Clinical Applications of Anterior Segment Optical Coherence Tomography: An Updated Review

Abstract

Since its introduction, optical coherence tomography (OCT) has revolutionized the field of ophthalmology and has now become an indispensable, noninvasive tool in daily practice. Most ophthalmologists are familiar with its use in the assessment and monitoring of retinal and optic nerve diseases. However, it also has important applications in the assessment of anterior segment structures, including the cornea, conjunctiva, sclera, anterior chamber, and iris, and has the potential to transform the clinical examination of these structures. In this review, we aim to provide a comprehensive overview of the potential clinical utility of anterior segment OCT (AS-OCT) for a wide range of anterior segment pathologies, such as conjunctival neoplasia, pterygium, scleritis, keratoconus, corneal dystrophies, and infectious/noninfectious keratitis. In addition, the clinical applications of AS-OCT (including epithelial mapping) in preoperative planning and postoperative monitoring for corneal and refractive surgeries are discussed.

Keywords: anterior segment; cornea; epithelial mapping; keratitis; keratoconus; keratoplasty; optical coherence tomography (OCT).

Figure 1

High-quality swept-source AS-OCT representation of a healthy cornea: (a) hyper-reflective tear film; (b) thin, hyporeflective corneal epithelium; (c) corneal stroma; (d) hyper-reflective pre-Descemet’s layer (or Dua’s layer)/Descemet membrane; (e) anterior surface of the crystalline lens.

Figure 2

High-quality swept-source AS-OCT showing healthy conjunctiva: (a) hyporeflective conjunctival epithelium; (b) hyper-reflective subepithelial tissue of the substantia propria; (c) band of hyper-reflective scleral tissue.

Figure 3

Clinico-morphological and AS-OCT features of conjunctival naevi: (A) pigmented lesion without cystic alterations on AS-OCT (B); (C) amelanotic naevus with macroscopically visible cysts, which are confirmed with AS-OCT examination (D); (E) small pigmented conjunctival naevus—cystic alterations are not be visible on slit-lamp examination, and intralesional cysts can be detected only with AS-OCT (F); (G) pigmented conjunctival naevus—intralesional cysts can be visualized with both slit-lamp examination and AS-OCT (H). (This figure was adapted from Vizvári et al. [29] and was reproduced unchanged under the terms of the Creative Commons (CC) BY 4.0 license https://creativecommons.org/licenses/by/4.0/, accessed on 28 September 2023).

Figure 4

A case of conjunctival/corneal intraepithelial neoplasia: (a) slit-lamp photograph demonstrating a white, gelatinous lesion encroaching on the conjunctival, limbal, and peripheral corneal region (red arrow); (b) AS-OCT delineating the thickened epithelium at the conjunctival, limbal, and corneal regions (yellow arrows).

Figure 5

Slit-lamp photograph and AS-OCT of conjunctival lymphoma: (a) slit-lamp photograph of conjunctival lymphoma; (b) on AS-OCT, there is a homogeneous, dark, hyporeflective subepithelial lesion with smooth borders and overlying thin epithelium (arrow). The lesion contains monomorphic, stippled, dot-like infiltrates corresponding to the infiltration of monoclonal lymphocytes (this figure was adapted from Venkateswaran et al. [39] and was reproduced unchanged under the terms of the CC BY 4.0 license, https://creativecommons.org/licenses/by/4.0/, accessed on 28 September 2023).

Figure 6

Salzmann nodular degeneration: (a) slit-lamp photograph demonstrating two Salzmann nodules on the cornea (red arrows); (b) AS-OCT demonstrating a corresponding hyper-reflective subepithelial lesion of the cornea (yellow arrow).

Figure 7

AS-OCT images of scleritis, comparing superior quadrant scleral thickness: (a) pretreatment; (b) post-treatment.

Figure 8

Acute corneal hydrops in advanced keratoconus: (a) slit-lamp photograph demonstrating a right acute corneal hydrops, characterized by significant central corneal edema, opacity, and bullae (red arrow); (b) AS-OCT demonstrating significant corneal edema with a break in pre-Descemet layer/Descemet membrane (PDL/DM; yellow arrow) and large type 1 PDL/DM detachment (green arrows). Attachment of posterior stromal fibers to PDL is visible (blue arrow).

