FP1269 : Ocular Axial Length Changes Following Trauma: Blunt vs. Penetrating

Dr. Hemant Ramesh Sonawane, S14424, Dr. Haripriya Aravind, Dr. Madhu Shekhar

Abstract

Aim:  To analyze factors statistically associated with changes in axial length in traumatic eyes.

Methods: Seventy cases of unilateral ocular trauma visited between Jan 2012 – Jan 2015 were studied retrospectively; the other (normal) eye served as control. Blunt and penetrating groups were formed based on nature of injury; patients with unilateral axial length record, duration since trauma <1 year, congenital cataract and bilateral trauma were excluded. Mode, nature, age at injury and presenting age were noted. The inter-ocular difference in axial length was analyzed. Multiple regression analysis was used to find factors associated with changes in axial length in traumatic eyes.

Results: Forty-six were males and twenty-four females; 47 were penetrating and 23 blunt traumas. Mean axial length in penetrating trauma group was 25.31mm; and in blunt trauma group was 24.05mm. Mean axial length (study eye) in age group ≤15yrs was 25.46mm and in >15 yrs it was 24.02 mm (p=0.0003). Using regression analysis, if the axial length in control eye increases by 1mm, then in the traumatic eye it increases by 1.34mm (p<0.001). Similarly, age at injury ≤15yrs (p=0.002), penetrating trauma (p=0.002) and longer duration between injury and presentation (p=0.001) were statistically significant factors associated with increase in axial length in the traumatic eyes.

Conclusion: Trauma at a younger age; presentation at a later age and penetrating type of trauma are statistically significant factors associated with an increase in axial length in the traumatic eye.

INTRODUCTON

The human eye is a very well programmed organ wherein the refractive elements within it exhibit a regulated growth pattern. ^[1] The developing eye adjusts the growth of its refractive components to achieve ‘emmetropization’. Animal studies have shown axial elongation following visual deprivation; with certain reservations, most authors believe it can help explain genesis of myopia in humans. ^[2-7]

Many hypotheses have been proposed to explain transient myopia after blunt eye trauma, such as ciliary spasm, uveal (cilia-choroidal) effusion, anterior displacement of the lens–iris diaphragm, and an increase in anteroposterior thickness of the crystalline lens.^[8]  Few studies have been directed to examine the effect of surgical delay in young adults with chronic traumatic cataract and the effect of infantile traumatic cataract on axial elongation.^[1,2]  A trend of increase in ocular axial length and myopic shift in refraction has been observed to occur following pediatric cataract extraction.^[9-15]

Out of the various presumed factors responsible for the changes in the axial length of human eye, post-traumatic changes in axial length is scarcely studied in younger and adult age groups.^[2-6] Even though the true cause of axial elongation remains elusive, many factors like trauma, visual deprivation, surgery at an early age, multiple surgeries, etc have been postulated. After reviewing the existing literature, we tried to study and correlate the long-term effects of trauma on axial length with the nature of trauma, taking a larger sample size relative to other studies. The analysis of two different ocular trauma groups was done by grouping cases according to their nature of trauma and doing intra-group and inter-group comparisons. Our article thus purposes to study the effect of nature of trauma on axial length and its clinical relevance in the management of the same.

METHODS

Study design:

This retrospective study was carried out at the Cataract Clinic, Aravind Eye Hospital,                                Madurai, India. The study protocol was conducted according to the principles described in the Declaration of Helsinki, and Institutional Review Board/Ethics Committee approval was obtained. The selection was done from outpatient cases visited between Jan 2012 – Jan 2015. Based on relevant history and medical records, 70 cases with presumed healthy eyes prior to trauma were selected retrospectively. The contralateral normal eye served as a control for the study eye. Patients with only unilateral axial length record, primary or secondary glaucoma, duration of trauma less than one year and those with bilateral trauma and congenital cataract were excluded from the study. Two groups were formed based on the nature of injury (blunt or penetrating). Birmingham Eye Trauma Terminology System (BETTS) was used to define blunt and penetrating trauma.^[16] A penetrating trauma was defined as laceration by a sharp object (there is only an entrance wound and no exit wound) e.g. thorn, nail, pen, etc.  A blunt trauma was defined as a closed-globe injury caused by a blunt object (there is no entrance or exit wound) e.g. cricket ball, closed fist, etc.

