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Intraoperative Autorefraction: Avoiding Intraocular Lens Power Surprises
relationship is widely agreed to be causal in nature. Steinert and Wasson also believe that chronic irritation of the iris (i.e., iritis) by incarcerated vitreous in the surgical wound resulted in CME in their patients. Yet if inflammation of the anterior uvea is the problem, why is one of the standard treatments for iritis or iridocyclitis, namely cycloplegia, generally not prescribed? One of us (R.J.M.) has long been a proponent of cycloplegia (e.g., scopolamine 0.25% twice a day) for the treatment of CME or as a prophylactic in high-risk situations (following aphakic penetrating keratoplasty, secondary intraocular lens implantation, etc.). We have, therefore, collectively witnessed scores of patients who have failed to resolve their CME with topical and systemic steroids and indomethacin who have responded dramatically to the addition of topical scopolamine to their regimen. Proof of our observation that cycloplegia can be extremely beneficial in the medical treatment of CME would require a prospective double-masked study, but until such is available we would urge our colleagues to consider the addition of cycloplegia to the medical regimen of patients with postoperative CME. Richard J. Mackool, M.D. Marc A. Sirota, M.D. Jan Arnett, M.D. Patricia A. Feller, M.D. P. Jeffrey Colquhoun, M.D. Astoria, New York
INTRAOPERATIVE AUTOREFRACTION: AVOIDING INTRAOCULAR LENS POWER SURPRISES To the Editor: In an attempt to eliminate the 5% or so of cases of inappropriate intraocular lens (IOL) power, 1 new IOL formulas (theoretical and regression) continue to be developed.2,3 The most recent, the Holladay formula, is actually a three-part system. 4 It identifies measurements of axial length or keratometry that are likely errors, suggesting repeat measurements to confirm these important sources of postoperative refractive disappointment. In addition, it develops a "surgeon factor" to compensate for constant bias. Finally, as the third part of the system, it uses an improved theoretical formula that more accurately predicts the effective position of the implanted IOL based not only on the axial length but also on the average corneal curvature. Although from our personal experience it seems that the Holladay formula represents an improvement, we are concerned about the relative inaccuracies of all IOL power formulas when dealing with short and long eyes J CATARACT
and especially when the potential for postoperative anisometropia exists. Thus, when dealing with unilateral cataracts with contralateral large ametropias we felt the need to know more certainly whether the postoperative refractive error was going to be the predicted power. In our community, we are aware of malpractice claims based upon postoperative anisometropia. Therefore, we developed an intraoperative method of refractive error determination. Our ultimate goal is to confirm intraoperatively the postoperative refractive error and, when unacceptable, to perform IOL exchange at that time rather than after the initial surgery. To assess the potential for this system, we first determined the correlation between intraoperative refractive error and stabilized postoperative refractive error. We adapted a commercially available objective autorefractor (Canon) for intraoperative use. We removed the active measuring component and mounted it on an arm with XYZ control. Following insertion of the posterior chamber lens into the capsular bag and after the wound was closed, we performed automated refraction (Figure 1). We avoided pooling of irrigating fluid on the corneal surface. In Study I, we were careful to reform the anterior chamber to provide normal intraocular pressure (lOP) as judged by external pressure. In Study II, we used a different parameter to judge the adequacy of reformation. In this study we used the appearance of tension lines in the posterior capsule after in-the-bag implantation. We reformed just enough to make the lines appear. Typically, these eyes were still quite soft. A superior rectus stay suture was used to help align the eye with the autorefractor. These measurements were taken and averaged. Six to
Fig. l.
(O'Donnell) Intraoperative photograph demonstrating the prototype used to perform the intraoperative autorefraction. Notice the undesirable bulk and proximity of the measuring device to the eye.
REFRACT SURG-VOL 15, SEPTEMBER 1989
597
nine weeks postoperatively, we performed subjective manifest refraction without knowledge of the intraoperative measurements. The results of these two studies are tabulated (Tables 1 and 2). This pilot study suggests that intraoperative autorefraction could be a useful adjunct in selected cases. The major source of intraoperative error seems to be the variable pseudophakic anterior chamber depth determined by how well pressurized the globe is at the time of the intraoperative refraction. In Study I, when we tried to "normalize" lOP, we were surprised to see consistently hypermetropic errors intraoperatively. We deduced that "normalized" lOP in these soft eyes was overdeepening the pseudophakic anterior chamber. In Study II, we used as our endpoint the anterior chamber depth which just caused the appearance of the tension lines in the posterior capsule and we obtained much more encouraging results. Obviously, this end-
point would not be helpful in sulcus or asymmetric IOL implantation. Another technical drawback to intraoperative autorefraction is the need to refine our prototype. Specifically, it would be helpful to have a fiberoptic system attached to the operating scope with all hardware remote from the operating field and a longer working distance. Finally, we also believe the system could be used to allow more accurate implant power prediction rather than just confirmation. Since dialing a posterior chamber lens out of the capsular bag and exchanging it for one with a more appropriate power is not atraumatic or risk free, even if done during the initial surgery, we believe the use of intraoperative autorefraction of the aphakic eye uust before insertion of the posterior chamber lens) with intraoperative ultrasound measurement (or optical measurement) of the posterior capsule position might improve the accuracy of power prediction.
