Unilateral eye elongation with resultant axial myopia has been reported to occur secondary to visual deprivation from birth or early childhood. Acquired axial length elongation secondary to visual deprivation in adults has rarely been reported.
To report acquired axial myopia in adults with visual deprivation due to long-standing unilateral traumatic cataract.
Eleven consecutive adult patients who presented for cataract surgery with unilateral, long-standing, mature, traumatic cataracts and an interocular axial length difference of more than 1 mm were studied. Patients with a post-operative best corrected visual acuity (BCVA) of < 6/12 were excluded to rule out possible pre-existing anisometropic amblyopia.
Of the 11 patients with significant interocular axial length difference, 5 patients were excluded on the basis of possible pre-existing amblyopia. The remaining 6 patients had final BCVA of 6/12 or better. The median length of the cataractous eyes was 2.83 mm longer than the fellow eyes (range 1.12 mm – 3.52 mm). The intraocular lens power required for emmetropia was 6.8 dioptres (range 3.5 dioptres – 11.5 dioptres) less in the cataractous eyes. A refractive outcome within 1 dioptre of the target refraction was achieved in all patients. The median delay between ocular trauma and cataract surgery was 20 years (range 8–24 years).
Significant unilateral axial length elongation may occur in adults with long-standing traumatic cataracts and visual deprivation. A potential correlation may exist between delay to surgery and degree of axial length difference. This rare phenomenon must be considered when determining intraocular lens power to avoid post-operative refractive surprises.
Refractive accuracy is important for patient satisfaction after cataract surgery. A large interocular axial length difference on biometry raises the suspicion of a measurement error. This occurs more commonly with unilateral mature cataracts due to the reduced accuracy of biometry.
Unilateral eye elongation with resultant axial myopia has been reported to occur secondary to visual deprivation. This has been described in animal models including primates,
The aim of our study is to describe significant unilateral axial myopia in eyes with long-standing visual deprivation due to traumatic cataract. The increase in axial length may be on the basis of visual deprivation.
This retrospective case series comprised consecutive adult patients who presented with unilateral mature traumatic cataracts and an interocular axial length difference of more than 1 mm. The study was conducted at the Department of Ophthalmology, Groote Schuur Hospital, University of Cape Town, between November 2009 and October 2013 and was approved by the institutional ethics committee (HREC REF: 131/2014).
Preoperative assessment included an ophthalmic history with emphasis on the timing of the ocular injury and visual loss. Distance best corrected visual acuity (BCVA), slitlamp examination findings and intraocular pressure were recorded. Fundus examination was not possible due to the maturity of the cataracts, and B-scan ultrasonography was performed to exclude posterior segment pathology. Axial length was measured by immersion ultrasonography with an Ocuscan RxP biometer (Alcon Laboratories, Inc.). Keratometry was conducted using a Nidek (Genop Holdings Pty Ltd.) or Huvitz (Eurotech Optical) autorefractor/keratometer. The SRK-T formula was used for IOL calculation.
Phacoemulsification with implantation of a posterior chamber IOL in the capsular bag was performed on all patients, except for one case of extensive zonular dehiscence requiring an intracapsular cataract extraction, anterior vitrectomy and a scleral-fixated posterior chamber IOL. Post-operative BCVA, refraction and any fundus abnormalities were recorded.
Data analysis was performed using Stata version 12 statistical software.
Eleven adult patients with long-standing, unilateral, mature traumatic cataracts and an interocular axial length difference of more than 1 mm were identified. Five patients had a post-operative BCVA of < 6/12 and normal fundoscopy. Even though these patients all gave a history of good vision prior to the development of their cataract, they were excluded to rule out the possibility of pre-existing amblyopia due to myopic anisometropia. The remaining six patients had final visual acuity of 6/12 or better, which we felt excluded pre-existing amblyopia.
Age at time of injury, biometric data, visual and refractive outcomes of the remaining six patients are outlined in
Trauma history, biometric data, visual and refractive outcome.
