Ординатура / Офтальмология / Английские материалы / Dry Eye and Ocular Surface Disorders_Pflugfelder, Beuerman, Elliot Stern_2004

epithelium by lissamine green, but not sulforhodamine B, was enhanced by treatment of the cells with detergents [157]. Therefore, lissamine green staining may indicate membrane abnormalities in ocular surface epithelial cells (Fig. 12). The staining characteristics of ophthalmic dyes are summarized in Table 4.

Interpretation of ocular surface dye staining is based on two criteria, intensity and location. Different grading schemes for ocular surface dye staining have been proposed [27,158,159], but a universal grading scheme has yet to be adopted. The van Bijsterveld grading scale evaluates the intensity of staining on a scale of 0–3 in three areas on the exposed ocular surface, the nasal conjunctiva, the temporal conjunctiva, and the cornea, with a maximum score of 9 [49]. Lemp’s grading scheme evaluates staining in five different zones on the cornea (central, superior, temporal, inferior, and nasal) [27]. The nasal and temporal conjunctiva are divided into three zones, with a triangle pointing toward the canthus and the remaining rectangular area divided into superior and inferior zones. The degree of staining in each zone ranges from 0 (none) to 3 (intense), yielding a maximum score of 15 for the cornea and 18 for the conjunctiva. We propose a slight modification of the NEI grading scheme for the cornea based on the number of stained dots, the number of confluent areas of staining, and the presence of filamentary keratitis (Table 5).

Rose bengal usually stains the conjunctiva more intensely than the cornea, but in severe cases of dry eye, it can stain the entire cornea. The classic location for rose bengal staining in aqueous tear deficiency is the interpalpebral conjunctiva, which appears in the shape of two triangles (nasal and temporal) whose bases are at the limbus (Fig. 12) [152]. Rose bengal staining intensity correlates well with the degree of aqueous tear deficiency, tear film instability measured by tear breakup time, and with reduced mucus production by conjunctival goblet cells and nongoblet epithelial cells [159–163]. A study of 100 consecutive dry eye patients found a rose bengal staining score > 3 in 89%, but not in any of the healthy controls [164]. Rose bengal staining was more sensitive and more specific for detecting dry eye than either reduced tear breakup time or a low Schirmer score [164]. Subjects with Sjögren’s aqueous tear deficiency had significantly greater rose bengal staining scores than subjects with non-Sjögren’s aqueous tear deficiency, meibomian gland disease, or healthy controls [7]. The non-Sjögren’s aqueous tear deficiency group also showed significantly greater staining than the normal control group. Total ocular surface rose bengal staining scores correlated strongly with xeroscope grid distortion and with loss of the nasal-lacrimal reflex, but did not correlate with pathological signs of the meibomian glands (orifice metaplasia, expressibility, and acinar atrophy) [7].

As with rose bengal, significantly greater fluorescein staining of the cornea and the ocular surface was observed for eyes with Sjögren’s aqueous tear deficiency than in normal eyes, or in eyes with non-Sjögren’s aqueous tear deficiency or meibomian gland disease (Fig. 11) [7]. The total corneal fluorescein

Table 5 Baylor Corneal Fluorescein Staining Scheme

Staining procedure:

Instill 3 L of 2% fluorescein without anesthesic

Wait 2 minutes

View staining through a yellow filter and grade

staining score correlated strongly with corneal surface regularity indices, suggesting that the computerized videokeratoscope can be used as an objective assessment of the severity of LKC [13].

O.Impression Cytology

Impression cytology is a practical and minimally invasive method performed under local anesthesia to obtain superficial cells by application of a small membrane against the conjunctival surface. It allows quantitation of goblet cells and a qualitative assessment of epithelial morphology in various conjunctival diseases. Asymmetrically cut cellulose acetate filters can be placed on different areas of the conjunctiva (nasal, temporal, superior bulbar, inferior palpebral). Gentle pressure is applied, after which the filter paper is removed with a forceps [92].

In advanced keratoconjunctivitis sicca, the conjunctiva epithelium undergoes squamous metaplasia, and the density of goblet cells decreases (Fig. 13). The tear film becomes unstable secondary to an abnormal balance and reduced concentration of mucin in the tear film. The extent and severity of squamous metaplasia is examined and graded based on three major cytological features, the loss of goblet cells, enlargement and increased cytoplasmic/nuclear ratio of superficial epithelial cells, and increased keratinization [14,92,165]. Squamous metaplasia can occur in a variety of other dry eye conditions, including vitamin A deficiency (xerophthalmia), ocular cicatricial pemphigoid [89,165], and superior limbic keratoconjunctivitis [166].

Figure 13 Temporal bulbar conjunctival impression cytology. (A) Goblet cells of a normal subject stained violet by periodic acid-Schiff (PAS) reagent (arrow). (B) Conjunctiva of a normal subject stained with antibody against goblet cell mucin MUC5-AC (bright spots indicated by the arrow). (C) Mild squamous metaplasia and absence of goblet cells [compare with (A)] in a Sjögren’s syndrome patient. (D) Severe squamous metaplasia with intense keratinization of some cells (red-stained cells indicated by the arrow) in a Stevens-Johnson syndrome patient.

