**Purpose**:
To evaluate the relationship between lens position parameters and intraocular pressure (IOP) reduction after cataract surgery in nonglaucomatous eyes with open angles.

**Methods**:
The main outcome of the prospective study was percentage of IOP change, which was calculated using the preoperative IOP and the IOP 4 months after cataract surgery in nonglaucomatous eyes with open angles. Lens position (LP), defined as anterior chamber depth (ACD) + 1/2 lens thickness (LT), was assessed preoperatively using parameters from optical biometry. Preoperative IOP, central corneal thickness, ACD, LT, axial length (AXL), and the ratio of preoperative IOP to ACD (PD ratio) were also evaluated as potential predictors of percentage of IOP change. The predictive values of the parameters we found to be associated with the primary outcome were compared.

**Results**:
Four months after cataract surgery, the average IOP reduction was 2.03 ± 2.42 mm Hg, a 12.74% reduction from the preoperative mean of 14.5 ± 3.05 mm Hg. Lens position was correlated with IOP reduction percentage after adjusting for confounders (*P* = 0.002). Higher preoperative IOP, shallower ACD, shorter AXL, and thicker LT were significantly associated with percentage of IOP decrease. Although not statistically significant, LP was a better predictor of percentage of IOP change compared to PD ratio, preoperative IOP, and ACD.

**Conclusions**:
The percentage of IOP reduction after cataract surgery in nonglaucomatous eyes with open angles is greater in more anteriorly positioned lenses. Lens position, which is convenient to compute by basic ocular biometric data, is an accessible predictor with considerable predictive value for postoperative IOP change.

^{1–9}There are greater IOP reductions after cataract extraction among patients with secondary and narrow-angle glaucoma compared to those with open-angle disease.

^{10,11}In eyes with narrow-angle glaucoma, the level of IOP lowering after cataract surgery is proportional to the resultant widening of the angle.

^{7,12,13}Thus, patients with the narrowest angles preoperatively may benefit the most from cataract extraction as a single procedure.

^{14}This may be due to greater changes in the anterior segment configuration after cataract surgery in eyes with shallower angles. An IOP reduction effect is also found in patients with open angles, although the mechanism remains poorly understood and the magnitude of this effect is highly variable and unpredictable. Cataract surgery is not currently part of the open-angle glaucoma treatment paradigm, largely due to difficulty in determining which open-angle patients will benefit from cataract surgery.

^{6,9,12}Shallower anterior chamber depth (ACD) has also been found to be a predictor of postoperative IOP reduction.

^{7,12,13}In 2005, Issa et al.

^{12}described a novel index for predicting the degree of IOP reduction based on the ratio of the preoperative IOP and ACD, which they termed the pressure-to-depth ratio (PD ratio). With the advent of anterior segment optical coherence tomography (AS-OCT), angle parameters such as angle opening distance (AOD) have also been reported to be associated with IOP reduction after phacoemulsification.

^{8,15–17}

^{16}demonstrated that lens thickness (LT) is associated with a reduction in IOP after cataract surgery in normal eyes.

^{16}A number of new lens position parameters assessed by AS-OCT have also been evaluated as potential predictors of IOP reduction. For example, lens vault (LV), defined as the perpendicular distance between the line joining the two scleral spurs and the anterior pole of the lens,

^{18}has been shown to be a preoperative predictor in angle widening and IOP reduction after cataract surgery in normal eyes.

^{17}In addition, the amount of IOP reduction is related to the anterior vault, which is defined as the maximum perpendicular distance between the posterior corneal surface to the horizontal line connecting the two scleral spurs. However, these parameters rely on AS-OCT scanning, which is not universally available to physicians, so more accessible and convenient predictors of postoperative IOP reduction are needed.

^{19}introduced lens position (LP)—defined as LP = ACD + 1/2 LT—and relative lens position (RLP)—defined as RLP = LP/AXL—as new characteristics of angle closure glaucoma.

^{19}Although subsequent studies did not reproduce this finding,

^{20–22}lens position and RLP could potentially be used to understand how the lens affects IOP in open angles. Lens position and RLP are similar ocular biometric parameters to LV and anterior vault in the sense that they are dependent on how anteriorly positioned the lens is relative to other structures in the anterior chamber. Lens position and RLP are more easily computed by optical ocular biometry, which is routine scanning for intraocular lens (IOL) power calculations prior to cataract surgery. Therefore, if these parameters show some significant association with IOP reduction after cataract surgery, they would be more accessible predictors.

*P*< 0.10 in the univariate regression model.

*z*transformation test to evaluate the difference between regression coefficients in multivariate models.

