Nuclear sclerosis in young myopic patients is a contributing factor to loss of visual acuity.1,2 Patients often present with progressive loss of visual acuity, monocular polyopia, and poor best corrected visual acuity (BCVA) inconsistent with the severity of cataract.1,2 To further understand this disease entity, we retrospectively reviewed the medical records of patients younger than 45 years with discrete nuclear sclerosis.
Patients and Methods
The medical records of all patients younger than 45 years who had cataract surgery at Chang-Gung Memorial Hospital, Taoyuan, from January 1995 to December 2000 were retrospectively reviewed. Only myopic patients with pure nuclear sclerosis were included in this study. Patients with previous ocular trauma, uveitis, intraocular tumor, retinal detachment, retinitis pigmentosa, congenital cataract, previous intraocular surgery, or other ocular conditions related to cataractogenesis were excluded. Patients with diabetes mellitus, autoimmune disease, galactosemia, hyperparathyroidism, or other systemic disease associated with cataract were also excluded.
All patients had a comprehensive ocular examination including slitlamp biomicroscopy, indirect ophthalmoscopy, measurement of refractive status (Topcon Refractometer, RK-8100), axial length measurement by ultrasound (Sonomed A-500), and assessment of BCVA before and after cataract surgery. The severity of nuclear sclerosis was graded according to the Lens Opacities Grading System III (LOCS III).3 The original refractive status, preoperative refractive status, and difference between the 2 were recorded. The original refractive status (ie, before the development of cataract) was determined by chart review; for patients without a record of refractive status before the development of cataract, the spectacle refraction was used. The patients had stabilized, well-corrected visual acuity with these spectacles for several years before the onset of blurred vision. For patients with a refractive error greater than –25.00 diopters (D) (the upper limit of refractive errors detectable by the refractometer), –25.00 D was used in the calculations.
Extracapsular cataract extraction or phacoemulsification with IOL implantation was performed in all eyes. The criterion for cataract extraction was based on visual performance. When patients stated that the symptoms of cataract interfered with normal daily life, cataract surgery was performed. Cataract extraction was performed in 1 eye only. No patient had clear lens extraction in the opposite eye to treat anisometropia.
Follow-up was from 6 months to 6 years. The data were analyzed by an unpaired t test.
From January 1995 to December 2000, 426 eyes had cataract surgery. Of these, 55 eyes of 35 patients younger than 45 years had pure nuclear sclerosis. The age the patients ranged from 32 to 45 years (Table 1). The chief complaints were progressive deterioration of visual acuity and rapid myopic shift in all eyes, monocular polyopia in 49 eyes, and dim vision in 23 eyes. The cataract typically presented as a small central nuclear sclerosis surrounded by a clear zone (Figure 1).
Twenty patients (13 men, 7 women) had bilateral cataract and 15 (8 men, 7 women), unilateral cataract. In 13 of the patients with bilateral cataract, the severity of the nuclear opacity was different between the eyes at the initial examination. Four patients presented initially with unilateral cataract but the involvement of the contralateral eye became apparent 6 months to 3 years later. Table 2 shows the clinical data in patients with bilateral and unilateral cataract. Although the mean age of the patients with bilateral cataract was greater, the difference was not statistically significant (P=.169). Of the 35 patients, 21 were 40 years or older and 32 had cataract surgery when they were 35 years or older.
The original spherical equivalent (SE) ranged from plano to –16.00 D (Table 3). Patients with bilateral cataract had higher original refractive errors than those with unilateral cataract, although the difference was not statistically significant (P=.076) (Table 2). After the development of cataract, all patients had a myopic shift as indicated by manifest refraction measurements. The preoperative SE ranged from –3.00 D to more than –25.00 D (Table 3). Patients with bilateral cataract had a slightly greater mean preoperative refractive error than those with unilateral cataract (P=.433) (Table 2). The mean change in SE before and after the development of cataract ranged from –3.00 D to more than –18.75 D. Forty-one eyes had a refractive change of –6.00 D or more (Table 3). The axial length ranged from 23.40 to 33.90 mm. Two eyes had an axial length less than 24.0 mm. In 12 eyes, the axial length was between 24.0 and 27.0 mm; in 41 eyes, it was greater than 27.0 mm (Table 3). The mean axial length in eyes in patients with bilateral cataract was longer than in patients with unilateral cataract (Table 2); the difference was statistically significant (P=.009).
The preoperative BCVA ranged from counting fingers to 20/30 (Table 3). Almost all patients had excellent visual results after surgery. The postoperative BCVA was 20/22 or better in 53 eyes. Of the 2 eyes with a poor visual outcome, 1 developed a retinal detachment 1 month after cataract surgery that was successfully repaired by vitrectomy and scleral buckling. The final BCVA was 20/200. The other patient developed postsurgical endophthalmitis and amikacin toxicity after intravitreal injection. The final visual acuity was counting fingers.
