A Brief Hitchhiker’s Guide to Lash and Lid Anatomy
Michael S. Cooper, OD
Hello there once again! While I’m deep in thought trying to solve the 42 puzzle (Hitchhiker’s reference), let’s dive right in and look at the important role eyelashes play with respect to protecting and maintaining lid margin health. Although the mechanisms to fulfill this ongoing responsibility are not fully understood, unraveling some of the mystifying components will stand to greatly improve the efficiency of eye care professionals’ interventional therapies. More on this in a moment!
Since eyelashes form a barrier between the external and internal ecosystems of the eye, they are extremely sensitive to a variety of threats and irritants with a high level of sophisticated innervation to perform this particular function including touch, pressure, vibration, heat, and mechanoreception.1,2 As one could tell, lashes are an essential part of the lid margin anatomy complementing the meibomian glands, eyelid skin, and biofilm for which contributes to the overall homeostasis of the ocular surface.3
The meibomian glands and lid margin are responsible for the production of the tear film lipid layer along with the protection of the eye from external trauma. Interestingly enough, aerodynamic studies have demonstrated that the ideal lash should be one-third the width of the eye.4 Subsequently, it appears that there is a direct relationship between aerodynamic flow of air comparatively to the curve and density of lashes in protecting the cornea from particulate matter.
With the natural blink, tears are distributed in a wiper-like fashion toward the nasolacrimal puncta found in the inner portion of the lid margin.5 If any part of the lid margin is inflamed, it can induce a tear film instability which potentially can, in turn, affect the harmonious balance of the ocular surface. Left untreated, this inflammatory cascade (inextricably meibomian gland dysfunction aka MGD) can develop into dry eye disease in approximately 86% of cases.5,6
So how does this fit into daily practice? In discussing the inherent lid and lash anatomy from this aerial view, we have to get back to the slit lamp where we visualize microflora signs such as crusting and saponification every day. The lashes typically contain a multitude of various species of commensal bacteria and parasites including Propionibacterium, Streptophyta, Staphylococcus, Corynebacterium, Enhydrobacter, and Demodex.7
With over 16 million dry eye patients in the US, invariably a large percentage have comorbid MGD.8 What this means to all of us is that there is a low hanging potential gold mine to discuss lid hygiene treatments including hypochlorous acid, a natural antibacterial agent produced within the human body by our white blood cells. The wow factor is not just the pathogen kill rate of approximately 15 seconds and reducing the inflammatory toxins plus bacterial lipase activity, but that the patient understand they are cleansing their lids and lashes with a relatively balanced organic formulation.9,10 Be aware though that the goal of introducing this compound is to truly stabilize the bacterial overpopulation, not fully eliminate it.
We touched briefly in the last edition on some of the choices including hypochlorous acid products such as HyClear (Contamac), Avenova (NovaBay), and HypoChlor (OCuSOFT). While each has their individual merits, there are some differences. HypoChlor is a first-generation formulation that exhibits good microbial activity; however, it will tend to burn more than other products and has reduced shelf life. Avenova has been the next logical step where it illustrates better microbial kill rate and minimized irritation, but does suffer from diminished potency over a 30-day period.9 The newest iteration is HyClear, which seems to have taken the lessons learned from the other products to produce a compound that has 18 months opened shelf life along with an excellent antibacterial action and minimal discomfort.9,10
Now that you all are prepared with your anatomy and product guides, it is time to get out there today to effect change by controlling your financial destiny by recommending these products from the chair! Remember, beyond the 16 million dry eye sufferers, about 50% of them may not have insurance coverage and are actively looking for affordable lid hygiene solutions. Scaling further, there is a fairly large segment of the contact lens population to the tune of 70 million wearers that accept some level of contact lens intolerance.11,12
Take a moment to soak these statistics in, considering every bottle of lid cleanser sold is a contact lens wearer likely staying in their lenses due to improved comfort, rather than dropping out (or worse, leaving your practice). From a practice management perspective, this provides an extra $200-800 per patient swing each year which translates to a nice extra stream of profit potential. Douglas Adams said it best with his other famous Dirk Gently work that I think is rather fitting, "I may not have gone where I intended to go, but I think I have ended up where I needed to be."13
Look out for next month’s edition when we interview a legendary ocular surface icon’s take on Demodex...
Montagna W, Ford DM. Histology and cytochemistry of human skin XXXIII. The Eyelid. Arch Dermatol, 1969; 100(3): 328-335.
Munger BL, Halata Z. The sensorineural apparatus of the human eyelid. Am. J. Anat. 1984; 170(2): 181-204.
Willcox MDP, Argüeso P, Georgiev GA, et al. TFOS DEWS II Tear Film Report. Ocul Surf. 2017; 15(3): 366-403.
Amador GJ, Mao WB, DeMercurio P, et al. Eyelashes divert airflow to protect the eye. J R Soc Interface. 2015; 12(105): 20141294.
Craig JP, Nichols KK, Akpek EK, et al. TFOS DEWS II Definition and Classification Report. Ocul Surf. 2017; 15(3): 276-283.
Lemp MA, Crews LA, Bron AJ, et al. Distribution of aqueous-deficient and evaporative dry eye in a clinic-based patient cohort: a retrospective study. Cornea. 2012;31(5): 472-478.
Lee SH, Oh DH, Jung JY, et al. Comparative ocular microbial communities in humans with and without blepharitis. Invest Ophthalmol Vis Sci, 2012; 53(9): 5585-5593.
Farrand KF, Fridman M, Stillman IO, et al. Prevalence of Diagnosed Dry Eye Disease in the United States Among Adults Aged 18 Years and Older. Am J Ophthalmol. 2017; 182: 90-98.
Stroman DW, Mintun K, Epstein AB. Reduction in bacterial load using hypochlorous acid hygiene solution on ocular skin. Clin Ophthalmol. 2017; 11: 707-714
Baudouin C, Messmer EM, Aragona P, et al. Revisiting the vicious circle of dry eye disease: a focus on the pathophysiology of meibomian gland dysfunction. Br J Ophthalmol. 2016; 100(3):300-306.
Vidal-Rohr M, Wolffsohn JS, Davies LN, et al. Effect of contact lens surface properties on comfort, tear stability and ocular physiology. CLAE. 2018; 41(1): 117-121.
Adams D. Chapter 13. Long Dark Tea-Time Of The Soul. New York: Pocket Books; 1990, p. 156.
Michael S. Cooper, OD currently practices and is the Director of Research and Technological Innovation at Solinsky EyeCare in the Greater Hartford area. He specializes in anterior segment disease, treating a variety of conditions including dry eye and external lid diseases, allergy, and uveitis. He has produced research, participated on expert ocular surface disease round tables, and lectured domestically on topics such as corneal disease states, uveitis management, Lyme disease, emerging pathogens, complex glaucoma management, sports-related eye injuries in children, and AMD pedigree relationships. Currently, he is actively involved in global clinical studies for novel anti-infective therapeutics, ocular surface diagnostic validation, and AMD genetic research.