3.1. Trabeculectomy Model of Rabbits
shows the PS-OCT images and histological cross-sections of 1 control eye and 3 eyes of rabbit model of trabeculectomy. , , and show histological cross-sections, , , , and show polarization diversity (scattering) OCT, and , , , and show phase retardation images. Note that the scattering OCT and phase retardation images were created from the same spectral data set, and hence perfectly registered to each other, while the histology was taken from a site in the eye not perfectly registered to but close by the OCT. –, –, –, and – were taken from a control eye, and post-operative eyes on day 0, 8, and 14, respectively.
Fig. 3 (a), (d), (g), (j) Histology images, (b), (e), (h), (k) intensity images, and (c), (f), (i), (l) phase retardation images of rabbit trabeculectomy model. (a)–(c) Control eye. Postoperative day (d)–(f) 0, (g)–(i) 8, and (j)–(l) (more ...)
In the histology image of the control eye (), cornea, conjunctiva, muscle, sclera, and iris were identified as labeled. These tissues were perceived also in the scattering image. In the phase retardation image of , strong birefringence was found at the muscle and inhomogeneous birefringence in the sclera. The muscle is appeared as a dark band in the corresponding intensity image (). This dark appearance of ocular muscle is consistent with a previous report [29
– were taken immediately after the surgery (day 0). A fluid pool of a bleb was found in the scattering OCT (arrow in ), consisting of a large cavity with hypo-reflective appearance. No abnormal birefringence was found in the phase retardation image () and no evident scarring was found in the histology (). Note that the vast green region above the flood pool in the phase retardation image is swelled conjunctiva and nictitating membrane. Since this OCT scan was performed immediately after the surgery, this severe swelling could be reasonable.
In the post-operative eyes of day 8 (–), and day 14 (–), collapsed blebs were observed. In the phase retardation images ( and ), abnormal strong birefringence was found at the location of the blebs (arrows). The histological cross-sections indicated that the strong birefringence is the indicator of bleb scarring.
3.2. Human Trabeculectomy
Five blebs of 5 trabeculectomy cases were scanned by PS-OCT. These 5 cases are referred as cases A to E as shown in
. The IOPs of the cases A to E were 10, 13, 16, 22, and 32 mmHg, respectively. In this paper, we consider a bleb which has IOP in a range from 10 to 21 mmHg as a functioning bleb. Based on this definition, cases A and B are classified as functioning blebs, and cases C, D, and E are classified as non-functioning blebs.
(left) Scattering OCT and (right) phase retardation images of trabeculectomy cases A–E.
As shown in , multiple microcysts and a large fluid pool were observed in case A. In the phase retardation image (), the sclera showed strong birefringence. However, no abnormal birefringence was found around the fluid pool.
The case B presented a diffusely thickened conjunctiva which appeared as a large moderately hypo-reflective area consisting of several small cavities as shown by scattering OCT (). Also in this case, the birefringence was only found in sclera and no abnormal birefringence was observed ().
In of case C, a large fluid pool surrounded by hyper-reflective tissue was observed. Despite of this hyper scattering appearance, it was not possible to determine the normality of this tissue from this scattering OCT. In contrast, the corresponding phase retardation image () presented strong birefringence above the fluid pool (arrow). According to the general anatomy of a bleb, the tissue above a normal bleb should be conjunctiva and should not possess birefringence. Hence this appearance in indicates abnormal birefringence.
A fluid pool with a thin wall was observed with case D as indicated by an arrow in . In the corresponding phase retardation image () a vast region with strong birefringence was found. According to the general anatomy of filtering bleb, this birefringence is believed not to be originated from the sclera, hence it is abnormal birefringence.
Case E was a collapsed bleb as shown in . In this bleb, a fluid pool is totally corrupted and cannot be observed. The whole region presented irregular and abnormal birefringence as shown by the corresponding phase retardation images ().
shows the PS-OCT measurement of a pterygium. Pterygium is abnormal growth of fibroblasts and degenerated collagen beneath the conjunctiva that penetrates to the corneal surface. The border of pterygium and cornea was clearly seen in the scattering OCT () and indicated by arrows. Although a moderately weak scattering area was seen at the tip of the pterygium, no evident contrast was observed. In contrast, strong birefringence appeared at the tip and in the body of the pterygium in the phase retardation image () as indicated by * and **. The anatomical structure indicates this strong birefringence is not from sclera, and hence this is likely to be an indicator of active growth of fibroblasts and abnormal collagen.
(a) Scattering OCT and (b) phase retardation images of a pterygium eye.
shows 3 cases of keratoconus corneas and 1 case of normal control. and ) show the control cornea without marked anterior disorder. The scattering OCT does not show evident morphological disorder (). Random phase retardation was observed in the stroma in the phase retardation image (). The mechanism of this random appearance is discussed in section 4.2.
Fig. 6 (left) Intensity images and (right) phase retardation images of (a), (b) a cornea without marked anterior disorder, (c), (d) a cornea with moderate but noticeable thinning keratoconus, (e)–(h) an advanced thinning keratoconus, and (i), (j) a keratoconus (more ...)
and are from a case with moderate but noticeable thinning, as indicated by arrows. In the scattering OCT () the stroma appeared homogenous and the phase retardation shows random appearance () similar to the control cornea.
– show a case with advanced thinning of the cornea, as indicated by arrows. In the scattering OCT (), the cornea shows corneal opacity which had inhomogeneous hyper-scattering. The corresponding phase retardation image () shows abnormal and inhomogeneous birefringence as indicated by arrows. The en face projection of scattering OCT () shows a hyper-scattering region at the left-lower part of the cornea, while the en face phase retardation map of the posterior surface of the cornea () shows strong and inhomogeneous birefringence in the corresponding region.
One of the cases was a case with a rupture of Descemet’s membrane ( and ). In the scattering OCT (), thickening of the cornea due to the rupture was observed, as indicated by arrows. The tissue beneath the stroma shows hyper-reflectivity. In the phase retardation image (), evident abnormal birefringence was observed in the corresponding region.
represents a case of keratoplasty. In the scattering OCT (), the graft is observed at the center and which is sutured to the host. At the graft-host interface (arrows), moderate thickening and rupturing of the epithelium were observed. Although moderate hyper-scattering was shown, evident alteration of cornea was not clearly observed. In contrast, the phase retardation image () showed strong birefringence at the graft-host interface. This is an indicator of microstructural alteration of collagen.
Intensity images and phase retardation images of keratoplasty patients.