A 36-year-man presented with poor visual acuity in the right eye that had been present for 3 months. He reported dimmer vision and difficulty focusing. No definite diagnosis was given, although the patient had visited several other physicians.
Slitlamp examination revealed indefinite nuclear sclerosis in the right eye and indirect ophthalmoscopy, a tessellated fundus in both eyes. The BCVA was 20/25 with –8.50 –1.50 × 180 in the right eye and 20/20 with –4.00 –0.75 × 180 in the left eye. Two years previously, the refraction had been –6.00 –0.50 × 180 and –4.00 –0.50 × 180, respectively.
Three months later, the patient returned to our clinic with further deterioration of vision and polyopia in the right eye. The manifest refraction was unchanged in the left eye and –9.25 –1.25 × 180 in the right eye, indicating further myopic shift. The BCVA in the right eye was 20/30 with –8.75 –1.25 × 180 and could not be improved with addition of a spherical lens. Keratometric readings were 42.25/43.00 in the right eye and 43.00/43.50 in the left eye. A well-defined, opalescent, small central nuclear opacity was noted in the right eye.
One year later, the manifest refraction was –11.75 –1.50 × 180 in the right eye and –5.50 –1.25 × 180 in the left eye. The BCVA was 20/60 with –9.50 –1.25 × 180 in the right eye and could not be improved with the addition of a spherical lens and 20/25 with –5.50 –1.00 × 180 in the left eye. The keratometric readings were 42.00/43.50 and 43.00/43.50, respectively. The axial length was 28.12 mm in the right eye and 27.01 mm in the left eye.
The patient had cataract surgery in the right eye, after which the BCVA returned to 20/20. However, deteriorated visual acuity and nuclear sclerosis were noted in the left eye 6 months later. He had cataract surgery in the left eye 1 year after surgery in the right eye. The preoperative manifest refraction in the left eye was –7.75 –1.00 × 150. The BCVA in the left eye was 20/60 with –7.00 –1.00 × 150 preoperatively and 20/20 postoperatively.
A 38-year-old man presented with poor visual acuity and a myopic shift, both of which had progressed over the preceding 4 years. Although he had changed his spectacle prescription several times, visual acuity remained poor. Two years previously, he was diagnosed with cataract.
Ophthalmologic examination showed moderately severe nuclear sclerosis confined to the central nucleus in both eyes. Fundus evaluation revealed tessellation in both eyes. The BCVA was 20/500 with –15.00 D in the right eye and 20/600 with –17.00 D in the left eye and did not improve with addition of myopic lenses. The keratometric readings were 42.00/42.50 and 42.00/42.25, respectively. The right eye had an axial length of 31.54 mm and the left eye, of 33.90 mm. The manifest refraction was greater than –25.00 D in both eyes. Based on the refraction of the old spectacle lenses, the original SE was –14.00 D in the right eye and –16.00 D in the left eye. The patient said he had worn the old spectacles for 4 to 5 years and had good visual acuity before the onset of blurred vision. At this point, a diagnosis of progressive myopia was made. Although the patient changed spectacle prescriptions frequently, he never had good BCVA thereafter.
After bilateral cataract extraction, the BCVA was 20/20 in the right eye and 18/20 in the left eye.
O'Donnell and Maumenee1 first described mild nuclear sclerotic cataract as the cause of unexplained visual loss in patients with axial myopia. Discrete nuclear sclerosis has since been noted as a reason for visual loss in young patients with axial myopia. Polyopia, rapid myopic shift, and poor BCVA inconsistent with the severity of cataract are the common complaints. Because cataract may not be identified at the early stage and the extent of visual loss often does not correspond with the severity of cataract, a diagnosis may be difficult in the early stage.1,2
Kaufman and Sugar2 report 12 patients younger than 55 years with axial myopia and early-onset nuclear sclerosis. In their series, the presence of simple and high myopia predisposed patients to early-onset nuclear sclerosis. Most patients presented with unilateral cataract, and only 1 patient had bilateral cataract. The results of their series suggest that a discrete nuclear sclerotic cataract can accompany axial myopia with or without notable induced myopic shift.
In our series, many patients' symptoms preceded the identification of cataract. At their first visit to our clinic, patients presented with unexplained visual loss or suspected myopic retinopathy. As the disease progressed, mild, opalescent nuclear opacity confined to the central portion of the lens was noted with an increase in myopia. Blurred vision, difficulty focusing, and dim vision were frequent complaints. After several years, the cataracts developed; denser nuclear sclerosis with the characteristic brunescent hue was accompanied by a greater lenticular myopic shift and further visual deterioration. However, the sclerosis remained confined to a small central portion of the nucleus and was surrounded by a clear zone. If left untreated, these patients often developed poor visual acuity that did not correspond to the severity of the cataract. Aging patients whose cataracts have a similar degree of severity but a more homogeneous nuclear sclerosis than in our patients often have better BCVA.
