I recently had a 55-year-old patient complaining of blurred distance vision, glare, and halos. When discussing the complaint, he reported it had been an issue for many years. I was skeptical of cataracts. Best visual acuity was 20/40 in each eye. Retina was clear. Mild ocular surface disease was present, but it did not account for the reduced visual acuity.  How do you document a cataract when it does not appear significant upon biomicroscopy?

I recently had a 55-year-old patient complaining of blurred distance vision, glare, and halos. When discussing the complaint, he reported it had been an issue for many years. I was skeptical of cataracts. Best visual acuity was 20/40 in each eye. Retina was clear. Mild ocular surface disease was present, but it did not account for the reduced visual acuity.  How do you document a cataract when it does not appear significant upon biomicroscopy?

Within optometry, cataracts are graded based upon biomicroscope appearance and visual performance on Snellen charts or via glare testing. These tests are performed to document the stage of cataract prior to performing surgery, primarily for insurance purposes but also for timing of surgery. There are several methods to objectively document the presence and progression of cataracts. These include LOCS III scoring and densometry, as well as measurement of visual function using the ocular scatter index and dysfunctional lens index.

LOCS III:  Direct measurement of cataract

The Lens Opacities Classification System III (LOCS III) is a subjective grading system performed at the biomicroscope that is used in clinical practice as well as in research studies. Evaluation of the cataract is performed at the slit lamp, comparing nuclear opalescence, nuclear color, cortical cataract, and posterior subcapsular cataract to standard color photographic transparencies. (Figure 1) Although OD’s may not actually have these images in each exam lane, this is how the majority of us measure cataracts.

Figure 1: The Lens Opacities Classification System III is used more for research to standardize cataract grading.

Densometry: Direct measurement of cataract

Scheimpflug cameras measure the “densometry” of the lens. Opacities of the crystalline lens are quantifiable using blue light illumination, allowing automatic, objective three-dimensional quantification of lens opacity. (Figure 2) 

Figure 2a:  Scheimpflug images of the right lens. Note the increase in lens density on the far right graph corresponding to the corneal (top spike) and lens (middle spikes).

Figure 2b: Scheimpflug images of the left lens is more significant than the left.

The Pentacam Nucleus Staging software (OCULUS Optikgeräte GmbH, Germany)  objectively evaluates lens density in 3 dimensions with a selected diameter of 4.0 mm.  Comparison of the LOCS III with the mean values of lens density has been performed.  One study of a single eye of 101 patients found a positive correlation between staging and grading results, there was low correspondence with LOCS III classification. Another study found the Coefficient of Repeatability was highest in peak mode, followed by linear along the vertical axis, and 3-dimensional (3-D). They concluded that while highly repeatable, repeatability was dependent on the analysis mode used and decreased with increasing opacification.

Anterior Segment OCT:  Direct Cataract Evaluation

Anterior segment ocular coherence tomography may be used to image lens opacification but is typically reserved for advanced cataracts to rule out phacomorphic glaucoma and assist with white cataracts. Anterior chamber area and depth assessment can be used to rule out angle closure. AS-OCT can also be used to manage white cataracts by identifying subscapular fluid pockets prior to creation of the capsulorhexis. Detection of the fluid allows better surgical planning by draining the fluid to prevent capsular runaway complications. 

Ocular Scatter Index (OSI): visual function assessment

This method considers the functional effect of the lens upon the visual system. It uses analysis of double-pass retinal images of a point source to create the Modulation Transfer Function (MTF) of the eye. The MTF incorporates all relevant effects of diffraction, higher-order aberrations and scatter degrading the retinal image quality. The retinal image is affected by both ocular aberrations and intraocular scattering. These two factors influence the light distribution on the retina. Some feel this technique is advantageous because slit-lamp imaging only provides information about back-scattered light. Subjective complaints may result from forward scatter of light by the crystalline lens. The OSI is defined as the ratio between the integrated light in the periphery and in the surroundings of the central peak of the double-pass image. OSI was found to be a sensitive test for cataract detection. Authors reported a 96% probability of having an OSI score of greater than 1.45 if the patient has a cataract equivalent to a LOCS III score greater than or equal to 3. At this level, one would expect the cataract to be visible to the examiner and subjectively noted by the patient.  (Figure 3)

Figure 3a: The right eye of the patient had an OSI of 3.1, which is visually significant, and supported cataract removal. The cataract development causes the MTF to fall steeply.

