Tear Osmolarity and Cataract Surgery
The American Society for Cataract and Refractive Surgery (ASCRS) has developed a preoperative algorithm for Ocular Surface Disease (OSD) (Figure 1) in response to the increasing incidence of OSD and the recognition of the negative impact it may have on outcomes with keratorefractive surgery.1
Figure 1. Simplified ASCRS Preoperative OSD Algorithm1
Who is at risk? In a prospective case series of 120 patients, more than one out of every two patients presenting for a pre-surgical cataract evaluation were shown to be hyperosmolar (56.7%), and over half had no prior history of ocular surface disease (Table 1).2
Table 1. Distribution of Osmolarity Testing in Study of Population Presenting for Cataract Surgery (Adapted from Gupta et al., 2018)2
Cataract patients with hyperosmolarity were 7X more likely to be dissatisfied with their quality of vision post-operatively.3 It has been shown that hyperosmolarity increases the risk of refractive surprises post-cataract surgery.4 One in six cataract patients risk >1D variation in keratometry measurements,4 and 1 in 10 have a refractive miss >1D (Figure 2).3
It is challenging to identify patients with tear hyperosmolarity without proper testing. Hyperosmolarity is not detected at the slit lamp with tear break-up time or corneal staining.1,3,4 For this reason, it is considered essential by ASCRS to test tear osmolarity in advance of surgery to find and manage cases of hyperosmolarity.1
Figure 2. Hyperosmolarity affects cataract surgery outcomes3
What exactly is the cause of these risks? Hyperosmolarity increases light scatter, which can lead to unpredictable surgical outcomes, imprecision of pre-surgical measurements, and dissatisfaction with postoperative visual quality.1,5 This light scatter impact has been shown to be equivalent to grade 2-3 cataracts (Figure 3).6-9
Figure 3. Ocular Scatter Index of Hyperosmolarity is similar to Grade 2 and 3 Cataracts.6-9
However, unlike cataracts, which present with constant blurriness, light scatter from hyperosmolarity fluctuates, creating visually significant disturbances between blinks. Of importance, pre-surgery, the fluctuating vision associated with hyperosmolarity may be masked by the cataract, and both the patient and surgeon may be unaware of this issue. However, after surgery, and usually after the eye completely heals 3-6 months later, this fluctuating vision can remain and may cause dissatisfaction, especially with the high expectations of a premium surgery. This creates a 20/20 unhappy patient due to fluctuating, impaired image quality even when target acuity is reached (Figure 4).6
Figure 4. 20/20 Unhappy Patient6
Clinical data indicates that 1 out of 2 cataract patients presenting with tear hyperosmolarity will be at risk for a negative visual impact after surgery unless it is identified and addressed.2 Tear osmolarity can increase one week after cataract surgery and may remain elevated for up to four weeks compared to pre-surgery levels, leading to dry eye symptoms.10 Additionally, medications prescribed after surgery can also impact osmolarity.1 Therefore, waiting at least a month before prescribing glasses is important, as hyperosmolarity can result in an inaccurate refraction.11
In our experience, managing hyperosmolar risks in cataract patients is straightforward. Once a patient is identified as hyperosmolar, we suggest flagging their chart and addressing the associated risks; however, this does not necessarily mean surgery needs to be delayed.
By identifying hyperosmolarity and its impact on light scatter early on, the surgeon can manage the associated risks in the surgical plan. Discussing this plan with the patient before the surgery is crucial. The patient will value the inclusion of advanced pre-surgical laboratory tests in their clinical evaluation. After the surgery, this proactive approach can help to prevent less-than-optimal postoperative outcomes and avoid a "20/20 Unhappy" patient.
What is the Latest Technology for Measuring Tear Film Osmolarity?
TearLab was founded in 2009, recognizing the importance of corneal health in eye care practice. In 2022, it rebranded as Trukera Medical and was acquired by Bausch+Lomb Surgical in July 2024. Since its inception, the TearLab Osmolarity System, the predecessor to ScoutPro, has administered more than 24 million tests globally.12 The TearLab Osmolarity System is no longer being manufactured.13
The latest osmolarity system, ScoutPro, is a CLIA-waived in-office laboratory test that measures the osmolarity of human tears to aid in diagnosing dry eye disease (Figure 5). It is used with clinical evaluation and other tests for dry eye disease.14 The system includes a ScoutPro pen, a charging base, control solutions, electronic check cards, and test cards purchased separately.14
Figure 5. ScoutPro
Clinical Implementation of ScoutPro
We initially faced challenges when we integrated the TearLab Osmolarity System into our clinical practice in 2011 due to its lack of portability compared to the ScoutPro. In our experience, ScoutPro has been user-friendly in our clinical settings. The latest model, although using identical Test Cards and tear collection technique as the original TearLab, offers a more seamless and efficient experience since it is portable and does not require time-sensitive testing. This portability has improved our clinical efficiency by allowing a single pen to measure two test results, one for each eye, which are stored in memory. Additionally, it ensures optimal test performance, even when ambient temperatures fluctuate—an important factor for maintaining testing accuracy. Overall, the device is easy to use, which simplifies staff training.
