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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 59  |  Issue : 1  |  Page : 28-31

Analysis of visual outcome following cataract surgery in axial myopic patients


1 Department of Glaucoma, Vasan Eye Care Hospital, Chennai, Tamil Nadu, India
2 Department of Glaucoma, Vasan Eye Care Hospital; Department of Ophthalmology, SSSMCRI, Chennai, Tamil Nadu, India

Date of Submission15-May-2020
Date of Decision20-Jul-2020
Date of Acceptance23-Dec-2020
Date of Web Publication27-Mar-2021

Correspondence Address:
Dr. Dhivya Ramakrishnan
Glaucoma Consultant, Vasan Eye Care Hospital, Chromepet, Chennai, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/tjosr.tjosr_56_20

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  Abstract 


Aim: The primary outcome is to assess visual outcomes following cataract surgery in axial myopic patients. The secondary outcome assessed is perioperative complications rate due to high axial length. Materials and Methods: Type of study: It was a retrospective, noncomparative case series study. Inclusion criteria: Patients with axial length more than or equal to 25 mm with visually significant cataract in one or both eyes were recruited for the study. Patients with pathological myopia were also included – visual recovery was assessed in conjunction with the preoperative best-corrected visual acuity. Exclusion criteria: Myopic patients with cataract with other causes of visual loss such as macular scar, diabetic retinopathy, age-related macular degeneration, disc edema, vein occlusion, and epiretinal membrane were excluded from the study. Sample Size: The sample size of the study was 32 patients (49 eyes). All patients recruited for the study underwent complete anterior segment examination in slit lamp with due importance to the type of cataract, visual acuity examination, and refraction to assess preoperative best-corrected visual acuity and posterior segment examination with 90 D lens. If the posterior segment was not visualized, B-scan was done. Blood investigations include complete blood count, random blood sugar, HIV, hepatitis B virus surface antigen, and urine albumin/sugar. With the test results and electrocardiogram, anesthetist fitness was obtained. Duct patency and intraocular pressure (IOP) were measured. Automated keratometry and axial length were measured by immersion technique done to calculate intraocular lens (IOL) power. IOL power calculation was performed using the SRK/T which was found to be reliable in axial lengths above 25 mm. Anterior chamber depth and lens thickness were also measured. All patients underwent phacoemulsification with IOL implantation by experienced single surgeon. The main outcomes measured were visual acuity after cataract surgery with implantation of zero or negative or very low IOL power at 1-month postoperative period and intraoperative and postoperative complications. The method of surgery did not influence the visual outcome. Results: The mean age of the patient operated on was about 61.9 years. In our study, the most common type of cataract was nuclear cataract (63.2%). Only 4.1% had previous refractive surgery. About 65.3% had 6/6 vision postcataract surgery with axial myopia. About 51.1% of axial myopic patients' fundus changes before cataract surgery which could be one of the causes for poor visual acuity. No significant perioperative complications were observed. Conclusion: Good postoperative outcomes following cataract surgery were observed in patients with cataract and high myopia. Refractive error is a potential complication as the hyperopic error appears to increase with axial length, especially in patients receiving negative power lens. If a sulcus IOL is inserted, it is more likely to be unstable or decenter because of the larger sulcus size. The need for Nd: YAG capsulotomy for posterior capsular opacity was found to be more common in myopes with high axial length compared to the general population. IOP reduction is slower and unstable for the first 30 days of postcataract surgery in highly myopic eyes.

Keywords: Anterior chamber depth, best-corrected visual acuity, intraocular lens, lens thickness, posterior capsular opacity


How to cite this article:
Ramakrishnan D, Sugantharaj V. Analysis of visual outcome following cataract surgery in axial myopic patients. TNOA J Ophthalmic Sci Res 2021;59:28-31

How to cite this URL:
Ramakrishnan D, Sugantharaj V. Analysis of visual outcome following cataract surgery in axial myopic patients. TNOA J Ophthalmic Sci Res [serial online] 2021 [cited 2021 Apr 22];59:28-31. Available from: https://www.tnoajosr.com/text.asp?2021/59/1/28/312283




  Introduction Top


Myopia affects approximately 25% of the general population.[1] It affects a larger proportion of Asians.[1] Axial myopia is defined as axial length more than or equal to 25 mm. High myopia refers to more than or equal to axial length of 26.5 mm.[1] High myopia affects 2% of the population.[2] Pathological myopia refers to an axial length of 32.5 mm or more.[1]

According to the Beaver Dam Eye Study and the Blue Mountain Eye Study, there is an association between myopia and nuclear cataract.[3],[4] The Blue Mountain Eye Study also found that myopia in young patients (<20) is also associated with posterior subcapsular cataract formation.[3]

The Singapore Malay Eye Study also determined patients with high myopia have 3–5 times increased risk of nuclear cataract and a 30% increased risk of posterior subcapsular cataracts. Praveen et al.[5] reported that high myopia was a powerful risk factor for the development of cataracts in young patients. It is a case–control study of the Indian population which showed association between nuclear cataract and axial high myopia but not posterior subcapsular cataract as showed in the Blue Mountain Eye Study. Limitations of these studies were the subjective classification of lens opacity – nonrepeatability of intra- and interobserver assessment.

