This activity is supported by an unrestricted grant from Bausch + Lomb.
This activity is supported by an unrestricted grant from Bausch + Lomb.
The title of this activity is clear: Optometrists treat patients with glaucoma — not just glaucomatous optic neuropathy. Treating fellow human beings makes the disease entity that much more important, and more challenging. Most people think that as long as they see well, their eyes are fine. Few truly understand the importance of regular eye care and screenings for asymptomatic diseases, such as glaucoma.
Human beings are not utopic patients, and many seem oblivious to the need for consistent adherence to and compliant use of their medications. To further complicate matters, pharmacies and insurance companies make their own bureaucratic intrusions into our best efforts to prescribe attentively for our patients. These companies may have legitimate concerns, but they pale in comparison to the higher calling of preserving sight and enhancing quality of life. One final sobering perspective is that lawsuits regarding “missed glaucoma” are commonly successful. Indeed, the most common reason (by far), “failure to diagnose,” represents the pinnacle of litigation. Before delving into therapeutic intervention, particularly regarding topical medications, let’s take a brief look at diagnostic considerations. After all, proper therapy is predicated upon a solid diagnosis.
Lest one think either diagnosis or medical management is always crystal clear, we want to assure the reader that many cases are diagnostically nebulous; fortunately, therapy is relatively less challenging.
Optometrists should first consider patient history to screen for a positive family history of glaucoma, particularly among siblings. A positive parental history is less important than a positive contemporary sibling history. Most patients are in their 50s or 60s when they receive a diagnosis of glaucoma; this means that your glaucoma suspect patient could have parents who were most likely diagnosed in the latter part of the 20th century. At that time, intraocular pressure (IOP) of more than 21 mm Hg was generally treated as glaucoma, irrespective of optic nerve head health, and pachymetry was not yet known to be of importance. Therefore, we place more diagnostic consideration on the ocular health status of the siblings, who are more likely to have been diagnosed using more recent diagnostic guidelines.
Beyond a solid family history of disease, we next carefully evaluate the character of optic nerve head anatomy. This is the most critical diagnostic maneuver, especially noting the neuroretinal rim tissue integrity, particularly the inferotemporal and superotemporal tissues of the optic nerve, as these tissues are most susceptible to IOP microtrauma (Figure 1).
Figure 1. This image shows a suspicious-appearing optic nerve head, but note the healthy-appearing neuroretinal rim tissues, which honors the ISNT — or inferior, superior, nasal, temporal — rule.
Next, measure IOP with either a Goldmann (Haag-Streit) or Icare tonometer (Figure 2). Note, however, that IOP without pachymetry is relatively worthless. It is critical to know if the cornea is thin (<500 µm), either physiologically or from alteration via refractive surgery, normal (500 µm to 580 µm) or thick (>580 µm). A physiologically thin cornea is an independent risk factor for glaucoma, while a cornea thinned through refractive surgery must be accounted for in roughly estimating its impact on IOP measurements. It is stressed that no accurate nomograms exist for calculating exact IOP based on corneal thickness. All that is needed is a characterization of thin, normal or thick — nothing more.
Figure 2. The Icare Tonometer (left) is a handheld unit that requires no topical anesthesia, which is a superb upgrade from air-puff tonometry, and may ultimately replace the Goldmann tonometer (right) as the gold standard.
In our practices, we commonly see normotensive patients with cup-to-disc (C/D) ratios of 0.7 (or higher) who have been diagnostically “missed,” because the normal IOPs lured the previous eye doctor into diagnostic complacency. The following example is a case study of a patient seen by one of us (RM):
A 62-year-old woman experiences an acute onset of floaters, and rather than see her habitual optometrist, she seeks medical attention elsewhere, because she now has a symptom that she thinks requires the care of an ophthalmologist; she decides to visit a large ophthalmology clinic where she saw one of us (RM). This is a common patient behavior, primarily because optometrists fail to educate their patients that they can provide comprehensive eye care. It is imperative that optometrists inform their patients that they are skilled to care for a wide array of eye conditions and do not just perform routine eye exams for glasses and contacts.
In this example case of the female patient with the sudden onset of floaters, the obvious diagnosis is an acute posterior vitreous detachment (PVD), but the new doctor (RM) she ended up seeing at the clinic observes a C/D ratio of 0.7 and feels obligated to conduct a comprehensive glaucoma workup at the follow-up visit in 1 month (Note: The large disc hemorrhage [Figure 3], which occurred at the time of the PVD, had resolved by the 1-month follow-up visit). The patient’s IOP measurements were 18 mm Hg in the right eye and 19 mm Hg in the left eye at the initial visit (coincidentally, the patient’s mother is also being actively treated for glaucoma). At the 1-month follow-up visit, the patient’s floaters had greatly subsided, and repeat retinal examination revealed no tears or breaks.
Figure 3. This large disc hemorrhage resulted from the microtrauma of an acute, symptomatic PVD and was fully resorbed by the patient's 1-month follow-up visit. More important to note is the thin neuroretinal rim tissue inferiorly.
The patient’s visual fields (Figure 4) perfectly correspond to the appearance of her optic nerve heads showing thinned inferior retinal nerve fiber layer. Because her impressive visual field loss occurred over many years, the patient was asymptomatic to her visual field loss (remember, the goal of glaucoma care is to keep the patient asymptomatic for as long as they live). So, in this respect, all is well.
Figure 4. Looking at the pattern deviation probability plots, one can readily note near-total superior loss OD and early superior loss OS. Because the patient's scotomas evolved over several years, she was asymptomatic to this loss of field.
The patient’s IOP measurements at follow-up were even lower than at her initial presentation (16 mm Hg in the right eye and 15 mm Hg in the left eye). This clearly demonstrates the relative unimportance of IOP compared with attentive ophthalmoscopy via slit lamp-with-condensing-lens observation. Despite efforts to have the patient return to her optometrist of many years, she chose to stay with her new doctor. This case illustrates the importance of not only providing good comprehensive care to patients but also ensuring your patients know you are skilled to treat a variety of eye conditions.
Although glaucoma diagnosis is usually straightforward, sometimes it can be challenging. If the comprehensive evaluation is inconclusive, do not worry. Clearly, the case is not obvious glaucoma, so simply see the patient every few months for follow-up, repeating the indicated testing as often as is medically necessary. If diagnostic testing remains stable over the years, then it is not glaucoma, because by definition, glaucoma is a progressive optic neuropathy. If, over time, the evaluation yields enough data to make a firm diagnosis, then, depending on numerous factors and considerations, continue to attentively follow the patient, or initiate treatment. There are two pivotal challenges in caring for patients: making a timely and accurate diagnosis; and determining whether and when to initiate therapy.
Both aspects of patient care require good training, clinical seasoning and deep thought. Remember, if there is a struggle with such decision-making, do not hesitate to get a second opinion from an optometric colleague, and understand that any other doctor will be challenged as well.
In summary, optometrists should perform at least the following diagnostic steps:
By performing these diagnostic maneuvers, it would be virtually impossible to miss glaucoma.
Figure 5. Performing four-mirror gonioscopy.
Figure 6. The four-mirror gonioscope (top), our favorite, and the Goldmann three-mirror lens (bottom).
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