Assessment of gestational age by examination of the anterior vascular capsule of the lens

September 1977

The Journal o f P E D I A T R I C S

455

Assessment of gestational age by examination of the anterior vascular capsule of the lens The disappearance of the anterior vascular capsule of the lens (pupillary membrane) was found to be useful in the preterm infant to estimate accurately gestational age between the twenty-seventh and the thirty-fourth weeks. Before the twenty-seventh week, the cornea was too opaque to allow good visualization of this vascular system. After the thirty-fourth week, these vessels had generally atrophied completely. One hundred infants between 27 and 34 weeks" gestational age as assessed by the Dubowitz scoring system were studied with the direct ophthalmoscope following dilatation o f the pupil Disappearance of the anterior vascular capsule was arbitrarily divided into four grades. The correlation between gestational age and the grade of anterior vascular capsule was found to be highly significant (1o < O.001).

Helen Mintz Hittner, M.D., F.A.C.S.,* Norma Jean Hirsch, M.D., F.A.A.P., and Arnold Jack Rudolph, M.D., Houston, Texas

THE HYALOID SYSTEM and the tunica vasculosa lentis are a complex vascular system which invades the developing eye posteriorly and anteriorly (Fig. 1). As m a n y embryonic vascular systems, this one is transitory. It nourishes the structures of the eye during its active growth and then atrophies completely. This system, first described in 1832,' has long been recognized to form and atrophy in an orderly manner. More recently, it has been regarded as a valuable method of estimating gestational age. ~ To date, these changes have not been correlated systematically with gestational age of preterm infant. Gestational age was assessed in 100 preterm infants by the Dubowitz scoring system by one of us (N. J. H.). The eyes of the same 100 infants were studied following dilatation with the direct ophthalmoscope by one of us (H. M. H.). The results on analysis were found to be highly significant (p < 0.001). MATERIALS

AND METHODS

Gestational aging. All infants less than 2,500 gm born at Jefferson Davis Hospital, Houston, Texas, or transferred From the Departments of Ophthalmology and Pediatrics, Baylor College of Medicine9 Supported by a grant from the Retina Research Foundation, Houston, Texas9 *Reprint address: 2415 Gramercy, Houston, TX 77030.

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Fig. 1. The vascular system of the eye in the human fetus of 85 mm (beginning of fourth month). Mp = Anterior portion of the tunica vasculosa lentis (anterior vascular capsule of the lens or pupillary membrane); my = lateral or capsulopupillary portion of the tunica vasculosa lentis; pv = posterior portion of the tunica vasculosa lentis; dcp = distal extremity of capsulopupillary system forming the annular vessel; pc = long posterior ciliary artery; ah = hyaloid artery; cah = central branch of hyaloid artery; rv = smaller branch of hyaloid artery; sv = superficial vessel of vitreous in stage of involution. (After Versari R: Estratto da Ricerche di Morfologia 3:1, 1923.)

Vot 91, No. 3, pp. 455-458

456

Hittner, Hirsch, and Rudolph

The Journal of Pediatrics September 1977

Fig, 2. Clinical appearance of anterior vascular capsule. Grade 4: Infant estimated to be 28 weeks' gestafional age. Grade 3: Infant estimated to be 30 weeks' gestational age. Grade 2: Infant estimated to be 32 weeks' gestational age. Grade 1: Infant estimated to be 34 weeks' gestational age.

Fig. 3. Grading system for assessment of gestational age by examination of the anterior vascular capsule of the lens.

there within the first 24 hours of life were evaluated. Gestational age was estimated for each infant based on the maternal obstetrical history and the infant's physical examination. The Dubowitz clinical assessment of gestational age was performed for each infant. ~ When the Dubowitz score was within two weeks of the gestational age given by maternal history, the age by maternal dates was used as the estimated gestational age. When the Dubowitz score differed in excess of two weeks in comparison to the maternal dates, the net gestational age was based upon averaging of the criteria. Three infants were excluded because of irreconcilable differences in the two criteria. One hundred consecutive infants judged to be between 27 and 34 weeks inclusive were selected for eye examination. Included in these 100 preterm infants were 45 boys and 55 girls. There were 83 singletons, 14 twins, and three triplets in the group studied. Eighty-six infants were appropriate for gestational age; 12 infants were small for gestational age, and two infants were large for gestational age. Ophthalmic evaluation. The eyes of each infant were dilated with one drop each of tropicamide 0.5% and phenylephrine hydrochloride 2.5%. The lids were held open approximately 5 seconds for good absorption. The excess was blotted away following closure of the lids. The infants were examined with the pupils fully dilated

