# AS-OCT and Ocular Hygrometer as Innovative Tools in Dry Eye Disease Diagnosis
## 2 Current Methods of Diagnosis  
After the collection of a complete history and details of the symptoms, the visit should start with an in-depth examination with a slit lamp, both with and without eye staining, in order to detect signs of DED. The first important marker of DED that can be measured by slit lamp biomicroscopy is the presence of a low tear film meniscus height. The inspection should continue with the assessment of DED-associated conjunctival hyperaemia, which usually involves the fine horizontal vessels of the exposed bulbar conjunctiva [20]. Furthermore, DED-associated redness can be objectively assessed by investigator grading scales and computer-automated redness grading scales, developed for both diagnostic and follow-up aims [20]. Subsequently, it is crucial to investigate the presence of meibomian gland dysfunction (MGD) by carefully examining the eyelid rim, eyelashes and glandular duct orifices for telangiectasias, collacrettes and chalazia [21]. Nevertheless, the operator dependent variability and low repeatability of the various MGD grading scales limit the classification of MGD [17; 21]. Lid-parallel conjunctival folds (LIPCOFs) is a promising DED diagnostic sign, although it needs to be evaluated with more objective methods, such as optical coherence tomography (OCT), for its classification [22; 23]. Fluorescein sodium staining can be used during slit lamp examinations to highlight defects in the corneal epithelium. The corneal surface is stained wherever there is a break in the epithelial cell-to-cell junctions. Resultant staining may show corneal superficial punctate epithelial erosions in patterns consistent with some of the causes of dry eye disease. For example, erosions identified in the lower third of the cornea could be due to eyelid-related exposure problems, such as infrequent or incomplete blinking or lagophthalmos. However, since corneal epithelial erosions can be related to other causes, fluorescein sodium staining is unable to provide direct evidence of DED, nor can it be considered a truly specific or sensitive test [24; 25]. Rose Bengal staining is an important tool in evaluating dry eye disease as it occurs in corneal or conjunctival areas that are devoid of membrane-associated mucins, but its clinical use is limited by its toxic effects on the corneal epithelium and by its poor sensitivity and specificity [26]. Moreover, rose Bengal staining can occur in asymptomatic patients and there is no clearly defined relationship between ocular surface damage that is specific to dry eye disease and the patient's symptoms [27]. Lissamine green dye has a similar staining pattern to rose Bengal but, unlike the latter, the former is better tolerated as it does not determine epithelial corneal toxicity [28; 29]. There are many grading systems for assessing ocular surface staining, including the Oxford Scheme, the van Bijsterveld system and the National Eye Institute/Industry Workshop guidelines [30; 31]. However, there is no common consensus among researchers and there are no published scientific papers showing that one grading system is superior to the others. For measuring tear production, the Schirmer test is still one of the most commonly used procedures. The Schirmer test type I is performed without instilling anesthetic drops and it measures total tear secretion, including both reflex and basal tears. One edge of the Schirmer strip is placed inside the lower conjunctival sac and, after 5 min, the length of wetting on the strip is recorded in millimeters. The result of the test is considered normal when the value obtained is greater than 10 mm [32]. However, a false negative result was found in patients who performed the Schirmer test type I with their eyes closed because the stimulation of the lid margin and eyelashes can increase the tear turnover rate. The Schirmer test type II, which uses topical anesthesia, only measures basal tear production by applying the same strips. The Schirmer test is more reproducible in advanced cases of DED.