Mitchell P. Weikert, MD, is assistant professor of Ophthalmology at Baylor College of Medicine.
Baylor College of Medicine assistant professor Mitchell P. Weikert, MD, in collaboration with Christian Hester, MD, covered the topic of ophthalmic photography and videography.
Fortunately, smartphones offer a cheaper and more flexible alternative, and Dr. Weikert
recommends a minimum of 5 megapixels, but adds that "really, the more the better.
also pointed out that a telephone contract isn't necessary to use a phone's camera as long as you have wi-fi connectivity.
ADAPTORS & APPS
uses a slit lamp adaptor from EyePhotoDoc (Haag-Streit BQ and Advanced I-Illuminator), which goes directly over the slit lamp ocular.
It has a little post so you can put it on the left ocular and it stabilizes it so it sits nice and horizontal (or vertical, but you get a little bit more real estate for your efforts in landscape mode).
shared that, with a light, it costs about $500, which, in the grand scheme of ophthalmic photography, is not that expensive.
The adaptor without the light costs about $350 and is available for iPhones as well as the iPad and iPad mini.
He pointed out that Zarf Enterprises and OculoCAM also have adaptors for iPhones and Android devices and noted that if you're more of a do-it-yourselfer, you can create your own adaptor with the cap from a Gillette shaving foam travel pack container, the rubber disc from an empty CD stack box and rubber-based adhesive.
According to Dr. Weikert
, ProCamera has a versatile, but inexpensive photography app.
"The advantage of the ProCamera app," he
says, "is that it allows you to separate your exposure and focus and move them independently.
also made a point about illumination, noting that, "if you just use a slit lamp and you put the broad beam on, you can't light the whole area of the eye.
It's about 8mm maximum.
explained that if you put a diffuser on and flip it up, you can get broader illumination.
added that a transilluminator works really well, explaining that you can hang it on the dial for the slit lamp or have a scribe or tech hold it for you.
Or, you can use a clip-on light source.
transilluminator is from EyePhotoDoc, and he
says it has a blue light and a white light, allowing him to also do some fluorescein photographs.
Additionally, the instrument also has a little rheostat, so he
can vary the illumination.
THE VALUE OF VIDEO
Before ending his
talk, Dr. Weikert
commented that taking a slit lamp video is helpful-especially in the operating room (OR).
"We all know that just seeing a static image is not always as valuable as seeing motion and being able to maneuver the light," he
The ProCamera app is capable of shooting video as well as taking still photographs, and you can do that with the app in the iPhone as well.
The Magnifi iPhone photoadapter case is useful in the OR, and he
says it fits well on a Zeiss scope with f125 oculars.
iPhone slit lamp photography and videography is a nice, inexpensive, portable and efficient alternative for ophthalmic photography, Dr. Weikert
added that physicians can bill for it just like any ophthalmic photography, and said it can be used to review surgical videos, etc. "It may be applicable in telemedicine, as you could FaceTime with it," he
"And it might be useful for screening clinics that are manned by nonMDs.
Keep HIPAA in mind, Dr. Weikert
cautioned, and don't record any images with identifying information (e.g., facial picture, date of birth).
You can use the medical record number to reference images.
final advice: don't underestimate using the zoom feature on your iPhone when it's on the eyepiece.
"Just remember, you're doing a digital zoom- not an optical zoom, so you may lose a few pixels," he
These days, patients expect painless, complication-free surgery at minimal cost and with instant excellent uncorrected visual acuity and minimal downtime," Mitchell P. Weikert, MD, began his second presentation.
submitted, good, accurate intraocular lens (IOL) calculations are absolutely necessary for meeting patients' expectations.
said that when many ophthalmologists consider IOL calculations, the formula is sort of a big black box.
"We take measurements and enter them into the calculator, which spits out the lens power that we're supposed to implant in our patient," he
believes it's valuable to look into this black box because it contains other black boxes that have limitations and make assumptions that can effect our results.
But first, Dr. Weikert
discussed IOL power calculation formulas.
As Dr. Weikert
noted, basically, you have light coming into the first surface, which creates an image that becomes the object for the second surface, which creates an image that becomes the object for the third surface, which hopefully is on the retina.
"That gives us the vergence formula," he
added, "which is the basis for the most common IOL calculation formulas used today."
noted that the effective lens position (ELP), true corneal power, index of refraction, and the axial length are all other black boxes, which he
went on to discuss.
THE "OTHER" BLACK BOXES
ELP. This is the estimate of the position where the IOL will sit in the eye.
It's not a physical distance; it's the effective refractive plane of the lens.
noted that ELP changes with axial length, so this black box has a lot of potential for improvement.
The following formulas rely on ELP.
explained that the Holladay 1 formula is based on corneal height and increases the base of the cornea proportionally with axial lengths, according to average axial lengths and average angleto-angle distances.
added that it also includes the surgeon factor (an optimization constant), which is the difference between the corneal height and the effective IOL plane.
explained that the Holladay 1 has a very shallow linear relationship, as ELP increases with axial length.
then pointed out that one source of error lies in the fact that although ACD will increase as the eye gets bigger and the axial link increases, the surgeon factor is a constant number and thus stays the same.
The SRK/T formula uses the same model, Dr. Weikert
"It changes how it increases the base of the cornea depending on the axial length," he
"The SRK/T formula has something called an offset, which is basically the same as the surgeon factor.
The SRK/T offset can be calculated from the IOL's A constant, so you can directly convert an A constant into a surgeon factor for ELP."
finished the roundup of formulas with the Hoffer Q, an empiric derivation dependent on axial length and corneal power to create a personalized A constant as its optimization factor, and the Haigis, another empiric derivation, that is a linear model that depends on axial length and preoperative ACD rather than on corneal power.
"All of these ELP formulas are different," Dr. Weikert
explained further that a flatter corneal is going to measure a larger area, and a steeper cornea is going to measure a smaller area.
"And we implant those results back into the same formulas," he
"Most devices that we typically use still measure the anterior surface only and reduce the index of refraction to account for the negative value of the posterior surface.
And they assume a fixed frontto-back curvature ratio for the cornea.
Corneal power also varies with pupil size," he
Index of refraction.
The cornea is a prolate surface, steeper in the center, flatter in the periphery.
"When you have incident light coming in, overall the effect is to have positive spherical aberration of the cornea with peripheral rays are refracted more strongly than paraxial rays, so you end up with a little overall myopic shift as you sample larger areas of the cornea," Dr. Weikert
In the United States, ophthalmologists use 1.3375 for our keratometers, which simply models the cornea as the sum of two refractive surfaces with a curvature ratio equal to the Gullstrand ratio.
In Europe, they use 1.3315 because their model factors in the corneal thickness.
Newer devices can measure the front and back cornea, but they rely on measuring elevation, which is more difficult to do because you need much higher resolution to extract curvature information.
This is one of the most critical steps in calculating IOL power, according to Dr. Weikert
"Small errors can have large effects on our postoperative results and errors about 0.1 mm can have 0.27D+ of error in the spectacle plane," he
advised the doctors in the audience to remember that these optical biometers are calibrated to ultrasound, which is calibrated to an average population of patients, and pointed this out as another source of error.
explained, "You're taking a direct measurement and changing it to agree with a bunch of other patients who are going to have variation in and of themselves."
This is the final black box Dr. Weikert
The refractive effect of an IOL depends o