Wael Soliman Department of Ophthalmology Assiut University Hospital Assiut University Assiut Egypt Tel: + 20 165 566530 Fax:+ 20 882 333327 Email: email@example.com
Purpose: To study the morphological patterns of pterygia and pingueculae using high-resolution anterior segment spectral domain optical coherence tomography (SD-OCT).
Methods: Prospective cross-sectional study of 25 eyes presented with pterygia and pingueculae was conducted, and the eyes were examined by anterior segment SD-OCT.
Results: We examined 25 eyes, including 13 eyes with primary pterygia, six eyes with recurrent pterygia, one case with a pseudopterygium and five eyes with pingueculae. Primary pterygia revealed elevation of the corneal epithelium by a wedge-shaped mass of tissue separating the corneal epithelium from the underlying Bowman’s membrane, which became wavy and interrupted. We found satellite masses of pterygium tissue advanced under the epithelium beyond the clinically seen pterygium margins. In recurrent pterygia, we detected that the central tip of the pterygium was more advanced and creeping beneath the basal corneal epithelium than the primary pterygium. In pseudopterygium, the SD-OCT images showed that the overgrowing membrane was not really attached to the underlying cornea. In cases of pingueculae, SD-OCT revealed a wedge-shaped mass that was nearly similar in pattern to that of the pterygia but stopped at the limbal region. Immediately after removal of pterygia, we noticed many remnants of the pterygia masses over the corneal stroma in spite of the clinically clear appearance of cornea.
Conclusions: SD-OCT provided us with high-resolution images of the pterygium and the pinguecula and showed clearly the anatomical relationship between the corneal tissues and these lesions. The use of this new modality of imaging may help to decrease the current recurrence rates after pterygium excision through using the anterior segment SD-OCT in the evaluation of these lesions.
Pterygium is a wing-shaped grey-white thickening located in either nasal or temporal limbus with an apex extending towards the cornea. Superficial blood vessels feature prominently and point towards the apex of the mass.
Histologically, pterygium is characterized by elastotic degeneration of conjunctival substantia propria, with associated eosinophilic or basophilic deposits. Epithelial changes are variable and include hyperkeratosis, parakeratosis or acanthosis. Recurrent pterygium lacks the histopathological features of elastotic degeneration and is more accurately classified as exuberant fibrovascular granulation tissue but without the ability to pass a probe beneath it. A pseudopterygium extends from the bulbar conjunctiva onto the cornea, and in this regard, it resembles a pterygium. The process is secondary to corneal damage (trauma or peripheral ulceration) and, unlike a pterygium, can occur anywhere along the 360 degrees of the corneal periphery. Clinically, the ability to pass a probe beneath the apex is a useful diagnostic feature. Histologically, a pseudopterygium consists of fibrovascular tissue that does not contain foci of elastotic degeneration. The epithelium often extends around the fibrovascular mass (Sehu & Lee 2005).
The histopathology of pinguecula resembles in many aspects that of the pterygium. Pinguecula is a nodular grey-white nodule of the conjunctiva located in the temporal or nasal bulbar conjunctiva but not involving the cornea. The histopathological findings include conjunctival epithelium changes, which vary between atrophy, hyperplasia, metaplasia and dysplasia, in addition to hyalinized subepithelial collagen with elastotic degeneration (Sehu & Lee 2005).
Both pterygium and pinguecula occur in the interpalpebral zone, and some researchers believe that there is a potential limbal barrier that normally does not allow a pinguecula to advance over the cornea. When this potential limbal barrier is crossed, pinguecula advances over the cornea as a pterygium (Raizada & Bhatnagar 1976; Archila & Arenas 1995; Dong et al. 2009).
Introduced in 2002, spectral domain optical coherence tomography (SD-OCT) provided detailed cross-sectional images of structures in biological tissues with an axial resolution of five microns and a transverse resolution of 15 microns. It scans at 26 000 A-scans per second. It provides real-time, artefact-free quantitative imaging (Wojtkowski et al. 2002, 2003). Although the technique was designed primarily to examine the posterior segment, imaging of the anterior segment was achieved by adjusting the anterior module (Sarunic et al. 2008).