Table 1. Study I: Intraoperative autorefraction with "normalized'' intraocular pressure.
Francis E. O'Donnell, Jr., M.D. Byron A. Santos, M.D. Dan Walsh, C.O.T.
Intraoperative Autorefraction *
Postoperative Manifest Refraction*t
1
+2.25
-0.75
2
+2.00
+0.25
Case Number
3
+5.50
+ 1.25
4
+5.00
-0.50
5
+2.50
-1.50
St. Louis, Missouri
REFERENCES l. Holladay JT, PragerTC, Ruiz RS, Lewis JW, et al: Improving the predictability of intraocular lens power calculation. Arch Ophthalmol 104:539-541, 1986 2. Thompson JT, Maumenee AE, Baker CL: A new posterior chamber intraocular lens formula for axial myopia. Ophthalmology 91:484-488, 1984 3. Donzis P, Kastle PR, Gordon RA: An intraocular lens formula for short, normal, and long eyes. CLAO I 11:95-98, 1985 4. Holladay JT, Prager TC, Chandler TY, Musgrove KH, et al: A three-part system for refining intraocular lens power calculations. I Cataract Refract Surg 14:17-24, 1988
*Spherical equivalent tPostoperative refraction done six to nine weeks after surgery
Table 2. Study II: Intraoperative autorefraction with intraocular pressure endpoint determined by appearance of tension lines in the posterior capsule.
Case Number
Intraoperative Autorefraction*
Postoperative Manifest Refraction*t
1
+1.50
+ 1.00
2
+2.25
+ 1.50
3
+2.00
+0.50
4
-0.25
-0.25
5
+ 1.25
+0.50
6
+ 1.50
+ 1.00
7
+ 1.00
+ 1.00
8
-0.25
+0.50
9
-1.25
-0.50
10
+ 1.00
+0.75
*Spherical equivalent tPostoperative refraction done six to nine weeks after surgery 598
J CATARACT REFRACT
INTRACAMERAL FAILURE OF POLYPROPYLENE To the Editor: Currently, polypropylene is ubiquitously used in ophthalmology 1 as a haptic loop material for posterior chamber intraocular lenses (IOLs). In the past, it has also been used as a haptic loop material for both anterior chamber and iris-fixated IOLs. When irisfixated IOLs were in vogue, polypropylene was widely used as a suture material, replacing nylon 2 and stainless steel. 3 I describe the intracameral failure of polypropylene in two cases, the first a 5-0 haptic loop on a Binkhorst iris-clip type IOL and the second a 10-0 iris-fixation suture on a Worst Medallion IOL.
Case 1 The patient, then 76 years old, presented on May 1, 1973, with chronic angle closure glaucoma, right eye, SURG-VOL 15, SEPTEMBER 1989
INTRAOPERATIVE AUTOREFRACTION: AVOIDING INTRAOCULAR LENS POWER SURPRISES To the Editor: In an attempt to eliminate the 5% or so of cases of inappropriate intraocular lens (IOL) power, 1 new IOL formulas (theoretical and regression) continue to be developed.2,3 The most recent, the Holladay formula, is actually a three-part system. 4 It identifies measurements of axial length or keratometry that are likely errors, suggesting repeat measurements to confirm these important sources of postoperative refractive disappointment. In addition, it develops a "surgeon factor" to compensate for constant bias. Finally, as the third part of the system, it uses an improved theoretical formula that more accurately predicts the effective position of the implanted IOL based not only on the axial length but also on the average corneal curvature. Although from our personal experience it seems that the Holladay formula represents an improvement, we are concerned about the relative inaccuracies of all IOL power formulas when dealing with short and long eyes J CATARACT
and especially when the potential for postoperative anisometropia exists. Thus, when dealing with unilateral cataracts with contralateral large ametropias we felt the need to know more certainly whether the postoperative refractive error was going to be the predicted power. In our community, we are aware of malpractice claims based upon postoperative anisometropia. Therefore, we developed an intraoperative method of refractive error determination. Our ultimate goal is to confirm intraoperatively the postoperative refractive error and, when unacceptable, to perform IOL exchange at that time rather than after the initial surgery. To assess the potential for this system, we first determined the correlation between intraoperative refractive error and stabilized postoperative refractive error. We adapted a commercially available objective autorefractor (Canon) for intraoperative use. We removed the active measuring component and mounted it on an arm with XYZ control. Following insertion of the posterior chamber lens into the capsular bag and after the wound was closed, we performed automated refraction (Figure 1). We avoided pooling of irrigating fluid on the corneal surface. In Study I, we were careful to reform the anterior chamber to provide normal intraocular pressure (lOP) as judged by external pressure. In Study II, we used a different parameter to judge the adequacy of reformation. In this study we used the appearance of tension lines in the posterior capsule after in-the-bag implantation. We reformed just enough to make the lines appear. Typically, these eyes were still quite soft. A superior rectus stay suture was used to help align the eye with the autorefractor. These measurements were taken and averaged. Six to
Fig. l.
