Morphological Evaluation of Transscleral Laser Retinopexy in Rabbits: Comparison of Optical Coherence Tomography and Histologic Examinations

Abstract

Transscleral retinopexy is a preventive technique used against retinal detachment. Fundus examination can allow the monitoring of morphological retinal changes in the progression of photocoagulation lesions, without offering details on the morphological changes by the retinal lesion. The aim of the study was to assess the progression of photocoagulation lesions induced by transscleral retinopexy (840 nm diode laser), by comparing the optical coherence tomography (OCT) and histological images over a period of six weeks on eight pigmented New Zealand healthy rabbits (four males and four females; n = 16 eyes). All rabbits underwent transscleral retinopexy on their left eye on day 0 (D0). Measurements of the photocoagulation lesions were obtained in vivo on D0, D7, D15, D21, and D42 by acquiring OCT images of both eyes from all rabbits. On D1, D7, D21, and D42, two rabbits were euthanized, and their eyes were enucleated. A significant effect by time on the decrease in the central retinal thickness of the photocoagulation lesion was observed from D1 to D7 (p = 0.001); however, no such effect was observed on the horizontal length ((HL) p = 0.584) of the lesion surface. The reliability between the OCT and histological measurements, which were evaluated using intraclass correlation coefficients, was excellent for measuring the retinal thickness at the center (ICC = 0.91, p < 0.001), moderate for the right side of the retinal lesions (ICC = 0.72, p = 0.006), and not significant for the left side and HL (p = 0.055 and 0.500, respectively). The morphological changes observed in the OCT and histopathological images of the photocoagulation lesions were qualitatively described over time. OCT is an effective tool for monitoring changes in photocoagulation lesions. Some measurements and qualitative changes showed an adequate correlation between the OCT and histological findings.

Keywords: diode laser; histology; optical coherence tomography; photocoagulation; rabbits; transscleral retinopexy.

Figure 1

Rabbit globe. (A) A green-colored line is drawn parallel to the myelin bands observed in the OCT images to orient the histological section plane. (B) The photocoagulation lesion is surrounded by retinal oedemas (thin arrow) and central coagulative necrosis (thick arrow) on D0. (C) The same lesion has progressed to show central pigmentation (thick arrow) and a peripheral white ring (thin arrow) on D7 (Kowa Genesis-D Retinal camera, Innova, Toronto, ON, Canada).

Figure 2

SD-OCT images of the same lesion progressing over time in a rabbit. (A) The OCT image reveals focal serous retinal detachments (red arrows) in an area of neuroretinal edema (bracket) on D0. The thickness of the neuroretinal edema (black line) contrasts with that of the adjacent healthy neuroretinal tissues (white line). (B) The OCT image reveals diffuse retinal edema with small superficial nerve fiber bullae, appearing as hypo-reflective intraretinal cysts (cystoid retinal edema) (red arrow) on D1. (C,D) The photocoagulation lesion appears hyper-reflective with decreased neuroretinal thickness and resolving retinal edema (black lines) on D7 and D15, respectively. (E,F) The retina Is completely atrophic and reduced to 1/10th of its original thickness (white line) on D21 and D42. (A–F) The choroid is slightly reduced in thickness in all Figures (asterisks).

Figure 3

Boxplots of the right side thickness (RS), central thickness (C), left side thickness (LS), and horizontal length (HL) of the surface retinal lesions as a function of time. Asterisks * represent a statistically significant difference.

Figure 4

Progression of different photocoagulation lesions in the histological and OCT images of a rabbit. Hematoxylin–eosin stained retinal section corresponding to the area depicted by the OCT image. (A) Neutrophilic cells in the vitreous (red circle), ganglion cell edema (red arrow), RPE interruption (asterisk), and focal scleral hyalinization (thick black arrow), were observed in the histological section on D1. (B) SD-OCT transversal scan shows hyper-reflective dots in the vitreous (red circle), a hyper-reflective area characterized by ganglion cell edema (red arrow), and RPE interruption/choroid collapse (asterisk) on D1. (C) The histological section shows the disappearance of the outer nuclear layer (black arrow), the reduction in the internal and external plexiform layers (black circle), the disappearance of the photoceptor layer (bracket), and RPE and choroidal interruption with RPE hyperpigmentation (asterisk) on D7. (D) SD-OCT transversal section shows mild hyper-reflectivity of all neuroretinal layers (bracket), and RPE and choroidal interruption (asterisk) on D7. (E) A histological section showing a thin damaged neuroretina (vertical black line) compared to the adjacent healthy neuroretina (vertical white line) and RPE hyperpigmentation and disruption line (asterisk) on D21. (F) SD-OCT section shows a thin, hyper-reflective neuroretina (vertical black line) compared to the adjacent healthy retina (vertical white line) on D21. (G) A histological section shows a thin and disorganized neuroretina (red arrow), RPE hyperpigmentation with melanin migration (asterisk), and a prominent normal retinal vessel (black arrow) on D42. (H) SD-OCT section shows neuroretinal hyper-reflectivity, retinal thinning (red arrow), RPE interruption/choroid collapse (asterisk), and a normal retinal vessel (white arrow) on D42.