The aim of this work was to study the SD-OCT morphological patterns of primary pterygium, recurrent pterygium, pseudopterygium and pinguecula.
Patients and Methods
The study was conducted at Assiut university hospital and EL Noor eye center from June 2009 to September 2009. In this observational prospective cross-sectional study, twenty five eyes of 25 patients presented with pingueculae, pterygia (primary, recurrent) and pseudopterygia were included. We also assessed the corneal surface morphology after pterygium excision in five of the included study eyes.
The study was conducted after getting the agreement of the ethics committee at the faculty of medicine and after obtaining informed consent from all patients. The study followed the declaration of Helsinki.
Anterior segment imaging was performed using SD-OCT (RTVue-100; Optovue, Freemont, CA, USA). This device uses two lens attachments, the cornea/anterior module-short (CAM-S) and CAM-long (CAM-L), to obtain anterior segment images. The CAM-S attachment provides a high-magnification view, whereas the CAM-L provides a wider viewing angle but at a slightly decreased resolution.
In our study, we used SD-OCT vertical and horizontal raster default scans with 6.0-mm scan lines with the add-on lens (CAM-L). All image analysis was performed using the built-in analysis program.
In this prospective observational study, we examined 25 eyes of 25 patients (21 men and 4 women). The patients’ mean age was 45 (ranging from 42 to 65).Thirteen eyes presented with primary pterygia, six eyes with recurrent pterygia, one case with a pseudopterygium and five eyes with pingueculae.
In the horizontal OCT scans (parallel to the axis of the pterygium growth), primary pterygia revealed an elevation of the corneal epithelium by a wedge-shaped mass of tissue separating the corneal epithelium from the underlying Bowman’s membrane, which became irregular, wavy and interrupted. Immediately central to the cap of pterygium, the epithelium, Bowman’s membrane and the corneal stroma appeared normal. Also, the SD-OCT scans showed extension of the pterygium tissue below the corneal epithelium beyond the edge of the corneal tip of the pterygium mass (Figs 1 and 2).
On the other hand, vertical scans of the primary pterygia (perpendicular to the axis of growth of the pterygium) revealed a characteristic triangular pattern. In these vertical scans, we were also able to see the destruction of Bowman’s membrane and affection of superficial corneal stroma beneath the pterygium mass (Fig. 2).
The extreme upper and lower edges of the pterygia showed apparently heaping lobes above the corneal epithelium mimicking a pseudoline of cleavage and satellite masses of pterygium tissue advanced under the corneal epithelium beyond the edge of the pterygium (Fig. 3).
In some cases of recurrent pterygia, there were wedge-shaped masses of tissue between the corneal epithelium and the underlying partly destroyed Bowman’s membrane, but in comparison to primary pterygia, the central tip of these wedges was found to be more advanced and creeping beneath the corneal epithelium. In the remaining cases of the recurrent pterygium, the mass appeared irregular with multiple humps and cystic changes compared to the smooth well-delineated appearance of the primary pterygia (Fig. 4).
In pseudopterygium, the SD-OCT images showed that the overgrowing membrane was not really attached to the underlying cornea. Also, there was a real plane of cleavage between the pseudopterygium mass and the underlying corneal epithelium. On the other hand, the central point of attachment to the cornea showed invasion below the epithelium and destruction of Bowman’s membrane (Fig. 5).
SD-OCT of pingueculae revealed wedge-shaped masses that were nearly similar in configuration to the SD-OCT pattern of the pterygia but stopped at the limbal region and did not elevate the corneal epithelium. A clearly defined line of separation was found between the pinguecula and the underlying scleral tissue (Fig. 1).
