The practice of optometry is constantly changing and evolving. It is vital that optometrists continually refine their ocular disease management skills to best serve their patients. This article will present practical techniques for monitoring AMD, diabetic retinopathy (DR) and glaucoma with technology, including OCT, OCTA and electroretinogram (ERG).

AGE-RELATED MACULAR DEGENERATION

Several key findings can indicate if/when AMD will progress and when treatment might be indicated.

Structurally, OCT can be used to examine specific retinal layers. A majority of patients diagnosed with AMD have the dry form, so continued monitoring for macular neovascularization (MNV) development is of utmost importance.¹ The presence of MNV represents pathology escalation from dry AMD to wet AMD and would necessitate treatment with anti-VEGF injections. When investigating the sub-retinal pigment epithelium (RPE) space in a patient who has AMD and drusen, specific attention should be given to the integrity of the Bruch’s membrane/RPE complex. A disruption here could indicate aberrant blood vessel formation to which anti-VEGF treatment is likely indicated.

A 69-year-old female presented to the practice with a complaint of reduced vision OD that she noticed when using a periscope with her grandson. Her BCVA went from 20/25 the year before to 20/100. OCT showed drusen with underlying disruption of Bruch’s membrane. Suspecting MNV, we referred her to a retinal specialist who promptly provided an intravitreal injection of an anti-VEGF.

When the need arose to examine vascular changes in the retina and choroid, fluorescein angiography (FA) was our go-to diagnostic test until the advancement of OCTA. SS-OCTA can be extremely useful in detecting possible MNV with anatomic localization.² Depending on your software platform, several slabs through the retinal and choroidal vasculature system exist. Images of the outer retina and choriocapillaris slab are useful in determining MNV formation. These also can be used sequentially over time in response to an anti-VEGF treatment.³

As we know with the anatomy of AMD, functional central vision will likely be affected. This can be monitored via VF testing, specifically the 10-2 test, which focuses on the central 10° of vision. While VF defects can be unpredictable in AMD, a decrease in mean lesion size for neovascular AMD via anti-angiogenic injection has shown an improvement in mean deviation (MD) over 12 months.⁴ This parameter can depict an idea of how the patient deviates from others of similar age and race and can be used over time or in conjunction with tertiary services (low vision aids) to improve the patient’s quality of life.

ERG can serve a similar purpose as VFs, but relies less on patient testability. Multifocal ERG (mfERG) is useful in this setting, as the degree of retinal dysfunction within the central 40° of the patient’s VF is quantified. This technology also has been found to be a useful technique to study the disease progression of AMD over short periods of time.⁵ A change in mfERG may be the first sign of conversion to wet AMD. Pattern ERG (PERG) may also be beneficial in detecting early functional loss due to AMD.⁶ As with mfERG, PERG may help identify dry AMD progression or conversion to wet AMD, resulting in more timely treatment with better outcomes.

DIABETIC RETINOPATHY

The management of patients who have diabetes, and, thus, are at risk of developing DR and other related eye diseases, includes close examination of retinal tissue and vasculature in relation to structure and function. The dilated fundus exam can be augmented with ophthalmic technology to accomplish this.

In clinical practice, OCT evaluation of the macula is of utmost importance in diabetics. Retinal swelling, cystoid macular edema and subretinal fluid accumulation are common findings in diabetics and can be detected and monitored with the help of OCT. When diabetic macular edema has reached clinical significance and treatment is indicated, OCT can further be utilized in co-management to determine the amount of macular thickness change post intravitreal injection or laser photocoagulation. Several OCT platforms offer a macular change analysis report that can give quantifiable thickness measurements over time and aid in the decision for continued monitoring vs. referral for treatment.

