Artifact Awareness: Optic Disc Imaging in Glaucoma
Artifact Awareness: Optic Disc Imaging in Glaucoma
Optometrists and ophthalmologists are increasingly relying on imaging instrumentation in routine glaucoma practice. Optical coherence tomography (OCT), scanning laser polarimetry (GDx; Carl Zeiss Meditec), and Heidelberg retina tomography (HRT) can contribute to the quality of care for our glaucoma patients, but only when used correctly.
How these instruments are used to augment patient care should be guided by our understanding of the nuances of each device. Each instrument measures and displays information on the basis of the diversity and extent of the database; therefore, they do not provide identical information. Each instrument has inherent limitations that must be considered when interpreting the test results.
Continuing education is a primary way to understand these evolving technologies. Presentations geared toward enhancing understanding of these instruments and how to incorporate them into routine practice are found in the programs of almost every national, regional, or state association meeting. For example, at the 2012 American Academy of Optometry (AAO) meeting in Phoenix, Arizona, more than 20 hours of continuing education presentations (separate from poster sessions) related to technology and its clinical applications were offered. The symposia presented by the Optometric Glaucoma Society at the AAO meeting included topics of interest related to imaging technologies and laid the foundation for new horizons for the future of glaucoma imaging. It is evident that through education, optometry practice embraces technology and strives to use it to provide state-of the-art eye care.
It is imperative that the results of any of the available imaging techniques not be considered in isolation of the overall clinical picture of the patient. This can occur in clinical practice, however, and can result in over- or underdiagnosis of glaucoma.
I have been involved in clinical education of students and residents for 27 years and have observed a trend for the newer generation of clinicians to rely primarily on technology to make and commit to a diagnosis, solely on the basis of an abnormal imaging printout. An implied "validity" is granted to the imaging results that can override other, normal clinical findings. Acceptance of a normal or abnormal imaging result as absolute truth, in lieu of consideration of other clinical findings, allows the instrumentation to usurp the clinician's decision-making skills. Lack of clinical experience and eagerness to embrace technology by students and residents lead to this endpoint.
Unless the flaw in this clinical approach is highlighted to our students and residents, misdiagnosis can result. In the same vein, a false-negative result can occur when clinical findings suggest glaucoma, but the diagnosis is eliminated on the basis of normal findings on OCT or HRT.
Seasoned clinicians can also fall victim to misinterpretation of abnormal or normal results, for various reasons. Time constraints during an office visit or financial limitations with third-party insurance carriers can lead to the same endpoint. In an attempt to provide the best possible care, using the information available at that time and with limited resources and reimbursement in private practice, decisions to initiate treatment primarily on the basis of abnormal OCT or HRT results are made with some frequency. In each of these situations, optic disc imaging alone was used to establish normalcy or diagnose glaucoma, without correlating the imaging with the appearance of the disc and other clinical findings.
This is much like using only an absolute erythrocyte sedimentation rate to diagnose temporal arteritis without considering the patient's symptoms or performing any other clinical investigation. The normal or abnormal result must be validated through comparison with the other clinical findings in the examination.
A normal display on OCT or GDx can be obtained despite observed rim changes consistent with glaucoma. An abnormal display in a patient with ocular hypertension, suggesting glaucomatous damage, may be artificially induced by the patient's high myopia. This reflects limitations in the extent of the instrument's database and occurs in the absence of pathologic nerve fiber layer (NFL) loss. This phenomenon is not exclusive to OCT, because specific normal data ranges are used to define the limits of normal vs abnormal for each instrument. In light of an abnormal finding on OCT, similar comparative findings can be obtained on HRT or GDx, which may confirm the "abnormality" but still does not reflect a definitive diagnosis. Eyes with NFL loss from either glaucoma or nonarteritic anterior ischemic optic neuropathy can produce the same color display on the OCT or GDx, yet until a detailed disc assessment is performed, the presence of rim pallor or glaucomatous loss cannot be ascertained.