In each case, details of history including age at injury, mode, nature and interval since the injury was documented and previous medical records were properly analyzed. Parameters including best-corrected visual acuity (BCVA), refractive error, intraocular pressure (IOP), keratometry and biometric values (IOL Master 500, Carl Zeiss Meditec) of both eyes were documented. Detailed anterior and posterior segment examination findings were noted. 

Statistical analysis:

Mean (SD) or Frequency (Percentage) was used to describe summary data.  Student t-test or Mann-Whitney U-test was used to compare means between groups.  Chi-square test was used to assess the association between categorical variables. A p-value <0.05 is considered as statistically significant.  All statistical analysis was done in STATA 11.1 (Texas, USA). Multiple regression analysis was used to determine factors associated with increasing axial length in traumatic eyes.  Fellow eye axial length (in mm), age at injury, type of injury and duration of presentation since trauma were included in the analysis.  All variables were significantly associated in the univariate and multivariate model.

RESULTS

Of the 70 cases; 14 presented with traumatic cataract, 43 with pseudophakia and 13 patients with aphakia; 14 (20%) patients were amblyopic. 24 cases (34%) presented with best-corrected visual acuity less than 6/18. The duration between trauma and presentation ranged between 1 to 53 yrs. 47 cases suffered penetrating trauma, 23 cases suffered blunt trauma.

Out of 70 cases, 47 cases suffered penetrating trauma and 23 cases suffered blunt trauma (mean age 34.34 yrs )  (p=0.888).Overall trauma was more seen in males 46 (65.70%) as compared to females 24 (34.3%), penetrating trauma was observed more than blunt trauma among both genders. The difference in two groups was not statistically significant considering both age (p=0.888) and gender (p=0.037).

Comparing keratometry in both groups mean K1 in penetrating trauma group was 43.36 D [37.29 – 51.00 D] and in blunt trauma was 43.72D [39.99 – 46.38 D]. Whereas mean K2 in penetrating trauma group was 45.72 D [40.52 – 59.00 D] and in blunt trauma was 44.54 D [40.71 – 47.47D]. The difference between mean K1 and K2 was more in the penetrating group as compared to blunt trauma group. There was no statistical difference between two trauma groups in both K1 (p=0.5593) and K2 (p=0.0983) readings. Cylinder power in penetrating trauma group was -2.36 D [ranging from 0.26 to -8.07D] much more than blunt trauma group -0.82D [ranging from 0.30 to -1.36 D]  which was statistically significant (p<0.001).

The mean axial length of the traumatic eye was 25.31mm and 24.05mm in penetrating trauma group and blunt trauma group respectively. In both groups, axial length was found to be more in the traumatic eyes compared to control eye (penetrating trauma: p<0.001 and blunt trauma: p=0.0123). The difference in axial length between traumatic eyes of two groups (penetrating > blunt) was statistically significant (p=0.0006).Table 1

Comparing age at injury with axial length; mean axial length in penetrating trauma group ≤15yrs was 25.81mm and in >15 yrs it was 24.19 mm (p=0.0061); while in blunt trauma group ≤15yrs (n=8) was 24.24 mm and in >15 yrs was 23.86mm (p=0.465). Overall 36 (51.42%) patients suffered trauma at ≤ 15 years of age and 27 (38.57%) at >15 years of age. In the remaining 7 (10%) patients, trauma occurred early in life but the exact age at injury was not known. The earlier the age at injury, greater the axial length in the injured eye (Penetrating trauma > blunt trauma) (p=0.0003).Table 2

The longer the duration between injury and presentation, greater the axial length in the traumatic eye, as well as the difference in axial length between two eyes (Penetrating trauma > blunt trauma). Figure 1(a, b)

Using regression analysis of the data, if the axial length in control eye increases by 1 mm then in traumatic eye it increases by 1.34mm (β = 1.34, 95% CI: 0.96 – 1.76, p<0.001) when other variables held constant. Similarly, age at injury ≤15yrs (β = 0.88, 95% CI: 0.34 – 1.42, p=0.002), penetrating trauma (β = 0.90, 95% CI: 0.33 – 1.47, p=0.002) and duration from injury to presentation (β = 0.98, 95% CI: 0.42 – 1.53, p=0.001) were statistically significant factors associated with increase in axial length in the traumatic eye. Table 3

DISCUSSION

In our study, overall 47 (67.14%) patients had more than 1mm elongation in their injured eye compared to the other (control) eye. The mean difference between the injured eye and fellow eye was 0.72mm (-0.18 – 2.91mm) in blunt trauma group and 2.23 mm (-2.19 – 6.97mm) in penetrating trauma group.  Elongation of the eyeball is significantly greater in penetrating trauma than in blunt trauma. Various studies report axial elongation following visual deprivation due to various causes. ^{[2, 6, 10, 13, 17, 18]}   The comparative evaluation of our data with previously published data is shown in Table 4.  The findings in our study are consistent with other studies showing that there is a significant elongation of the eye following trauma.

