Faster, More Precise Diagnoses With iTrace Visual Function Analyzer

The iTrace Combo provides dynamic analysis of five different eye measurements, including topography and aberrometry.

By Kenneth Daniels, OD, FAAO

In my practice, which involves primary care, disease management and co-management, topography has long been an essential tool. More recently, wavefront aberrometry has become essential as well. All three optometrists and a visiting ophthalmologist use these technologies daily. Since purchasing the iTrace Combo Visual Function Analyzer (Topcon Medical Systems, Inc.) we've been able to do so more efficiently and effectively.

The iTrace Combo Visual Function Analyzer is a multifunctional instrument. It's a topographer, ray-tracing wavefront aberrometer, autorefractor, keratometer and pupillometer all in one. As such, it's an advanced and accurate way to analyze an eye's total visual capabilities. One of its key capabilities is distinguishing between corneal and lenticular aberrations. This allows us to precisely determine the source of patients' vision complaints. As a result, we can make accurate diagnoses faster and choose the best vision correction solutions, including recommending the most appropriate surgical option for an IOL or LASIK, as well as custom contact lenses (Wavetouch) or spectacles.

With the iTrace, we can utilize several graphical methods to represent and define the patient's visual functions, such as PSF (Point Spread Function), MTF (Modulation Transfer Function), Simulated Snellen E (representation of ocular imaging), Retinal Spot image (imaging quality appreciated at the retinal level), graphical equivalents of Zernike levels of aberrations and quantitative listing of various LOA (lower-order aberrations) and HOA (higher-order aberrations), while differentiating between corneal and lenticular influences. We can see what the patient sees, demonstrate and educate the patient and address the visual complaint of the patient with precision. The system also performs multi-zonal dynamic refraction, allowing us to assess visual function in photopic, mesoptic and scotopic conditions (see Case 1).

Case 1: Myopic Shift, Difficulty Driving at Night

This patient presented with a chief complaint of difficulty driving at night. The iTrace Combo allowed us to evaluate pupil dynamics in relation to objective refraction and aberrations, revealing a myopic shift from small pupil to large pupil (Figure 1). From a baseline refraction of −0.87 −0.50 x 118° OD and −0.62 −0.75 x 75° OS, refraction changed with pupil size as follows:

Figure 1. In this patient, who complained of poor night-driving vision, the iTrace Combo shows a myopic shift as pupil size increases (Case 1).

■ right eye, 2-mm pupil/−0.43 −0.93 x 126°
right eye, 6-mm pupil/−1.64 −0.35 x 98°
■ left eye, 2-mm pupil/−0.32 −0.83 x 70°
left eye, 6-mm pupil/−1.66 −0.73 x 85°

The iTrace listed potential visual complaints of night myopia, glare/halo and blurred/double vision and represented those effects with the Point Spread Function and Simulated Snellen E, thus objectively confirming the patient's subjective complaints.

We offered this patient two pairs of eyeglasses, one with the best correction for daytime and room light and one for night driving and dim light.

Case 2: Pediatric Exam

This patient, a 5-year-old male, presented for his first eye exam. In this case, as in many others, the iTrace exam was an acceptable alternative to a cycloplegic exam.

■ objective refraction
OD: +1.87 −3.12 x 9°
OS: +2.87 −3.62 x 169
■ subjective refraction
OD: +1.50 −2.50 x 10° (20/30)
OS: +2.00 −2.75 x 170° (20/30)

Without the need to use drops, the instrument defined the level of ametropia, leading us to a diagnosis of refractive amblyopia (Figure 2).

Figure 2. The iTrace Combo Visual Function Analyzer was instrumental in diagnosing this 5-year-old patient with refractive amblyopia (Case 2).

The Point Spread Function and Simulated Snellen E are excellent parental education tools. We can illustrate what their children actually see. These representations of visual function also can be used to help teachers understand and accommodate a child's condition.

Case 3: Converting GP Patient to Wavetouch Soft Lenses

This patient had been wearing gas permeable contact lenses for more than 20 years and wanted to pursue LASIK. As part of the corneal rehabilitative process, the patient was taken out of GP lenses and placed into soft lenses until corneal stability could be achieved.

Upon removal of the GP lenses, a baseline exam with the iTrace Combo showed coma that was consistent with corneal topographic measurements, a high RMS aberration level and the corresponding distorted Point Spread Function and Simulated Snellen E (Figures 3-6).

Figures 3-6. Case 3 is a long-time gas permeable contact lens wearer who was interested in LASIK. The iTrace facilitated design and fitting of a Wavetouch aberration-correcting soft lens that can be worn until the cornea stabilizes. Figures 3 and 4 are images and measures for the Wavetouch lens; Figure 5 is the Wavefront Summary over the Wavetouch lenses, and Figure 6 demonstrates Point Spread Function, immediately after GP lens removal.

Guided by the information provided by the iTrace, we fit this patient with Wavetouch aberration-correcting soft lenses. This process involves a predicate or acquisition lens that uses a base curve consistent with topographic measures and power in close approximate range of the subjective refractive spherical power. The lens is placed on the eye, assessed for proper fitting characteristics and then measured by the iTrace. The lens has three dots to identify proper positioning, and lines are used to verify dot location later used in lens fabrication.

When the patient was fitted with Wavetouch lenses, the iTrace measured a significant decrease in the RMS value and increase in the clarity of the Point Spread Function and Simulated Snellen E. Even more impressive was the decrease in total RMS aberration level, from 2.806 μm to .303 μm OD and from 3.708 μm to .332 μm OS. This patient achieved two lines better visual acuity than her original refraction after discontinuation of GP lens wear.

Precise and Practical

As these cases show, the iTrace Combo provides us with a wealth of useful diagnostic information in a very practical way. The system is easy to use, similar to a point-and-shoot camera, and we have realized extensive workflow efficiency improvements. The iTrace has taken the place of several other instruments, and fosters more complete doctor-patient communication. It helps us deliver a positive patient experience while ensuring the best possible quality of vision for all patients.

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Dr. Daniels practices at Hopewell-Lambertville Eye Associates in New Jersey. He is an adjunct assistant clinical professor at the Pennsylvania College of Optometry at Salus University. He can be reached at 609-466-0055 or kennethdaniels@att.net. He has no financial interest in Wavetouch, Topcon nor Tracey Technologies.