Optimal postoperative refraction for good unaided near and distance vision with monofocal intraocular lenses.

Abstract

Forty five eyes with up to 2 dioptres of myopic astigmatism and up to 1 dioptre sphere either plus or minus following cataract extraction and implantation of a monofocal intraocular lens were examined to assess their unaided visual acuities. Forty three percent were able to see 6/12 and N8, and 60% were able to see 6/12 and N10. Subjects with between 1 and 2 dioptres of myopic astigmatism and virtually no sphere were able to see 6/12 and N10 in 82% of cases. This study confirms the benefits to both distance and near vision of myopic astigmatism as an alternative to multifocal intraocular lenses. '-3 In a previous study' we found that patients with up to 2 dioptres of myopic astigmatism obtained a vision of 6/12 and N8 in 50% of cases. The myopic astigmatism in that study was artificially constructed by correcting the spherical element of the refraction, leaving the myopic astigmatic element uncorrected.This study was undertaken to assess the patient ages uncorrected visual acuities of subjects who had a best manifest corrected refraction of up to 2 dioptres of myopic astigmatism with up to 1 dioptre sphere either plus or minus. Materials and methodsWe studied 45 eyes in 45 patients after cataract extraction with implantation of a J loop intraocular lens into the capsular bag. Patients were admitted consecutively to the study as they presented for routine review and were at least 3 months post cataract extraction. Patients with a corrected visual acuity of less than 6/12 and N6 were excluded from the study. All patients had preoperative biometry performed on a 3M Digiecho A scan biometer using the SRK Mk 2 formula and were calculated to obtain a spherical equivalent refraction of -1 5 dioptres postoperatively.Postoperative keratometry was performed on a Haag-Streit Javal-Schiotz keratometer.The following parameters were measured on each patient.(1) Unaided and best corrected visual acuities at both near and distance. The distance acuity was measured at 6 metres using an illuminated Snellen chart, and the near at 0 3 metres with illumination from a 60 W light over one shoulder giving approximately 50 ft lm.

Analysis of patients with good uncorrected distance and near vision after monofocal intraocular lens implantation

“…From these studies, it is not clear whether the astigmatism was ATR or WTR. Bradbury et al 10 also concluded that refraction with no spherical error and only a myopic astigmatism of À1.5 D at 180 degrees giving WTR is desirable for good postoperative 6/12 and N/10 vision in 82% of cases. Trinidade et al 8 and our previous study 9 showed that eyes with no spherical error and only low ATR myopia can have good visual acuity for reading and distance.…”

“…20 Moreover, age was also found to be inversely related to this phenomenon. 18 Studies analyzing this phenomenon have compared it with phakic eyes, 2,3,12,13 without any comparative group, 1,4,6,7,[9][10][11]16,19 in an in vitro setup, 17 or as a single factor. 1,4-14 Therefore, we designed this study to evaluate more than 1 factor contributing to this phenomenon of pseudoaccommodation 4,5,6,13,[27][28][29][30] in the clinical scenario in which controls were also pseudophakic.…”

“…However, our clinical experience has shown that patients with monofocal IOL implantation occasionally have good uncorrected visual acuity (UCVA) for distance and near vision. [1][2][3] Various factors such as astigmatism, 1,[4][5][6][7][8][9][10][11][12] pupil size, 2,3,12-14 axial IOL movement, 15,16 axial length, 17 age, 18 corneal multifocality, 19,20 and aberrations 20 have been shown to be responsible for such a phenomenon.…”

Optimum target refraction for highly and moderately myopic patients after monofocal intraocular lens implantation

“…[10][11][12][13] Studies show that slight myopia accompanied by a certain degree of astigmatism enhances the depth of focus in eyes with a monofocal IOL. [14][15][16][17] It is difficult, however, to produce the optimum degree of astigmatism after cataract surgery, whereas small-incision cataract surgery affects astigmatism only slightly. 18 The appropriate choice of IOL power with reference to preoperative astigmatism may thus be the most accurate method for obtaining optimum refraction.…”

Influence of simple myopic against-the-rule and with-the-rule astigmatism on visual acuity in eyes with monofocal intraocular lenses

“…In order to consider the proper indication of toric IOLs and comprehend the influence of residual astigmatism, it is important to understand the relation between astigmatism and visual function. The astigmatic power and axis orientation have been shown to play an essential role in postoperative visual performance [4][5][6][7][8][9][10][11][12][13]. Several studies have shown that eyes with uncorrected oblique astigmatism have poorer visual performance than those with uncorrected against-the-rule (ATR) or with-the-rule (WTR) astigmatism [14][15][16][17][18][19].…”