Highly myopic eyes tend to develop cataracts earlier than normal eyes and to have a higher prevalence of co-existing disease and complications such as retinal detachment. Poor visual prognosis was associated with longer axial length and retinal myopic degeneration.[6] High myopia is known risk factor and progression factor for primary open-angle glaucoma.[7],[8],[9],[10]

The visual outcome depends on disease conditions like retinal detachment or myopic retinal degeneration. Tsai et al. reported good final visual outcomes in highly myopic eyes, in cases without diabetes or maculopathy. However, this study did not correlate between the severity of myopia and the visual outcome.[11] Our purpose in this study was to assess the characteristics and visual outcome following cataract surgery in axial myopic patients.


  Patients and Methods Top


Medical records of 49 eyes of 32 consecutive axial myopic patients who had undergone phacoemulsification with intraocular lens (IOL) implantation between January 2016 and January 2018 were reviewed. An eye was classified as myopic if the axial length was more than or equal to 25 mm and highly myopic if the axial length is equal to or more than 26 mm. All intraoperative and postoperative complications were recorded and treated accordingly.

All the patients underwent complete ophthalmological examination which includes measurement of best-corrected visual acuity by Snellen chart, refractive error pre and at 1 month postoperative period, and slit-lamp evaluation of anterior and posterior segment. Nuclear cataract was graded with slit beam at 30–45° angle to the cataract, whereas cortical and posterior subcapsular cataract was graded by retroillumination using the WHO criteria.[12] Axial length was measured by immersion technique and keratometry was done by autokeratometry. IOL power was calculated by SRK/T formula.

Phacoemulsification with ' in the bag ' implantation of posterior chamber IOL was performed through a superior limbal incision of 2.2/2.8 mm. We used IOL whose A constant varies between 118/118.4/118.5/118.9/119. Three patients had negative power IOL and 7 patients had IOL power <10 diopters. Postoperative refractive error was determined 1 month after the surgery.

No significant perioperative complications such as globe perforation, shallow anterior chamber, peaking of the pupil, decentered IOL, and retinal detachment were noted. Mild corneal edema or striate keratopathy which resolved in 2 weeks were noted in few patients.


  Results Top


Thirty-two patients (49 eyes) were analyzed for best-corrected visual acuity at 1-month postoperative period following cataract surgery in axial myopic patients. Of the 49 eyes, 25 were female eyes and 24 were male eyes [Table 1]. There were no gender differences.

The mean age of the patients operated was between 61.9 years. Common range falls between 61 and 70 years [Table 2].
Table 1: Sex distribution

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Table 2: Age distribution

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In our study, the type of cataract more prevalent in myopes was nuclear sclerosis (63.2%) [Table 3].
Table 3: Cataract occurrence

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Only 2 eyes (4.1%) underwent previous refractive surgery. IOL power calculation was done using the American Society of Cataract and refractive surgery (ASCRS) site and the availability of pre- and post-Lasik data. Haigis L and Barrett formula was used. Patients with a history of refractive surgery have a higher likelihood of refractive error after cataract surgery. Hyperopic surprise most commonly results if the history of refractive surgery is not taken into account when calculating IOL power.

The visual prognosis depends on individuals [Table 4]; 65.3% of the myopic patients with axial length ≥25 mm had 6/6 vision, 20.4% had 6/9 vision, 8.2% had 6/18 vision, 4.1% had 6/24 vision, and only 2% had <6/60 vision. These data indicate a good visual prognosis in myopic patients; however, lack of adequate sample size is a limitation.
Table 4: Visual outcome

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Severe funduscopic findings [Table 5] were related to poor visual prognosis. Normal fundus implies normal or tilted disc without chorioretinal changes. Myopic fundus implies tilted disc with chorioretinal changes that may or may not impairs vision. Others imply glaucoma, age-related macular degeneration, etc., Eyes with mild retinal changes showed no difference in postoperative visual acuity. However, eyes with myopic fundus changes showed a poor visual prognosis. Three patients had primary open-angle glaucoma and were under treatment at the time of cataract surgery.
Table 5: Retinal changes

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Statistical analysis

The paired Student's t-test was used to compare best-corrected visual acuity in myopes preoperative and postoperative. P < 0.05 was deemed to be statistically significant.


