IntroductionChapter 1

This book of ophthalmic pathology provides a brief review of the study of ocular tissue and fluid specimens with clinicopathological correlation of common ocular lesions.

Sir William Osler, Canadian-born famous physician of his time wrote: "As is our pathology, so is our practice". This phrase underlines the importance of the subject in understanding diseases.

Ophthalmic pathology as a subspecialty is a relatively new field. General pathologists are not usually exposed to ophthalmic slides and ophthalmo-logists are not commonly exposed to pathology laboratories and specimens. In India, there are only few ophthalmic pathology laboratories, so that this brief introduction to ophthalmic pathology will be of great interest and use to general pathologists as well as clinical ophthalmologists.

Histopathology of the eye includes the pathology of the skin of various structures of the eye itself, central nervous system pathology as well as a large number of benign and malignant tumors. The eye can be affected in various systemic disorders, some of them presenting primarily with ocular symptoms. Thorough understanding of the eye's normal structures and pathologic changes can be important for the diagnosis of potentially serious sight or even life-threatening diseases. Recent advances, including immunohistochemistry, chromosome in situ hybridization, real time PCR, proteomics, microarray as well as micro RNA and electron microscopy add to the numerous aspects of ocular histopathology. This book gives an overview of the basic concepts and practices in ocular histopathology, introduces normal histology of the eye and provides clinicopathological correlations of selected common ocular lesions often subjected to histopathological analysis in practice.

deals with the descriptions of pathology specimens, fixation, grossing and sectioning of the globe in a systemic way to help the reader understand the basic techniques required in ophthalmic pathology. deals with the most commonly encountered diseases affecting the eye and its adnexa, divided into pathology of the lid, conjunctiva, cornea, lens, uvea, retina and orbit. The last part introduces topics such as cytopathology of the eye, AIDS-associated ocular diseases, frozen section and telepathology. A list of Sankara Nethralaya publications on ophthalmic pathology and selected references are included at the end for further reading.

We hope this book will be a great resource for resident trainees in ophthalmology and pathology, fellows, practicing ophthalmologists, general pathologists, ophthalmic pathologists and oncologists.

This data forms the basis for pathologic reporting

The globe is usually opened horizontally, but in case of previous surgery which involves the limbal region, e.g. cataract, glaucoma or any other operation, sectioning is done vertically to incorporate the surgical scar. For the same reason, it is also cut in a different plane according to the lesion seen clinically or by site of the transillumination defect.

The globe is opened by a new sharp razor blade for each eye, 2–4 mm on either side of the optic nerve. During sectioning a right handed individual holds the eyeball with the left hand with cornea placed down against the cutting block. The razor blade is held between the thumb and middle finger of the right hand. With a sawing motion, the eye is opened from behind, 2–4 mm away from the optic nerve moving to the front. The globe is opened in a way that includes the pupil and optic nerve in the same section. This is called pupil-optic nerve section (P-O section) of the globe (Figures 1.3A to D).

In case of any interesting findings, gross photography can be taken of the calotte at this stage (Figure 1.3).

After the interior of the globe is examined, a second plane of section parallel to the first is made again passing from back to front.

The other two calottes are examined for any gross pathology. The P-O section is submitted for paraffin processing, the other two calottes are stored and if needed can be studied later, on the basis of examination of the section (Figure 1.5).

Tiny pieces of conjunctiva or iris tissue, which must be kept flat for proper orientation, tend to roll up in formalin fixative. Such tissues are laid on filter paper or a wooden tongue depressor by the surgeon, who indicates the orientation of the specimen by a pencil drawing on the paper or on the pathology requisition slip. In the laboratory the specimen can be pinned to the paper or tongue depressor and placed in a large container of fixative. Using this method the specimen stays flat and is easily removed from the container. If the specimen is exposed to air for about 20s, it adheres to the filter paper. The filter paper and the specimen then can be studied easily under the dissecting microscope.

Small biopsy specimens tend to be lost from the cassettes during processing. Therefore they should be wrapped in tissue paper before they are enclosed in cassettes. If the specimen is only a maximum of 1–2 mm in size it may be placed in the center of a circle marked on a paper and wrapped. Other procedures, such as marking the specimen with blue tissue pencil or staining it by presoaking in eosin help to identify the tissue during paraffin embedding and sectioning.

Ribbons of serial sections are taken and placed on cleaned glass slides lightly coated with a tissue adhesive, such as chrome alum gelatin. Two or three sections should be mounted and placed for staining on each slide. Routinely two or three slides of hematoxylin and eosin (HE) and one of periodic acid-Schiff (PAS) stain are prepared. Several histochemical or immunohistochemical stains may be performed when necessary, but if several unstained slides can be prepared at the time of sectioning for later special staining (e.g. immunohistochemistry, fungi or bacteria), the tissue is used most effectively.

In the first of these methods, immunofluorescence, a fluorescence microscope is needed to visualize the complex and the technique usually does not allow for prolonged storage. Moreover, formalin-fixed tissue may not be ideal for this technique because such tissue emits autofluorescence. Lens and retinal pigment epithelium may also emit autofluorescence. The immunoperoxidase technique is much more convenient for use with ophthalmic specimens because it can be performed on formalin-fixed and paraffin embedded tissue. This technique does not require a fluorescence microscope and the stained sections can be stored for a long time. Modifications of this method include the peroxidase-antiperoxidase (PAP) method or the avidin-biotin complex (ABC) method, both of which have higher sensitivity and specificity than the immunoperoxidase method.