Laser confocal microscopy is a valuable, non-invasive tool for early diagnosis and characterisation of epithelial nests


Dr Ming-Cheng Tai, Department of Ophthalmology, Tri-Service General Hospital, National Defense Medical Center, No. 325, Sec. 2, Cheng Gong Road, Taipei 114, TAIWAN, E-mail:


A 22-year-old woman presented with blurred vision and glare in the right eye, which had been present for three months. The patient had undergone laser-assisted in situ keratomileusis nine months previously and enhancement three months thereafter. On ophthalmological examination, visual acuity was 6/8.6 in the right eye and 6/6 in the left eye. An opaque epithelial nest below the flap with a visible demarcation line was detected along the pupil margin in the right eye. Subsequent laser confocal microscopy revealed the presence of epithelial cells in a whorled pattern with irregular astigmatism on corneal topography. Three months later, the clinical symptoms had worsened and a denser and larger wedge-shaped epithelial nest was observed. The nest was scraped. Six months later, the patient exhibited restored visual acuity (6/6) without glare. Laser confocal microscopy is a valuable, non-invasive tool and provides in vivo pathological images for early diagnosis and localisation of lesion depth in epithelial nests to guide appropriate surgical management.

Epithelial nests are an aggressive type of epithelial ingrowth that may occur following laser-assisted in situ keratomileusis (LASIK). They are characterised by the formation of a nest of epithelial cells (introduced into the interface by the microkeratome during keratectomy or during irrigation of the stromal bed after laser treatment) that do not contact the corneal incision wound.1,2 Epithelial ingrowth is typically diagnosed by slitlamp examination and is characterised as one of three grades, depending on severity.3 Herein, we report the case of a patient who developed an epithelial nest after LASIK and describe the successful management of this complication following early diagnosis using in vivo images of the pathology from laser confocal microscopy.


A 22-year-old woman presented with blurred vision and glare in the right eye. These symptoms had been present for three months. The patient had undergone LASIK in both eyes nine months previously and enhancement three months later. The patient's vision was initially perfect following this procedure, but progressive blurred vision with glare ensued. The patient denied any past history of trauma, infection or ocular surgery.

On ophthalmological examination, the patient's visual acuity was 6/8.6 with +1.50/-1.75 × 50 in the right eye and 6/6 with +1.00/-0.25 × 90 in the left. Slitlamp examination findings appeared normal except for the presence of corneal haze in the right eye. Below the flap, an epithelial nest was observed in the pupil margin, seen as a digit-like opacity with surrounding whitish dots and a visible demarcation line (Figure 1A). A keratometric map revealed irregular astigmatism with focal thickening on the cornea. Laser confocal microscopy (Heidelberg Retina Tomograph, 2 Rockstock Cornea Module, Heidelberg Engineering GmbH, Heidelberg, Germany) revealed the presence of an epithelial nest in the flap interface (Figure 2). The nest was arranged in a whorled pattern with a necrotic centre. Intercellular media showed intracellular vacuoles without prominent nuclei among these epithelial cells. Reflective particles with activated keratocytes were apparent near the epithelial nest border.

Figure 1.

Slitlamp examination findings. (A) On initial presentation, a finger-like corneal haze with a clear demarcation line was observed below the flap. (B) Three months after initial examination, a wedge-shaped growing epithelial nest occupied the pupil margin with an elevated surface. (C) Mild focal corneal oedema was noted over the previous epithelial nest site after debridement surgery. (D) One week after surgery, focal fibrotic change with mild residual focal oedema was noted without residual epithelial nesting.

Figure 2.

Laser confocal microscopy on presentation revealed a high-resolution, histological-like image of the epithelial nest. The nest was arranged in a whorled pattern with a central necrotic area. Surrounding hyperplastic keratocytes were evident, suggesting inflammation, while clear intercellular contact with the vacant intracellular space is indicative of late-stage low-proliferative activity.