^{7–12,13,16,17}In order to compare our results with these previous studies, we also evaluated absolute IOP change as an outcome. In addition, we compared the absolute IOP change and percent IOP change as outcomes for predictors of interest. For all analyses, a

*P*value of less than 0.05 was considered statistically significant.

*B*= −0.013,

*P*= 0.002), AXL (

*B*= 0.024,

*P*= 0.028), ACD (

*B*= 0.146,

*P*= 0.007), and LT (

*B*= 0.073,

*P*= 0.043) were associated with percent IOP change after cataract surgery. Similar associations were found using general multiple linear regression models.

**Table 1**

*B*= 0.165,

*P*= 0.002). The RLP was not associated with percent IOP change after adjusting for sex, age, preoperative IOP, and LPI (

*B*= 0.231,

*P*= 0.849). Similar associations were found using general multiple linear regression models.

**Table 2**

*P*< 0.001). According to the

*r*

^{2}value, LP (

*r*

^{2}= 45.5%) was the best predictor of percentage change in IOP, followed by PD ratio, ACD, and preoperative IOP (

*r*

^{2}= 39.0%, 38.3%, and 18.5%, respectively). After adjusting for age, sex, LPI, and AXL, LP was still the parameter with the best predictive value for the outcome (standardized coefficient,

*β*= 0.457,

*P*< 0.001,

*r*= 0.717,

*r*

^{2}= 51.4%), followed by PD ratio (

*β*= −0.400,

*P*= 0.001,

*r*= 0.703,

*r*

^{2}= 49.4%), preoperative IOP (

*β*= −0.269,

*P*= 0.006,

*r*= 0.682,

*r*

^{2}= 46.5%), and ACD (

*β*= 0.335,

*P*= 0.018,

*r*= 0.670,

*r*

^{2}= 45.0%). However, using Fisher's

*z*transformation test, the result showed that there was no statistically significant difference between the coefficients of LP and other parameters in such a limited sample size (preoperative IOP,

*z*= 1.48,

*P*= 0.0694; ACD,

*z*= 0.98,

*P*= 0.1635; PD ratio,

*z*= 0.47,

*P*= 0.3192).

**Table 3**

**Figure 1**

**Figure 1**

**Figure 2**

**Figure 2**

**Figure 3**

**Figure 3**

**Figure 4**

**Figure 4**

*r*= −0.727,

*r*

^{2}= 52.9%,

*P*< 0.001) than LP (

*r*= 0.691,

*r*

^{2}= 47.8%,

*P*< 0.001). When percent IOP change was used as the outcome, LP was relatively better as a predictor (

*r*= 0.674,

*r*

^{2}= 45.4%,

*P*< 0.001) than PD ratio (

*r*= −0.625,

*r*

^{2}= 39.0%,

*P*< 0.001).

**Table 4**

^{23}prospectively demonstrated an average IOP reduction of 1.5 mm Hg at 3 years. In the years following, numerous other studies consistently showed approximately 2 mm Hg of reduction in IOP in patients undergoing routine extracapsular cataract extraction or clear cornea cataract extraction.

^{24–26}Patient-specific factors, including angle anatomy and lens factors, are likely important predictors of the expected postoperative reduction. However, elucidation of such factors has been suboptimal to date, and little is known about the magnitude and duration of the IOP reduction.

^{6,9,12}In addition, among patients with narrow-angle glaucoma, the level of IOP lowering after cataract surgery is proportional to the resultant widening of the angle.

^{7–10}We would therefore expect the smallest reduction in IOP among patients with open angles and “normal” IOP. However, as far as we are aware, there is still no good predictor for the expected amount of IOP reduction in this specific group of patients, and the mechanism for the effect remains poorly understood. In this study, we excluded patients with occludable angles and high IOP measurements in order to specifically analyze how cataract extraction affects IOP in this population.

^{12,15,16,25,26}For example, Tennen and Masket

^{25}reported a mean IOP reduction of 2.19 mm Hg (14.1%) at 1 year from baseline (mean 15.57 mm Hg), and Singleton et al.

^{26}reported a mean IOP reduction of 2.04 mm Hg (12.42%) at 6 months from baseline (mean 16.42 mm Hg).

^{26}The majority of prior studies evaluating the relationship between predictors and IOP reduction after cataract surgery did not subdivide their subjects into groups based on angle assessment. However, Huang et al.

^{8}used gonioscopy to separately study nonglaucomatous eyes with narrow and open angles, making their study most similar in design to the present study. They reported a mean IOP reduction of 1.95 mm Hg (13.39%) from baseline (mean, 14.68; range, 9–20 mm Hg) after uneventful cataract extraction in the open-angle group.