Volume 91 Number 3

Assessment of gestational age by examination of lens

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approximately 15 minutes after instillation of the above medications. A direct ophthalmoscope was set between + 6 and + 12, and the lids were separated to view the red reflex. If it was difficult to separate the lids for adequate visualization of the red reflex, one drop of proparacaine hydrochloride 0.5% was instilled and an infant-sized speculum was introduced between the lids. Disappearance of the anterior vascular capsule was arbitrarily divided into four grades (Figs. 2 and 3): Grade 4, 27-28 weeks; Grade 3, 29-30 weeks; Grade 2, 31-32 weeks; Grade 1, 33-34 weeks. All ophthalmic examinations in this study were performed within the first 30 hours of life. Statistical analysis. Significance was tested by calculation of the linear regression coefficient r for two variables and the X~ test with Yates correction. RESULTS Many infants were examined. Those infants who were less than 27 weeks' gestational age had corneas which were too hazy to visualize the vascular system and those infants who were greater than 34 weeks rarely had anything but trivial vascular remnants of the system. The anterior vascular capsules were graded in 100 consecutive preterm infants estimated to be between 27 and 34 weeks' gestational age (Fig. 4). In every infant examined, the vascular patterns were found to be almost identical in both eyes. Twenty-four infants had an anterior vascular capsule whose component parts covered virtually the entire anterior surface of the lens (Grade 4). Twenty-two infants had evidence of early atrophy of

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Fig. 5. Distribution of gestational age in weeks against grade of anterior vascular capsule in 100 infants. The regression line is represented by y = 17.11-0.48x.

the anterior vascular capsule; the central portion of the lens was not covered by vessels, and there was thinning of the vessels peripherally (Grade 3). Twenty infants had additional evidence of atrophy of the anterior vascular capsule as judged by more of the central portion of the lens being visible and more thinning of the peripheral vessels (Grade 2). On occasion, a few strands reached the center of the lens, but definitely not in the same pattern as those judged to be Grade 4.

458

Hittner, Hirsch, and Rudolph

Twenty-eight infants had only a small number of vessels contributing to the anterior vascular capsule; these vessels did not approach the center of the lens (Grade 1). Six infants had no definitive anterior vascular capsule. There was a significant negative correlation between gestational age and grade of anterior vascular capsule ( r - - - 0 . 8 7 7 , t = 18.1, p < 0.001) (Fig. 5). Of those infants whose gestational age was 30 weeks or less, 24 of 48 had an anterior vascular capsule judged to be Grade 4. No infant of more than 30 weeks had a grade of 4 (X=' = 22, p < 0.0005). Of those infants whose gestational age was 31 weeks or greater, 27 of 52 had an anterior vascular capsule judged to be Grade !. Only one infant less than 31 weeks had a grade of 1 (X'-'= 28, p < 0.0O05). Of the 12 preterm infants estimated to be small for gestational age, one was Grade 4, five were Grade 2, and six were Grade 1. There was a significant negative correlation between gestational age and grade of anterior vascular capsule (r = -0.913, t = 7.08, p < 0.001)i Thus, the grading system correlates well with gestational age, even in small-for-gestational age infants. DISCUSSION The disappearance of the anterior vascular capsule of the lens was found to be of valu e i n estimating gestational age. Grades 4, 3, 2, and 1 wer e found to correlate with gestational ages 27 and 28 weeks, 29 and 30 weeks, 31 and 32 weeks, and 33 and 34 weeks, respectively. It must be realized that this grading system is an arbitrary div!sion of a continuous process and, therefore, in using this grading system, if a decision of grade cannot be made, it is suggested that the grades be adjusted accordingly: Grade 4 - / 1 + , 28-29 weeks; Grade 3 - / 2 + , 30-31 weeks; Grade 2-/1 +, 32-33 weeks. It shoul d also be noted that occasionally strands of the anterior vascular Capsule will persist and cross over the entire surface of the lens, although the

The Journal of Pediatrics September 1977

majority of the vascular capsule has atrophied. In these cases, only the major vascular arcades should be considered in the grading of that infant. The accuracy of this technique will be greatly improved if the examination of the eyes is done during the initial physical examination or at least in the first 24 to 48 hours of life. The vascular system was found to atrophy rapidly after that period and even a Grade 4 anterior vascular capsule might disappear within a few days. This simple technique, requiring only observation with a direct ophthalmoscope following dilatation of the pupils, can be used routinely in the nursery a s an adjunct to estimating gestational age. The pediatric house staff, neonatology fellows, and neonatology staff have been performing this examination in the Jefferson Davis Hospital nursery for several months. They have mastered the technique quite readily and have confirmed the value of the system. Utilization of this grading system certainly should also improve the diagnosis of ocular abnormalities in the nursery. ! n this series of 100 preterm infants, one cataract was identifie d. In addition, if the fundus is viewed in those infants whose anterior vascular capsule permits, which is generally i n infants of 31 weeks or greater (Grade 2 or less), retinal and optic nerve abnormalities will undoubtedly be discovered occasionally.

REFERENCES

1. Henle: De membrana pupillar! aliisque oculi membranis pellucentibus observationes anatomicae, Dissertatio inauguralis, Bonn, 1832. 2. McCormick AQ: Ophthalmological observations in the newborn, Atlantic City, N. J., April 30, 1968, in Dancis J, editor: Proceedings of interdisciplinary conferences: Idiopathic respiratory distress syndrome: Therapeutic approaches, Washington, DC, 1969, US Government Printing Office, p 80. 3. Dubowitz LMS, Dubowitz V, and Goldberg D: Clinical assessment of gestational age in the newborn infant, J PEDIATR77:1, 1970.