Imaging in Glaucoma Practice
Optometrists and ophthalmologists are increasingly relying on imaging instrumentation in routine glaucoma practice. Optical coherence tomography (OCT), scanning laser polarimetry (GDx; Carl Zeiss Meditec), and Heidelberg retina tomography (HRT) can contribute to the quality of care for our glaucoma patients, but only when used correctly.
How these instruments are used to augment patient care should be guided by our understanding of the nuances of each device. Each instrument measures and displays information on the basis of the diversity and extent of the database; therefore, they do not provide identical information. Each instrument has inherent limitations that must be considered when interpreting the test results.
Continuing education is a primary way to understand these evolving technologies. Presentations geared toward enhancing understanding of these instruments and how to incorporate them into routine practice are found in the programs of almost every national, regional, or state association meeting. For example, at the 2012 American Academy of Optometry (AAO) meeting in Phoenix, Arizona, more than 20 hours of continuing education presentations (separate from poster sessions) related to technology and its clinical applications were offered. The symposia presented by the Optometric Glaucoma Society at the AAO meeting included topics of interest related to imaging technologies and laid the foundation for new horizons for the future of glaucoma imaging. It is evident that through education, optometry practice embraces technology and strives to use it to provide state-of the-art eye care.
Technology as a Tool in Patient Care
It is imperative that the results of any of the available imaging techniques not be considered in isolation of the overall clinical picture of the patient. This can occur in clinical practice, however, and can result in over- or underdiagnosis of glaucoma.
I have been involved in clinical education of students and residents for 27 years and have observed a trend for the newer generation of clinicians to rely primarily on technology to make and commit to a diagnosis, solely on the basis of an abnormal imaging printout. An implied "validity" is granted to the imaging results that can override other, normal clinical findings. Acceptance of a normal or abnormal imaging result as absolute truth, in lieu of consideration of other clinical findings, allows the instrumentation to usurp the clinician's decision-making skills. Lack of clinical experience and eagerness to embrace technology by students and residents lead to this endpoint.
Unless the flaw in this clinical approach is highlighted to our students and residents, misdiagnosis can result. In the same vein, a false-negative result can occur when clinical findings suggest glaucoma, but the diagnosis is eliminated on the basis of normal findings on OCT or HRT.
Seasoned clinicians can also fall victim to misinterpretation of abnormal or normal results, for various reasons. Time constraints during an office visit or financial limitations with third-party insurance carriers can lead to the same endpoint. In an attempt to provide the best possible care, using the information available at that time and with limited resources and reimbursement in private practice, decisions to initiate treatment primarily on the basis of abnormal OCT or HRT results are made with some frequency. In each of these situations, optic disc imaging alone was used to establish normalcy or diagnose glaucoma, without correlating the imaging with the appearance of the disc and other clinical findings.
This is much like using only an absolute erythrocyte sedimentation rate to diagnose temporal arteritis without considering the patient's symptoms or performing any other clinical investigation. The normal or abnormal result must be validated through comparison with the other clinical findings in the examination.
A normal display on OCT or GDx can be obtained despite observed rim changes consistent with glaucoma. An abnormal display in a patient with ocular hypertension, suggesting glaucomatous damage, may be artificially induced by the patient's high myopia. This reflects limitations in the extent of the instrument's database and occurs in the absence of pathologic nerve fiber layer (NFL) loss. This phenomenon is not exclusive to OCT, because specific normal data ranges are used to define the limits of normal vs abnormal for each instrument. In light of an abnormal finding on OCT, similar comparative findings can be obtained on HRT or GDx, which may confirm the "abnormality" but still does not reflect a definitive diagnosis. Eyes with NFL loss from either glaucoma or nonarteritic anterior ischemic optic neuropathy can produce the same color display on the OCT or GDx, yet until a detailed disc assessment is performed, the presence of rim pallor or glaucomatous loss cannot be ascertained.