^{8}

^{6,9,15}However, this observation may be partly due to the statistical phenomenon known as regression to the mean caused by an inadequate number of baseline preoperative IOP measurements, especially among the patients with high-pressure IOPs.

^{1}In addition, eyes with higher baseline IOP measurements tend to have greater absolute IOP reductions compared to eyes with lower baseline IOP measurements. However, the percent change in IOP may be similar among eyes with different baseline IOP measurements; thus we used percent IOP change as our main outcome.

^{11}reported that the IOP reduction was weakly inversely related to preoperative ACD (

*r*= 20.455,

*r*

^{2}= 21%).

^{11}Yang et al.

^{16}reported that ACD was not associated with IOP decrease after adjusting for other parameters such as preoperative IOP, LT, and anterior chamber area change. Lens thickness was reported to be an effective predictor among nonglaucomatous patients.

^{16}Studies have shown that AXL was associated with postoperative IOP reduction in nonglaucomatous eyes.

^{27}By AS-OCT, angle parameters such as AOD and LV have also been reported to be strongly associated with IOP reduction after phacoemulsification.

^{8,16,17}

^{12}and strongly predicts IOP reduction after cataract surgery (

*r*= 0.852;

*r*

^{2}= 73%;

*P*< 0.01). The utility of the PD ratio has since been confirmed by Dooley et al.

^{15}with slightly weaker predictability (

*r*= 0.56;

*r*

^{2}= 34.1%;

*P*< 0.001). In our study, PD ratio was also shown to be an index with good predictive value for both absolute IOP change (following previous studies) and percent IOP change as outcomes (

*r*= −0.727;

*r*

^{2}= 56.9%;

*P*< 0.001 and

*r*= −0.625;

*r*

^{2}= 39.0%;

*P*< 0.001, respectively).

^{12,15}Using percent IOP change as the outcome in univariate and multivariate analyses, we found preoperative IOP, ACD, PD ratio, and LP to be parameters with good predictability (all with

*P*values < 0.05). However, LP showed the greatest predictive value (standardized coefficient,

*β*= 0.674 and 0.457,

*r*

^{2}= 45.5% and 51.4%, in the univariate and multivariate models, respectively) compared to preoperative IOP, ACD, and PD ratio (Table 3). Although there was no statistically significant difference between the predictive coefficients of the predictors using Fisher's

*z*transformation test, LP was thought to be a potentially stronger predictor in this group of patients. Further studies with larger sample sizes are needed to assess this relationship.

^{8,16,17}Third, because ocular biometry measurement is required before any cataract surgery for IOL power calculation, LP is a convenient and simple parameter to obtain and calculate. Finally, the diurnal fluctuation in IOP has been well described, and this variation makes other predictors, such as preoperative IOP and PD ratio, less reliable. Lens position is computed by ACD and LT, which are more stable parameters and may thus be more accurate.

^{7–12,13,16,17}We compared absolute IOP change and percent IOP change as outcome variables and found that they were associated with different predictor variables. When using percent IOP change as the outcome, LP was the best predictor (

*r*= 0.674;

*r*

^{2}= 45.5%;

*P*< 0.001), followed by PD ratio (

*r*= −0.625;

*r*

^{2}= 39.0%;

*P*< 0.001). However, when using absolute IOP change as outcome, PD ratio showed better predictability (

*r*= 0.727;

*r*

^{2}= 52.9%;

*P*< 0.001) than LP (

*r*= 0.691;

*r*

^{2}= 47.8%;

*P*< 0.001).

^{28}the posterior chamber–anterior chamber pressure gradient is inversely proportional to the height of the iris-lens canal. When the lens is more anteriorly positioned and the height is decreased, the higher pressure gradient will cause a situation similar to pupillary block. Such a partial blockage may be relieved with lens extraction, which could be a potential mechanism of IOP reduction after cataract surgery for eyes with open-angle configuration.

*r*

^{2}becomes problematic in linear mixed-effects regression models. Thus, we had a reduced sample size for that analysis. Fourth, the follow-up time was only 4 months, and it is possible that the IOP reductions we found after cataract surgery may change over time, although prior studies have found that IOP reduction after cataract surgery is typically long-lasting. Finally, we selected only nonglaucomatous patients with open angles and relatively low IOP. Therefore, a rather small absolute IOP reduction was noted after cataract surgery. Clinically, glaucomatous patients are those who require reductions in IOP, so future studies will show whether similar relationships and IOP reductions are observed among glaucomatous eyes.

**C.-H. Hsu**, None;

**C.L. Kakigi**, None;

**S.-C. Lin**, None;

**Y.-H. Wang**, None;

**T. Porco**, None;

**S.C. Lin**, None

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