|Year : 1983 | Volume
| Issue : 5 | Page : 511-516
Study of ocular tissue response to paraffin wax
RK Murthy, KN Rajkumar, SK Shankar
Prabha Eye Clinic, III Block, Jayanagar, Bangalore, India
R K Murthy
Prabha Eye Clinic, III Block, Jayanagar, Bangalore-560011
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Murthy R K, Rajkumar K N, Shankar S K. Study of ocular tissue response to paraffin wax. Indian J Ophthalmol 1983;31:511-6
An ideal implant material in ophthalmic surgery should satisfy a few criteria for its use. Firstly, the material should be well tolerated by the ocular tissues, with low or no antigenicity and should not provide nidus for infection. It should be easily mouldable, physically and chemically stable after sterilisation and implantation and be easily available. So far, many nonabsorbable materials like poly viol and silicone implants have been used in retinal detachment surgery with fairly good results ,. Of these, sensitivity to Poly viol was identified in a few instances. 
In our country, these implant materials need to be imported and their availability puts a restriction on the surgery. Paraffin wax which is easily available and an economical material has been used in human body since long for various reconstructive procedures and as a haemostatic plug in orthopedic surgery. A mixture of wax and 'Myodil' is injected into the brain during stereotaxic psychosurgery with no untoward effects and permanent palliation to the patient. The present experimental study was undertaken to evaluate the ocular tissue response to a wax buckle placed in the scleral bed, which essentially an avascular collagenous matrix, unlike brain.
| Materials and Methods|| |
Enucleated eyes from six white Belgian rabbits about 8 weeks old, in which scleral wax buckle was implanted, formed the material for the study: In each rabbit only one eye was operated and one buckle was implanted. One rabbit in which no surgery was done, formed the control animal:
The wax implant was made by injecting molten paraffin wax (B.D.H. Paraffin wax. Melting points 50° 60°C) into circular mould and later sterilised by ethylene oxide. It was trimmed to the required size (7 mm x 2 mm x 1 mm) just before surgery.
The rabbits received injection of Calmpose 10 mg one hour before surgery. They were anesthetized by intravenous injection of Pentathlon Sodium 25 mg (diluted in 5 ml of distilled water), which was repeated when needed. Xylocaine drops were instilled into the eye and the pupils were kept dilated with atropine. Upper outer quadrant of the globe in line with the ear was chosen for surgery. Conjunctiva was incised at the limbus; the superior rectus muscle hooked and stay suture was passed beneath, to use it to rotate the eye ball. An adequate scleral bed was dissected under magnification in that quadrant and mattress sutures of 5 `O' merciline or 5 `O' nylon were inserted: A sterilised and trimmed wax buckle were tied to obtain a visible indentation on the retina: It was not possible in all the animals to cover the wax mould completely with scleral flaps. Antibiotics were instilled at the site of surgery and the conjunctiva was sutured into place with 5 0' silk: In the post-operative period daily instillation of mydriatic and antibiotic drops was continued for 30 days: Eyes were examined regularly, throughout the period of study, for any evidence of infection, conjunctival and retinal haemorrhages:
The eyes were enucleated taking care not to disturb the conjunctival cover over the implant, on 3, 10, 22, 35, 57 and 120 days respectively. The eyes with the buckle intact were fixed in 10 % neutral formalin. Following gross examination 0.2 0.3 ml of formalin was injected into the eye using a fine needle through the limbus and the puncture site was sealed with a hot needle. The eyes were sectioned through a line passing obliquely through the wax, the centre of a pupil and the entry point of optic nerve. The tissue was processed, embedded in paraffin and sectioned at 6 micron thickness:
Serial sections were stained with hematoxylin-eosin, and Masson's trichrome for collagen. Gomeri's reticulin stain was used in a few instances.
The wax used for implant was examined under dissection microscope to study the surface. Similarly 10 micron thick section of it was examined under low power view of microscope using transmitted light and under polarized light.
| Results|| |
The wax that apparently looked solid, was confirmed to have a porous structure. The surface was irregular. A 10 micron thick section, under the microscope showed irregular, flat, elongated flakes arranged randomly, with void spaces in between. This feature was better appreciated under the polarized light. Shaving the wax block to the required size proved a superior method to cutting which resulted in premature cracking.
Gross examination of the eye ball revealed the wax distinctly during the initial period, while later it was slightly smaller in size, covered by a capsule. Similarly, the buckle produced on the retina, well seen at the end of surgery, was not so distinct in later periods.
