fovea [4, 5]. Stage 1 macular holes are difficult to diagnose by slit lamp biomicroscopic examination alone, leading to a lot of subjective variation in diagnosis [6].

**Figure 3.** Grading scheme proposed and revised by Gass.

OCT is based on the imaging of reflected light. In addition to measuring transverse dimensions, it also resolves depth. OCT is akin to noninvasive tissue "biopsy"—it provides in vivo cross-sectional views (tomography) of internal tissue structures similar to tissue sections under a microscope [2, 3]. The depth resolution of OCT is typically of the order of 0.4 thou-

**Figure 1.** (a) Layers of retina. (b) The inner HRL (corresponding to the photoreceptors IS/OS junction) is thinner than the

outer, which corresponds to a hyper-reflective normal complex formed by RPE and choriocapillaris.

**Figure 2.** Full thickness macular hole (a) OCT cross sectional image; (b) color fundus photograph).

A macular hole is defined as a full-thickness defect of retinal tissue involving the anatomic fovea and primarily the foveola of the eye (**Figures 1a**, **b** and **2**). Since its development, OCT is the gold standard in the diagnosis and management of this condition. The high-resolution imaging on OCT allows cross-sectional and three-dimensional evaluation of the macula, thereby providing far greater details than what can be discerned clinically. It is helpful in detecting subtle early MHs as well as staging the more obvious and larger ones. OCT is now used to guide management of macular holes based on various parameters, as highlighted in

Evolution of macular hole and *clinical appearance* of the different stages of its development has been described by Gass [4, 5]. The earliest stage is an impending hole, characterized by a

sandth of an inch.

84 OCT - Applications in Ophthalmology

the subsequent sections.

**2. Classification of macular holes and OCT**

**Figure 4.** Stages of macular hole on OCT.

Since its introduction, OCT has been an extremely useful tool for diagnosing and staging macular holes. On OCT, a stage 1 hole appears as a cystic lesion in the inner layers of the retina (**Figure 3**) [7, 8]. *Stage 2* macular holes present as a *full-thickness defect at the fovea* (*size < 400um* in diameter). *Stage 3* macular hole is a completely evolved hole (size >400 um in diameter). In some patients, a small operculum can be seen suspended in front of the lesion. *Stage 4* macular holes appear similar to stage 3 holes except that in stage 4 holes there is *complete posterior vitreous detachment*, as frequently evidenced by a visible Weiss ring.

Hee et al. firstdescribedthe use ofOCTindiagnosing and monitoring macular holes [9]. Gaudric et al. later described the sequence of events in the evolution of macular holes using OCT—from anteroposterior vitreofoveal traction to full-thickness macular hole formation (**Figure 4**) [7].