(O'Donnell) Intraoperative photograph demonstrating the prototype used to perform the intraoperative autorefraction. Notice the undesirable bulk and proximity of the measuring device to the eye.
REFRACT SURG-VOL 15, SEPTEMBER 1989
597
nine weeks postoperatively, we performed subjective manifest refraction without knowledge of the intraoperative measurements. The results of these two studies are tabulated (Tables 1 and 2). This pilot study suggests that intraoperative autorefraction could be a useful adjunct in selected cases. The major source of intraoperative error seems to be the variable pseudophakic anterior chamber depth determined by how well pressurized the globe is at the time of the intraoperative refraction. In Study I, when we tried to "normalize" lOP, we were surprised to see consistently hypermetropic errors intraoperatively. We deduced that "normalized" lOP in these soft eyes was overdeepening the pseudophakic anterior chamber. In Study II, we used as our endpoint the anterior chamber depth which just caused the appearance of the tension lines in the posterior capsule and we obtained much more encouraging results. Obviously, this end-
point would not be helpful in sulcus or asymmetric IOL implantation. Another technical drawback to intraoperative autorefraction is the need to refine our prototype. Specifically, it would be helpful to have a fiberoptic system attached to the operating scope with all hardware remote from the operating field and a longer working distance. Finally, we also believe the system could be used to allow more accurate implant power prediction rather than just confirmation. Since dialing a posterior chamber lens out of the capsular bag and exchanging it for one with a more appropriate power is not atraumatic or risk free, even if done during the initial surgery, we believe the use of intraoperative autorefraction of the aphakic eye uust before insertion of the posterior chamber lens) with intraoperative ultrasound measurement (or optical measurement) of the posterior capsule position might improve the accuracy of power prediction.
Table 1. Study I: Intraoperative autorefraction with "normalized'' intraocular pressure.
Francis E. O'Donnell, Jr., M.D. Byron A. Santos, M.D. Dan Walsh, C.O.T.
Intraoperative Autorefraction *
Postoperative Manifest Refraction*t
1
+2.25
-0.75
2
+2.00
+0.25
Case Number
3
+5.50
+ 1.25
4
+5.00
-0.50
5
+2.50
-1.50
St. Louis, Missouri
REFERENCES l. Holladay JT, PragerTC, Ruiz RS, Lewis JW, et al: Improving the predictability of intraocular lens power calculation. Arch Ophthalmol 104:539-541, 1986 2. Thompson JT, Maumenee AE, Baker CL: A new posterior chamber intraocular lens formula for axial myopia. Ophthalmology 91:484-488, 1984 3. Donzis P, Kastle PR, Gordon RA: An intraocular lens formula for short, normal, and long eyes. CLAO I 11:95-98, 1985 4. Holladay JT, Prager TC, Chandler TY, Musgrove KH, et al: A three-part system for refining intraocular lens power calculations. I Cataract Refract Surg 14:17-24, 1988
*Spherical equivalent tPostoperative refraction done six to nine weeks after surgery
Table 2. Study II: Intraoperative autorefraction with intraocular pressure endpoint determined by appearance of tension lines in the posterior capsule.
Case Number
Intraoperative Autorefraction*
Postoperative Manifest Refraction*t
1
+1.50
+ 1.00
2
+2.25
+ 1.50
3
+2.00
+0.50
4
-0.25
-0.25
5
+ 1.25
+0.50
6
+ 1.50
+ 1.00
7
+ 1.00
+ 1.00
8
-0.25
+0.50
9
-1.25
-0.50
10
+ 1.00
+0.75
*Spherical equivalent tPostoperative refraction done six to nine weeks after surgery 598
J CATARACT REFRACT
INTRACAMERAL FAILURE OF POLYPROPYLENE To the Editor: Currently, polypropylene is ubiquitously used in ophthalmology 1 as a haptic loop material for posterior chamber intraocular lenses (IOLs). In the past, it has also been used as a haptic loop material for both anterior chamber and iris-fixated IOLs. When irisfixated IOLs were in vogue, polypropylene was widely used as a suture material, replacing nylon 2 and stainless steel. 3 I describe the intracameral failure of polypropylene in two cases, the first a 5-0 haptic loop on a Binkhorst iris-clip type IOL and the second a 10-0 iris-fixation suture on a Worst Medallion IOL.
Case 1 The patient, then 76 years old, presented on May 1, 1973, with chronic angle closure glaucoma, right eye, SURG-VOL 15, SEPTEMBER 1989