it can be a sign of loss of transparency, the partial cloudiness of the normally crystal clear and
totally transparent cornea (Figure 4). All cases with corneal involvement are severe red eyes to be treated by an ophthalmologist! All corneal lesions can worsen with time, therefore spe- cific and effective therapy should be started without delay!
Fluorescein staining can be helpful in deciding whether the corneal surface is intact or epithelial defects are pre- sent. This is especially important to rule out possible her- petic (HSV) infection of the cornea that is hard to see with the naked eye (Figure 5), while the characteristic appearance of a branching epithelial defect (dendritic keratitis) is clearly recognisable after instilling one drop of 2 % sodium fluorescein eye drops (Figure 6).
Once the two most important questions (possible visual acuity changes and corneal involvement) are answered, further careful inspection of the eyeball and the surroun- ding areas has to be performed. By pulling down the lower eyelid, the lower conjunctival fornix (exudates, mucous threads, folliculi) and the inner surface of the lower eyelid can be exposed for careful visual examina- tion; by everting the upper eyelid, the inner surface of the upper eyelid (common site for small foreign bodies trap- ped in the subtarsal sulcus) can similarly be exposed and examined. By examining the lid margins, signs of blepha- ritis (crusts, scales, ulcers, pustulae) can be found, by pal- pating the eyelids chalazeon can be detected, by feeling the regional lymph nodes enlargement and tenderness can be identified. Palpation of the eyeball is not a precise mode for evaluating the intraocular pressure, but “hard Figure 5 – Dendritic keratitis without staining Figure 6 – Dendritic keratitis with fluores- cein staining as a rock” and painful red eye can help the diagnosis of a glaucomatous attack, and a hypotonic eye can confirm the supposed diagnosis of a penetrating eye injury. The pupil is typically constricted (miotic) in acute, and irregular, (due to the presence of posterior synechiae), in chronic forms of iritis and iridocyclitis. A wide pupil and the absence of light response can be present in acute angle closure glaucoma and following blunt injury of the eyeball (traumatic mydriasis). Differences in the size and the light reaction of the pupils can have neurological (head trauma, brain tumor,
circulatory changes) or pharmaceutical (use of miotic or mydriatic eye drops) causes.
THE DIFFERENTIAL DIAGNOSIS OF VARIOUS TYPES OF CONJUNCTIVITIS
Once the diagnosis of conjunctivitis is made and the doctor is sure that other more severe causes of red eye can be excluded, the next question is whether it is a dry eye (keratoconjunctivitis sicca, inflammation of the cornea and the conjunctiva due to drying out of the ocular surface), or an allergic, or infectious form of conjunctivitis. The following three chapters deal with the
THE DIFFERENTIAL DIAGNOSIS OF THE RED EYE
diagnosis and therapy of these diseases in detail. In the last part of this chapter, only some
hints are given on how to differentiate between the main types of conjunctivitis. The charac- teristics and therapy of dry eyes and of different types of allergic and infectious conjunctivitis are dealt with in the remaining chapters of this brochure.
The differentiation between different types of conjunctivitis is usually possible based on evalu- ation of the appearance of the conjunctiva, the type of hyperaemia, and any conjunctival exu- date (diffuse bright red conjunctiva with serous exudate is typical of viral conjunctivitis, dif-
fuse hyperaemia and swelling of the conjunctiva with purulent or mucopurulent exudate and crusts on the lid margins is the usual appearance of bacterial conjunctivitis, while a more swol- len rather than hyperaemic conjunctiva with a “milky appearance” and the presence of itching is very characteristic of allergic conjunctivitis). Enlarged preauricular lymph nodes are present in chlamydial and in certain types of viral conjunctivitis. Microscopic evaluation of smears of conjunctival exudates (stained with Haematoxilin or Giemsa) can be helpful in supporting the diagnosis (polymorphonuclear leucocytes and bacteria in bacterial conjunctivitis, eosinophils in allergic conjunctivitis, mononuclear leucocytes in viral conjunctivitis, inclusion bodies in epi- thelial cells in chlamydial disease, fungi in fungal conjunctivitis are all very characteristic). Most microbiological laboratories offer immediate diagnosis from smears including Gram staining of the bacteria, but those GPs (and ophthalmologists) who have a microscope and a little expe- rience in evaluating blood smears and urinary sediments can also evaluate conjunctival smears themselves. Culturing and antibiotic sensitivity tests not only help in the identification of the causative microorganism but make therapy more precise and more effective.
TABLE II DIFFERENTIAL DIAGNOSIS OF COMMON FORMS OF CON- JUNCTIVITIS
Preauricular Lymph Nodes
Bacteria, poly- Usually normal morphonuclear leucocytes
of the Conjunctiva
Highly hyper- aemic, suffu- sions may be present
More oedema- Serous
Adapted from: Hollwich F.: Ophthalmlogy. A short textbook. 2nd ed., Thieme (1985) 
Acute or chronic
Course of the Appearance
THE DIFFERENTIAL DIAGNOSIS OF THE RED EYE