All pre-surgical assessments for cataract surgery should include an osmolarity test because 56.7% of patients presenting for cataract surgery are hyperosmolar, and over half have no prior history of ocular surface disease.2
ScoutPro can be integrated into the clinical workflow using DEWS II:1,15
- Ask questions to prod complaints further (i.e., how severe, do you have dry mouth?)
- Risk factor analysis (smoking, medication, contact lens wear)
- Diagnostic testing
- Screening questionnaire: DEQ or OSDI
- Homeostasis markers: NITBUT, osmolarity, and ocular surface testing
- Subtype classification tests
- Evaporative dry eye: Abnormal lipid and MGD
- Aqueous-deficient dry eye disease: Tear volume
- Determine severity
- Meibomian gland dysfunction: Mild, Moderate, Severe
- Aqueous-deficient dry eye disease tear meniscus height: 0.2mm (mild), 0.1mm (moderate), 0.0mm (severe)
- Determine plan and treatment options
- Treat and reassess before cataract surgery.
ScoutPro is a practice grower that requires detailed documentation for billing and coding. Since it is a CLIA-waived lab test, it can be used on the same day as a “vision” visit, although the osmolarity test will be billed to the patient’s Medical insurance and may require a patient co-pay or deductible.
Laboratory tests are exempt from CMS global period exclusions16 and can be billed 100% to CMS and private payers under the Clinical Laboratory Fee Schedule (CPT 83861), including normal tests that “rule out” visually significant dry eye.17
Based on our experience, the prevailing regulatory perspective is that the medical necessity for the osmolarity test largely depends on the physician's medical opinion, especially given the absence of non-coverage policies. Blurry vision in cataract patients, which can also indicate dry eye symptoms (as noted by ASCRS1, AAO5, and DEWS II15), may point to a manageable contraindication for keratorefractive surgery, as discussed above. This reinforces the medical necessity of osmolarity testing when documented appropriately in the medical record using the following steps:
- Document symptoms of blurry vision (ICD-10 H53.8).
- Enter an order for the "tear osmolarity test."
- Notate test results, indicating whether they are "normal" or "abnormal."
- Reference the osmolarity test results in the management plan, regardless of whether they are normal or abnormal.
Patient and Clinical Impact
ScoutPro has changed how we manage our patients. We’ve integrated it into our practice flow and use it daily. It’s a device that can be used in any practice and on any patient, whether it's a surgical-based practice like Dr. Parekh’s or a hybrid like Dr. McGee’s.
ScoutPro provides objective testing for dry eye disease, whether the patient is symptomatic or asymptomatic. Sometimes, patients may be symptomatic but have a normal osmolarity level, and it’s important to note that while it may be within normal limits, it likely points to a non-dry eye comorbidity.18
From our experience, it provides early detection, supports treatment adherence, and can help motivate patients to continue treatment by showing improvement in osmolarity with treatment at follow-ups.
Tear osmolarity testing can help with patient communication by managing expectations. Identifying ocular surface disease (OSD) before surgery and discussing it with the patient can rule out cataract surgery or the IOL as the cause of symptoms patients may experience post-op. One option of the ASCRS guidelines, if the surgeon deems it appropriate, is to rehabilitate and prime the ocular surface before surgery. This helps to reduce refractive surprises and minimizes the occurrence of unhappy patients with 20/20 vision.
Case Studies
Final Thoughts
Evaluation of tear osmolarity plays a key role in dry eye patient management, especially those about to have cataract surgery. Patients exhibiting elevated osmolarity levels are at a higher risk of postoperative dissatisfaction and may experience complications, including unanticipated refractive changes, even in patients who have not previously been diagnosed with dry eye disease. Practitioners can enhance diagnostic accuracy and refine treatment strategies by incorporating osmolarity testing into the clinical workflow.