Interestingly, SD-OCT, which was performed immediately after the removal of 5 pterygia using a bare sclera dissection technique, revealed many remnants of the pterygia masses over the corneal stroma in spite of the clinically clear appearance of cornea after excision of the pterygium (Fig. 6).
In 2003, Buchwald et al. used both the anterior segment OCT and the UBM to describe ocular surface lesions including patients with pterygia. They reported that the pterygium appeared as a hyper-reflective lesion above the cornea, but in our study, we reported more detailed description because of the higher resolution that was revealed owing to the use of SD-OCT (Buchwald et al. 2003).
Our SD-OCT is the first detailed report about pterygium and pinguecula using this new modality of imaging.
SD-OCT of both pingueculae and pterygia revealed some similarities. In agreement with our results, Raizada et al. reported that histopathology of pinguecula resembles in many aspects the histopathology of pterygium. They also mentioned that there is a potential limbal barrier that normally does not allow a pinguecula to advance over the cornea, and this suggestion was shown also in our SD-OCT scans, which revealed that the pinguecula mass stopped at the limbus and did not cross to creep beneath the corneal epithelium (Raizada & Bhatnagar 1976).
Also, our study confirmed much of the results of a study conducted by Seifert et al. 2001 who studied the topological and histological patterns of the pterygium. In their study, they proved histologically the presence a narrow strip of newly formed layer of pathological pterygium stroma lying between the corneal epithelium and the Bowman’s membrane beyond the end of the pterygium boundaries, and this finding was also clearly demonstrated in our study.
In the current study, we confirmed the presence of the lobes of pterygium stromal tissue that projected sideways from the continuous base of the pterygium, a pattern that was described also by Seifert et al. 2001 (Seifert et al. 2001).
In our study, we showed that at the extreme superior and inferior periphery of the wing of the pterygium, there were satellites of pterygium masses beyond the apparent peripheral end of the lesion like the pterygium masses described before around the corneal tip of the pterygium. Therefore, we assumed that the excision of the pterygium with a large safety margin at the conjunctival or the corneal sides of the pterygium mass may lead to a change in incidence of recorded recurrence rates attributable to removal of the nonclinically seen pterygium tissue. This suggestion was also recommended by Seifert et al. (Seifert et al. 2001) in their topological and histological study about pterygium and by Hirst (2008) who showed that there was a higher incidence of recurrence in conservative surgical approaches of pterygium removal and lower in the aggressive extended surgical ones.
It is well known that a recurrent pterygium is more difficult to control, and various treatment modalities have been proposed (Fallah et al. 2008; Hirst 2009). Using SD-OCT for the evaluation of recurrent pterygium in this study, we were able to show that the tongue-like mass of the pterygium was more advanced beneath the corneal epithelium, a view that may explain the difficulty of managing and the high incidence of repeated recurrences after recurrent pterygium surgery. The broad explanation for this is that we only see and remove the tip of the iceberg and not the whole one.
SD-OCT immediately performed after excision of the primary pterygium using the bare sclera technique revealed multiple remnants on its corneal and conjunctival sides, and this may elucidate the importance of smoothening of the corneal and conjunctival sides after excision of the pterygium (Helal et al. 1996; Hirst 2008, 2009) Although we did not use SD-OCT for evaluating the corneal surface after different pterygium excision techniques, this could lead us to do such study in the future.
The use of anterior segment SD-OCT provided us with high-resolution images of the cornea and the pterygium and helped us to understand more about the anatomical relationship between the corneal tissues and the pterygium mass and the morphological similarity between the pinguecula and the pterygium.
Also, the use of this new modality of imaging may help to decrease the current recurrence rates after pterygium excision through using the anterior segment SD-OCT in the evaluation of these lesions. In the future, the use of a hand-held anterior segment SD-OCT will be of great help during performing anterior segment surgeries including pterygium excision through giving a real-time in vivo imaging to ensure total removal of this lesion (Maldonado et al. 2010; Vinekar et al. 2010).