|Year : 2012 | Volume
| Issue : 4 | Page : 117-121
Accommodation in pseudophakic eyes
University of Teesside, UK; University of Hawaii, Honolulu, HI, USA
|Date of Web Publication||7-Dec-2012|
55 South Kukui Street, Honolulu, HI
Source of Support: None, Conflict of Interest: None
Purpose: Today, many patients who have undergone cataract surgery want to enjoy good non-spectacle corrected distant vision and nonspectacle corrected near vision with glasses independence. According to the literature, the implantation of an accommodative intraocular lens (AIOLs) can achieve the level of vision after cataract surgery. However, there is a debate regarding the true accommodative capability of the AIOLs (i.e., whether the IOLs can move forward when attempting to accommodate like the natural crystalline lens of a phakic eye). This review aims to answer the following questions: (1) Can pseudo-phakic eye accommodate? (2) If pseudophakic eyes can accommodate, how long does this accommodation last? (3) Is there pseudoaccommodation?
Methods: This is a systematic review of randomized and nonrandomized controlled trials that have compared different IOLs in accommodation using subjective and objective methods of testing accommodation. All peer reviewed randomized and nonrandomized controlled trials that compared different IOLs in accommodation were included.
Results: There was evidence of pseudophakic accommodation up to 12 months postoperatively for AIOLs (mostly 1CU): subjective accommodation [95% confidence interval (CI), 0.36–0.98], objective optic shift (95% CI, 0.12–0.76). However, accommodation decreased at 12 months postoperatively (95% CI, 0.55–1.00). In addition, several papers have reported evidence of pseudoaccommodation.
Conclusion: There is pseudophakic accommodation up to 1 year post cataract surgery, mostly 1CU AIOL. Pseudoaccommodation may coexist.
Keywords: accommodation, cataract surgery, intraocular lens implant, intraocular lens optic shift, pseudoaccommodation
|How to cite this article:|
Chen M. Accommodation in pseudophakic eyes. Taiwan J Ophthalmol 2012;2:117-21
| 1. Introduction|| |
The ability of accommodation in accommodative intraocular lens (AIOLs) has been demonstrated in multiple studies by objective and subjective methods.
Accommodation involves three mechanisms: contraction of the ciliary muscle, convergence of the eye, and constriction of the pupil.
Accommodation is a necessary physiological mechanism that enables the human eye to see things up close.
Pseudophakic accommodation refers to the accommodation of an eye when its crystal lens has been replaced byan intraocular lens (IOL) during cataract surgery. This change in the power of the eye may be accomplished by a forward movement the intraocular lens upon contraction of the ciliary muscle; at that point, convergence of the eye, and constriction of the pupil are actively occurring.
Some eyes that were corrected for distant vision with a monofocal IOL (nonaccommodative) also achieved a high level of near visual acuity with distance correction after cataract surgery. This raises the question, “Is there a pseudoaccommodative effect?” Pseudoaccommodation is not a true accommodation of pseudophakic eyes; rather, it is the ability of the eyes to allow near vision, possibly due to various aberrations in the optical system of the eyes. These optical aberrations are independent of the ciliary muscle’s contraction.,,,,,
The factors that allow for pseudoaccommodation include the depth of field, which may be affected by pupil size, ptotic eyelids, and squinting. Pseudoaccommodation may also involve residual myopic astigmatism and polychromatic and monochromatic higher-order aberrations of the eye (e.g., spherical aberration and coma). Therefore, subjective tests alone cannot easily distinguish the accommodative and pseudoaccommodative components that together allow near vision.
In the control trials analyzed in this review, the following methods were used to measure accommodation: objective techniques (PlusOptix PowerRefractor videorefractometry, streak retinoscopy) and subjective techniques [subjective near point (push-up test, accommodometer), defocusing]; static with pharmacologic stimulation after Pilocarpine 2% eye drops directly (conventional refractometry); indirectly (change in the anterior chamber depth with Zeiss IOLMaster).,,,, Objective measurements of accommodation are necessary to evaluate commercially available AIOLs in a scientific manner. The objective parameters include measurements of changes in the anterior chamber depth as well as measurements of autorefraction.
| 2. Methods|| |
The meta-analysis was not considered because the trials were not all homogeneous. In order to draw some conclusion for a relative merit of this topic, a systematic review of the best-quality data is necessary. Peer-reviewed randomized and nonrandomized control trials were selected because of their validity and the objective outcomes.