Patient number | Age (years) | Delay (years) | Axial length (mm) | Average K (dioptre) | IOL for emmetropia (dioptre) | IOL used (dioptre) | Preoperative BCVA (Snellen) | Post-operative BCVA (Snellen) | Post-operative spherical equivalent (dioptre) | ||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Injury | Surgery | Cataractous eye | Fellow eye | Cataractous eye | Fellow eye | Cataractous eye | Fellow eye | ||||||
1 | 16 | 34 | 18 | 25.64 | 23.38 | 43.75 | 43.87 | 13.5 | 20.0 | 15.0 | CF | 6/9 | Not recorded |
2 | 19 | 27 | 8 | 23.66 | 22.54 | 44.75 | 44.75 | 18.5 | 22.0 | 19.0 | HM | 6/5 | −0.50 |
3 | 9 | 30 | 21 | 27.14 | 24.34 | 41.25 | 42.00 | 12.0 | 19.0 | 12.0 | HM | 6/12 | −1.00 |
4 | 27 | 41 | 14 | 27.42 | 23.90 | 43.75 | 43.25 | 8.0 | 19.5 | 10.0 | CF | 6/6 | −0.25 |
5 | 18 | 39 | 21 | 27.66 | 24.81 | 42.00 | 42.00 | 10.5 | 18.0 | 10.0 | HM | 6/6 | +1.00 |
6 | 29 | 53 | 24 | 30.42 | 27.51 | 42.25 | 42.50 | 3.0 | 9.5 | 5.0 | CF | 6/9 | −1.25 |
K, keratometry; IOL, intraocular lens; BCVA, best corrected visual acuity; CF, counting fingers; HM, hand motion.
The median length of the cataractous eyes was 2.83 mm longer than the fellow eyes (range 1.12 mm – 3.52 mm). This translated to a 6.8 dioptres (range 3.5 dioptres – 11.5 dioptres) median difference in IOL strength for emmetropia. All six patients achieved a post-operative BCVA of 6/12 or better, with a refractive outcome within 1 dioptre of the target refraction. One patient was lost to follow-up after the first post-operative visit and was not refracted. Her uncorrected distance visual acuity was 6/9 on the first post-operative day.
Linear regression analysis suggested that each year delay in surgery was associated with an increase of 0.08 mm in axial length but the numbers were too small to be statistically significant (95% CI –0.25 to 0.41;
Correlation between delay to cataract surgery and interocular axial length difference.
This case series presents adult patients with unilateral axial myopia in eyes with long-standing unilateral mature traumatic cataract. We propose that axial length elongation may have occurred due to long-standing visual deprivation despite the median age of 18 years at the time of visual loss.
This phenomenon has important clinical implications for correct IOL power selection during cataract surgery. In our study, the median IOL power for emmetropia was 6.8 dioptres less in the cataractous eyes than the fellow eyes. Since axial length measurements are known to be less accurate in eyes with mature cataracts,
Visual deprivation myopia is well described in animal studies.
Several authors have described a similar phenomenon in humans with unilateral visual deprivation from birth or early childhood. Huo et al. found a higher frequency of ipsilateral myopia in patients with severe unilateral congenital ptosis (55.3% ptotic eye vs. 37.6% control eye,
The only human study in the English literature describing this phenomenon in adults was published by Gradin et al.
Afsari et al. reported that anisometropia of > 1 dioptre in early childhood is significantly associated with amblyopia (OR 12.4, 95% CI 4.0 to 38.4), and the risk increases with higher degrees of anisometropia.
It appears that there may be a correlation between the delay to cataract surgery and the degree of interocular axial length difference. The trend was not statistically significant due to small numbers (
Limitations of our study include small sample size and absence of intraocular pressure measurements in the period between trauma and cataract surgery. However, none of our study patients had an elevated intraocular pressure at the time of preoperative assessment, and no other features of glaucoma were present.
Unilateral axial length elongation may occur in adults with visual deprivation due to long-standing mature traumatic cataract. It is important to be aware of this rare phenomenon to facilitate correct IOL selection when performing cataract surgery on these patients.
The authors declare that they have no financial or personal relationships which may have inappropriately influenced them in writing this article.
J.S. did the literature review, designed data collection tools and drafted the manuscript. She was the project leader. N.d.T. assisted with the literature review and revised the manuscript. J.C.R. did the statistical analysis and revised the manuscript. S.A. was responsible for data collection.