Overview of OSDx Tests

OSDx examines complementary components of the ocular surface and tear system. These tests are best interpreted together: tear volume, blinking, lipid-layer behaviour, meibomian-gland structure, tear-film stability, fluorescein behaviour and lid-margin appearance each provide a different part of the clinical picture.

About reference values: Published values vary with age, environment, technique and instrument. The figures below are intended as clinical reference guides rather than stand-alone diagnostic thresholds. Always interpret them with symptoms, examination findings and the other OSDx measurements.

Meniscometry

Assesses the lower tear meniscus, which acts as a reservoir for the precorneal tear film. OSDx measures tear meniscus height (TMH) and tear meniscus radius (TMR).

Reduced tear-meniscus dimensions support reduced aqueous tear volume, while a large meniscus may occur with reflex tearing or impaired drainage.

Reference guide: TMH is commonly around 0.2–0.3 mm in normal eyes. Values around ≤0.1 mm have been proposed as abnormally low.1 Reflective meniscometry studies report a mean lower TMR of about 0.37 mm, with substantial physiological variation.2
Clinical role: tear-volume assessment
TMH and TMR are technique-dependent; a single value should not be used in isolation to diagnose aqueous-deficient dry eye.

Blink

Blinking redistributes the aqueous and lipid layers, clears the exposed surface and helps maintain optical quality. OSDx records blink timing and identifies complete and incomplete blinks.

Reduced blink frequency or incomplete blinking can increase inter-blink exposure and contribute to evaporative dry eye, particularly during visually demanding tasks and prolonged screen use.

Reference guide: Resting spontaneous blink rate is frequently reported at approximately 12–15 blinks/min, but normal values vary widely and may change markedly with concentration, reading and digital-device use.3
Clinical role: exposure & tear redistribution

Lipimetry

Evaluates the interference pattern and estimated thickness of the tear-film lipid layer. This layer is largely derived from the meibomian glands and contributes to tear-film stability and resistance to evaporation.

OSDx also displays spatial distribution, variability and the proportion of thicker lipid regions, helping the clinician judge whether the lipid layer is uniform or heterogeneous.

Reference guide: There is no universal normal LLT range across instruments. LipiView-based studies have reported healthy-control averages near 65 nm.4 Some studies classify <60 nm as thin and 60–99 nm as an intermediate/normal range.5 These cut-offs should not be transferred directly between devices.
Clinical role: lipid-layer function
A thicker lipid layer is not automatically normal: thick LLT can also occur in symptomatic dry eye. Distribution, stability, blinking and gland status remain important.

Meibography

Infrared imaging shows the architecture of the upper and lower eyelid meibomian glands. It can demonstrate gland shortening, distortion and partial or extensive gland loss.

Meibography is an anatomical test: gland appearance should be interpreted together with lid-margin findings, meibum expression and lipimetry.

Reference guide: Classical meiboscore grading describes grade 0 = no gland loss, grade 1 = <33%, grade 2 = 33–66% and grade 3 = >66% loss. More recent quantitative work suggests that gland dropout above about 20% may have diagnostic relevance, but age and method strongly influence the result.6
Clinical role: meibomian-gland structure

NIBUT

Non-Invasive Break-Up Time assesses tear-film stability without fluorescein. OSDx observes distortion or disruption of the reflected pattern after a complete blink.

Earlier breakup indicates reduced tear-film stability and is an important objective sign in dry eye assessment.

Reference guide: A NIBUT of approximately >10 seconds is generally reassuring. TFOS DEWS II methodology uses ≤10 seconds as a commonly applied dry-eye cut-off for subjective non-invasive methods.7,8
Clinical role: tear-film stability
NIBUT depends on the instrument and detection algorithm. Follow-up is most meaningful when measurements are made under comparable conditions.

Fluorescence

Fluorescein imaging provides complementary information about tear-film breakup, corneal epithelial integrity and lacrimal drainage. OSDx fluorescence examinations therefore address several different aspects of ocular-surface disease.

Corneal staining: Fluorescein highlights areas where the corneal epithelial barrier is disturbed. The distribution, density and pattern of staining are clinically important and may support the presence and severity of ocular-surface disease. OSDx additionally quantifies the fluorescein-stained area as a percentage of the corneal area, providing a continuous objective measure that may be particularly useful for documenting change during follow-up and response to treatment.13,14 Published literature supports digital area-based quantification of corneal staining, while conventional clinical grading remains largely ordinal. A literature search did not identify another currently marketed dry-eye device that automatically reports corneal fluorescein staining specifically as percentage of total corneal area; OSDx therefore appears to offer an unusual, and potentially unique, quantitative capability. This should not, however, be interpreted as a formal claim of worldwide commercial exclusivity. Corneal staining remains non-specific and must be interpreted in the clinical context.7,10

Fluorescein tear break-up: Observation of the interval between a complete blink and the first appearance of tear-film disruption provides an invasive measure of tear-film stability and complements NIBUT.