2.1. Inclusion criteria
2.1.1. Types of studies
All peer-reviewed randomized and nonrandomized controlled trials that compared different IOLs in the context of accommodation were included.
2.1.2. Types ofparticipants
The participants were individuals aged 19 years or older who had undergone cataract surgery and received intraocular lens implants.
2.2. Exclusion criteria
Congenital cataract patients were excluded from the study due to potential differences in the treatment plans.
2.3. Search methods: electronic search
The Cochrane Central Register of Controlled Trials (Central) on the Cochrane Library, MEDILINE, Journal of Cataract and Refractive Surgery, and PubMed from 1966 to 2010 were searched. Seventeen papers were identified as meeting the inclusion criteria for this review. These included 13 randomized control studies and four nonrandomized control studies. A total of 1111 eyes were included in the 17 trials.
2.4. Assessment of study validity and quality
Trial quality was assessed according to the methods described in Section 6 of The Cochrane Handbook for Systematic Reviews of Interventions. A score ranging from 0 to 5 was allocated according to the method of Jadad et al. Each question required either a “yes” or “no” answer. Each “yes” answers would score a single point and each “no” answers scored zero points. The questions were as follows:
- Was the study described as randomized?
- Was the study described as double blind?
- Was there a description of withdrawals and dropouts?
Additional points were given if
- The method of randomization was described in the paper, and the method was appropriate.
- The method of blinding was described and it was appropriate.
Points were deducted if
- The method of randomization was described but was inappropriate.
- The method of blinding was described but was inappropriate.
2.5. Data extraction
Data were collected for the following outcome measures:
- More accommodative power in accommodative IOLs compared to controls
- More optic shift in accommodative IOLs compared to controls
- Postoperative time at time of study
2.6. Data synthesis
Data syntheses were performed by creating a table listing all 17 papers with the comparison among accommodative IOLs and standard IOL in terms of accommodation, optic shift, and the postoperative time.
This study has been approved by the institutional review board of the University of Teesside for ethical issues and complied with the Declaration of Helsinki.
| 3. Results|| |
3.1. Search results
The initial electronic searches found a total of 332 papers: PubMed 33, Cochrane 11, Medline 109, Journal of Cataract Refractive Surgery 168, and Reference & Manufacturer 11. A total of 164 titles and abstracts were selected for review, as shown in [Table 1].,,,,,,,,,,,,,,,,
After reading the full text as a second selective procedure, 17 papers were identified as meeting the inclusion criteria for this review (PubMed 2, Cochrane 2, Medline 7, JCRS 6) There were 13 randomized control studies and four nonrandomized control studies A total of 1111 eyes were included from the 17 trials as shown in [Table 2].
|Table 2: Results after reading the full text of articles from the first selection.|
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3.2. Quality ofthe included studies
- The Jadad scores for the 17 trials included were as follows: 76.4% had a score of 2 or higher, 23.6% had a score of 0, 42.4% had a score of 2,10% had a score of 3, and 24% had a score of 4 [Figure 1].
- The Critical Appraisal Skills Program (CASP) was used to evaluate randomized control trials. Most trials complied with the requirements for validity [Figure 2].
|Figure 1: Pie distribution of Jadad's scores for the17 trials: 76.4% had scores of 2 and above.|
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|Figure 2: Summary of the appraisal of 17 trials with CASP (Critical Appraisal Skills Program). RCT (Randomized control Trials).|
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The following criteria were assessed for the (CASP) program:
Question: Was there a clearly focused question? All 17 trials
RCT: Was this a randomized controlled trial? Thirteen trials (76%)
Allocation: Were participants appropriately allocated to the intervention and control groups? All 17 trials
Blind: Were the participants, staff, and study personnel “blind” to the participants’ study groups? Four trials
Drop out: Did any of the participants who entered the study subsequently leave? One trial
Data collection: Were data collected in the same way for all the groups? All 17 trials
Power: Did the study have enough participants? One trial
Results: What were the main results, and how were the results presented? All 17 trials
Precise: Were the results precise? All 17 trials
Apply: Could the outcome be applied to other populations? Sixteen trials [Table 3] and [Table 4].
|Table 3: List of standard monofocal posterior chamber IOLs compared in this review.|
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3.3. Results of data synthesis
Results of data synthesis are shown in [Table 5].
|Table 5: A list of control trials that demonstrated the presence or absence of “more accommodation” and “more optic shift” in AIOLs compared to standard IOLs|
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3.4. Summary of the results
Of the 17 trials, 12 investigated AIOLs (71%) and nine trials investigated 1CU AIOLs (75%). Two trials investigated Tetraflex AIOLs, one studied the Crystalens AIOLs, and one studied the Bio- Comfold AIOLs.
