Article

Improve Patients’ Dx Testing Experience

Use functional and structural testing for early diagnosis

One of my patients, a plaintiff’s attorney, and I have presented lectures in a clinical legal course at the University of Alabama School of Optometry. One of his salient points to budding clinicians is this: “If I have you on the stand, I’m not going to ask what you did, but what you could have done.” This mantra echoes in my brain any time I am confronted with a diagnostic dilemma, especially when considering how the early detection and intervention of ocular disease can impact the patient experience in our practices.

Here, I will present two cases that illustrate the importance of functional and structural testing in early detection, so optometrists can increase the likelihood of an excellent patient experience.

CASE 1: THE GLAUCOMA SUSPECT

A situation that every optometrist confronts is the glaucoma suspect: This patient’s signs may include optic disc asymmetry, a questionable change in disc appearance, an aberrant IOP reading, etc. that suggests the need for more detailed testing.

Repeatable VF depression (functional data) coupled with OCT (structural data) now allows for improved early diagnosis and intervention. Specifically, documenting early structural changes may offer corroborating evidence of the glaucoma diagnosis.

OCT offers detailed measurements of the retinal nerve fiber layer (RNFL) and quantitative parameters of the optic nerve head. The resolution and narrow variability provides exact and precise numerical foundations to differentiate a normal from abnormal RNFL, as well as a way to assess disease progression, complementing the quantitative data from VF testing.

Additionally, some OCT devices offer a further means for assessing early structural change. For example, ganglion-cell (GC) analysis at OCT adds a layer that quantitates and compares the analysis to a reference database. In fact, a Clinical Ophthalmology study shows good correspondence between attenuated GC thickness and subtle VF depressions consistent with early glaucoma.

Also, consider this: A 73-year-old long-time patient presented with 20/20 VA OU at distance without correction. At previous appointments, her IOP had always been below 21 mmHg with healthy (non-suspicious) optic disc appearance OU. At this particular appointment, the patient revealed her brother had been diagnosed with glaucoma.

Suspicious for early signs of the sight-threatening disease, we employed OCT to measure central corneal thickness, a structural biomarker associated with glaucoma risk. Her values, 575 µm and 613 µm (OD, OS), were considered in a “protective” range. However, imaging of the macular nerve fiber layer (“ganglion-cell complex”), focusing on the inner retinal layers, showed abnormalities on both absolute values, as well as abnormalities in comparison with a reference database. (See Figure 1.) While it may be less consistent with glaucoma for ganglion-cell thinning to cross the horizontal raphe, these functional data allowed guidance for a clinical recommendation of first a prostaglandin analog to be used at night, which did not reduce IOP, and eventually SLT surgery, which reduced and stabilized the patient’s IOP.

Figure 1. Right color fundus photograph with arrow indicating a vessel deflection describing a thinner inferior rim than had been documented previously. Right panel showing absolute macular nerve fiber layer thinning (thickness map) based on the color scale to the right and relative thinning based on the reference database (less than 1% of those with such a thin value).
All images courtesy of Leo Semes, O.D., F.A.A.O.

It’s worth noting that an Investigative Ophthalmology & Visual Science study concluded that the GC thinning pattern may be more helpful in cases of suspicious glaucoma complicated by high myopia. In these confusing cases, thinning that is confined by rather than crossing over the horizontal raphe is a good differentiator between myopic glaucoma and myopia.

From OCT angiography (OCT-A) imaging of the capillaries, there may emerge another early structural indicator of early (sub-clinical, “pre-perimetric”) glaucoma. Briefly, OCT-A evaluates motion within a stationary environment. For sake of simplicity, let’s presume that the capillaries are stable while red blood cells within them are in motion. Think of a time-lapse photograph of a roadway at night. Blood in motion defines capillary routes. This allows for representations of capillary density. Thus, capillary networks can be imaged and evaluated. Still the question remains whether capillary dropout precedes or is a result of GC loss that can correspond with subtle VF depressions, according to a Journal of Glaucoma study.

CASE 2: EARLY AMD

Dark adaptation testing (DA) (functional data) and OCT-A (structural data) may also complement each other, in terms of aiding the practitioner in making a definitive diagnosis.

Preceding the clinical appearance of even the first drusen, subretinal deposits, known as basil linear and laminar deposits, may be seen. These are impediments to nutrient transport from the choroid to the overlying photoreceptors. The result is impaired rod-mediated DA, which is a predictor of the appearance of drusen, the first clinically visible evidence of AMD, up to three years early, reports an Ophthalmology study.

What may be critical to prompt DA testing is a complaint of difficulties seeing in low-light situations or with adjusting from bright to dim environments.

Consider the example of a 68-year-old patient who had a history of blunt ocular trauma OD 50 years earlier, but with corrected 20/20 VA OU. (While the macula was uninvolved, it disqualified the patient from DA protocol testing.) The left eye was undamaged and appeared clear but with a family history of AMD, he was tested for DA. (See Figure 2.) In this case, the rod-intercept time, also known as RIT, was normal and the patient was reassured and placed on an appropriate periodic recall schedule.

Figure 2. Left color fundus photograph showing absence of drusen, or pigmentary abnormalities. Right panel: rod-mediated dark adaptation results indicating normal dark adaptation. If the rod-intercept time had been greater than 6.1 minutes, further testing would be indicated along with closer scrutiny.
All images courtesy of Leo Semes, O.D., F.A.A.O.

Regarding OCT-A, its role in this vision-threatening disease has yet to be completely crystallized, though it’s worth mentioning that a validated staging classification of AMD based on clinical signs, such as the appearance of drusen and pigmentary changes within the macula, is available. Thus, it seems that DA testing, along with the honing of OCT-A data will be valuable for earlier diagnoses.

PROVIDING AN EXCEPTIONAL EXPERIENCE

By using some diagnostic devices together and staying abreast of what is coming, optometrists can detect ocular disease early, increasing the likelihood patients will be able to maintain their current vision and, thus, day-to-day activities. I should also mention that having the latest devices can create patient loyalty: A neighbor of mine was diagnosed with AMD. He had the same optometrists for roughly 20 years. When I asked him why he switched, he told me it was because he noticed the office technology hadn’t changed in all that time. Exceptional care translates to an exceptional experience. OM