Figure 9

Severe Pseudomonas aeruginosa keratitis with corneal perforation: (a) slit-lamp photograph demonstrating significant corneal infiltrate and stromal melt/threatened perforation (red arrow), with a negative Seidel sign; (b) AS-OCT demonstrating significant corneal melt (yellow arrow) with a very thin residual layer of epithelium and 360-degree iridocorneal touch and absence of anterior chamber (blue arrow), indicating the presence of corneal perforation. The absence of anterior chamber resulted in a negative Seidel sign, providing a false reassurance of corneal integrity.

Figure 10

Pseudomonas aeruginosa keratitis with severe anterior chamber reaction: (a) slit-lamp photograph demonstrating a central infiltrate (red arrow) with severe anterior chamber reaction and hypopyon (black arrow); (b) AS-OCT demonstrating severe anterior chamber reaction, evidenced by increased hyper-reflective cellular changes in anterior chamber (yellow arrow).

Figure 11

Candida keratitis with retrocorneal plaque: (a) slit-lamp photograph demonstrating a deep stromal infiltrate (red arrow) with extension into the anterior chamber; (b) AS-OCT demonstrating a posterior stromal infiltrate with a homogeneous increased hyper-reflectivity (yellow arrow) between posterior stroma and pre-Descemet layer/Descemet membrane (blue arrows), and hyper-reflectivity in anterior chamber (green arrow), suggesting an extension of fungal infection into the anterior chamber.

Figure 12

Corneal endothelial graft rejection: (a) slit-lamp photography demonstrating a mild corneal endothelial graft rejection with keratic precipitates (red arrows) in an eye with previous penetrating keratoplasty for keratoconus; (b) AS-OCT showing keratic precipitates as mild excrescences on the corneal endothelium (yellow arrows). Considerable graft–host ectasia (green arrows) is also noted.

Figure 13

Descemet stripping automated endothelial keratoplasty in an aphakic eye with previous glaucoma tube drainage surgery: (a) AS-OCT demonstrating complete graft detachment postoperatively (red arrow); (b) complete graft attachment was achieved (yellow arrow) after rebubbling and suturing of the glaucoma tube.

Figure 14

A case of interface infectious keratitis (IIK) following Descemet stripping automated endothelial keratoplasty (DSAEK): (A) slit-lamp photography demonstrating an inflamed right eye with diffused stromal haze in a crisscross pattern at the graft–host interface (blue arrows), consistent with a diagnosis of IIK. The edge of the DSAEK graft is visible (yellow arrow); (B) hyper-reflective changes at the graft–host interface (red arrows) are clearly delineated on AS-OCT, highlighting the value of AS-OCT in facilitating the assessment of infectious keratitis; (C) slit-lamp photography demonstrating complete resolution of the IIK following intensive topical antifungal treatment, evidenced by the disappearance of the stromal haze on slit-lamp photograph; (D) this corresponds to the disappearance of the hyper-reflective changes at the graft–host interface on AS-OCT (this figure was adapted from Song et al. [155] and was reproduced unchanged under the terms of the CC BY 4.0 license, https://creativecommons.org/licenses/by/4.0/, accessed on 5 November 2023).

Figure 15

Late-onset traumatic dislocation of LASIK flap: (A,B) slit-lamp photos revealing a right hazy and thickened corneal flap, central epithelial ingrowth (red arrow), superior-nasal corneal neovascularization, and a large area of nasal corneal flap folded and tucked under the central flap (green arrows—edge of the original nasal flap; blue arrows—edge of the fold); (C) AS-OCT delineating the extent of the infolded flap (red arrows); (D) Scheimpflug corneal tomography showing significant corneal flattening nasally with irregular astigmatism and steeping centrally; (E) slit-lamp photo showing a clear cornea with an area of very mild interface haze (blue arrow) following the repositioning of the dislocated LASIK flap and removal of epithelial ingrowth; (F) AS-OCT demonstrating a small hole within the LASIK flap postoperatively (red arrow); (G) mild recurrence of epithelial ingrowth (blue, left arrow) was noted 9 months postoperatively; (H) corneal tomography showing significant improvement in the anterior corneal curvature and irregular astigmatism 9 months post-operation (this figure was adapted from Ting et al. [91] with permission from the licensor Springer Nature, https://link.springer.com/article/10.1007/s10792-018-0946-7#Fig1, accessed on 14 November 2023).

Figure 16

Epithelial ingrowth postcataract surgery: (a,b) AS-OCT showing a hyper-reflective layer of presumed epithelial cells (red arrows) extending through the previous paracentesis (yellow arrows); (c–e) slit-lamp images showing the corresponding area of epithelial ingrowth.