How tear proteomics can help optometry

Laboratory testing has not traditionally been a feature of an eyecare practice. Optometrists may obtain blood work for a patient with a recurrent anterior uveitis or order imaging for a suspected orbital fracture, but routine ocular point-of-care (POC) tear testing isn’t part of our normal daily routine.

I suggest it should be now, and I predict that it will be in the near future.

Think about what occurs when you visit your doctor for a cold. Technicians will gather your vital signs; likely draw blood to check your white cell count; obtain a throat swab for a Streptococcal pharyngitis, a sinus swab for flu, and a chest X-ray. The results of these tests are at the physician’s disposal before he ever steps foot into the exam room to see you.

Related: How point-of-care diagnostic lab tests help clinical decisions

POC tear testing, eyecare professionals now have the ability to gather laboratory data to aid diagnostic decision making.

Advantages of tear testing

In-office POC tear testing is feasible due to the multifaceted functions of tears and advances in proteomics, a branch of biotechnology concerned with applying the techniques of molecular biology, biochemistry and genetics to analyzing the structure, function, and interaction of proteins produced by a particular cell, tissue, or organism.¹

Despite the small sample volume, tear fluid offers advantages for biochemical analysis.

Tear sample collection is a non-invasive process. Tears can be easily obtained from healthy subjects, while other ocular fluids (i.e., aqueous and vitreous) are not realistic for routine collection and carry risks with their capture, such as endophthalmitis.

Perhaps the greatest advantage is that tears are close to the disease site (as in ocular surface disease) as compared to detecting cancer biomarkers in blood where the biomarker molecules are highly diluted.²

Ocular surface disease

The tear layer covering the ocular surface is a complex body fluid containing thousands of molecules of varied form and function from several origins. Close to 2,000 tear proteins have been reported in humans.³ At least 90 small molecule metabolites have been seen in human tears.⁴

This comprehensive array of biomolecules in human tears is a potential source for the discovery of disease biomarkers.

Related: In-office lab testing provides diagnositc information

Ocular surface disease is among the first eye diseases studied using proteomics, and currently five POC tests that make use of human tears in the diagnosis of ocular disease:

• Osmolarity, TearLab Corporation 

• InflammaDry Matrix metalloproteinase (MMP) 9 inflammatory marker, Quidel Corporation

AdenoPlus, Quidel Corporation

• Lactoferrin, Advanced Tear Diagnostics (ATD)

• Immunoglobulin E (IGE), Advanced Tear Diagnostics

Other possibilities exist for additional POC testing.

Meibomian gland dysfunction (MGD) also contributes to dry eye, and one study demonstrated that levels of some lipids critical for the maintenance of tear film stability increased after a 12-week eyelid warming treatment in MGD.⁵

Tear bioassays may have advantages over conventional clinical assessments (i.e., Schirmer test, tear break-up time, corneal staining) for patient diagnosis, prognosis, and monitoring treatment responses.⁶

Potential

The potential for in-office POC testing is colossal. The tear film proteomic profile has been found to provide basic biological information for many ocular diseases such as keratoconus,⁷ thyroid eye disease,⁸ vernal keratoconjunctivitis,⁹ diabetic retinopathy,¹⁰ and primary open-angle glaucoma.¹¹

While human tear proteins are different from blood plasma proteins, nonetheless there are about 500 to 600 plasma proteins found in tears.³ This overlap may yield opportunities to observe systemic disease proteins in tears. Examples include breast cancer,¹² type 2 diabetes,¹³ Alzheimer’s disease,¹⁴ and rheumatoid arthritis.¹⁵ Because some systemic diseases affect the eye, tear film proteomics has the potential to use tears as a means to assess systemic as well as ocular disease.

Developments

While tear proteomics has tremendous possibilities for future development, the near future of POC diagnostic testing is very promising.

ATD is working to significantly increase the number of single or multi-analyte tests that correlate with a variety of other specific ocular conditions, according to company CEO Marcus Smith.

“ATD has one goal: to provide ophthalmic physicians POC science-based lab testing tools necessary to yield diagnostic precision, guide focused treatment decisions, measure treatment efficacy and improve clinical workflow efficiency on a platform that is rapid, inexpensive, and simple to use,” he says.

Related: Incorporating lactoberrin and immunoglobin testing

Other players in this space also foresee expansion. TearLab plans a global launch for its Discovery platform in 2018.

“The TearLab Discovery platform utilizes a lab-on-a-chip technology to simultaneously collect and analyze nanoliter samples of tear fluid in less than two minutes,” says David C. Eldridge, OD, FAAO, vice president of clinical affairs and professional development.

Dr. Eldridge says that the first test card that TearLab will commercially launch includes osmolarity plus two inflammation markers, IL1-RA and MMP-9.

RPS Diagnostics is developing a second-generation, quantitative single-use test for inflammation that should be available in two years, according to Robert Sambursky, MD, CEO, president, and chairman.

The new test will provide a quantitative result instead of the positive/negative result the test now yields. Note that InflammaDry and AdenoPlus were acquired by Quidel Corporation from RPS Diagnostics in May 2017.

Future is now

The future of tear proteomics is exciting, but clinicians have been slow to adopt POC testing.

“Optometry has an opportunity to blow out point-of-care testing in contact lenses and dry eye,” says Dr. Sambursky. “There are many more indications for the technology’s use, such as glaucoma, dry eye, cataract, LASIK, and PRK.”

