According to its different causes, dry eye can be divided into five types:
1.Evaporative Dry Eye (EDE), this type is mainly caused by abnormalities in the lipid layer (either in quality or quantity), such as Meibomian Gland Dysfunction (MGD), Stye, Blepharitis, etc, or increased evaporation caused by a defect of the eyelids or heterophthalmia.
Video-digital termination syndrome (computer vision syndrome) patients blink less, thus causing an increase in eye evaporation, larger palpebral fissures, and greater exposure, and so can also be classified into this kind of dry eye.
2.Tear Deficiency Dry Eye (TDDE) originates in aqueous tear deficiency, like that stemming from Stevens-Johnson syndrome and other systemic factors. Aqueous tear abnormality also results in tear film instability and dry eyes.
3.Mucoprotein Deficiency Dry Eye (MDDE) is mainly due to damage to the epithelial cells of the ocular surface, including chemical and thermal burns to the ocular surface, and corneal limbus dysfunction.
4.Some patients with chemical injuries have normal lacrimal secretion. For example, in the Schirmer’s test their result is more than 20mm, but there is something wrong with their corneal epithelium, mostly because of mucoprotein deficiency.
5 .Tear Dynamic Dysfunction Dry eye caused by lacrimal dynamic dysfunction, including dynamic dysfunction generated by ophthalmitis, caused by abnormal blinking, slowed tear secretion, conjunctivochalasis, etc.
6.Compound Type Dry eye associated with two or more of the above causes.
Common causes of dry eye:
Prolonged computer usage and extreme concentration leads to less blinks of the eyes per minute.
Prolonged TV viewing, especially in the dark.
Prolonged driving, particularly with heated air blowing directly towards one’s face.
Prolonged reading, without resting when eyes become tired.
Prolonged playing of video games.
Crying oneself to sleep, especially after giving birth.
Other prolonged activities causing one to blink less.
Dirty environment. Dust clogging one’s lacrimal gland and meibomian gland.
Persons with oily skin. Their meibomian gland is more likely to clog.
More common as age increases, because fewer tears are produced with age.
DIAGNOSIS AND TESTING:
Tear Secretion Test
10-15mm is normal; 10mm low secretion; 5mm can be diagnosed as dry eye. Test should be conducted without ocular surface anesthesia, to test the secretion function of the main lacrimal gland; then the secretion of the minor lacrimal gland. Observation time 5 min.
Tear Break Up Time ( BUT)
A time of less than 10sec indicates tear film instability.
Tear Ferning Test
In patients with mucoprotein deficiencies, such as ocular pemphigus, or Stevens-Johnson syndrome, “ferns” are less or even absent.
Biopsy and Impression Cytology Examination
Patients with dry eyes have decreased conjunctiva goblet cell density, increased nucleoplasmic ratio, epithelial cells squamous metaplasia, corneal epithelium keratoconjunctivalised. Through conjunctival goblet cell density measurements, we can indirectly evaluate the severity of the disease.
A positive result indicates a corneal epithelial defect. And this test also allows us to observe the height of the tear meniscus.
Rose Bengal Staining
The sensitivity of Rose Bengal Staining is higher than fluorescein staining.And inactive corneal, conjunctival cells will stain positive.
lysozyme in Tears
Amount< 1200ug/ml or Lytic area < 21.5mm2
For persons with dry eyes, or those wearing contact lenses, tear osmolarity is 25mOsm/L higher than normal people. If the reading is above 312mOms/L, it can be diagnosed as dry eye. This technique is unique in that it has high value for early diagnosis.
It can be diagnosed as dry eye if the amount is below 1.04bg/ml for those aged under 69 or below 0.85mg/ml for those aged over 70.
Tear Clearance Rate Test
This test is for knowing if tear clearance is delayed or not. Apply Fluorescein to test.
Tearscope Plus or Lipid Layer Interference Patterns of The Lacrimal Film
Abnormalities of the tear film lipid layer can be observed through understanding the dry eye sufferer’s tear film lipid layer, especially in LTD patients. When compared with pictures of normal eyes, the severity of the dry eye can be determined.
Corneal Topography Test
Evaluating the regularity of the corneal surface. The regularity indexes of the corneal surface of dry eyes (surface regularity index and surface asymmetry index) are higher than in normal people. And there is a positive correlation between the height of the index and the severity of the dry eye.
SS (Sjogren’s syndrome dry eye) patients will test positive for autoantibodies, commonly found are ANA antibody, rheumatoid factor, etc. This is useful for diagnosis of dry eye resulting from immunological diseases.