Multiple mechanisms could be possible for progressive ipsilateral elongation. These include trauma, age at surgery, duration and severity of vision deprivation, amblyopia, IOP changes, change in scleral rigidity and multiple surgeries.^[13] In our study, it is possible that both trauma and vision deprivation are confounding factors for axial elongation. Despite the association of various factors with axial elongation in adult eyes, the actual cause remains elusive. Our study also reflects that younger the age, the greater the magnitude of axial length elongation. Table 3

Furthermore, the induction of traumatic cataract usually requires a very forceful blow to the eye and it may be the trauma itself that starts the elongation process of the globe or it may be complementary to visual deprivation.^[6] The existence of certain growth factors which may modulate the growth of the adult eyeball after trauma has also been postulated.^[19,20]   We tried to reliably extract the data regarding the interval from the injury to the time of presentation/surgery in most of the cases using clinical history and medical records. Additionally, regression analysis of the data proved that increase in axial length in the traumatic eye is greater compared to the normal (control) eye. Hence, we were able to establish a correlation between the degree of elongation and the interval between trauma and surgery statistically. Certain studies depict that there is no direct linear correlation between the onset of trauma and degree of elongation of an eye. ^[6] However, the assumption that the inter-ocular axial length difference was zero before trauma may not be valid in all cases.

Among the cases, despite IOL implantation at an early age (7 cases) with good visual recovery, there was significant axial myopia. Therefore, we can deduce that the nature and the age at injury are strongly related to the axial elongation along with visual deprivation. Similarly, M. Vanathi, et al ^[13] reported the occurrence of unilateral progressive axial myopia ipsilaterally in a retrospective analysis of 12 children (age group 4 years to 14 years) following uniocular cataract surgery, postulating trauma or multiple ocular surgeries as predisposing factors. Sorkin et al ^[15] studied longitudinal changes in axial length in pseudophakic children (3-9 yrs) and concluded that eyes with traumatic cataracts experienced more axial elongation than eyes with developmental/ congenital cataracts (0.97 mm versus -0.01 mm; p = 0.03). Leiba H et al ^[12] demonstrated a tendency toward greater axial lengthening in pseudophakic eyes of children when compared with their non-operated eyes without any significant difference between traumatic and congenital cataracts. Similarly, Crouch ER et al ^[21] showed that there is no statistically significant difference in refractive change when comparing amblyopic to non-amblyopic eyes or traumatic to non-traumatic cataracts.

Hoevenaars NE et al ^[22] studied children < 12 months of age and experienced higher myopic shifts and a larger mean rate of refractive change per year compared with older children proving that age at surgery and laterality are factors to consider when deciding which IOL power to implant in children. Enyedi LB et al ^[11] demonstrated an increasing trend towards postoperative myopia in pediatric patients undergoing intraocular lens implantation. This myopic shift was being greatest in younger age groups and persistent until at least 8 years of age, further showing that there is much variability in the postoperative refractive changes, and predicting exactly when refraction will stabilize for an individual patient is difficult.

Griener ED et al ^[23] showed that there might be a reduction in axial growth in infantile eyes following cataract extraction and IOL implantation reducing the magnitude of the myopic shift in these eyes. Similarly, Scott R. Lambert et al ^[24] studied axial elongation following cataract surgery during the first year of life in the Infant Aphakia Treatment Study and concluded that at baseline, eyes with cataracts were shorter than fellow eyes. The change in AL was smaller in operated eyes treated with a CL (contact lenses) than in operated eyes treated with an IOL but was not significantly related to age at surgery.

VanderVeen DK et al ^[25] reported in Infant Aphakia Treatment Study that short axial length correlates with higher PE (predictive errors) after IOL placement in infants. Less hyperopia than anticipated occurs with axial lengths of less than 18mm or high-power IOL’s. The Holladay 1 and SRK/T formulae gave equally good results and had the best predictive value for infant’s eyes, showing the importance of axial length and proper formulae for calculations while implanting IOL in infants. It would thus be prudent to consider age, proper formulae and biometry to calculate IOL power with minimal predictive errors to avoid postoperative refractive surprises especially in infants and young patients with penetrating trauma.

