**4. Preoperative role-OCT factors**

Apart from a major role in diagnosis, *preoperative OCT is an important tool for counseling patients* regarding postoperative prognosis on the basis of various OCT-based measurements (**Figure 6a–d**).

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**Figure 6.** (a) Schematic representation of OCT factors; (b) HFF = (b + c)/a; (c) MHI = height/base (h/b); (d) Tractional hole index.

**a.** Hole form factor (HFF)

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 vitre-*

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].

Diagnosing early macular hole lesions and differentiating them from other mimicking conditions are the clinical challenges in the management of macular holes. Fluorescein angiography (FA) was the earlier imaging modality of choice to identify macular holes. Although useful in characterizing full-thickness holes, this test does not help in identifying stage 1 macular holes, which are the source of clinical dilemma. The purpose of FA was largely to demonstrate other biomicroscopically similar lesions that have classic angiographic features (e.g., choroidal neo-

Optical coherence tomography, as compared to FA, provides noninvasive diagnostic imaging helping early and accurate diagnosis. At the same time, it rules out other mimicking conditions, allowing the clinician to distinguish these from pseudohole and prehole conditions in almost all instances (**Figure 5**). It has been useful in demonstrating the sequence of events leading to macular hole formation over time and has thus increased our understanding of the

Apart from a major role in diagnosis, *preoperative OCT is an important tool for counseling patients* regarding postoperative prognosis on the basis of various OCT-based measurements

*ous detachment*, as frequently evidenced by a visible Weiss ring.

vascular membranes), thereby excluding the diagnosis of macular hole.

**3. Aiding early differential diagnosis**

86 OCT - Applications in Ophthalmology

anatomic relations in macular holes [9–11].

**4. Preoperative role-OCT factors**

**Figure 5.** (a) Lamellar macular hole; (b) pseudohole.

(**Figure 6a–d**).

	- It is the ratio of hole height to base diameter (ratio of perpendicular and horizontal dimensions of the hole). It can be calculated from OCT transverse images of the macular area.
	- The MHI represents the **preoperative configuration** of a macular hole and is a prognostic factor for visual outcome. It was suggested that **MHI value of ≥0.5** could be used to predict better postoperative outcomes [13].

#### **4.1. Clinical significance**

In a study of large macular holes (low MHI macular holes) by Kumar et al. [14], preoperative screening for low MHI macular holes was done using spectral domain OCT. In view of large base diameters and low MHI, an additional maneuver was incorporated during surgery intraoperative tapping of macular hole edges in all quadrants from the inner side. This leads to an in situ increase in perpendicular height of the macular hole compared with the base diameter, thus translating to an intraoperative increase in MHI and facilitating hole closure. This was done along with other surgical modifications including a large arcade to arcade ILM peel and removing any ERM associated with it. An improvement in the postoperative visual outcome was observed with large macular holes with MHI as low as 0.25.

Thus, OCT not only facilitates an accurate diagnosis, but preoperative surgical planning based on OCT factors also helps in improving anatomic and functional prognosis.

Another surgical technique proposed for large macular holes, to improve anatomic and functional outcomes of surgery by *preventing postoperative flat-open configuration* of macular holes, is the inverted ILM flap technique [15]. In this technique, after core vitrectomy and dye staining, the ILM is not completely removed from the retina but is left in place, attached to the edges of the MH. This ILM remnant is then inverted to cover and fill the MH (**Figure 7**).

The rationale for tissue repair that occurs following the use of this technique is: the inverted ILM, containing Muller cell fragments, induces glial cell proliferation, resulting in the macular hole filling with proliferating cells that enhance closure. It also works as a scaffold for tissue proliferation, creating a microenvironment that encourages correct photoreceptor alignment. This allows a near-perfect anatomic restoration, *with OCT demonstrating restoration of normal foveal architecture*. Hence, this technique results in better postoperative anatomic and functional outcome.

Also, because ILM is a basement membrane, it allows glial cell proliferation, allowing large MHs to fill with tissue over time further expanding its use to repeat MH surgery [16].

	- It is the ratio of minimum diameter of MH to base diameter and is an indicator of extent of tangential traction.
	- It is the ratio of maximal height of MH to minimum diameter and is an indicator of AP traction and retinal hydration.

Patients with higher THI values (>1.41) and low DHI values (<0.50) had the best post-op VA recovery [17].

**5. Intraoperative OCT (iOCT)**

nal architecture [20].

in the operating room and guiding surgical decisions.

hyaloid and the green surface is toward the RPE-thus "inverted".

OCT is fundamental to our clinical decision-making for management of macular holes. It has now been incorporated as intraoperative OCT (iOCT)—supplementing surgical assessments

**Figure 7.** Line diagram demonstrating inverted ILM flap technique. (a) The surface of the ILM facing the hyaloid is depicted in green and the surface facing the retinal surface is depicted in red. (b) Trimming of the peripheral part of the ILM. (c) Inverting the central ILM flap over the macular hole. Now the surface of the ILM depicted in red faces the

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Intraoperative OCT consists of spectral domain optical coherence tomography (SD-OCT) on an OCT-mounted surgical microscope. It identifies intraoperative changes in the macular anatomy and provides additional information to predict visual outcomes of macular surgery. The SD-OCT scan taken immediately after ERM removal identifies a cleavage plane for the subsequent ILM peeling, allowing an accurate ILM peel causing minimum disruption of reti-

Intraoperative OCT has been described in several types of retinal surgeries, including vitrectomy for the macular hole. During membrane peeling, the surgeon's impression of membrane

As an increasing number of surgeons opt for ILM peeling to facilitate hole closure, vital dyes have become useful tools for the membrane and ensuring its complete removal [18]. Also, mixtures of dyes with high-density dextrose or polyethylene glycol (PEG) solution have improved the staining of the macula [19]. These high-density solutions when combined with the dye promote immediate settling of the dye onto the macula and minimize its dispersion throughout the vitreous cavity.

With the availability of several dyes and formulations, concerns regarding chemical or phototoxicity are always expressed. Hence, the need to develop new methods to enhance the visualization of the ILM. One example is the use of intraoperative optical coherence tomography (iOCT), which has the potential to visualize the ILM during vitrectomy with immediate surgical feedback.

**Figure 7.** Line diagram demonstrating inverted ILM flap technique. (a) The surface of the ILM facing the hyaloid is depicted in green and the surface facing the retinal surface is depicted in red. (b) Trimming of the peripheral part of the ILM. (c) Inverting the central ILM flap over the macular hole. Now the surface of the ILM depicted in red faces the hyaloid and the green surface is toward the RPE-thus "inverted".