Six out of the nine 1CU trials (67%) showed more accommodation in diopters compared to the standard IOL [95% confidence interval (CI), 0.36–0.98] when measurements were obtained from 2 months to 1 year postoperatively. Four out of the nine 1CU AIOLs (44%) trials demonstrated an optic shift (95% CI, 0.12–0.76).
There were two Tetraflex accommodative IOL trials. Both demonstrated an increase in accommodation but no optic shift compared to the control IOL at up to 6 months postoperatively.
Some nonaccommodative IOLs (NAIOLs) such as the Akeros and the AcrysoftIQ had more accommodation compared to the other NAIOLs. Akeros IOL (Hydrophilic Acrylic, Bausch-Lomb) showed more accommodation and optic shift compared to MA60BM (Alcon, multipiece Acrysof) at up to 1 year.
Overall, 75% of the trials found more accommodation in AIOLs compared to standard IOLs. However, seven out of the nine trials (78%) that reported more accommodation in accommodative IOLs showed a decrease in accommodation as the postoperation time increased to 12 months (95% CI, 0.55–1.00). The remaining accommodation could not be differentiated from pseudoaccommodation.
| 4. Discussion|| |
This review included 17 trials that measured and compared pseudophakic accommodation among AIOL and NAIOLs. Trial quality was rigorously evaluated using the Jadad score and the CASP. Most trials complied with the requirements for validity. However, some showed weakness in blinding, power, or description of dropouts. Most of the trials investigated 1CU AIOLs, indicating that the results were mostly pertinent to 1CU AIOLs. According the result, patients who received AIOLs after cataract surgery enjoyed more accommodation compared to those patients who received NAIOLs up to 1 year. There was one trial that demonstrated more accommodation from the Akeros IOL (Hydrophilic Acrylic, Bausch-Lomb NAIOL) compared to another NAIOL MA60BM (Alcon, multipiece Hydrophobic Acrysof) at up to 1 year. Therefore, the design and the material of AIOLs or NAIOLs may be the contributing reason to those patients to have short-term ability of accommodation.
There was a lack of valid studies on other AIOLs such as the Crystalens. In this review, the characteristics of pseudoaccommodation were studied and described to explain the ability of pseudo-phakic participants in these studies to read without accommodation. Pseudoaccommodation and monovision may contribute to the success of AIOLs despite a decrease in accommodation over time.
For clinical and practical reason, in the attempt to allow patients to use a standard NAIOL without reading glasses, the following features of pseudoaccommodation can be considered.
- Achieving less negative accommodation (back shift of the IOL).
- Incorporating the formula of for mini-monovision in the IOL power calculation.,,
- Leaving 1–2 diopters of myopic astigmatism and virtually no sphere in the nondominant eye.
- Leaving the eyes with larger vertical coma aberrations that can achieve a larger range of accommodation.
- Maintaining total spherical aberration without aspheric IOL implantation, which may enhance distance-corrected near and intermediate vision.,
- The posterior position of the IOL in the eye (closer to the nodal point).
- The presence of a small pupil (Increased depth perception).
- An uncomplicated small-incision phacoemulsification surgery with a continuous curvilinear capsulorhexis and an in-the-bag implanted soft lens.
- The improvement of distance-corrected near vision is better with a larger continuous curvilinear capsulorhexis and with less overlapping of the optic.
- Good patient selection and preoperative consultation.
Future studies should focus on how to further develop new generation of accommodative IOLs such as the Synchrony (dual-optic design) or NuLens.
| 5. Conclusion|| |
This review showed evidence of pseudophakic accommodation in AIOLs and NAIOLs up to 12 months postoperatively (mainly in 1CU AIOLs). However, most of the IOLs showed a decrease in accommodation as the postoperative time increased to 12 months. Pseudoaccommodation may play a role in the ability to attain distant corrected near vision.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]