A Videographic Observational Evaluation of Goldmann Applanation Tonometrys Contact with the Ocular Surface

Glaucoma is the leading cause of irreversible blindness both in the United States and across the globe. The accurate measurement of intraocular pressure (IOP) is the foundation of both its diagnosis and management. High-quality tonometry is critical. The Goldmann applanation tonometer (GAT) replaced the Schiotz tonometer as the gold standard for tonometry in the 1950s. GAT requires the tonometer tip (3.06 mm in diameter) to contact the cornea (approximately 11.5 mm in diameter). There is no evidence in the literature that the GAT does touch the conjunctiva.

Current disinfection guidelines classify GAT as semicritical, along with other instruments that contact the mucous membranes. Semicritical items require high-level disinfection using chemical disinfectants. Glutaraldehyde, hydrogen peroxide, ortho-phthalaldehyde, and peracetic acid with hydrogen peroxide are cleared by the Food and Drug Administration (FDA) and are dependable high-level disinfectants. The eye’s mucous membranes are the bulbar and palpebral conjunctiva and do not include the cornea; this is evident in the much higher infection rate in the conjunctiva versus the cornea. Due to the belief that GAT tips touch the mucous membrane (the conjunctiva), high-level disinfection is required. High-level disinfection for GAT can result in damage to instrumentation by dissolving the glue holding the tip together causing it to both swell and crack. This can harm patients and cause inaccurate intraocular pressure readings. To avoid the need for high-level disinfection, many healthcare systems have opted for disposable tonometer tips which have generated large amounts of plastic waste and imposed unstainable costs on healthcare systems.

Currently, tonometer tips are classified as semicritical instruments and as such are in the same category as Cervical Diaphragm Fitting Rings, Cryosurgical Instrumentation, and Endocavity Probes by the CDC. Structural damage has been observed with a 1:10 sodium hypochlorite (5,000 ppm chlorine) and 3% hydrogen peroxide. Although these disinfectants and exposure times should kill pathogens that can infect the eyes, no studies directly support this.  The guidelines of the American Academy of Ophthalmology for preventing infections in ophthalmology focus on only one potential pathogen: HIV. Because a short and simple decontamination procedure is desirable in the clinical setting, swabbing the tonometer tip with a 70% isopropyl alcohol wipe is commonly performed. Preliminary reports suggest that wiping the tonometer tip with an alcohol swab and then allowing the alcohol to evaporate might be effective in eliminating HSV, HIV, and adenovirus. However, because these studies involved only a few replicates and were conducted in a controlled laboratory setting, further studies are needed before this technique can be recommended. In addition, two reports have found that disinfection of pneumotonometer tips between uses with a 70% isopropyl alcohol wipe contributed to outbreaks of epidemic keratoconjunctivitis caused by adenovirus type 8.

Therefore, GAT tips currently require high-level disinfection, a practice normally reserved for instrumentation contacting mucous membranes, which the tonometer does not. The diameter of the GAT tip is much smaller than the cornea (3.06 mm vs. 11.5 mm), and there is no evidence in the literature or by way of practical experience that the GAT tip touches the conjunctiva. However, all high-level disinfection protocols, which are indicated for semicritical instruments such as tonometers, cause tonometer tips to deteriorate. For instance, treating the tonometry tip with sodium hypochlorite for greater than 5 minutes or using heat or steam will irrevocably damage the tonometer tip. Additionally, it roughens the surface touching the cornea, potentially causing corneal abrasions and micro-abrasions.

We are therefore interested in providing videographic evidence in an observational study of what part of the eye is in actual contact with the tonometer tip as well as the frequency, if any, of any tonometer-mucous membrane touch and tonometer-eyelid touch.