Ocular histology, specimen handling and special stains
Key Takeaways
Agree specimen transport and testing before biopsy when fresh material or special media may be required.
Orientation and separately labelled sites are essential for meaningful margin and map-biopsy interpretation.
Dysplasia or in situ disease differs from invasion across the basement membrane.
Special stains support a specific differential and must be interpreted with morphology and clinical context.
A useful diagnosis starts before the biopsy
Histopathology examines tissue architecture and cells; cytology examines individual cells or small groups. The clinical question determines the specimen, transport and tests. A biopsy for a solid tumour, a conjunctival sample for direct immunofluorescence and a vitreous sample for suspected lymphoma cannot all be handled identically. Communicate with the laboratory before surgery when a special pathway may be needed.
Routine ocular histology begins with recognizing normal layers and anatomical boundaries. In cornea, identify epithelium, Bowman layer, stroma, Descemet membrane and endothelium. In conjunctiva, epithelial and stromal changes have different implications. In a lid specimen, determine whether the lesion involves skin, tarsus, glands or conjunctiva. In retina, postmortem or processing separation can mimic pathological detachment; the surrounding tissue and clinical history help interpretation.
Degeneration, dystrophy, inflammation and neoplasia
Degeneration is acquired tissue deterioration; dystrophy often denotes an inherited tissue disorder, although the clinical category and genotype must be specified. Inflammation can be acute, chronic, granulomatous or mixed. A granuloma is an organized collection of activated macrophages, not a synonym for any fleshy clinical mass. Necrosis, organisms and the tissue response help distinguish causes, but morphology alone may not identify the pathogen.
Dysplasia means disordered epithelial maturation with atypia. Carcinoma in situ remains above the basement membrane, whereas invasive carcinoma breaches it. A small superficial sample may therefore show atypia but fail to establish whether deeper invasion exists elsewhere. Tumour differentiation, mitotic activity, necrosis, invasion and margins all contribute to interpretation. The same stain colour does not establish the same biological behaviour.
Acquisition and orientation
Provide patient identifiers, exact side and site, relevant history, suspected diagnosis, treatment exposure and the requested question. Label separate specimens separately, especially map biopsies and margins. Mark orientation with an agreed suture or diagram and explain what the mark means. A specimen labelled only 'eye tissue' may be impossible to correlate with the lesion or margin needing further surgery.
Handle delicate conjunctiva and cornea gently to avoid crush and curling artifacts. Avoid excessive cautery through the diagnostic tissue. Discuss fixation and transport with the receiving service. Most routine histology uses neutral buffered formalin, but fresh material, a specific transport medium or another fixative may be needed for microbiology, flow cytometry, immunofluorescence or electron microscopy. Do not put the entire irreplaceable specimen into formalin before confirming these needs.
| Question | Specimen consideration | Preventable error |
|---|---|---|
| Tumour margins | Orientation and separately mapped edges | Unlabelled pieces without a site map |
| Suspected infection | Appropriate sterile microbiology portion | Fixing all material before culture |
| Cicatrising autoimmune disease | Direct immunofluorescence pathway | Assuming routine paraffin tissue is sufficient |
| Lymphoma | Planned fresh and fixed allocation | Delay and loss of viable cells |
| Rare dystrophy | Histology and selected ultrastructure | Choosing a fixative without consultation |
Stains and their interpretation
Haematoxylin and eosin (H&E) is the routine starting stain. Periodic acid–Schiff highlights carbohydrate-rich structures such as basement membranes and can help identify some organisms. Gram stain and fungal stains such as Grocott are selected for suspected infection; an absent organism on one stained section does not exclude infection. Acid-fast methods are used for relevant organisms and require a compatible laboratory approach.
Congo red supports amyloid identification with the appropriate optical interpretation. Masson trichrome can aid assessment of stromal deposits, Alcian blue highlights acidic mucopolysaccharides, Perls stain demonstrates iron and von Kossa identifies mineralization indirectly through the associated salts. Choose a stain for a specific differential rather than requesting every stain indiscriminately. Artifacts and nonspecific staining can otherwise be mistaken for a diagnosis.
Electron microscopy can reveal ultrastructural deposits or organisms in selected cases. It requires suitable preparation and is not routine for every corneal button. Immunohistochemistry identifies antigen patterns and is interpreted with morphology and controls. Neither technique can recover tissue that has been lost or badly damaged during acquisition.
Reading and acting on the report
Check the specimen site, diagnosis, margin statements, limitations and recommended additional tests. Correlate the report with the clinical lesion. If a clinically suspicious mass has a nondiagnostic superficial biopsy, discuss adequacy rather than declaring the lesion benign. A positive margin may change excision or adjuvant treatment, but the decision depends on tumour type and the patient's circumstances.
An oriented lid excision can guide a focused additional resection. A poorly labelled set of fragments cannot provide the same information. Record communication of urgent results and ensure that the patient has a follow-up plan. Histology closes a diagnostic loop only when the result is reviewed and acted upon.
Sources: RCPath tissue pathways, RCOphth pathology guidance and Moorfields pathology service.
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