LIMITATIONS

One of the limitations of the present study is the assumption that the two eyes of each patient were similar prior to the injury. It may be possible that injured eye was myopic prior to the injury, and more susceptible to injury because of its poor vision as myopia itself is associated with nuclear cataracts as demonstrated by Kubo E et al ^[26] and Praveen MR et al. ^[27]    The time interval between the ages at which injury occurred to the time of presentation for examination to determine axial length was not available in all cases. There is much variability in the postoperative refractive changes and predicting exactly when and where the refraction will stabilize for an individual patient is difficult; hence predicting the appropriate IOL power with any degree of accuracy is quite difficult.

CONCLUSION

Trauma leading to visual deprivation may cause unilateral axial elongation. The younger the patient is when trauma occurs, the greater the magnitude of axial length elongation; the longer the duration between the age of trauma and time of presentation the greater the axial length of the traumatic eye. Elongation of the eyeball is significantly greater in penetrating trauma than in blunt trauma. Rapid rehabilitation of injured eyes is absolutely essential to minimize the duration of visual deprivation.  It is difficult to predict exactly the amount of axial length elongation following trauma and or cataract surgery hence further studies with a larger database may be required to understand this relationship better.

References:

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Table 1   Axial length distribution of both eyes among trauma groups

Group	Mean (SD) [mm]	Min – Max	p-value*
Penetrating trauma Trauma eye Other eye	25.31 (1.75) 23.08 (0.76)	21.81 – 29.96 20.91 – 24.61	<0.001
Blunt trauma Trauma eye Other eye	24.05 (1.14) 23.32 (0.67)	22.27 – 26.43 21.68 – 24.36	0.0123
Total Trauma eye Other eye	24.89 (1.68) 23.16 (0.73)	21.81 – 29.96 20.91 – 24.61	<0.001

*t-test

SD- Standard deviation

Table 2 Distribution of axial length in traumatic eye according to age at injury

Age at injury	n*	Mean(SD) [mm]	Min – Max	p-value
Penetrating trauma ≤15 years >15 years	28 13	25.81 (1.78) 24.19 (1.38)	21.81– 29.96 22.42 – 26.7	0.0061
Blunt trauma ≤15 years >15 years	8 14	24.24 (1.43) 23.86 (0.98)	22.69 – 26.43 22.27 – 25.74	0.465
Total ≤15 years >15 years	36 27	25.46 (1.81) 24.02 (1.18)	21.81 – 29.96 22.27 – 26.70	0.0003

* Exact age at trauma was not known for 7 cases

n – number of cases; SD – Standard deviation 

Table 3   Factors associated with increase in axial length in trauma cases

Variable	β*	95% CI	p-value
Axial length (control eye)	1.34	0.96 – 1.73	<0.001
Age at injury (1 – ≤15 yrs, 0 – ≥15 yrs)	0.88	0.34 – 1.42	0.002
Group (1-Penetrating, 0-Blunt)	0.90	0.33 – 1.47	0.002
Duration between injury and presentation (1 – >10 years, 0 – ≤10 yrs)	0.98	0.42 – 1.53	0.001

*Values obtained using regression analysis

Table 4 Comparative evaluation of data with previous studies

Author	Year	Number of cases	Mean AL in traumatic eye [mm]	Mean AL in fellow eye [mm]	Mean difference between injured eye and fellow eye [mm]
Antonio Calossi	1994	13	25.9 (21.9 – 34.2)	23.42 (21.9 – 25.2)	2.48 (0.1 – 11.5)
Vanathi	2002	12 (10 traumatic)	25.22 (23.52-34.2)	–	2.2 + 0.9 (1.0 – 3.5)
Dan Gradin	2008	17	26.1 (25.5-26.8)	23.3 (22.7-23.7)	3.09 (2.45 – 4.13)
Our  study	2015	23 blunt	24.05 (22.27 – 26.43)	23.32 (21.68 – 24.36)	0.72 (-0.18 – 2.91)
		47 penetrating	25.31 (21.81 – 29.96)	23.08 (20.91 – 24.61)	2.23 (-2.19 – 6.97)

Data represented as mean (95% CI)

AL – Axial length

Figure 1 (a) Scatter plot comparing axial length with the duration between injury and presentation (b) Scatter plot comparing difference in axial length between traumatic and control eye with the duration between injury and presentation: