lS
Hwhite-to-white" right?
K. Buol Heslin, M.D. New York, New York
Stable fixation without pseudophacodonesis or uveal irritation has long been the goal of implant surgeons. The paths of development have led Cornelius Binkhorst to the posterior capsule and others to the scleral spur. Credit for the development of anterior chamber implants rests with Mr. Peter Choyce, who believed that the reason some eyes with early anterior chamber lens designs did well and others did not was intimately related to lens design. Advances in lens design, quality control and manufacturing techniques continue to corroborate this belief. However, proper placement and length of the implant are also critical, raising the question: given the variablity of most anatomic parameters, is the dictum of externally measuring the horizontal corneal "white-to-white" diameter and adding one millimeter consistently accurate in predicting the true internal anterior chamber diameter? Or, in an era of microsurgical precision, are we being seduced by the apparent simplicity of this rule into placing inappropriate sizes of implants into the one critical area of the eye we can't directly visualize at the time of implantation? Does the performance of this familiar measurement insure that gonioscopy will later show the foot of the implant to be in the proper position and of the correct length? (Gonioscopy on the table at
the completion of the procedure can be performed to check placement. [Fig. I]) To evaluate the relationship of external whiteto-white measurements to actual internal measurements of anterior chamber diameter, we dissected cadaver eyes. The corneoscleral cap was dissected free of uveal tissue, starting posterior to the muscle insertions and moving anteriorly (Fig. 2). Diameter
Fig. 2 (Heslin). Removal of corneoscleral cap to show the scleral spur and Schwalbe's line.
Fig. I (Heslin). Gonioscopic photo of a Kelman anterior chamber implant.
Presented at the U.S. Intraocular Lens Symposium in Los Angeles, March 1978. 50
measurements were taken of the exposed scleral spur, which was confirmed to be a circle internally. Data from twenty eyes show significant variability between what was found after dissection and what was predicted by white-to white plus one millimeter (Table I). The skew is towards a larger internal diameter than predicted. We then made similar measurements at surgery. External white-to-white diameter was measured and the cataract removed. A dip stick (an irrigating spatula with O.5-mm gradations marked on its surface) was advanced across the anterior chamber to
AM INTRA-OCULAR IMPLANT SOC J-VOL. V, JANUARY 1979
the inferior angle until the eye was just moved as resistance was met (Fig. 3). A reading was then taken at that point approximating the center of the pupillary aperture. This distance was doubled to obtain the direct internal measurement of anterior chamber diameter. In fifty consecutive cases, significant variability was found, again skewed towards underestimation of actual anterior chamber size (Table 2). Measurements were not exact: there is some slight error introduced in the dip stick measurement, due to parallax and estimation. Table 2. Variation of dip stick measurements from white-towhite plus one estimates of anterior chamber diameter.
Number of Cases
Variation (mm) -1.00 -0.75
I
-0.50
3
-0.20 -0.10
20
0.00
3
+0.20
I
+0.30
9
+0.50 +0.60
Fig. 3 (Heslin). Kelman dip stick.
2
+0.70
5
+ 1.00 +1.10
Table 1. Variation of direct cadaver measurements from whiteto-white plus one estimates of anterior chamber diameter.
Number of Cases
-0.10 0.00
1
+0.10
2
+0.20
2
+0.40
3
+0.50 +0.70 +0.80 +1.20
20
50
Variation (mm) -0.25
7
+1.50
It is our opinion that many of the problems reported with anterior chamber implants are related to improper lens length and/ or lens placement. Our experience with the Kelman lens indicates that a correctly sized and placed lens can give excellent results. However,lens lengths based on "white-towhite plus one" estimates are often inaccurate. In our studies, more than 50% of both the 20-case sample and the 50-case sample showed a discrepancy between white-to-white plus one estimates and direct measurements of the anterior chamber. We therefore feel that actual anterior chamber measurements and verification of implant postion can and must be performed at the time of surgery.
AM INTRA-OCULAR IMPLANT SOC J-VOL. V, JANUARY 1979
51
Hwhite-to-white" right?
K. Buol Heslin, M.D. New York, New York
Stable fixation without pseudophacodonesis or uveal irritation has long been the goal of implant surgeons. The paths of development have led Cornelius Binkhorst to the posterior capsule and others to the scleral spur. Credit for the development of anterior chamber implants rests with Mr. Peter Choyce, who believed that the reason some eyes with early anterior chamber lens designs did well and others did not was intimately related to lens design. Advances in lens design, quality control and manufacturing techniques continue to corroborate this belief. However, proper placement and length of the implant are also critical, raising the question: given the variablity of most anatomic parameters, is the dictum of externally measuring the horizontal corneal "white-to-white" diameter and adding one millimeter consistently accurate in predicting the true internal anterior chamber diameter? Or, in an era of microsurgical precision, are we being seduced by the apparent simplicity of this rule into placing inappropriate sizes of implants into the one critical area of the eye we can't directly visualize at the time of implantation? Does the performance of this familiar measurement insure that gonioscopy will later show the foot of the implant to be in the proper position and of the correct length? (Gonioscopy on the table at
the completion of the procedure can be performed to check placement. [Fig. I]) To evaluate the relationship of external whiteto-white measurements to actual internal measurements of anterior chamber diameter, we dissected cadaver eyes. The corneoscleral cap was dissected free of uveal tissue, starting posterior to the muscle insertions and moving anteriorly (Fig. 2). Diameter
Fig. 2 (Heslin). Removal of corneoscleral cap to show the scleral spur and Schwalbe's line.
Fig. I (Heslin). Gonioscopic photo of a Kelman anterior chamber implant.
Presented at the U.S. Intraocular Lens Symposium in Los Angeles, March 1978. 50
measurements were taken of the exposed scleral spur, which was confirmed to be a circle internally. Data from twenty eyes show significant variability between what was found after dissection and what was predicted by white-to white plus one millimeter (Table I). The skew is towards a larger internal diameter than predicted. We then made similar measurements at surgery. External white-to-white diameter was measured and the cataract removed. A dip stick (an irrigating spatula with O.5-mm gradations marked on its surface) was advanced across the anterior chamber to
AM INTRA-OCULAR IMPLANT SOC J-VOL. V, JANUARY 1979
the inferior angle until the eye was just moved as resistance was met (Fig. 3). A reading was then taken at that point approximating the center of the pupillary aperture. This distance was doubled to obtain the direct internal measurement of anterior chamber diameter. In fifty consecutive cases, significant variability was found, again skewed towards underestimation of actual anterior chamber size (Table 2). Measurements were not exact: there is some slight error introduced in the dip stick measurement, due to parallax and estimation. Table 2. Variation of dip stick measurements from white-towhite plus one estimates of anterior chamber diameter.
Number of Cases
Variation (mm) -1.00 -0.75
I
-0.50
3
-0.20 -0.10
20
0.00
3
+0.20
I
+0.30
9
+0.50 +0.60
Fig. 3 (Heslin). Kelman dip stick.
2
+0.70
5
+ 1.00 +1.10
Table 1. Variation of direct cadaver measurements from whiteto-white plus one estimates of anterior chamber diameter.
Number of Cases
-0.10 0.00
1
+0.10
2
+0.20
2
+0.40
3
+0.50 +0.70 +0.80 +1.20
20
50
Variation (mm) -0.25
7
+1.50
It is our opinion that many of the problems reported with anterior chamber implants are related to improper lens length and/ or lens placement. Our experience with the Kelman lens indicates that a correctly sized and placed lens can give excellent results. However,lens lengths based on "white-towhite plus one" estimates are often inaccurate. In our studies, more than 50% of both the 20-case sample and the 50-case sample showed a discrepancy between white-to-white plus one estimates and direct measurements of the anterior chamber. We therefore feel that actual anterior chamber measurements and verification of implant postion can and must be performed at the time of surgery.
AM INTRA-OCULAR IMPLANT SOC J-VOL. V, JANUARY 1979
51