Three months later, slitlamp examination revealed a wedge-shaped epithelial nest of a denser quality and larger size (Figure 1B). The patient's symptoms had also worsened. The patient consented to surgical intervention. The flap was lifted and the layer gently scraped from the stromal bed. Histopathological examination of the epithelial nest revealed the presence of epithelial cells surrounded by hyperkeratotic tissue (Figure 3). The flap was repositioned carefully and covered with a contact lens (Figure 1C). The cornea healed smoothly with mild residual haze evident at one week (Figure 1D). The patient's visual acuity was 6/6 in both eyes without glare after six months.

Figure 3.

Histopathological examination of the epithelial nest revealed epithelial cells surrounded by hyperkeratotic tissue (hematoxylin and eosin staining: original magnification ×400)


Epithelial ingrowth is a relatively uncommon complication after LASIK. Reasons for epithelial ingrowth following LASIK enhancement surgery include traumatic flap displacement,4 re-treatment LASIK flap,5 diabetes mellitus,6 limited surgical experience, poor surgical technique7 and flap complications, such as early epithelial defects, flap oedema and inflammation.7 The risk of occurrence is almost doubled with additional surgery.6 Epithelial ingrowth might also occur due to epithelial basement membrane dystrophy or diffuse lamellar keratitis after surgery.6 Thus, the best strategy for reducing the occurrence of an epithelial ingrowth is to properly exclude patients that have potential risk factors, have adequate surgical experience, use proper surgical technique and minimise the potential of flap complications. Intra-operatively, irrigation, the wiping of the stromal interface with sponges, aspiration of irrigation fluid and debris with a suctioning lid speculum and post-operatively the use of a bandage contact lens for the first day after surgery can reduce the potential of epithelial ingrowth.8

Slitlamp biomicroscopy is traditionally used for the diagnosis of epithelial nests. This examination facilitates the characterisation of epithelial nests into three morphological grades.3 Grade 1 is indicated by a thin, non-growing cell colony, one or two cell layers thick and located within two millimetres of the limbus. No surgical management is needed. Grade 2 is an intermediate condition, necessitating treatment within two to three weeks if progression is observed.4 Treatment is indicated for grade 3 epithelial nests as epithelial nests less than two millimetres from the flap edge might lead to corneal melting. As patients are initially asymptomatic, early diagnosis is important. Even after uneventful management, recurrence of epithelial ingrowth occurs in around 25 per cent of cases.5 Early diagnosis may reduce such recurrence.1

Laser confocal microscopy offers several advantages for the diagnosis of epithelial nests. It is a non-invasive procedure, with no requirement for sectioning and staining of samples. Perhaps more importantly, this method allows for the earlier detection of epithelial nests than slitlamp biomicroscopy and hence potential earlier implementation of treatment before deleterious progression. Laser confocal microscopy is associated with the production of high-resolution histological images, which facilitates characterisation of the flap interface.

Despite the advantages, there are some limitations to laser confocal microscopy. Its small field of view makes scanning of the whole cornea prohibitive and the information obtained is purely descriptive. Close examination of lesions identified by slitlamp examination might allow a practitioner with enough clinical experience to make a proper diagnosis at an early stage without the need for histopathological examination of a tissue sample. If there is any question of the diagnosis, a tissue sample of the lesion can be obtained.

In the patient in the present study, the epithelial nest was arranged in a whorled pattern with a necrotic centre, a pattern not previously reported in the literature. Intracellular vacuoles without prominent nuclei (compatible with low proliferative activity) and reflective particles were apparent within the flap. Possible origins for these particles after LASIK include metal particles from the microkeratome, cellular debris, activated keratocytes and meibomian gland secretions; however, these do not interfere with visual quality and serve to mark the location of the flap interface.9

While most isolated nests of epithelial cells regress within a few months with no adverse consequences,10 significant ingrowth is most successfully treated within one month of diagnosis11 or if very severe, as soon as it is diagnosed,5 before scar tissue develops or stromal melting occurs. Several different ways to treat epithelial nests have been described, which include vigorous scraping of the corneal bed and the stromal side of the flap with tight apposition (may use sutures),11–13 alcohol debridement, phototherapeutic keratectomy14,15 and placement of fibrin glue at the flap edges after removal of the epithelial ingrowth.16

In conclusion, laser confocal microscopy is a valuable and non-invasive tool that provides in vivo images, which allow the early diagnosis and lesion characterisation of epithelial nests to guide appropriate management.