Fluorescein Dye Disappearance Test (FDDT): FDDT assesses the clearance of fluorescein from the tear lake over time and provides a functional assessment of lacrimal drainage. Delayed persistence of dye may indicate impaired lacrimal outflow, whereas relatively rapid and symmetrical clearance is expected when drainage is unobstructed.9 Importantly, delayed dye disappearance can also occur when the lacrimal passages are anatomically patent but physiological drainage is impaired. In the appropriate clinical setting, particularly when syringing demonstrates patency, an abnormal FDDT can therefore support the diagnosis of functional epiphora or lacrimal pump failure.15,16 OSDx records the change in fluorescence over the study period to provide an objective representation of dye clearance, which may help document functional drainage and treatment response.17

Reference guide: For fluorescein tear break-up time, <10 seconds is conventionally regarded as abnormal, although published work shows that an 8-second threshold may improve discrimination in some populations.7 In the conventional dye-disappearance test, little fluorescein should remain after approximately 5 minutes when lacrimal drainage is unobstructed; persistence at 5 minutes suggests delayed drainage.9
Clinical role: tear breakup, epithelial staining & lacrimal drainage

Lid Margin

Magnified lid-margin imaging provides a permanent record of eyelid-margin abnormalities and is particularly useful for documenting blepharitis and following change over time or after treatment.

For meibomian gland dysfunction (MGD), imaging can document gland-orifice plugging, pouting or displacement, altered mucocutaneous junction, lid-margin irregularity, telangiectatic or other vascular changes, and associated inflammatory features. It therefore provides the clinical surface correlate of the structural changes seen on meibography and the functional changes suggested by lipimetry.

In suspected Demodex blepharitis, special attention should be paid to collarettes (cylindrical dandruff or cuffs) encircling the base of the eyelashes. Collarettes are regarded as the characteristic, and clinically pathognomonic, sign of Demodex blepharitis.11,12 High-quality lid-margin photographs are useful for recording their presence, extent and response to therapy.

Reference guide: There is no single numerical normal range. A healthy lid margin should have a regular contour, readily identifiable gland orifices and no significant plugging, inflammatory vascular change or lash-base debris. Collarettes/cuffs at the lash base are abnormal and should raise strong suspicion of Demodex blepharitis.11
Clinical role: documentation of blepharitis, Demodex & MGD

References

  1. Doughty MJ, Laiquzzaman M, Button NF. The tear (lacrimal) meniscus height in human eyes: a useful clinical measure or an unusable variable sign? Cont Lens Anterior Eye. 2002;25:57–65.
  2. Yokoi N, Bron AJ, Tiffany JM, Maruyama K, Komuro A, Kinoshita S. Relationship between tear volume and tear meniscus curvature. Arch Ophthalmol. 2004;122:1265–1269.
  3. Abusharha AA. Changes in blink rate and ocular symptoms during different reading tasks. Clin Optom (Auckl). 2017;9:133–138.
  4. Kumar M, et al. Repeatability of lipid layer thickness measurements using the LipiView interferometer and comparison with published healthy-control values. Indian J Ophthalmol. 2025.
  5. Lee Y, et al. Characteristics of dry eye patients with thick tear film lipid layers. Graefes Arch Clin Exp Ophthalmol. 2021;259:1235–1243.
  6. Wang MTM, et al. Quantitative infrared meibography diagnostic thresholds for meibomian gland dysfunction. Cont Lens Anterior Eye. 2025.
  7. Wolffsohn JS, Arita R, Chalmers R, et al. TFOS DEWS II Diagnostic Methodology Report. Ocul Surf. 2017;15:539–574.
  8. Pauk SV, Petriček I, Jukić M, et al. Noninvasive tear film break-up time assessment. Med Arch. 2019;73:261–264.
  9. American Academy of Ophthalmology. Dye disappearance testing in the evaluation of lacrimal drainage obstruction. Fluorescein persistence after approximately 5 minutes suggests delayed outflow.
  10. Stapleton F, Alves M, Bunya VY, et al. TFOS DEWS II Epidemiology Report. Ocul Surf. 2017;15:334–365.
  11. Rhee MK, et al. Demodex blepharitis: a comprehensive review of the disease, current management, and emerging therapies. Eye Contact Lens. 2023;49:311–318.
  12. Ayres BD, et al. Clinical diagnosis and management of Demodex blepharitis: the DEPTH panel. Clin Ophthalmol. 2023;17:3067–3078.
  13. Pellegrini M, et al. Assessment of corneal fluorescein staining in different dry eye subtypes using digital image analysis. Transl Vis Sci Technol. 2019. The corneal staining index was calculated as the ratio of stained area to total corneal area.
  14. Kourukmas R, Roth M, Geerling G. Automated vs. human evaluation of corneal staining. Graefes Arch Clin Exp Ophthalmol. 2022;260:2605–2612.
  15. Guzek JP, Ching AS, Hoang TA, et al. Clinical and radiologic lacrimal testing in patients with epiphora. Ophthalmology. 1997;104:1875–1881.
  16. Lee MJ, et al. Lacrimal silicone intubation for anatomically successful but functionally failed external dacryocystorhinostomy. Korean J Ophthalmol. 2009;23:70–73. Slow dye disappearance in anatomically patent drainage systems was considered suggestive of lacrimal pump dysfunction.
  17. Atkova EL, Zhukov OV, Yartsev VD. Objective assessment of the drainage function of the lacrimal drainage system based on the dye disappearance test. Quant Imaging Med Surg. 2025;15:12447–12453.

Reference ranges are presented for clinical orientation and are not intended to replace validated device-specific diagnostic criteria.