Squamous metaplasia of the bulbar (but not tarsal) conjunctiva, mucous aggregates adherent to the bulbar conjunctiva, and inflammatory cell infiltration of the inferior tarsal were found in a significantly greater percentage of patients with Sjögren’s syndrome than in those with other forms of dry eye [93]. Squamous metaplasia was graded significantly higher in patients with Sjögren’s syndrome LKC than in those with non-Sjögren’s LKC [167].

The diagnostic specificity of impression cytology can be increased by immunostaining cells on cytology membranes to detect inflammatory cells on the ocular surface, as well as antigens expressed by conjunctival epithelial cells (Fig. 14) [93,162,168]. Cells for flow cytometry can also be obtained by impression cytology [169,170].

Impression cytology is a highly sensitive method to detect pathological changes in the conjunctival surface and confirm a clinical diagnosis. However,

Figure 14 Impression cytology showing HLA-DR expression in conjunctival epithelium. (LC, Langerhans cells). (A) From a normal subject. (B) From a keratitis sicca patient, in whom Langerhans cells and epithelial cells stained positive.

its routine use in clinical practice has been limited by the lack of facilities for staining and microscopic examination.

P.Fluorometric Evaluation of Corneal Epithelial Barrier Function

Corneal epithelial barrier function can be assessed objectively and quantitatively in a noninvasive manner with a scanning computerized fluorophotometer system (Fluorotron Master, OcuMetrics) [84]. Its optical head delivers a focused excitation beam of blue light, and a photodetector measures the intensity of the emitted fluorescent green light. It is capable of measuring fluorescence in different ocular

tissues and fluids from the cornea posteriorly to the retina. Fluorophotometric analysis correlated with biomicroscopic grading of corneal epithelial fluorescein staining [83,171,172], consistent with threeto fourfold greater fluorescein permeability in dry eye patients than in normal subjects [83,173,174]. Benzalkonium chloride, a preservative in many artificial tear formulations, increased permeability to fluorescein in rabbits [175], whereas use of artificial tears without preservatives significantly decreased fluorescein permeability [173].

Using a regression formula, tear volume and secretion can be determined by fluorophotometric analysis after instillation of a small known amount of fluorescein dye, either disodium fluorescein or carboxyfluorescein, eliminating

the need for a tear sample [84]. Mean tear secretion in 56 eyes of dry eye patients determined by this method was 2.48 L/min compared with 3.4 L/min in con-

trol subjects; however, mean tear volume was not significantly different between the two groups [84].

This instrument can also measure tear pH, using the pH sensitive dye bis-carboxyethyl-carboxyfluorescein (BCECF). Using this method, the pH of tears was found to be approximately 7.5, a value similar to that measured with a micro-pH meter [176].

The computerized fluorophotometer has been used in clinical studies to evaluate tear dynamics [177] and corneal permeability to fluorescein after excimer laser photorefractive keratectomy [178], and also in diabetic patients [179].

III.APPROACH TO THE DRY EYE PATIENT

The approach recommended for diagnosis of LKC based on dysfunction of the integrated lacrimal functional unit is presented in Fig. 15. Patients with ocular irritation should first be evaluated for an unstable tear film. Further tests can be conducted to assess performance of components of the lacrimal functional unit, in order to arrive at a final, detailed diagnosis.

IV. SUMMARY

1.Dry eye patients report a variety of symptoms, many of which overlap with symptoms of other ocular surface diseases, complicating diagnosis.

2.Exacerbation of ocular irritation by environmental stresses such as air conditioner drafts and smoky or desiccating environments, or worsening of symptoms during prolonged reading or viewing of a computer screen, are suggestive of dry eye disease.

3.The patient’s history of medication use and possible symptoms of autoimmune syndromes may point to causes of decreased tear secretion.

Figure 15 Flow diagram for diagnosis of lacrimal keratoconjunctivitis (LKC). (TBUT, tear break-up time; CVK, computerized videokeratoscopy.)

4.Assessments of tear film stability and regularity, tear secretion, and dye staining of the cornea and conjunctiva are among the most important objective clinical measures of lacrimal keratoconjunctivitis.

REFERENCES

1.Belmonte C, Garcia-Hirschfeld, Gallar J . Neurobiology of ocular pain. Prog Retinal Eye Res 1997; 16:117–156.

2.Toda I, Fujishima H, Tsubota K. Ocular fatigue is the major symptom of dry eye. Acta Ophthalmol (Copenh) 1993; 71:347–352.

3.McMonnies CW, Ho A. Marginal dry eye diagnosis: history versus biomicroscopy. In: Holly FJ, ed. The Preocular Tear Film in Health, Disease and Contact Lens Wear. Lubbock, TX: Dry Eye Institute, 1985.

4.Bjerrum KB. Test and symptoms in keratoconjunctivitis sicca and their correlation. Acta Ophthalmol Scand 1996; 74:436–441.

5.Schiffman RM, Christianson MD, Jacobsen G, Hirsch JD, Reis BL. Reliability and validity of the Ocular Surface Disease Index. Arch Ophthalmol 2000; 118:615–621.