Taking this imaging a step further, OCTA allows optometrists to visualize those capillaries that have sustained structural damage from high blood glucose. OCTA has been found to demonstrate clinically relevant vascular changes (microaneurysms, impaired perfusion, retinal edema, vascular loops, IRMAs and neovascularization).⁷ As OCTA software can often provide images of the superficial capillary plexus, the deep capillary plexus and the choriocapillaris slab, it can provide valuable information about the structural damage that has occurred in DR.⁸ Identifying DR earlier in the disease process may allow for quicker referrals to endocrinology or primary care. It may also lead to an escalation of treatment for better blood sugar control. The vitreoretinal interface slab has shown comparable with FA to detect neovascularization and may distinguish between intraretinal microvascular abnormalities and diabetic papillopathy vs neovascularization.⁹

Perhaps of most structural benefit of this software are the details given about the foveal avascular zone (FAZ). Abnormalities in this area can have a significant impact on vision and can be used as a screening tool earlier in the disease state to detect eyes at higher risk for DR. Diabetics have been found to have an increased FAZ area compared with controls, and remodeling of this critical visual location also occurs at a higher rate.¹⁰ An expanding FAZ is suggestive of DR. These images can be sequentially analyzed to give an indication of vascular damage (with subsequent ischemia) as a contribution to vision loss when other findings are not apparent. This clinical insight allows the optometrist to recommend more aggressive diabetic control to the primary care provider or endocrinologist.

Pathological states require an analysis of both structure and function. In determining the extent of functional impact from structural damage in DR, several modalities can be used.

Automated VF can be used to determine the functional capacity of a damaged retina (and beyond). While VF defects in diabetics can be diffuse and follow nonlinear patterns, MD and pattern standard deviation (PSD) can be used over time in conjunction with structural findings. These indices can allude to differences in the average deviation from the mean (MD) and the uniformity of the deviation (PSD) compared to age-matched controls. Those who have reduced retinal function tend to have more depressed MD values (negative) and higher PSD values (positive).¹¹ While there is no generally accepted VF staging system in DR, it is helpful to monitor MD and PSD for change over time. Binocular VF tests can be used post panretinal photocoagulation to determine the level of visual function safe for driving.

ERG can be useful in diabetes to detail retinal dysfunction, even when no clinical signs of DR are noted. MfERG implicit time has been found to show high accuracy in the prediction of DR and edema when used in models that also incorporate other risk factors.¹² This functional test offers another tool in your arsenal to further evaluate DR.

GLAUCOMA

While most glaucoma patients progress slowly, we must be vigilant to identify fast progressors, and technology can help with that. One way to help identify patients who progress quickly is OCT. OCT can aid in identifying progression by using event-based or trend-based methods. Event-based methods analyze whether the OCT changed from the last scan by looking at the reflectance pattern of the retinal nerve fiber layer and/or ganglion cell complex.¹³ The TSNIT or NSTIN is another way to utilize the event-method. The second way is trend-based, which monitors progression over time. Trend-based is easy to use and is less susceptible to fluctuation. But this method may require several tests before providing a useful statistical analysis.¹⁴

Glaucoma progression can also be measured functionally by using VF software analysis. Similar to OCT, VF progression can be analyzed with both event-based and trend-based methods.¹⁵ Generally, event-based methods are used early in the patient’s follow-up period, and trend-based analysis is utilized once a sufficient number of VFs are taken.

If progression is found with the help of OCT, VF or both, then new treatment or more aggressive treatment is warranted. Most clinicians begin initial treatment with a prostaglandin analogue, but the recent LiGHT study suggests that selective laser trabeculoplasty (SLT) should be considered as first line therapy.¹⁶ If the patient is already using topical treatment, then additional drops, SLT, MIGS or a filtering procedure should be considered.

MONITOR DISEASE PROGRESSION

Ocular disease progression can be monitored via several platforms. It is imperative that we stay up-to-date with these advancements to best serve our patients and stay relevant in this constantly evolving world of optometry. OM

REFERENCES

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DR. CYMBOR is the co-director of the Glaucoma Institute of State College and is a member of the Optometric Glaucoma Society. He is a managing partner at Nittany Eye Associates. Disclosures: Key Opinion Leader for Optovue and Quidel. Consultant for Telasight. He can be reached at mcymbor@nittanyeye.com.

DR. STILES serves as an active duty Army optometrist. She is completing a primary care residency facilitated through the Oklahoma College of Optometry. She can be reached at jvs5310@gmail.com.