Figure 3b: The left eye of the patient had an OSI of 3.6, which is more visually significant, and supported cataract removal. The simulated display can be useful to direct technicians to focus on cataracts during a workup.

Dysfunctional Lens Index: Assessment of Visual Function

Like the OSI, the Dysfunctional lens Index (DLI) was developed to assess patients with Dysfunctional Lens Syndrome (DLS). Dysfunctional Lens Syndrome is characterized by reduced vision due to aging and progressive presbyopia, as described by George O. Waring IV. The clinical findings include: lens opacities, the inability to accommodate due to presbyopia, and a changed aberration profile. DLS needs to be assessed when the patient’s visual complaints sound like cataracts, but the slit lamp exam does not reveal a significant cataract. The DLI is calculated based on internal higher-order aberrations, analysis of contrast sensitivity, and pupil size dynamics using the iTrace (Tracey Technologies, Houston, TX). The iTrace measures the cataract using the DLI as well as an opacity map.  The iTrace evaluates the variance and intensity of the energy reaching the retina generating a map of the opacity or scatter. This grading is 1-5, a familiar grading scale, but not intended to match the LOCS grade. (Figure 4)

Figure 4a:  The Dysfunctional Lens Analysis OD demonstrates the visual function of the visual system behind the anterior corneal surface.  The MTF slope suggests cataracts, and the Snellen E is significantly blurred. The opacity maps are mildly significant (1.5), meaning not all the light that enters the eye is getting to the retina.

Figure 4b:  The Dysfunctional Lens Analysis OS.  The  MTF slope suggests cataracts, and the Snellen E is slightly blurred. The opacity maps are not significant, which is not surprising since the biomicroscopic view was also low on the LOCS III cataract scale.

Wang and Tang investigated the dysfunctional lens index (DLI) value measured by iTrace visual function analyzer (Tracey Technologies, Houston, TX) in patients divided into nuclear cataract group (39 eyes), cortical group (48 eyes) and posterior subcapsular group (45 eyes). Preoperative best corrected distant visual acuity (LogMAR vision), LOCS III grading system, and cumulative dissipated energy (CDE) during subsequent phacoemulsification were investigated. They found for each of the different types of age-related cataract, the DLI shows good correlations with LogMAR and LOCS III scores, and the DLI can reflect the degrees of visual impairment, lens opacity, and may provide references for energy use in phacoemulsification of nuclear cataract. Faria-Correia, et al, investigated the correction between the Dysfunctional Lens Index from ray-tracing aberrometry, logMAR corrected distance visual acuity (CDVA), lens grading based on the Lens Opacities Classification System III (LOCS III) and the Scheimpflug-based lens density. The DLI showed a high negative linear correlation with the LOCS III nuclear opalescence score (r = -0.662; P < .01). Average lens nucleus density was positively correlated with the LOCS III nuclear opalescence score (r = 0.682; P < .01). The CDVA had a stronger relationship with the DLI parameter (r = -0.702, P < .01) compared to the average density values (r = 0.630, P < .01).

Aberrometry:  Assessment of visual function

Cataract development increases higher order aberrations. Both overall wavefront also called “total wavefront”, and internal wavefront indicates changes in the system associated with cataracts. Total wavefront changes have been investigated in the cataractous eye and found to increase with age. A study of 135 eyes found coma predominated eyes with cortical cataracts, while spherical aberration predominated eyes with nuclear cataracts.  Several systems subtract the corneal wavefront derived from corneal topography from the total wavefront directly obtained from raytracing or Hartman–Shack aberrometry. A significant correlation between quantification parameters derived from Scheimpflug lens densitometry and ocular higher-order aberrations have been reported.

These modern methods are most helpful to my practice when I have a patient presenting with glare and halo complaints, reduced best-corrected vision, a normal corneal topography and retinal OCT, and little cataract change upon biomicroscopy. The preceding images in this article belong to such a patient. The densometry supports the presence of the cataract, and the OSI was elevated (3.1 OD, 3.6 OS). The DLI was 4.26 OD, 5.88 OS, and the opacity map was 1.5 OD, 0.5 OS. Note that while methods may not agree, they do support the patient’s complaint of vision loss.

Applying modern testing methods can be particularly helpful in the assessment of patients post-refractive surgery with vision complaints. These patients have irregular corneas and are at higher risk of dry eye. They also have high expectations for their vision and tend to assume any vision change after refractive correction is related to the vision correction. Use of these imaging methods can also be useful when educating the patient regarding the etiology of the visual symptoms and discussion surgical planning. 

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