  Discussion Top


Cataract surgery outcomes have greatly improved due to advances in surgical technique, IOL technology, preoperative testing, and calculations. With improvements, expectations from patients regarding postoperative visual acuity and independence from spectacle correction have increased.[13] The most commonly used endpoints for measuring refractive error in the literature were the percentage of patients achieving final refraction within 0.5D and 1.0D of the intended target.[14]

Praveen et al.[5] reported that high myopia was a powerful risk factor for the development of cataract in young patients. However, to date, there have been no other data reported regarding the relationship between age, high myopia, and cataract.[6]

Nuclear subcapsular cataract is known to be more predominant in myopic eyes.[15],[16],[17] In our study, the frequency of nuclear cataracts was significantly higher than other types of cataract. Praveen et al.[5] reported a prospective case–control study of 800 eyes in the Indian population, which showed an association between nuclear cataracts and axial high myopia.

However, unlike in the findings of the Blue Mountain Eye Study, PSC was not associated with high myopia.[3],[4],[18],[19],[20]

Calculation of the IOL power is critical in obtaining good visual outcomes. The presence of posterior staphyloma may cause errors in IOL power calculation. B-Scan ultrasonography should be performed in these patients to avoid error in axial length measurement.[21],[22]

The SRK/T formula has been found to be more accurate than other formulas in determining the IOL power in myopic patients. The SRK/T formula was used to determine the IOL power in the present study. Mild postoperative myopia is generally recommended for cataract patients with high myopia.

Visual prognosis depends on disease conditions such as myopic retinal degeneration, maculopathy, and retinal detachment. Tsai et al.[11] reported good final visual outcome in highly myopic eyes, in cases without maculopathy or diabetes. In our study, one patient (2.0%) with axial length 31 mm had good postoperative visual acuity. Postoperativecorrected visual acuity showed a negative correlation with the axial length.

Eyes with large inter-eye axial length difference were often regarded to have anisometropic amblyopia with limited postoperative visual prognosis.[23]

The highly myopic patients may also have myopic macular degeneration, epiretinal membrane, or other significant changes. These may limit the postoperative vision achieved.

Cataract surgery in myopic eyes becomes challenging due to the increased depth of the anterior chamber, floppy and large capsular bag, and zonular weakness in some cases.[24]

Surgical technique

We feel that the advantage of cataract surgery in myopic patients was the larger anterior chamber depth, allowing more working room during phacoemulsification. However, the infusion pressure can cause over inflation and a tendency to push the entire lens iris diaphragm posteriorly. From our study, to address this issue, infusion pressure can be reduced by lowering the bottle; this will result in less inflow of fluid and a higher tendency for surge.

Lens-iris diaphragm retropulsion syndrome is characterized by 360° of irido-capsular contact leading to reverse pupillary block, pupil dilatation, and pain. Zonular weakness predisposes to this condition. To address this issue, we feel the use of spatula, cannula, or Sinskey hook to elevate the pupil margin to allow fluid to flow past the pupil.[25],[26]

Postoperative retinal detachment is high in myopic patients if there is tension or traction on the vitreous base during surgery. We feel this can be avoided by preventing anterior chamber collapse by inflating it with viscoelastic while removing probe from ac.

Postoperative refraction in myopes can take time to stabilize as the capsular bag wraps around the IOL. Inflammation should be controlled by topical steroids and NSAID for a month. A repeat dilated fundus examination is indicated to search for retinal breaks or degenerations that may have been created during a surge.


  Conclusion Top


Good postoperative outcomes following cataract surgery were observed in patients with cataract and high myopia. Refractive error is a potential complication as the hyperopic error appears to increase with axial length, especially in patients receiving negative power lens (3 of 49 eyes). If a sulcus IOL is inserted, it is more likely to be unstable or decenter because of the larger sulcus size. From our study, cataract surgery can be done more safely with minimal perioperative complications (IOL decentration) in high myopic patients. The need for Nd: YAG capsulotomy for posterior capsular opacity was found to be more common in myopes with high axial length compared to the general population. Intraocular pressure reduction is slower and unstable for the first 30 days of postcataract surgery in highly myopic eyes.[13] Our study summarizes the characteristics and visual prognosis of cataract surgery in axial myopic eyes. Further study is needed to examine the pathophysiology of cataract formation in myopic eyes.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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