St. John’s, Canada, 14th October 2013
Bense Vision has announced the use of the next generation of the Optical Quality Analysis System, the HD Analyzer, following the system becoming available in North America and after recent issuance of the European CE mark for the system.
The HD Analyzer is a unique diagnostic system that allows for an objective analysis of optical quality in a persons eye. The system provides an objective measure of ‘light scatter’, which is caused by a host of ocular factors including corneal disease or imperfections on the ocular surface as well as cataract formation, which can lead to degradation in retinal image quality. Light scatter is not measurable using traditional wavefront aberrometry techniques such as the WaveScan measurements and presents a diagnostic challenge that only the HD Analyzer is now able to answer.
An objective Analysis
This latest generation Optical Quality Analysis System, the HD Analyzer Optical Quality Analysis System (OQAS), is based on the double-pass technique and provides an objective measurement of the quality of the retinal image, including higher-order aberrations and scattered light.1,2 When scatter is present, the quality of the retinal image is degraded.3 The higher the OSI, the worse the patient’s quality of vision (retinal image quality).
Employing double-pass retinal imaging, the HD Analyzer uses a near infrared light source that is imaged on the retina. The size and shape of the light are analyzed by the system in order to determine the higher order aberrations present as well as scattered light. The system provides ophthalmologists and optometrists with a Point Spread Function (PSF), Objective Scattering Index (OSI), as well as the derived Modulation Transfer Function (MTF) and its cutoff.
The HD Analyzer has been well received by US ophthalmologists. The HD Analyzer gives ophthalmologists the ability to go beyond traditional subjective means of vision assessment, which is increasingly important in today’s ophthalmology practice.
The HD Analyzer OQAS is versatile and can be used for:
v Diagnosing and monitoring the evolution over time of ocular pathologies such as an unstable tear film in dry eye situations or of refractive disorders.
v Evaluation of the level of ‘objective light scatter’ (OSI) for the early detection of a cataract and the determination of its effect on retinal imagery.
v Optometric or ophthalmic screening of refractive patients: the OSI is an invaluable tool to predict if a good visual outcome is likely. (see below)
v Comparing pre and post-cataract and refractive surgery measurements.
v Precise measurement of MTF (Modulation Transfer Function), which is often overestimated by WaveScan aberrometers when scattering exists, as in cataract patients.
v Evaluation of tear film quality.
v Objective measurement of the amplitude of accommodation and pseudo-accommodation in IOL patients.
v Objective assessments of the pre and post-KAMRA insert client. (Corneal Vertex, P1 Image, Angle Kappa, Inlay placement and more).
A Unique Approach to Selecting Patients for Refractive Surgery including KAMRA Vision clients
We use this unit as a diagnostic device that measures light scatter, which allows optometrists and ophthalmologists to identify the origin of patients’ visual problems. We measure the position and direction of the client’s Corneal Vertex and Pupil Centre in order to establish the 1st Purkinje Image that will guide surgeons as to best centration spot for a KAMRA Vision Inlay.
Obtaining images with the HD Analyzer is easy and straightforward. Most traditional measurements of visual quality are subjective. The HD Analyzer, in comparison, objectively measures the quality of the retinal image and provides eye doctors with an understanding of what the patient likely sees. This analysis quickly identifies whether the visual problem is ocular or neurologic in origin and allows eye practitioners to know the limits of the patient’s current vision.4
New patients who come to Bense Vision for a candidacy evaluation for refractive surgery, all undergo testing with the HD Analyzer. Patients who wear contact lenses or glasses are tested while wearing them. Those who meet the traditional requirements for refractive surgery and who have an OSI of less than 2 are generally considered good candidates as far as retinal image quality is concerned. An OSI higher than 2 indicates significant optical scatter advocating caution.
We do not recommend laser vision correction if the origin of the scatter (>2) is due to cataract formation. If poor tear quality or a decreased tear volume is the cause, we treat the problem accordingly and reassess the OSI in 2-4 weeks time.
Patients who are good candidates objectively still go through the consultation process. Knowing what level of vision patients are starting from, helps us to set appropriate expectations for the client. If their expectations are reasonable, we proceed with treatment.
To date, the most valuable use of the HD Analyzer at Bense Vision has been for patients who achieved good results with refractive surgery (LASIK/PRK) initially the 1st time around, but who are now experiencing a decline in their vision and seek further enhancement or touch-up surgery. They may have an acceptable 20/20 or 20/25+ corrected DVA in an examining lane, but still show a significantly increased OSI (for example >2). If the tear film and tear volume are satisfactory, the optical scatter is likely due to cataract formation. Here we recommend against further laser treatment and suggest considering cataract extraction if appropriate.
Improved patient outcomes
Patients enjoy seeing their HD score pre-operatively as well as the simulation of their retinal image. In our experience, the HD Analyzer has improved the selection of patients for refractive surgery and the consultation process. Knowing the optical limits of a clients’ vision is important in making the appropriate choice for their needs.
To summarize: Performing refractive surgery on individuals with significant light scatter (OSI) in hopes of correcting their visual problems will often lead to their disappointment. Our early experience with the HD Analyzer has been positive and has given us more confidence in selecting patients who could benefit from an initial or repeat laser treatment.
- Westheimer G, Liang J. Evaluating diffusion of light in the eye by objective means. Invest Ophthalmol Vis Sci. 1994;35(5):2652-2657.
- Westheimer G, Liang J. Influence of ocular light scatter on the eye’s optical performance. J Opt Soc Am A Opt Image Sci Vis. 1995;12(7):1417-1424.
- Gatinel D. Documenting the need for cataract surgery in eyes with good visual acuity. Cataract & Refractive Surgery Today Europe. May 2009;4(5):68-71.
- de Witt GC, Franssen L, Coppens JE, vandenBerg TJ. Simulating the stray light effects of cataract. J Cataract Refract Surg. 2006;32(2):294-300.
Thanks to Richard N. Baker, OD, in private practice at Slade & Baker Vision Center in Houston for his insight in the use of this HD Analyzer in his practice.