“Manufacturers are making continuous progress in terms of research and development to create new products with newer, advanced technology,” says Smith. “The adoption of diagnostic lab testing has been measured but is growing steadily, and in the future testing will be incorporated into the great majority of ophthalmic clinics worldwide. Unfortunately, some states still prohibit optometrists from performing POC laboratory testing on their patients, and that will need to be addressed.”

Human tears are a complex extracellular fluid of the ocular surface which contains molecular information useful in the diagnosis and treatment of ocular surface diseases and has the ability to address an emphasis on personalized medicine and disease biomarkers.¹⁶

Tear collection is fast, safe, non-invasive, and yields data helpful in determining local pathology close to the disease site. The relatively simple sample preparation techniques make tears an ideal source for laboratory diagnosis and prognosis.

Related: A new player in point-of-care allergy testing

The time will arrive when a tear test used in eye clinics will become as valuable as a blood test or a urine test to aid in the diagnosis and treatment of our patients’ diseases.

Says Smith, “The clinical value of POC testing is simple: It is better to know than to think you know.”

Read more from Dr. Bowling here

References:

1. Definition of proteomics. Merriam-Webster Dictionary. Available at: www.merriam-webster.com/dictionary/proteomics. Accessed 4/21/2017.

2. Zhou L, Bewerman RW. The power of tears: how tear proteomics research could revolutionize the clinic. Expert Rev Proteomics. 2017 Mar;14(3):189-191.

3. Zhou L, Zhao SZ, Koh SK, Chen L, Vaz C, Tanavde V, Li XR, Beuerman RW. In-depth analysis of the human tear proteome. J Proteomics. 2012 Jul 16;75(13):3877-85.

4. Chen L, Zhou L, Chan EC, Neo J, Beuerman RW. Characterization of the human tear metabolome by LC-MS/MS. J Proteome Res. 2011 Oct 7;10(10):4876-82.

5. Lam SM, Tong L, Duan X, Acharya UR, Tan JH, Petznick A, Wenk MR, Shui G. Longitudinal changes in tear film lipidome brought about by eyelid warming treatment in a cohort of meibomian gland dysfunction. J Lipid Res. 2014 Sep;55(9):1959-69.

6. D'Souza S, Petznick A, Tong L, Hall RC, Rosman M, Chan C, Koh SK, Beuerman RW, Zhou L, Mehta JS.Comparative analysis of two femtosecond LAASIK platforms using iTRAQ quantitative proteomics. Invest Ophthalmol Vis Sci. 2014 May 6;55(6):3396-402.

7. Lema J, Brea D, Rodriguez-Gonzalez R, Díez-Feijoo E, Sobrino T. Proteomic analysis of the tear film in patients with keratoconus. Mol Vis. 2010 Oct 13;16:2055-61.

8. Matheis N, Grus FH, Breitenfeld M, Knych I, Funke S, Pitz S, Ponto KA, Pfeiffer N, Kahaly GJ. Proteomics differentiate between thyroid-associated orbitopathy and dry eye syndrome. Invest Ophthalmol Vis Sci. 2015 Apr;56(4):2649-56.

9. Leonardi A, Palmigiano A, Mazzola EA, Messina A, Milazzo EM, Bortolotti M, Garozzo D. Identification of human tear fluid biomarkers in vernal keratoconjunctivitis using iTRAQ quantitative proteomics. Allergy. 2014 Feb;69(2):254-60.

10. Kim HJ, Kim PK, Yoo HS, Kim CW. Comparison of tear proteins between healthy and early diabetic retinopathy patients. Clin Biochem. 2012 Jan;45(1-2):60-7.

11. Pieragostino D, Agnifili L, Fasanella V, D'Aguanno S, Mastropasqua R, Di Ilio C, Sacchetta P, Urbani A, Del Boccio P. Shotgun proteomics reveals specific modulated protein patterns in tears of patients with primary open-angle glaucoma naïve to therapy. Mol Biosyst. 2013 Jun;9(6):1108-16.

12. Böhm D, Keller K, Pieter J, Boehm N, Wolters D, Siggelkow W, Lebrecht A, Schmidt M, Kölbl H, Pfeiffer N, Grus FH. Comparison of tear protein levels in breast cancer patients and healthy controls using a de novo proteomic approach. Oncol Rep. 2012 Aug;28(2):429-38.

13. Li B, Sheng M, Xie L, Liu F, Yan G, Wang W, Lin A, Zhao F, Chen Y. Tear proteomics analysis of patients with type 2 diabetes and dry eye syndrome by two-dimensional nano-liquid chromatography coupled with tandem mass spectrometry. Invest Ophthalmol Vis Sci. 2014 Jan 9;55(1):177-86.

14. Kalló G, Emri M, Varga Z, Ujhelyi B, TÅ‘zsér J, Csutak A, CsÅ‘sz É. Changes in the chemical barrier composition of tears in Alzheimer’s disease reveal potential tear diagnostic biomarkers. PLoS One. 2016 Jun 21;11(6):e0158000.

15. Aluru SV, Shweta A, Bhaskar S, Geetha K, Sivakumar RM, Utpal T, Padmanabhan P, Angayarkanni N. Tear fluid protein changes in dry eye syndrome associated with rheumatoid arthritis: A proteomic approach. Ocul Surf. 2017 Jan;15(1):112-129.

16. Zhou L, Beuerman KW. Tear analysis in ocular surface diseases. Prog Retin Eye Res. 2012 Nov;31(6):527-50.