Allergic Conjunctivitis Workup
- Author: Mark Ventocilla, OD, FAAO; Chief Editor: Hampton Roy Sr, MD more...
Approach Considerations
In seasonal and perennial allergic conjunctivitis, superficial conjunctival scrapings may help to establish the diagnosis by revealing eosinophils, but only in the most severe cases, since eosinophils are typically present in the deeper layers of the substantia propria of the conjunctiva. Therefore, the absence of eosinophils on conjunctival scraping does not rule out the diagnosis of allergic conjunctivitis.
Many investigators have described measurement of tear levels of various inflammatory mediators, such as IgE, histamine, and tryptase, as indicators of allergic activity. Additionally, skin testing by an allergist may provide definitive diagnosis and pinpoint the offending allergen(s).
In vernal keratoconjunctivitis (VKC), conjunctival scrapings of the superior tarsal conjunctiva and of Horner-Trantas dots show an abundance of eosinophils. Conjunctival scrapings of patients with atopic keratoconjunctivitis (AKC) may demonstrate the presence of eosinophils, although the number is not as significant as that seen in VKC. Additionally, free eosinophilic granules, which are seen in VKC, are not seen in AKC.
Histologic Findings
Vernal keratoconjunctivitis
Conjunctival scrapings of the superior tarsal conjunctiva show an abundance of eosinophils. Conjunctival biopsy reveals that there are a large number of mast cells within the substantia propria. Histochemical analysis of mast cells, present in VKC, reveals neutral proteases tryptase and chymase. There is enhanced fibroblast proliferation, which leads to the deposition of collagen within the substantia propria and, as result, induces conjunctival thickening.
B-cell and T-cell lymphocytes are present locally, which combine to produce IgE. Specific IgE and IgG as well as the inflammatory mediators histamine and tryptase have been isolated from tears of patients with VKC. Although VKC is typically recognized as a type I hypersensitivity reaction, evidence has been found that supports some involvement of type IV hypersensitivity reaction.
Atopic keratoconjunctivitis
Conjunctival scrapings of patients with AKC may demonstrate the presence of eosinophils, although the number is not as significant as that seen in VKC. Additionally, free eosinophilic granules, which are seen in VKC, are not seen in AKC. Mast cells also may be found within the substantia propria of the conjunctiva in greater numbers.
There is an increased amount of IgE in the tears of patients with AKC. Although AKC is typically recognized as a type I hypersensitivity reaction, evidence has been found that supports some involvement of type IV hypersensitivity reaction, as is the case in VKC.
Giant papillary conjunctivitis
Histologic findings in GPC consist of cellular infiltration of the conjunctiva by a number of cell types. Plasma cells, lymphocytes, mast cells, eosinophils, and basophils have been identified within the substantia propria. Mast cells also may be found in the epithelium. There is also elevated tear levels of immunoglobulin, especially IgE and tryptase also are elevated, as in AKC and VKC.
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| Characteristics | VKC | AKC |
| Age at onset | Generally presents at a younger age than AKC | - |
| Sex | Males are affected preferentially. | No sex predilection |
| Seasonal variation | Typically occurs during spring months | Generally perennial |
| Discharge | Thick mucoid discharge | Watery and clear discharge |
| Conjunctival scarring | - | Higher incidence of conjunctival scarring |
| Horner-Trantas dots | Horner-Trantas dots and shield ulcers are commonly seen. | Presence of Horner-Trantas dots is rare. |
| Corneal neovascularization | Not present | Deep corneal neovascularization tends to develop |
| Presence of eosinophils in conjunctival scraping | Conjunctival scraping reveals eosinophils to a greater degree in VKC than in AKC | Presence of eosinophils is less likely |
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