Levin4 describes this type of cataract as opalescent nuclear cataract in which the refractive index of the small central zone of opacity increases, resulting in up to –16.00 D of lenticular myopia. Because the small central zone of opacity is separated from the adult nucleus by a clear zone, it creates a double focus, resulting in polyopia and difficulty focusing. This might explain why, even though they were fully corrected in terms of preoperative manifest refraction, our patients' visual acuity was poor.
There was a predominance of men in our series, especially in patients with bilateral cataract. Myopia is more often seen in women, however. Thus, there might be an even higher incidence of cataract in myopic men than in myopic women.
Contrary to the findings in previous reports,1 more than half the patients in our series had bilateral nuclear sclerotic cataract. This might be because these patients were followed for a long time or had cataract surgery at a more advanced stage of the disease, allowing time for the contralateral eye to develop cataract. Four unilateral cataract patients developed cataract in the contralateral eye within 6 months to 3 years of follow-up. Since the severity of nuclear sclerosis in most bilateral cataract cases differed in our series, most patients likely developed cataract in 1 eye before the other eye. The unilateral cataract patients were not followed for very long, so it is possible that their contralateral eyes would develop cataract within a few years.
A myopic shift occurred in all our patients. The calculations of myopic shift were not precise because in some patients, the original refractive status was hard to trace and the refraction of old spectacles was used to estimate the original refractive status. However, these spectacles provided stable and well-corrected vision and were used for years before the onset of deteriorated visual acuity. We believe that if the original SE and the refraction of the old spectacles were disparate, the disparity would be small. In addition, the trend toward myopia was obvious in all patients as the disease progressed during the period preceding cataract extraction. Myopic shift has not been clearly defined in other reports.1,2 Documentation of this shift in our series could be attributed to the fact that most of our patients had cataract surgery at a later stage, providing time for a myopic shift to occur.
In our study, most patients did not have BCVA with the manifest refraction. They often obtained BCVA with a spherical lens several diopters lower than the manifest refraction; addition of a myopic lens did not improve the visual acuity. Axial myopia was an important predisposing factor in the development of nuclear sclerosis in our young cohort. Patients with high myopia, characterized by a long axial length, had the greatest risk; 74% of our patients had an axial length greater than 27.0 mm. Simple myopia with a moderately elongated axial length also predisposed to cataract formation; 22% of patients had an axial length between 24.0 mm and 27.0 mm. Only 2 eyes had an axial length less than 24.0 mm.
De Natale and coauthors5 found that myopic lenses have higher opacity values than emmetropic lenses and are more likely to develop opacification at an earlier age. Because eyes with myopia are prone to develop changes with aging, vitreous liquefaction and primary open-angle glaucoma occur at an earlier age. Nuclear sclerosis might be another change that appears earlier in myopic eyes. Patients younger than 32 years were included in our series.
In our study, cataract surgery was therapeutic in most cases. All patients had an excellent visual outcome except 2, who developed retinal detachment or endophthalmitis as complications of the surgery.
In conclusion, ours is the largest series of young patients with nuclear sclerosis reported in the literature. The relationship between axial myopia and the onset of nuclear sclerosis was clearly established. Bilaterality was common, especially in patients with a longer axial length. If left untreated, patients developed poor visual acuity unrelated to the severity of the nuclear sclerosis. Myopic shift can always be demonstrated given a long enough follow-up. Thus, nuclear sclerotic cataract with a myopic shift is not a rare cause of visual loss in young myopic patients in Taiwan.
1. O'Donnell FE Jr, Maumenee AE. “Unexplained“ visual loss in axial myopia: cases caused by mild nuclear sclerotic cataract. Ophthalmic Surg 1980; 11:99-101
2. Kaufman BJ, Sugar J. Discrete nuclear sclerosis in young patients with myopia. Arch Ophthalmol 1996; 114:1178-1180
3. Chylack LT Jr, Wolfe JK, Singer DM, et al. The Lens Opacities Classification System III; the Longitudinal Study of Cataract Study Group. Arch Ophthalmol 1993; 111:831-836
4. Levin ML. Opalescent nuclear cataract. J Cataract Refract Surg 1989; 15:576-579
5. De Natale R, Romero G, Famà F, Scullica L. Human lens transparence in high-myopic subjects. Ophthalmologica 1992; 205:7-9