Histological features showed a chronological sequence of events. On the third day, the scleral bed bearing the implant and the adjoining soft tissues were oedematous and infiltrated by a few acute inflammatory cells. Dense acute inflammatory cell exudate infiltrated and extended along the intricate, intercommunicating spaces of the wax [Figure - 1][Figure - 2]. The choroid at the site of implant was congested.
The cornea, ciliary body and the retina were unremarkable. By 10th day, the wax was enclosed in a thin capsule made up of proliferating fibroblasts. The scleral bed had a superficial layer of granulation tissue containing dilated, newly formed vascular channels, while the deeper layers of collagen lamellae were intact. Within the voids of implant dense acute polymorphonuclear leucocyte component persisted, while the surrounding soft tissue showed minimal chronic inflammatory element [Figure - 3]. The neovascularisation observed along the margin appeared to be derived essentially from the sub-conjunctival tissue.
The capsule around had become compact by the end of 3rd week. At many places, the internal surface of the capsule was lined by foreign body giant cells, confining to the contours of the wax voids. In the centre the cellular infiltrate had transformed to chronic type, though the removal of the polymorphs and the nuclear debris were tardy. Admixed with the existing acute inflammatory cells, a few giant cells were observed. The neovascularisation had become more prominent and the vessels were seen extending towards the luminal aspect. The soft tissue around showed focal chronic inflammatory cell component and the oedema had subsided [Figure - 4]. The choroid, ciliary body and retina were normal.
The 35th day specimen revealed essentially a giant cell response along with a few lymphocytes within the voids [Figure - 5][Figure - 6]. The neovascularisation had extended deep along the thin reticulin fibres. The changes observed in 57 days sample were not significantly different from the 35th day one. The giant cell response was still persistent, lining the spaces in the wax. The vascular element was still seen.
At the end of 120 days, the features were in total contrast to the earlier ones. The capsule was compact and dense. The vascular channels observed earlier were totally atretic. The wax void had sparse nuclear debris, fine grains of calcium, and an occasional giant cell. The underlying structures were all normal.
In all the specimens, the wax was contained at the site of implantation and there was no spillage or migration of particles.
| Discussion|| |
The wax is an inert hydrocarbon, which is not degraded by the tissue enzymes. It is successfully utilised in psychosurgery, by injecting it into the brain in a liquid . Proliferation of multinucleated giant cells in the area was the most noticeable tissue reaction along with the infiltration of compound granular corpuscles at the site of injection in the brain . There was no evidence of migration of the wax along the vascular channels and it was not degraded by the lysosomal enzymes in the brain (Unpublished personal data). Similarly a wax buckle implanted in the eye was fairly stable, even at the end of 120 days. However the implant had altered its shape and reduced in size with time.
The wax, similar to silicone sponge appeared to have a porous structure, having intercommunicating void spaces. This fact is best demonstrated by the path taken by the inflammatory cells. In contrast to silicone sponge, the degree of foreign body response was intense. However, after 4 months, in both instances the surface is covered by a thin fibrous capsule, having no cellular element in the centre ,. The wax is well tolerated and has no adverse effects on the ciliary and conjunctival epithelial and the retina. The vascularity of the choroid is not altered. None of the specimens in our study revealed features of infection or rejection. The material was not absorbed or degraded by the giant cells. The wax being relatively mouldable, did not shift from the site of implantation, with movement of the eye ball, which was reported with silicone implants .
Technically, preparing a scleral shelf and covering the implant with the scleral flaps was not possible, as the scleral of the rabbit was thin. This probably can be achieved using an experimental animal having thicker sclera. This study has shown that wax block can be utilised as a scleral buckle and satisfies many of the criteria for an ideal implant. However, in spite of lack of evidence of infection in the present study, the fact that void spaces exist in the wax through which cells and plasma could permeate, raises the question whether this could form a potential nidus for micro organisms in course of time. How these spaces can be reduced and the wax be made more firm, to withstand the friction and maintain the size and shape, needs further study.
| Summary|| |
Utility and tissue tolerance of paraffin wax, when implanted as a scleral buckle, as a substitute to sillicone sponge, was studied in rabbits. The wax is found to have a porous structure, through which the inflammatory exudate could permeate around. Though significant foreign body response was elicited, this material is found stable and well tolerated by the ocular tissues with no toxic effect on choroid, ciliary body and retina. The wax can be sterilised and handled with ease. In view of porous structure, the possibility of the implant forming a nidus for infection is suggested, which needs further substantiation.
| References|| |
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Schephens, C.I., I.D„ Brockhurst, R.J., et al., Scleral buckling procedures, V. Synthetic sutures and silicone implants, Arch. Ophthal., 64, 868, 1960.
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6]